New Generation Green Solvents for Separation and Preconcentration of Organic and Inorganic Species 0128185694, 9780128185698

Table of contents :
Cover
New Generation Green Solvents for Separation and Preconcentration of Organic and Inorganic Species
Copyright
Contents
List of contributors
1 Historical backgrounds, milestones in the field of development of separation and preconcentration methods
Abbreviations
1.1 Introduction
1.2 Historical development of separation and preconcentration methods
1.2.1 Historical development of coprecipitation methods
1.2.2 Historical development of liquid phase extraction/microextraction methods
1.2.2.1 Classification of liquid–liquid extraction systems
1.2.3 Historical development of cloud-point extraction
1.2.4 Historical development of solid phase extraction/microextraction methods
1.3 Conclusions
References
2 Historical background: milestones in the field of development of analytical instrumentation
2.1 Introduction
2.2 Development in the field of chromatography
2.3 Development in the field of spectroscopy
2.3.1 Development of ultraviolet visible spectrometry
2.3.2 Development of infrared spectrometry
2.3.3 Development of nuclear magnetic resonance spectrometry
2.3.4 Development of mass spectrometry
2.3.5 Development of luminescence spectroscopy
2.3.6 Development of atomic absorption spectroscopy
2.3.7 Development of atomic emission spectroscopy
2.3.8 Development of plasma emission spectroscopy
2.3.9 Development of atomic fluorescence spectrometry
2.4 Development of electroanalytical techniques
2.4.1 Electrogravimetry
2.4.2 Coulometry
2.4.3 Conductometry
2.4.4 Potentiometry
2.4.5 Voltammetry
2.4.6 Polarography and analytical voltammetry
2.4.7 Amperometry
2.5 Hyphenated techniques
2.5.1 GC-NMR
2.5.2 LC-NMR
2.5.3 GPC-NMR
2.5.4 CE-NMR
2.5.5 SFC-NMR
2.5.6 SFE-NMR
2.5.7 GC-MS
2.5.8 LC-MS
2.5.9 CE-MS
2.5.10 GC-ICP-MS
2.5.11 HPLC-ICP-MS
2.5.12 CE-ICP-MS
2.6 Advancement in sampling systems for analytical instruments
2.7 Conclusion
References
3 Type of new generation separation and preconcentration methods
3.1 Introduction
3.2 Liquid phase microextraction
3.2.1 Single-drop microextraction
3.2.1.1 Direct immersion single-drop microextraction
3.2.1.2 Headspace SDME (HS-SPME)
3.2.1.3 Three-phase single-drop microextraction
3.2.1.4 Continuous-flow microextraction
3.2.1.5 Applications of single-drop-based liquid phase microextraction methods in analysis of organic and inorganic species
3.2.2 Hollow-fiber liquid phase microextraction
3.2.2.1 Applications of hollow-fiber liquid phase microextraction methods in analysis of organic and inorganic species
3.2.3 Dispersive liquid–liquid microextraction
3.2.4 Solidified floating organic drop microextraction
3.3 New-generation solid phase extraction methods
3.3.1 Solid phase microextraction
3.3.2 Stir-bar sorptive extraction
3.3.3 Magnetic solid phase extraction technique
3.3.4 Immunoaffinity solid phase extraction
3.3.5 Microextraction in a packed syringe
3.3.6 Molecularly imprinted solid phase extraction
3.3.7 Dispersive micro-SPE
References
4 New methodologies and equipment used in new-generation separation and preconcentration methods
4.1 The historical development and overview of these preconcentration and separation methodologies
4.2 Hyphenated and nonhyphenated chromatographic techniques for extraction and/or separation of target compounds
4.3 Ultrasound-assisted emulsification microextraction
4.4 Cloud point extraction
4.5 High-diffusion liquids
4.6 Pressurized liquid extraction
4.7 Microwave-assisted extraction
4.8 Vacuum microwave-assisted extraction
4.9 Supercritical fluid extraction
4.10 Dispersive liquid–liquid microextraction
4.11 Solidified floating organic drop microextraction
4.12 Modern techniques of isolation and/or preconcentration
4.12.1 Liquid phase microextraction
4.12.2 Aqueous two-phase system
4.12.3 Dispersive-μ-solid phase extraction
4.12.4 Stir-bar sorptive extraction
4.13 The application of carbon nanotubes and nanoparticles in separation
4.14 Conclusion
References
5 Type of green solvents used in separation and preconcentration methods
Abbreviations
5.1 Introduction
5.2 Green analytical chemistry
5.2.1 History, principles, and recent trends in green analytical chemistry
5.2.2 The 12 Principles of green analytical chemistry
5.2.3 Stages of analytical procedure description
5.2.4 Application of the green analytical procedure index
5.2.4.1 Application of the green analytical procedure index
5.2.4.2 Evaluated analytical procedures
5.2.5 New-generation solvents
5.2.5.1 Solvent selection guides
5.2.5.2 Ionic liquids
5.2.5.3 Deep eutectic solvents
5.2.5.4 Amphiphilic and supramolecular solvents
5.3 Switchable hydrophilicity solvents
5.3.1 Supercritical fluids
5.3.1.1 Superheated water (subcritical water)
5.3.1.2 Magnetic liquids
References
6 Ionic liquids in separation and preconcentration of organic and inorganic species
6.1 Introduction
6.2 Physical properties of ionic liquids
6.3 Application of ionic liquids in extraction of organic and inorganic compounds
6.3.1 Application of ionic liquids in solid phase microextraction
6.3.2 Application of ionic liquids in dispersion–liquid microextraction
6.3.3 Application of ionic liquids in liquid phase microextraction
6.3.4 Application of ionic liquids in aqueous two-phase system extraction
6.3.5 Other extraction methods based on ionic liquids
6.4 Magnetic ionic liquids and theory application
6.5 Conclusion
References
7 Supramolecular solvents in separation and preconcentration of organic and inorganic species
Abbreviations
7.1 Introduction
7.2 Background
7.3 Solvent extraction system
7.4 Preparation of supramolecular solvents
7.5 Formation mechanism of SUPRAS phase
7.6 Components of supramolecular solvents
7.7 Supramolecular solvents in separation and preconcentration methods
7.8 Efficiency
7.9 Thermodynamics
7.10 Environment
7.11 Types of SUPRAS molecular extraction
7.12 Supramolecular solvents in liquid–liquid microextraction
7.13 Integrated use of supramolecular solvents with nanomaterials
7.14 Ultrasonic-assisted supramolecular solvent extraction
7.15 Microwave-assisted supramolecular solvent extraction
7.16 Vortex assisted supramolecular solvent extraction
7.17 Temperature-assisted supramolecular solvent extraction
7.18 Trends
7.19 Conclusion
References
8 Switchable solvents in separation and preconcentration of organic and inorganic species
Abbreviations
8.1 Introduction
8.2 Switchable-hydrophilicity solvents
8.3 Synthesis and chemistry of switchable-hydrophilicity solvents
8.4 Applications of switchable-hydrophilicity solvents
8.5 Switchable-hydrophilicity solvents in large-scale extractions
8.6 Switchable-hydrophilicity solvents in microextractions
8.6.1 Switchable-hydrophilicity solvents for extraction of organic analytes
8.6.2 Switchable-hydrophilicity solvents for extraction of inorganic analytes
8.6.3 Maximizing extraction efficiency with switchable-hydrophilicity solvents
8.6.4 Trends in switchable-hydrophilicity solvents–based microextractions
8.7 Future aspects
References
9 Deep eutectic solvent in separation and preconcentration of organic and inorganic species
Abbreviations
9.1 Introduction
9.2 Deep eutectic solvent (definition and preparation)
9.3 Physicochemical properties of deep eutectic solvents
9.3.1 Freezing point
9.3.2 Viscosity
9.3.3 Density
9.3.4 Conductivity
9.3.5 Polarity
9.3.6 Acid-base behavior of deep eutectic solvents
9.3.7 Miscibility of the novel deep eutectic solvents with protic and aprotic solvents
9.3.8 Toxicity
9.3.9 Thermal stability study
9.4 Application of deep eutectic solvents in extraction techniques
9.4.1 Application of deep eutectic solvents in aqueous two-phase extraction method
9.4.2 Application of deep eutectic solvents in liquid/solid extraction/microextraction
9.5 Conclusion
References
10 Supercritical fluid extraction in separation and preconcentration of organic and inorganic species
Abbreviations
10.1 Introduction
10.2 Properties of supercritical fluid
10.3 Instrumentation
10.4 Mechanism and kinetic of supercritical fluid
10.5 Applications of supercritical fluid
10.5.1 Supercritical fluid in the environment
10.5.2 Supercritical fluid in foods and herbs
10.5.3 Supercritical fluid in drug and biological sample
10.6 Conclusion
References
Index
Back Cover

Citation preview

NEW GENERATION GREEN SOLVENTS FOR SEPARATION AND PRECONCENTRATION OF ORGANIC AND INORGANIC SPECIES

NEW GENERATION GREEN SOLVENTS FOR SEPARATION AND PRECONCENTRATION OF ORGANIC AND INORGANIC SPECIES Edited by

Mustafa Soylak Department of Analytical Chemistry, Faculty of Pharmacy, Near East University, Nicosia, TRNC, Mersin, Turkey

Erkan Yilmaz Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, Turkey ERNAM—Erciyes University Nanotechnology Application and Research Center, Kayseri, Turkey

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States Copyright © 2020 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-818569-8 For Information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Susan Dennis Acquisitions Editor: Kathryn Eryilmaz Editorial Project Manager: Billie Jean Fernandez Production Project Manager: Sojan P. Pazhayattil Cover Designer: Mark Rogers Typeset by MPS Limited, Chennai, India

Contents 4. New methodologies and equipment used in new-generation separation and preconcentration methods

List of contributors ix 1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

MOHAMMAD HOSSEIN AHMADI AZQHANDI, TAHERE KHEZELI, MEHRORANG GHAEDI AND ALI DANESHFAR

ERKAN YILMAZ AND MUSTAFA SOYLAK

Introduction 45 Development in the field of chromatography 46 Development in the field of spectroscopy 49 Development of electroanalytical techniques 62 Hyphenated techniques 67 Advancement in sampling systems for analytical instruments 70 2.7 Conclusion 71 References 71

4.1 The historical development and overview of these preconcentration and separation methodologies 149 4.2 Hyphenated and nonhyphenated chromatographic techniques for extraction and/or separation of target compounds 150 4.3 Ultrasound-assisted emulsification microextraction 151 4.4 Cloud point extraction 153 4.5 High-diffusion liquids 155 4.6 Pressurized liquid extraction 156 4.7 Microwave-assisted extraction 157 4.8 Vacuum microwave-assisted extraction 159 4.9 Supercritical fluid extraction 159 4.10 Dispersive liquid liquid microextraction 160 4.11 Solidified floating organic drop microextraction 164 4.12 Modern techniques of isolation and/or preconcentration 170 4.13 The application of carbon nanotubes and nanoparticles in separation 195 4.14 Conclusion 198 References 198

3. Type of new generation separation and preconcentration methods

5. Type of green solvents used in separation and preconcentration methods

Abbreviations 1 1.1 Introduction 2 1.2 Historical development of separation and preconcentration methods 3 1.3 Conclusions 36 References 36

2. Historical background: milestones in the field of development of analytical instrumentation NASRULLAH SHAH, MUHAMMAD BALAL ARAIN AND MUSTAFA SOYLAK

2.1 2.2 2.3 2.4 2.5 2.6

ERKAN YILMAZ AND MUSTAFA SOYLAK

ERKAN YILMAZ AND MUSTAFA SOYLAK

3.1 Introduction 75 3.2 Liquid phase microextraction 76 3.3 New-generation solid phase extraction methods 117 References 138

Abbreviations 207 5.1 Introduction 208 5.2 Green analytical chemistry 209 5.3 Switchable hydrophilicity solvents References 258

v

251

vi

CONTENTS

6. Ionic liquids in separation and preconcentration of organic and inorganic species TAHERE KHEZELI, MEHRORANG GHAEDI, ALI DANESHFAR, SONIA BAHRANI, ARASH ASFARAM AND MUSTAFA SOYLAK

6.1 Introduction 267 6.2 Physical properties of ionic liquids 270 6.3 Application of ionic liquids in extraction of organic and inorganic compounds 274 6.4 Magnetic ionic liquids and theory application 6.5 Conclusion 304 References 307

7.17 Temperature-assisted supramolecular solvent extraction 341 7.18 Trends 342 7.19 Conclusion 342 Acknowledgment 343 References 343

8. Switchable solvents in separation and preconcentration of organic and inorganic species 300

7. Supramolecular solvents in separation and preconcentration of organic and inorganic species MUHAMMAD BALAL ARAIN AND MUSTAFA SOYLAK

Abbreviations 319 7.1 Introduction 319 7.2 Background 322 7.3 Solvent extraction system 325 7.4 Preparation of supramolecular solvents 327 7.5 Formation mechanism of SUPRAS phase 329 7.6 Components of supramolecular solvents 331 7.7 Supramolecular solvents in separation and preconcentration methods 331 7.8 Efficiency 337 7.9 Thermodynamics 337 7.10 Environment 338 7.11 Types of SUPRAS molecular extraction 338 7.12 Supramolecular solvents in liquid liquid microextraction 338 7.13 Integrated use of supramolecular solvents with nanomaterials 339 7.14 Ultrasonic-assisted supramolecular solvent extraction 339 7.15 Microwave-assisted supramolecular solvent extraction 340 7.16 Vortex assisted supramolecular solvent extraction 340

USAMA ALSHANA, ERKAN YILMAZ AND MUSTAFA SOYLAK

Abbreviations 347 8.1 Introduction 347 8.2 Switchable-hydrophilicity solvents 348 8.3 Synthesis and chemistry of switchable-hydrophilicity solvents 349 8.4 Applications of switchable-hydrophilicity solvents 353 8.5 Switchable-hydrophilicity solvents in large-scale extractions 354 8.6 Switchable-hydrophilicity solvents in microextractions 356 8.7 Future aspects 377 References 377

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species TAHERE KHEZELI, MEHRORANG GHAEDI, SONIA BAHRANI, ALI DANESHFAR AND MUSTAFA SOYLAK

Abbreviations 381 9.1 Introduction 381 9.2 Deep eutectic solvent (definition and preparation) 383 9.3 Physicochemical properties of deep eutectic solvents 385 9.4 Application of deep eutectic solvents in extraction techniques 402 9.5 Conclusion 416 References 417

CONTENTS

10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species TAHERE KHEZELI, MEHRORANG GHAEDI, SONIA BAHRANI AND ALI DANESHFAR

Abbreviations 425 10.1 Introduction 425 10.2 Properties of supercritical fluid

10.3 Instrumentation 427 10.4 Mechanism and kinetic of supercritical fluid 429 10.5 Applications of supercritical fluid 430 10.6 Conclusion 440 References 447

Index 453 426

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List of contributors

Tahere Khezeli Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, Iran

Usama Alshana Department of Analytical Chemistry, Faculty of Pharmacy, Near East University, Nicosia, TRNC, Mersin, Turkey Muhammad Chemistry, Pakistan

Nasrullah Shah Department of Chemistry, Abdul Wali Khan University Mardan, Mardan, Pakistan

Balal Arain Department of University of Karachi, Karachi,

Mustafa Soylak Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey; Technology Research & Application Center (TAUM), Erciyes University, Kayseri, Turkey

Arash Asfaram Medicinal Plants Research Center, Yasuj University of Medical Sciences, Yasuj, Iran

Erkan Yilmaz Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, Turkey; ERNAM—Erciyes University Nanotechnology Application and Research Center, Kayseri, Turkey; Technology Research & Application Center (TAUM), Erciyes University, Kayseri, Turkey

Mohammad Hossein Ahmadi Azqhandi Applied Chemistry Department, Faculty of Gas and Petroleum (Gachsaran), Yasouj University, Gachsaran, Iran Sonia Bahrani Department of Chemistry, Yasouj University, Yasouj, Iran Ali Daneshfar Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, Iran Mehrorang Ghaedi Department of Chemistry, Yasouj University, Yasouj, Iran

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C H A P T E R

1 Historical backgrounds, milestones in the field of development of separation and preconcentration methods Erkan Yilmaz1,2 and Mustafa Soylak3 1

2

Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, Turkey ERNAM—Erciyes University Nanotechnology Application and Research Center, Kayseri, Turkey 3 Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey G GC GCB GC FID

Abbreviations AµE APDC ASE C60 CE CF-SD-LPME CNTs CP CPE CPT DDTC DESs DI-SDME EPA ETAAS FAAS FIA FIP

adsorptive microextraction ammonium pyrrolidinedithiocarbamate accelerated solvent extraction fullerenes capillary electrophoresis continuous-flow microextraction/ single-drop microextraction carbon nanotubes coprecipitation cloud-point extraction cloud-point temperature diethyldithiocarbamate deep eutectic solvents direct immersion single-drop microextraction environmental protection agency electrothermal atomic absorption spectrometry flame atomic absorption spectrometer flow injection analysis international pharmaceutical federation

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00001-2

GC MS/MS GFAAS GO HGAAS HPLC HR-CS-ETAAS

HS-SDME ICP-AES ICP-OES ILs ISO

1

graphene gas chromatography graphitized carbon black gas chromatography flame ionization detection gas chromatography tandem mass spectrometer graphite furnace atomic absorption spectrometer graphene oxide hydride generation atomic absorption spectrometry high-performance liquid chromatography high resolution continuum, source electrothermal atomic absorption spectrometer head space single-drop microextraction inductively coupled plasma atomic emission spectrometry inductively coupled plasma optical emission spectrometer ionic liquids international organization for standardization

© 2020 Elsevier Inc. All rights reserved.

2 LC-UV LLE LLLME LPME LSA LSE MAE MALDI-MS MIPs MISPE MOFs PAHs PGC PLE PS-DVB PTFE RAM RDSE SBSE SCSE SDME SFE SFODME SIA SPE SPME SRSE SSs SUPRAs TAN WCED TSP-MS-MS UAE UNWFP WHO WPC

1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

liquid chromatography ultraviolet spectrophotometer liquid liquid extraction liquid liquid liquid microextraction liquid phase microextraction liquid solid adsorption liquid solid extraction microwave-assisted extraction matrix-assisted laser desorption/ ionization mass spectrometer molecularly imprinted polymers molecularly imprinted solid phase extraction metal organic frameworks polycyclic aromatic hydrocarbons porous graphitic carbon pressurized liquid extraction polystyrene-divinylbenzene polytetrafluoroethylene restricted-access materials rotating-disc sorbent extraction stir-bar sorptive extraction stir-cake sorptive extraction single-drop microextraction supercritical fluid extraction solidified floating organic drop microextraction sequential flow injection analysis, solid phase microextraction solid phase extraction solid phase microextraction stir-rod sorptive extraction switchable solvents supramolecular solvents 1-2-thiazolylazo-2-naphthol World Environment and Development Commission thermospray tandem mass spectrometer ultrasound extraction United Nations World Food Programme World Health Organization World Pharmacy Council

1.1 Introduction In parallel with the development of technology, there has been a significant increase in the amount of harmful trace organic, inorganic, and biological species in living areas, living organisms, and ecological environment [1,2].

The scientific community and the public have become aware of and concerned about the presence of organic trace species such as active ingredients, pesticides, azo food additives, and inorganic trace species such as heavy metal ions, metal compounds, anions, and nanoparticles in their working and living environments and about the health impact of these substances [3,4]. There is an increasing requirement to estimate the potential health risk of these trace organic and inorganic species under the conditions in which they are used. These species are found in biological, food, environmental samples, and pharmaceutical products as naturally or synthetic at different concentrations, and they have been made for useful purposes; however, their prolonged use has become harmful. Even if some of these species are useful for living cells to a certain extent, they have adverse effects on living cells in prolonged exposures [5 7]. When humans come into contact with or consume these organic and inorganic species in liquid, solid, and gaseous forms at different levels, these species can irritate and damage the skin, eyes, and respiratory tract; can damage internal organs such as the nervous system, liver, and kidneys; and especially can cause specific diseases such as cancer [4 8]. Worldwide foundations, organizations, administrations, and environmental protection agencies such as the World Health Organization (WHO), United Nations World Food Programme (UNWFP), World Pharmacy Council (WPC), International Pharmaceutical Federation (FIP), Environmental Protection Agency (EPA) have set up organizations for the long-term monitoring and identification of organic and inorganic species in various biological, food, environmental samples and pharmaceutical products, including the effects at different levels on living cells and the ecology. Moreover, maximum permissible levels of the organic and inorganic species in real samples

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

3

FIGURE 1.1 Subject areas that require trace or ultratrace detection of the analytes.

Household Sewage treatment

Foodanalysis

Energy production

Biotechnology

Trace analysis Pharmaceutical andchemical industry

Environmental analysis and monitoring Transportation

Agriculture

are recommended by these organizations. Hence the analysis of trace amounts of organic and inorganic species in biological, food, and environmental samples and in pharmaceutical products have an important place in all environments containing living cells (Fig. 1.1).

1.2 Historical development of separation and preconcentration methods In the end of 19th century, Wilhelm Ostwald described analytical chemistry as the art of separating, recognizing different substances, and determining the constituents of a sample [9]. Taking the human health and environment safety into consideration, the fast, accurate, and sensitive determination of these organic and inorganic species, especially at trace levels in biological, food, and environmental samples and pharmaceutical products, is always a subject of great interest, especially in the field of analytical chemistry.

In the age of classical analysis, while gravimetric and titrimetric methods were used for the determination of the major and minor components of materials such as rock and ores, the proximity of the sum of components approaching 100% was seen as a measure of the quality of the analysis. Although it is known that trace elements are present, however, they are not considered to have a significant contribution to clustering in very small amounts. An early authority was Hillebrand [10], who published his classic book Analysis of Silicate and Carbonate Rocks in 1919 and used the word “trace” to identify components below 0.01% or 0.02% below the quantitative detection limit. In 1944 Sandell published Colorimetric Determination of Traces of Metals. Sandell classified the major, minor, and trace constituents as follows: Major constituents of the fraction correspond to higher than 1% of the total sample amount; minor constituents are those present in amounts between 0.01% and 1%; and trace constituents are those below 0.01% [11]. In a book Trace

New Generation Green Solvents for Separation and Preconcentration

4

1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

Analysis, published in 1965, reported the modern description of “trace” as more flexible [12]. This book contains beautiful and important comments such as “The connotation of the term ‘trace’ varies with the background or interests of the reader” and “any sharp division is, of course, superfluous, and will depend on the nature of the sample to be analyzed, the analytical technique employed, and the analyst.” In that book, the upper limit of trace level was considered to be about 100 ppm by weight, and the term “ultratrace” was considered for constituents below 1 ppm. The development of novel analysis methods by analytical chemists allows for the determination of lower concentrations of analyte or analytes in different sample matrices. A brief history of analytical chemistry in terms of milestones in detection limits is shown in Fig. 1.2. For trace analysis to emerge as an area of expertise in itself, two conditions had to be met: special needs and applicable methods. In general, qualitative methods appeared much earlier than quantitative ones. There were a

FIGURE 1.2

few qualitative tests and even some quantitative sensitivity methods before the beginning of the century, but they did not cause much curiosity until needed. The 1940s created a new need for extraordinarily sensitive and difficult analytical procedures. World War II had a very stimulating influence on new needs, but it also suppressed free publication for several years. This resulted in the release for publication of a large amount of previously classified information shortly after the end of the war in 1945. The instrumentation and procedures built up to solve specific war-related questions became available for wider applications [12]. Analysis of trace levels of organic and inorganic species in biological, food, and environmental samples and in pharmaceutical matrices is a difficult process. Generally, a complete process of analysis of organic and inorganic species in a sample takes five steps: (1) collection of the sample, (2) conservation of the sample, (3) preconcentration and separation of analyte/analytes from sample matrix,

Brief history of analytical chemistry in terms of milestones of detection limits.

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

(4) instrumental analysis, and (5) data processing. A survey carried out in 1991 declared that sample preparation can account for around two-thirds (61%) of the effort of the typical analytical chemist, and 92% of the respondents considered sample preparation as very important or moderately important [13]. No doubt it should be stated that, in the last 50 years, analytical chemists have been able to present many developments in their work, as well as cost- and time-saving methodology. And hence the classic gravimetric and titrimetric analysis methods, which allow the analysis of a single or at most two analytes, are now in most cases replaced by instrumental detection techniques that can provide two- and multidimensional information at quantities of a few nanograms, pictograms, or even femtograms [14]. Though most modern instrumental detection systems provide excellent detection limits, combined methods, consisting of several stages such as sampling, decomposition, preconcentration, separation, and determination, bring important improvements in relative detection limits, as well as in the accuracy and precision of the analytical results [15]. The other important advantages of such combinations are illustrated in Table 1.1. Though the importance of sample preparation is often overlooked, it must be recognized that the most important and critical stage in this process is the separation and preconcentration step due to the complexity of sample matrices and lower levels of these species at trace levels and even lower than the detection limits of the available measurement system (from ng L21 to mg L21 or from ng kg21 to mg kg21). In this way, analyte concentration is increased above the detection limit of the measurement system, interference effects of the matrix species is decreased or eliminated, and the analyte in sample matrix is converted into a more suitable form for detection, which can

5

promote the loss of analytes or contamination of sample. A wide range of separation and preconcentration techniques have been developed over the last 100 years. While development was slow until the 1990s, the developments in this field have gained momentum in the last two decades because scientists continue to explore accurate, sensitive, simple, cheap, and widely available sample preparation procedures with reasonable detection limits. Solid phase extraction (SPE), liquid liquid extraction (LLE), cloud-point extraction (CPE) and coprecipitation (CP) applications were the conventional and more used sample treatment techniques until 2000s. However, the production of the new extraction mediums, such as nanosized sorbents and new-generation solvents, and the advent of new extraction equipment, such as minisized extraction columns, minisized extraction tubes, microinjection systems, ultrasonic and microwave vibration shakers, vortex mixer equipment, and so on, have led to an important transition from macroscale separation and preconcentration methods to microscale ones. Microscale separation and preconcentration methods may become more simple and rapid without causing deterioration in the analytical accuracy and precision. The microscale new-generation separation and preconcentration methods have come to be known as solid phase microextraction (SPME) and liquid phase microextraction methods (LPME) for 30 years. When the literature studies are examined, it is seen that while separation and preconcentration procedures, especially coprecipitation, liquid liquid extraction and solid phase extraction for the extraction of the major components in real samples, have been used over the last 100 years, they have been frequently used for extraction and preconcentration of trace organic, inorganic, and bioactive analytes for 70 years [16 84].

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

TABLE 1.1 Comparison of the direct instrumental analysis and combined methods with instrumental techniques for trace organic and inorganic analyte analysis. Items Direct analysis with instrumental techniques Interferences Strong matrix effects interferences may occur

Combined methods with instrumental techniques Matrix interferences can be eliminated by separating trace analytes from the sample matrix

Detectability Detection limits depend on the sensitivity of the detector and the signal generation area of the instrumental technique

Trace analytes in the sample are completely concentrated into a small volume, which lead to a strong increase in the detection limit

Calibration

Reference materials are used

Calibration can be done readily by applying the standard solutions

Systematic errors

Loss of analytes, contamination, and blank problems are minimal level

Contamination, volatilization hazards and blank problems are more common However, these drawbacks can be eliminated by careful operations

Economical aspects

Simultaneous analysis of analytes are simple and rapid

The coprecipitation method is one of the first separation and preconcentration applications for trace analytes, followed by liquid liquid extraction and solid phase extraction methods.

1.2.1 Historical development of coprecipitation methods In the coprecipitation method, a precipitating agent is used for the reliable isolation of the analyte precipitates in optimum conditions. The precipitates are isolated from the sample solution with centrifugation or filtration with membrane filters. Isolated analyte precipitates are dissolved in a suitable solvent such as different concentrations of HNO3, H2SO4, HCl, and the like. Then analyte concentration in the last phase is analyzed by means of a suitable detection technique. The mechanism of the coprecipitation method was explained for first time by Shapiro and Kolthoff in 1896 [16]. They explained the

Expert person, capability, time, and more apparatus are generally required, but the methods can also be carried out rapidly and simply by using well designed techniques and apparatus

precipitation of silver bromide with the coprecipitation mechanism. After this report, many studies were carried out to explain the coprecipitation mechanisms for different species. For example, in 1924 McCandless and Burton proposed the coprecipitation mechanism for the determination of phosphoric acid by the molybdate-magnesia method [17]. In a different study, in 1934 a benzoate method was developed by Kolthoff and coworkers to separate the iron, aluminum, and chromium from other ions of the third group and alkaline earth ions [18]. This study may be the first work to report on the separation and analysis of the metals with the coprecipitation method. Currently, the search for new precipitating agents for the quantitative precipitation and determination of metal ions is ongoing. Mover and Remington provided magnesium and 8hydroxyquinoline precipitation as a coprecipitation agent for zinc in 1938. Moreover, they explained the importance of the pH of the sample solution phase on coprecipitation efficiency and reported that the separation of ferric iron

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

and aluminum is possible within in same conditions with zinc ions [19]. In 1939 a report was declared by Kolthoff and Overholser on the coprecipitation of divalent zinc, nickel, cobalt, magnesium, calcium, and manganese ions. They used ferric hydroxide as the coprecipitation agent and checked the influence of the concentration of ammonia and ammonium chloride on the coprecipitation efficiency of the metal ions. They found that coprecipitation efficiencies of cobalt, nickel, and zinc ions decrease with increasing concentrations of ammonia and ammonium chloride, while those of calcium, manganese, and magnesium decrease with increasing concentrations of ammonium chloride but increase with increasing concentrations of ammonia [20]. In 1941 Louis Waldbauer and coworkers used barium sulfate as a coprecipitation agent for the coprecipitation of nickel, chromium, cobalt, iron, and manganese ions and used lead sulfate as the coprecipitation agent for the coprecipitation of copper and zinc ions. They found that chromium, manganese, and iron could be coprecipitated with barium sulfate, while nickel and cobalt did not coprecipitate with barium sulfate. Zinc and copper were coprecipitated with lead sulfate [21]. Witte provided a coprecipitation method for the determination of tungsten as BaWO4 in 1943 [22]. The first known study for the separation and analysis of small amounts of arsenic, antimony, and tin in lead and lead alloys by coprecipitation method was performed by Luke in 1943. In this study, Luke used manganese dioxide as the coprecipitation agent [23]. The turning point in this area took place in 1948 with the first study on the analysis of the trace level of metal ions reported by Kolthoff and Carr. They used magnesium ammonium phosphate as the coprecipitation agent for the accumulation of traces of arsenate. In this method, 150 μg L21 of arsenic can be analyzed with an accuracy of 2%. They used an excess of tartrate

7

to prevent the precipitation of other metal ions in the ammonia medium. They suggested that the developed coprecipitation method can be successfully used for the determination of arsenic in steel samples that contains more than 0.01% of arsenic [24]. Almost at the same time, investigation various organic and inorganic precipitating agents for coprecipitation methods has been stepped up. In 1950 West and Conrad reported in an extensive work titled “A Comparison Study of the Coprecipitation of Cations by Organic and Inorganic Precipitants.” They carried out the experiments on the typical classes of inorganic organic precipitation reactions in relation to their tendency to coprecipitate foreign cations. They found that organic coprecipitation agents tend to coprecipitate cations to a greater extent than inorganic ones. The possible mechanisms in this sort of precipitation include the formation of coagulated colloidal particles under the action of the electrolytes present at the time of the reaction. Trivalent cations have very suitable flocculation values, and as a result the precipitation will be at the highest level [25]. In the 1950s, it was possible to measure the analytes in lower concentrations in parallel with the developments in instrumental measurement techniques, and the studies in this field gained speed. In 1951 Garrison and Gile developed a method for the radiochemical analysis of At211 in fat, bone, skin, and muscle of rats using a coprecipitation method. According to our best knowledge, the developed method may be the first report on the analysis in biological samples. They used the metallic tellurium as coprecipitation agent and analyzed At211 with an alpha-particle-X-ray counting method [26]. Fr223 has a half-life of 21 min; hence it is imperative to use a very fast method for analysis of Fr223. Based on this requirement, Hyde, who was a researcher at the University of California, used silicotungstic acid as coprecipitation agent for the

New Generation Green Solvents for Separation and Preconcentration

8

1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

precipitation and isolation of francium-87 from bombarded thorium targets [27]. The important advancements on the coprecipitation method has been lived after 1950s with the application of new analytical instruments and combined separation methods, such as ion exchange, adsorption, and liquid liquid extraction for trace analysis. Some of important coprecipitation applications to date are described here. In 1963 Girardi and Pietra found that the separation of trace species from the matrix environment prior to isotope analysis was a very important stage. They used ion exchange, isotopic exchange, and coprecipitation methods for the separation of 13 trace impurities in aluminum prior to neutron-activation analysis. The carrier free coprecipitation step provided the simpler and faster final separation of individual rare earths [28]. Though the photometric determination of tin with the phenylfluoron method provides an improved sensitivity, matrix ions show adverse effects on accurate determination. Shimizu and Ogata developed a coprecipitation method based on the formation of ferric hydroxide at pH 6B7, which led to the collection of tin in the sample solution. After this step, the precipitate was dissolved and adsorbed on an anion-exchange column. Zirconium, selenium, germanium, titanium, and antimony were removed by elution with 0.5 N hydrochloric acid. Mercury and bismuth were removed in a hydrochloric acid sulfuric acid solution by using isobutyl ketone as a liquid phase extraction medium. The obtained results showed that as little as 1 μg kg21 of tin in common salt, seawater, and bittern could be analyzed with satisfactory results [19]. In 1966 Abdel-Rassoul and coworkers preferred a combined use of separation methods consisting of adsorption on silica gel, liquid liquid extraction, and coprecipitation for the simultaneous determination of iron, chromium zinc, and cobalt in metallic uranium, uranium oxides samples, and uranium

concentrates prior to neutron-activation analysis. They used aluminum chloride as a coprecipitation agent. In last step, they used ionexchange chromatography for the fractional separation of the elements. The method developed allowed the determination of iron, chromium zinc, and cobalt at parts per million levels with a reproducibility of 10% 15% [30]. In 1967 a combined method designed as coprecipitation with alkaline earth salts, followed by solvent extraction of transition metal dithiocarbamates, was developed by Joyner and others for the separation and preconcentration of nickel, manganese, iron, cobalt, zinc, lead, and copper at trace levels in seawater samples. They were able to recovery more than 90% for these elements prior to atomic absorption or flame emission analysis [31]. Fujinaga et al. developed a preconcentration method based on organic coprecipitation for trace levels of zinc, copper, vanadium, molybdenum, aluminum, and uranium in natural water samples prior to neutron-activation analysis. The soluble ions were converted to oxine chelates at pH 5.2, followed by extraction with o-phenylphenol above 56 C and solidification at room temperature. The solid particles were accumulated on a filter, dried, and wrapped up in a polyethylene sheet. In last step, amounts of analytes were measured by neutron-activation analysis at the parts per billion level [32]. In 1975 a combined coprecipitation X-ray fluorescence method was developed by Bruninx and Van Meyl for the preconcentration and determination of zinc and lead between the 10 and 100 μg L21 levels in surface waters. Zinc and lead in surface waters were precipitated by formation of iron hydroxide precipitants [33]. In the same year, Rollier and Ryan searched the applicability of solid-state fluorescence analysis for trace elements by using aluminum as the example element. They precipitated the aluminum as aluminum oxinate with a high amount of oxine and measured the luminescence of the

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

aluminum oxinate precipitate (λex, 385 nm: λex, 524 nm). The developed method allows the analysis of the parts per billion level of aluminum. In the 1970s, the importance of separation and preconcentration methods in determining trace elements was understood by scientists, and interest in this field increased day by day. An important research on the coprecipitation, ion exchange, and solvent extraction was carried out by Okochi in 1975. Okochi developed eight kinds of coprecipitation, three kinds of ion exchange, and three kinds of solvent extraction methods for the separation and preconcentration of trace elements in metals. Okochi investigated the possibility of the separation and preconcentration of smaller amounts of elements than in the conventional methods, which led to the creation of new ideas [34]. From the literature, it is seen that iron hydroxide is one of the most used of coprecipitation agents. In 1975 Bruninx used ferric hydroxide as a coprecipitation agent for the precipitation of trace amounts of Zn, Cd, and Hg [35]. One of the most comprehensive coprecipitation methods for trace elements was carried out by Nagatsuka and Tanizaki in 1976. They developed a coprecipitation method based on the formation of Fe(OH)3 and PbS precipitants for the separation and preconcentration of Ca, Al, Mg, Dy, V, Ti, As, Ag, Cr, Co, Cu, Cs, Fe, Eu, Lu, Na, Rb, La, Sc, Se, Sb, W, Zn, and Sm prior to neutron-activation analysis. They applied this developed method for analysis of these trace elements in river waters [36]. Takemoto and coworkers suggested a coprecipitation X-ray fluorescence analysis procedure for microgram levels of Pb(II), Fe (III), Cu(II), Zn(II), Mn(II), Cd(II), Cr(III), Sb(III), and As(III) in industrial wastewater and river water samples. They used model solutions including diethyldithiocarbamate (DDTC) or ammonium pyrrolidinedithiocarbamate (APDC) as complexing agents at pH 5.0 5.5. The metal chelate complex formed was

9

precipitated by the addition of dibenzylideneD-sorbitol. The precipitates were collected on a filter paper, dried, and analyzed by X-ray fluorescence spectrometer. The obtained analytical results were in good agreement with those obtained by the atomic absorption method [37]. Ueda and Yamazaki developed a coprecipitation procedure for trace amounts of cadmium prior to flameless atomic absorption spectrometric and the differential-pulse polarographic determinations in 1986. Cadmium changing from 0.01 μg to at least 1000 μg amounts in 50 400 cm3 of a sample solution was precipitated quantitatively by using a hafnium hydroxide coprecipitation agent. They successfully used these methods for the determination of trace amounts of cadmium in river water samples [38]. A combined sequential separation/preconcentration method, consisting of coprecipitation with iron hydroxide and bismuth phosphate, ion exchange, electrodeposition, and counting by alpha spectrometry, was provided by Pu and Am at trace levels in environmental samples. To determine Th in a chicken bone sample, a combined sequential separation/preconcentration method was used as follows: oxalate precipitation, ion exchange, electrodeposition, and alpha spectrometry [39]. In 1989 Eller et al. used Se as a coprecipitation agent for gold, platinum, palladium, and rhodium at the nanogram and picogram levels in natural water, geological and biological standards, and manganese crust. They achieved the quantitative isolation for these elements prior to Zeeman graphite furnace atomic absorption spectrometry and total reflection Xray spectrometry analysis [40]. In the same year, Kurata et al. suggested an easy and rapid procedure consisting of coprecipitation and Xray fluorescence for the analysis of As, Sb, Bi, Sn, Fe, and Pb at trace levels in copper. In the procedure, they solved a copper sample ranging from 0.2 to 2.0 g in 20 mL of 8 M HNO3 by heating. After cooling, 1 mL from 1 mg mL21

New Generation Green Solvents for Separation and Preconcentration

10

1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

of Zr solution was put in sample solution, and the pH was adjusted to 9.4 9.5. The volume of the sample solution was increased to 70 mL with pure water and left to sit for 1 h to complete the precipitation, and precipitates were collected on the 1.0 μm membrane filter. The precipitate on the filter was dried prior to Xray analysis. Three percent of relative standard deviation (RSD) was obtained for analysis of 20 μg of all elements. They applied their method for analysis of certified reference materials (CRMs). The obtained results were in good agreement with the certified values [41]. In 1990 McLaren et al. used the isotope dilution ICP-MS for multielement trace determination in seawater and the nondefatted lobster hepatopancreas tissue certified reference materials and HPLC-ICP-MS for determination of tributyltin and dibutyltin in the harbor sediment reference material. While the elements in seawater were separated from the matrix medium by using either adsorption on immobilized 8-hydroxyquinoline or by reductive coprecipitation with iron and palladium, butyltin compounds in the harbor sediment reference material were separated from the matrix medium by cation-exchange high performance liquid chromatography (HPLC). Detection limits for tributyltin and dibutyltin were found as 5 and 12 ng Sn g21, respectively [42]. A different usage of coprecipitation and ICP-MS procedure was reported by Nakamura and Fukuda to determine Sb, As, Bi, Pb, and Sn traces in high-purity copper. They dissolved 1.0 g of copper sample in 8 mL of 7 M HNO3 and added 10 mg of La to the solution. As, Sb, Bi, Sn, and Pb ions were coprecipitated with lanthanum ions as their hydroxides by adjusting the pH of the sample solution between 9 and 10. The precipitate was collected on a filter and dissolved with acidic solution, and concentrations of Sb, As, Bi, Pb, and Sn were determined by ICP-MS. The respective detection limits were found between 0.01 and 0.08 ng mL21

with the RSD less than 2.5% for 100 ng of analytes [43]. Niskavaara and Kontas suggested a reductive coprecipitation method to separate Pd, Au, Rh, Pt, Se, Ag, and Te traces from geological samples. In this method, while mercury was used as a collector, tin(II) was used as a reductant. After the coprecipitation step, graphite furnace atomic absorption spectrometer (GFAAS) was used to measure the concentration of analytes. The accuracy of the developed method was checked on the analysis of geochemical reference samples [44]. In a different application, lanthanum hydroxide as a coprecipitation agent was used for the separation of hydride-forming Bi(III), As(V), Sb(V), Te(IV), and Se(IV) trace elements in a Mo matrix prior to analysis with continuous hydride generation and inductively coupled plasma atomic emission spectrometry. Detection limits for As, Bi, Sb, Se, and Te were found as 0.2, 0.7, 2, 0.5, and 2 μg g21, respectively [45]. The transition from macroscale coprecipitation methods needing large sample amounts and reagents to the microsized minimum sample amounts and reagents has gained importance in recent years. The most important step in the development of microsized coprecipitation techniques is the solving of precipitates in microliter levels of final solvents before the detection step. The improvements have led to high preconcentration factors and reach to lowered detection limits. An example application was carried out by Agaki and Haraguchi in 1990. They used coprecipitation and inductively coupled plasma atomic emission spectrometry (ICP-AES) for preconcentration and determination of Cr, TI, Al, Fe, Mn, Ni, Co, Zn, Cu, Pb, and Y traces in seawater. They precipitated trace elements with gallium hydroxide and dissolved the precipitate with 50 μL of nitric acid. A cross-flow nebulizer was used to introduce the 50 μL of solution into the plasma. The detection limits of these elements were found to be 10 500 ng L21 with about 10%

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

precision. In this analytical method, about 50 samples of 10 mL volume could be enriched and analyzed within 1 h. The low sample volume needed and the speed of the method were the most important advantages [46]. Takeda et al. used the coprecipitation method for the preconcentration of trace amounts of tin before electrothermal atomic absorption spectrometry (ETAAS). They used yttrium hydroxide for the precipitation of tin at pH 9.5 11.2. A linear calibration graph between 0.004 and 0.12 μg mL21 was obtained. They used this developed coprecipitationelectrothermal atomic absorption spectrometry (ETAAS) procedure for the determination of tin in zinc metal [47]. Hiraide et al. developed a coprecipitation method based on the formation of indium hydroxide at pH 9.5 for parts per billion levels of Cu(II), Cr(III), and Mn(II). After the preconcentration step, the precipitate was dissolved in 0.5 M hydrobromic acid and determined with GFAAS. They applied this developed method to water samples [48]. The transition metals have different oxidation steps because the oxidation steps for each element have different health effects on living cells. Therefore in a sample, the analysis of the species with the correct oxidation steps is more important than the total quantification of the relevant element. In 1991 Wengi et al. provided a chelate coprecipitation graphite furnace AAS procedure to determine parts per billion levels of Cr(III) and (VI) in natural water and human urine samples. They checked several metal ion chelating agent coprecipitation carriers: Co(II)-l-nitroso-2-naphthol, Co(II)-dithizone, Ni-dimethylglyoxime, Ni(II)-dithizone, Co(II)-pyrrolidinedithiocarbamate, Fe(II)-dithizone, Fe(III)-diethyldithiocarbamate (DDTC), Zn(II)-APDC(APDC), Mn(II)-DDTC, and Cu (II)-DDTC. They found that Mn(II)-DDTC was the most suitable chelate carriers for the separation of Cr(III) and Cr(VI) at suitable pH. While the recovery values for Cr(III) were changing from 87.4% to 105.3%, the recoveries

11

for Cr(VI) were changing from 85.4% to 108.2% [49]. In another study, Zhang et al. suggested a coprecipitation method for the determination of arsenic(III) and arsenic(V) traces in water samples. In this study, As(III) was coprecipitated quantitatively with a Ni-ammonium APDC complex at the pH between 2 and 3, but, in the same experiment conditions, arsenic (V) was not coprecipitated with the Ni-PDC complex. So the developed method was based on the precipitation of As(III). The amount of As(III) in the precipitate was measured by solid sampling ETAAS. As(V) was converted to As(III) by using sodium thiosulfate and potassium iodide, and the total As concentration was analyzed. The detection limit was found as 0.02 ng mL21 for 500 mL portions of water samples [50]. Currently, the prospect of developing online preconcentration and analysis methods, which enables automatic analysis in a short time, has created excitement in the scientific community. In 1992 Fand and Dong suggested an online flow injection coprecipitation system coupled to an electrothermal atomic absorption spectrometer for the determination of heavy metal traces in whole blood digests. They used the iron(II)-hexamethylenedithiocarbamate (HMDTC) complex to collect nickel and cadmium on the walls of a knotted reactor. The precipitate was dissolved in 60 μL of isobutyl methyl ketone and introduced onto a graphite furnace platform of atomic absorption spectrometer. The precipitate collection times were 20 40 s, and sample flow rates of 2 mL min21 for Ni and 3 mL min21 for Cd were applied. The detection limits for cadmium and nickel were found as 0.003 and 0.02 μg L21, respectively [51]. In another study, Dong and Fang designed a flow injection technique including an online coprecipitation and flame atomic absorption spectrometer determination for trace amounts of cadmium, nickel, and cobalt. Metal ions were coprecipitated with APDC-Fe

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

complex on a knotted reactor (KR). The precipitate was dissolved in MIBK and directly injected into flame atomic absorption spectrometer (FAAS). The enhancement factors for Ni, Cd, and Co were 30, 33, and 42, respectively. They applied the developed method for the analysis of bovine liver (NBS1577a) and urine (GBWO9103) standard reference materials with good agreement [52]. A different flow injection online preconcentration procedure was developed for silver at trace level in geological samples. The separation and preconcentration of silver ions were accomplished by using an online coprecipitation with iron(II)diethyldithiocarbamate complex in the presence of 1,10-phenanthroline in a flow injection system. A knotted reactor was used to collect the precipitate. The precipitate, dissolved in isobutyl methyl ketone, was injected into the nebulizer of an atomic absorption spectrometer. High concentrations of iron(II) were masked with 1,10-phenanthroline. Enhancement factor, detection limit (3σ), concentration efficiency, coprecipitation time, and sampling frequency were found as 26, 0.5 μg L21, 28 min21, 45 s, and 62 h21, respectively [53]. Nielsen et al. combined hydride generation atomic absorption spectrometry (HGAAS) with online coprecipitation. The developed flow injection procedure was used for analysis of ultratrace amounts of selenium(IV). The suggested application provided an online addition of the coprecipitant to the time-based aspirated sample. In this system, the sample solution and lanthanum nitrate as the coprecipitating agent were mixed online and merged with an ammonium buffer solution of pH 9.1, which led to precipitation and quantitative collection on the walls of the microline reactor. Afterward, the precipitate was dissolved in hydrochloric acid and analyzed with hydride generation atomic absorption spectrometry (HGAAS) [54]. In 1998 Mao et al. designed a flow injection online coprecipitation preconcentration, combined with FAAS for the accurate analysis of trace

silver. Copper-diethyldithiocarbamate (DDTC) chelate was used as the coprecipitation agent. The detection limit for silver was 0.6 μg L21 for a loading time of 30 s. The scientists successfully analyzed trace amounts of silver in geological samples [55]. Liu et al. used Ni(II)diethyldithiocarbamate (DDTC) coprecipitation agent in the flow injection online coprecipitation system for preconcentrations of trace lead, copper, iron, and cadmium in environmental and biological samples. They also used a knotted reactor to collect the precipitate prior to FAAS determination. While enhancement factors for iron, lead, cadmium, and copper were 59, 58, 65, and 60, the detection limits for iron, lead, cadmium, and copper were 2.5, 2.7, 0.2, and 0.5 μg L21, respectively [56]. Divrikli and Elci provided a cerium(IV) hydroxide coprecipitation method to separate and preconcentrate Co, Cu, Pb, Ni, and Cd traces prior to FAAS determination. They used this method for accurate determination of the trace metals in aqueous solutions, water, and sediment samples [57]. Usage of coprecipitation methods, together with the electroanalytical techniques, has an important place in the literature. Sekharan et al. developed a coprecipitation method for the separation of the antimony in impure zinc sulfate electrolyte, followed by its voltammetric determination in 1996 [58]. Hydrous manganese dioxide was used as the coprecipitation agent [58]. In a different method, Kirgo¨z et al. designed a voltammetric cell allowing direct measurement of precipitates without any need for dissolution or filtration steps. They successfully used this system on the preconcentration of Pb(II) traces in aqueous solution by using Al(OH)3 as the coprecipitation agent. The obtained peak currents from voltammetric determination were found to be much higher than those without applying centrifugation. The detection limit of the developed method was 2.2 3 1029 M [59].

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

Soylak and Balgunes provided a gadolinium hydroxide coprecipitation-atomic absorption spectrometry system to determine trace amounts of cobalt(II), lead(II), copper(II), and manganese(II). The pH of the sample solution was adjusted to 11 to obtain gadolinium(III) hydroxide from gadolinium(III) salt. At this stage, cobalt(II), lead(II), copper(II), and manganese(II) ions were precipitated. The precipitate was dissolved in 1 mL of 1 mol L21 HNO3 and analyzed by FAAS. The detection limits of the analytes were found between 0.52 and 12.0 μg L21 [60]. A important microprecipitation method based on the formation of Cd(II) 1-(2-thiazolylazo)-2-naphthol (TAN) microprecipitate was provided by ALOthman et al. for the preconcentration of cadmium traces. In this system, microvolume of the last phase was injected into a flame atomic absorption spectrometer using a microinjection system. The optimum precipitation medium was obtained at pH 8. The limit of detection, limit of quantification, and relative standard deviation were found 0.25 μg L21, 0.83 μg L21, and 5.5%, respectively. They applied the developed microprecipitationmicrosampling FAAS procedure to the analysis of cadmium in food samples [61].

1.2.2 Historical development of liquid phase extraction/microextraction methods Liquid liquid extraction (solvent extraction) has been one of the best processes known for two centuries for separating the components of a liquid (the feed) by contact with a second liquid phase (the solvent). The basis of the process is based on the dispersion rates of the components between two essentially immiscible liquids. When the relevant analytes/analytes in the sample solution are transferred to the other phase, the matrix components remain in the sample solution or vice versa. In this way, extraction of the

13

analyte/analytes from the matrix environment is carried out successfully. In other words, the transfer of the components from one phase (the feed) to the other is guided by a deviation from the thermodynamic equilibrium, and the equilibrium state depends on the interactions between the two phases [31,62 95]. The foundations of solvent extraction are probably based on the studies conducted by Buchoz in 1805 [62,63]. He discovered that uranyl nitrate is freely soluble in diethyl ether. The first known application of liquid liquid extraction (LLE) was by E. Peligot [64]. In 1842 uranyl nitrate was extracted from nitric acid solution to the ether phase in this study. Nearly 100 years later, nuclear energy, of great interest during World War II, was used in the extraction and enrichment of large amounts of uranium from the matrix environment. In 1867 Skey suggested the extraction of various metal ions as thiocyanate forms into the ether phase, a method that is still popular, but did not use this method himself. He provided ether-based thiocyanate extraction for the separation of gold from platinum, iron from the alkaline earths aluminum, chromium, manganese, uranium, platinum and nickel, and cobalt from nickel [65]. Ether extraction was becoming increasingly popular, and in 1892 Rothe succeeded in extracting ferric chloride present in concentrated nitric acid into the ether phase. These applications continued rapidly up to the ether extraction of gallium trichloride in 1924 [66]. One of the most important milestones in the history of solvent extraction is the synthesis and use of organic chelating agents that form organic soluble complexes with various metal ions. A very important application in this field was carried out by Fischer. Dithizone, a versatile chelating agent, was used in the extraction and quantitative determination of various metal ions in his study [66,67]. In order to perform the desired extraction and analysis, the effects of pH and the use of masking agent variables that are important

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

in extraction studies were investigated. Then different organic chelating reagents such as β-diketones, dimethylglyoxime, and 8hydroxyquinoline were successfully used in LLE procedures. In the 19th century, LLE was a popular procedure to extract and obtain valuable ingredients, such as perfume and paint, from different plant sources. In the 1800s three research studies conducted by Berthelot and Jungfleisch, Nernst, and Gibbs were introduced to explain the theory of phase equilibrium, the dissolution rates of solutes dissolving between two unmixed liquids, and presented data describing the scientific facts of liquid liquid extraction [68,69]. These and other advances have made significant contributions to the development of the chemical industry. In 1883 Goering developed a countercurrent extraction process using ethyl acetate to recover acetic acid from “pyrolytic acid” produced by the pyrolysis of wood [70]. In the late 1890s, the emergence of the chemical engineering profession paved the way for further consideration of process designs and quantitative foundations in process development. Most of the pathway recorded in distillation and absorption studies was readily adapted to liquid liquid extraction due to its similarity with another diffusionbased operation. The use of liquid liquid extraction studies in the chemical industry increased day by day and became one of the most popular methods in the 1930s. Many of the liquid liquid extraction methods still used today in the chemical industry are the result of innovations and developments made between 1920 and 1970. For example, in the 1940s, the Dow Chemical and Universal Oil Products Companies introduced a well-known commercial Udex procedure. In this procedure, aromatic compounds were separated from hydrocarbon mixtures by using diethylene glycol.

The 1920s 1940s are considered important milestones in the progress of liquid liquid extraction methods since the production of new solvents and innovative apparatus, such as centrifugal extruders, mixer-settling equipment, and mechanically agitated extraction columns, were starting to be used in extraction procedures. At the end of the 1920s, oil refineries and chemical companies were able to produce different alcohol, ketone, ester and chlorinated hydrocarbon derivatives in large volumes by using petroleum-refining processes or natural gas products. After these developments, many specialty solvents such as sulfolane (tetrahydrothiophene-1,1-dioxane) and NMP (N-methyl-2-pyrrolidinone) were provided to extract aromatics from hydrocarbons in the same years. Moreover, special organophosphorous extraction solvents were also utilized for extraction and recovery of metals dissolved in aqueous solutions. After the 1950s, liquid liquid extraction methods began to gain popularity for separation and preconcentration of trace amounts of organic and inorganic analytes due to the accessibility of new extraction solvents and detection systems. Although the LLE methods were frequently used in the separation and enrichment of the organic and inorganic species at the trace level between 1950s and 1990s, in this 40-year period, the main important developments came about in the analysis step, combined with the LLE extraction methods, and no significant further improvement was made in LLE extraction. Major developments and innovations were experienced with the introduction of green chemistry, new-generation extraction solvents, and microextraction methods in the 1990s. Therefore LLE can be explained in two parts, before and after 1990. Developments up to the 1990s are explained in the some literature studies.

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

1.2.2.1 Classification of liquid liquid extraction systems Extraction can be classified on the basis of the • nature of extracted species and • process of extraction. On the basis of nature of extracted species, there are two types 1. chelate extraction and 2. ion association Classification based on the basis of process of extraction, there are four types 1. extraction by chelation or chelate formation, 2. extraction by ion pair formation, 3. extraction by salvation, and 4. synergistic extraction. The organic extraction solvents commonly used until the 1990s for the extraction of analytes from aqueous phase to organic phase in the LLE are as follows: Carbon-based solvents: Carbon tetrachloride (CCl4), chloroform (CHCl3), dichlromethane (CH2Cl2), carbon disulfide (CS2), N-hexane. Acid-based solvents: Carboxylic acids (naphthenic acids, Versatic acids, decanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid), alkyl phosphoric acids [Di2ethylhexyl phosphoric acid (DEHPA)]. Amine-based solvents: Primary amines, secondary amines, tertiary amines, quaternary amines (N,N-dimethyl cyclohexylamine, N,Ndimethyloctylamine, triethylamine, primene JMT, Adogen 283, Alamine 336, Adogen 381). Alcohol-based solvents: Decanol, undecanol, heptanol. Cyclic structure solvents: Cyclohexane, cyclohexanone. In 1951 Andrews and Lloyd developed an LLE method for the separation of zinc traces prior to its colorimetric determination. Zn complexed with di-beta-naphthylthiocarbazone gives a cherry-red soluble complex in carbon tetrachloride. Other metals, which show interference effect upon determination, were

15

eliminated by applying a preliminary extraction as diethyl-dithiocarbamates. The method was developed and used for analysis of 0.01 ppm zinc in liquid or 0.05 ppm in solid samples [71]. In 1953 Garner and Hale researched the effect of surface-active materials on LLE procedures. As a model application, they researched the effect of Teepol added in the water phase on the rate of extraction of diethylamine from toluene drops by water. Results showed that extraction efficiency was reduced to 45% with the addition of only 0.015% of surface-active material (Teepol) [72]. Pijck et al. developed a different LLE method for the separation of radioactive trace analytes. They used isoamylacetate for extraction of chromium traces from iron matrix with high amounts. Cuproine in isoamylalcohol as the extraction solvent phase was used to separate copper at trace levels from zinc matrix [73]. In 1962 Attaway et al. developed a procedure for LLE and the gas-liquid chromatography fraction of trace amounts of carbonyl components in orange essence. Carbonyl components were converted to their dinitrophenylhydrazones by reactions of carbonyl with 2,4dinitrophenylhydrazine sulfate in ethanol and analyzed as dinitrophenylhydrazones. The carbonyl components identified include hexanal, hexenal (two isomers), acetaldehyde, octenal, octanal, neral, furfural, carvone and geranial [74]. In 1965 Brooks checked the usability of extraction solvents lighter than water. He developed a new method to separate and analyze trace elements in silicate rocks. The method was based on the extraction of elements as chloro complexes into methyl isobutyl ketone phase and subsequent spectrographic analysis. The results showed that trace elements in silicate rock could be extracted from the main matrix medium and could be fractionated from each other. The method developed provided fast, flexible, relatively free extraction and simple analysis with

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

quantitative results. Authors claimed that the method developed was applicable for separation radioactive species and different oxidation states of the same element, for example, antimony(III) from antimony(V) [75]. In 1967 Joyner et al. introduced a simple separation and preconcentration procedure for metal traces. The procedure consists of coprecipitation with alkaline earth salts, followed by liquid liquid extraction of transition metal dithiocarbamates prior to flame emission or atomic absorption determinations. The method developed was applied to the quantitative analysis of iron, manganese, cobalt, nickel, lead copper and zinc at trace levels [31]. In 1968 Campbell developed a liquid liquid extraction for the separation of rhodium and palladium from waste solutions. They used tricapryl monomethyl ammonium chloride as extraction solvent. They used flame photometry to determine rhodium and palladium in the last phase. The method developed provided 0.05 μg mL21 of detection limit [76]. Mirza suggested an LLE for 115Cd and 89,90Sr as fission products. They succeed the extraction of these elements with 1-phenyl-3-methyl-4-caprylpyrazolone-5. The LLE method provided extraction efficiency of more than 80% for 89,90Sr and 90% for 115Cd [77]. In a different study, Farrar et al. used 2thenoyltrifluoroacetone-xylene as the extraction solvent phase for liquid liquid extraction of 249Bk. They used the beta counting system for analysis of 249Bk [78]. In 1971 Bonsack developed an LLE method for the separation of trace levels of niobium from industrial titanium sulfate solutions. Cyclohexanone and diisobutyl carbinol were used as extraction solvents in acidic extraction medium. Niobium was separated from the matrix medium with a high extraction efficiency (92% 98%) [79]. In 1972 Barratt et al. introduced an LLE method for separation and preconcentration of trace amounts of nickel prior to gas-liquid chromatography analysis.

Ni(II) in aqueous phase at pH 4.5 5.0 was extracted to the extraction phase consisting of monothiotrifluoroacetylacetone and n-hexane. The LLE method applied for determination of trace amounts of nickel in fat and tea samples [80]. Yatirajam and Ram introduced an LLE method for the separation of molybdenum from a hard matrix medium including aluminum, uranium manganese, chromium, zirconium, iron, nickel, cobalt, and titanium. Molybdenum was turned to phosphomolybdenum blue complex in acidic medium and extracted to isobutyl ketone phase. Concentration of molybdenum in the last phase was determined by cerimetry or other standard methods [81]. Tinsley and Iddon used a liquid ion exchanger Amberlite LA 2 in thiocyanate form as the extraction phase for the separation and extraction of copper prior to atomic absorption determination [82]. Generally LLE methods are used in the extraction of analytes in the aqueous phase into the organic phase. However, in some studies, an opposite application has been made. For example, Lamey and Maloy used sulfuric acid as a selective extraction solvent for extraction of anthracene traces from cyclohexane solutions of phenanthrene. In this method, anthracene was removed, and high amounts of ultrapure phenanthrene were easily obtained [83]. In 1970s in order to find the optimum and best separation-preconcentration procedure, the scientists started to make comparison studies between extraction methods for trace analytes. Mieure et al. developed three different extraction methods, which were liquid liquid extraction, preconcentration of analytes in a porous polymer resin column, and preconcentration of analytes in porous polymer resin column. They selected organic components as trace analytes. It was reported that detection limits of 0.01 0.1 ppm were obtained with these methods [84].

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

As a result of the fact that the methods of trace analysis have become important and a lot of studies have been made in this field, a literature data source was formed. Scientists have begun to write review studies in this area by using these resources. One of the most important developments in extraction methods was to collect all information about extraction in reviews. In 1975 Eisenbrand wrote a review titled “Recent Developments in Trace Analysis of Volatile Nitrosamines: A Brief Review.” In this review, many extraction and detection techniques up to the 1970s were discussed [85]. As in other sample preparation methods, online extraction applications in LLE started to attract attention at this time. In 1976 Wu and Suffet designed new continuous LLE devices, which paved the way to the design and construction of new online extraction apparatus. The main part of this device was a helical Teflon mixing coil. The continuous delivery of the sample solution and the extraction solvent to the extraction medium was provided by a dual-channel micropump. Separation of the extraction phase from the aqueous sample phase was accomplished by a glass column phase separator and a continuous solvent evaporator concentrator. In this way, the extraction solvent separated was prepared for recycling. The developed apparatus had a simple and cheap modular concept that provide greater analytical flexibility and was capable of recycling the extraction solvent. The developed apparatus was used for analysis of organophosphate pesticides in water samples. Moreover, the authors claimed that this continuous LLE apparatus is applicable for the extraction and analysis of any trace organic molecules [86]. Nord and Karlberg also introduced an automated liquid liquid extraction system for the separation and preconcentration of trace amounts of metal ions prior to flame atomic absorption spectrometer determination [87]. Coello et al. introduced a continuous-flow LLE combined with flame

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atomic absorption spectrometer for extraction and analysis of indium. In this procedure, indium traces in diluted nitric acid solution were extracted into bis(2-ethylhexyl)phosphoric acid phase dissolved in 4-methylpentane2-one. The continuous-flow LLE system was connected to online flame spectrometry to use a fully mechanized system. The detection limit, relative standard deviation, and sample throughput of the developed method were 0.03 mg L21, 1.5%, and 60 h21, respectively [88]. Oliver and Bothen combined the LLE method with a capillary gas chromatography electron capture detection system for the separation, preconcentration and analysis of trace amounts of 12 chlorobenzenes in water samples. They used pentane as the extraction solvent in the LLE method. They achieved a preconcentration factor of 1000 2000 and detection limits of 0.01 500 ng L21 (ppt) for chlorobenzenes [89]. In a different application, trace levels of herbicides and nitro derivatives were extracted with CH2Cl2 and analyzed by gas chromatography and capture electron detector [90]. In 1983 Vahtila compared the applicability and analytical performance values of different preconcentration methods, such as liquid liquid extraction, solid phase extraction, ion exchange, and the like, for analysis of trace metals in seawater, biological materials, and marine sediments [91]. Agostiano et al. applied a different LLE method for separation and preconcentration of some trace pesticides (carbamates, chlorinated, carbonates phosphorated) in water samples. GC (gas chromatography) and HPTLC were used in the measurement stage [92]. In 1987 Petrov and Zhivopistsev used antipyrine and diantipyrylmethane salts instead of organic solvents for extraction of trace elements prior to spectrochemical analysis [93]. Hamann and Kettrup combined LLE and SPE methods for the separation and preconcentration of phenoxy acid herbicides in water

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

samples. Analyses were conducted by HPLCUV [94]. In a different application, LLE and SPE methods was used together for the separation and preconcentration of trace metals [95]. As the world population increases, the needs of people and production required to meet these needs have increased rapidly. In parallel, there has been a linear increase in the amount of chemical activities in both research laboratories and industry in order to meet production needs. Chemical activities in the laboratory and industry can negatively affect living cells and the natural environment and may lead to a decrease in the quality of life. Perhaps environmental awareness for most of us started with the book Silent Spring published by Rachel Carson in 1962 [96]. One of Carson’s alarming observations was the environmental pollution caused by pesticides such as DDT, leading to the death of millions of birds. During this time, the industry was striving to protect the nearby environmental zones by building long chimneys. But it could not account for serious environmental problems in the long run. After 20 years, the UN Conference on Environment and Development (the Earth Summit) was organized, and many reports were published. In 1987 The World Environment and Development Commission (WCED) published a report called “Our Common Future.” In this report, for the first time, the concept of sustainable development was mentioned [97]. In 1993 a technical committee, coded as 207, was founded by the International Organization for Standardization (ISO) for environmental management. ISO/TC 207 was established as an umbrella committee under ISO 14,000 environmental management standards. Environmental management systems, life cycle assessment, environmental labeling, greenhouse gas management, and similar activities are evaluated by this committee. These studies, published reports, and books, as well as organized meetings, are the

most important milestones in creating a more sustainable future. Awareness of life and of the need for environmental protection has led chemists to reconsider the techniques, processes, chemicals, and therefore all chemical events and to develop environmentally friendly processes. In 1991 the term “green chemistry” was introduced with the 12 principles agreed upon by different key individuals, scientists, and institutions [98 101]. The main rules of green chemistry are related to the developments of the “greening of methodologies” by applying lower consumptions of energy, atom economy, eliminating hazardous chemical processes and the use of toxic chemicals and materials and reducing waste. Seven principles that can be applied to green analytical chemistry, taken from the 12 principles of green chemistry accepted by all branches of chemistry and industry, must be considered [99 101]: 1. Prevention of wastes that may occur after the process or minimizing them as much as possible, for example, by using smaller extraction systems in solid phase or liquid phase extraction systems or smaller inner diameter columns in chromatography. 2. Use of nontoxic environmentally friendly or as little toxic chemicals and solvents as possible. 3. Design and use of minimal energyconsuming analytical systems and methods to ensure energy efficiency. 4. Avoiding the use of chemical catalysts, derivatization reagents, and other auxiliaries avoided as much as possible. 5. Use of catalysts instead of stoichiometric reactions. 6. Use of in situ analysis instead of offline analysis. 7. Use of safer chemistry to prevent accidents such as explosions and fires.

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

Analytical chemists, who have taken on the seven foundations of green analytical chemistry as their own, have demonstrated the importance in developing methods of sample preparation methods that fulfill most of the requirements of green chemistry. They have used new-generation sample digestion systems such as microwave ovens, ultrasonic irritation, and the like. They have developed simpler, environmentally friendly, and cheaper separation and preconcentration procedures, such as SPME, membrane extraction, liquid phase microextraction (LPME), accelerated solvent extraction (ASE), microwave-assisted extraction (MAE), ultrasound extraction, among others. And they have produced more green solvents such as ionic liquids (ILs), deep eutectic solvents (DESs), supramolecular solvents (SUPRAs), switchable solvents (SSs), and supercritical solvents for analytical applications and have used automated analysis systems such as flow injection analysis (FIA), sequential flow injection analysis (SIA), and multicommutation flow systems [100 104]. Several review articles [99 104], as well as a few books [105,106], describing the area of green analytical chemistry. For instance, Armenta et al. [98] described the timeline and concepts for many of the analytical techniques identified as being green, including microwave-assisted extraction (MAE), supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), solid phase microextraction (SPME), stir-bar sorptive extraction (SBSE), single-drop microextraction (SDME), and liquid liquid liquid microextraction (LLLME), among others. The focus has been on sample preparation, since this part of the analytical chain is well recognized as the least green, mainly due to the large consumption of solvents. Although liquid liquid extraction (LLE) is a method that can be classified as a very effective prescription method on both a laboratory scale and an industrial scale, the most important disadvantages of this method are the use of

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expensive and toxic chemicals, the application of time-consuming and multistage extraction steps, and the use of high-volume laboratory equipment. These disadvantages rapidly removed liquid liquid extraction from green analytical chemistry and restricted its use in sample preparation. This situation has pushed analytical chemists to research faster, less costly, easier, and more environmentally friendly— green—analytical sample preparation techniques. They first predicted that the amount of solvents used in liquid liquid extraction methods could be reduced. In this sense, the first applications were reported by two different research groups. In 1996 Liu et al. reported the first application of microsized liquid liquid extraction called as LPME. Scientists have taken the first steps in the transition from macrosized extraction solvents or systems to a microdrop extraction system SDME [107,108]. The basis of this LPME method, SDME, is essentially the same as with conventional liquid liquid extraction. However, the most important difference in this method is to extract the analytes in the aqueous phase into the microvolume of the hydrophobic extraction phase. Liu and Dasgupta used this method for the separation and preconcentration of sodium dodecyl sulfate (a methylene blue active substance) prior to analysis with a light-emitting diode based absorbance detector. In this SDME application, they suspended B1.3 μL of extraction solvent drop (chloroform) inside a flowing aqueous sample solution, and a multitube assembly was used to obtain a drop-indrop system. The aqueous sample solution containing the ion pair of analyte is continuously sent to the outer drop and aspirated from the meniscus of the drop. Then, by washing this organic drop with a wash solution, a clean extraction phase was obtained. In the last stage, the concentration of analyte was

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

measured by using a light-emitting diode based absorbance detector. This important SDME system as a kind of LPME provided easy and flexible extraction, use of only microliter-level extraction solvent, and combination with other detection systems [107]. Jeannot and Cantwell accomplished the extraction of 4-methylacetophenone from aqueous phase into 8 μL of the n-octane phase by using a different mode of single-drop microextraction. In this procedure, 8 μL of n-octane drop as extraction phase was located at the end of a Teflon rod, and the single-drop Teflon rod apparatus was immersed in the sample solution on the magnetic stirrer. The solution was stirred for a certain time, and the singledrop Teflon rod apparatus was taken out of the sample solution. The organic drop was sampled by using a microsyringe, and the concentration of 4-methylacetophenone in the last phase was analyzed with GC [108]. The method developed is a static LPME and is called direct immersion single-drop microextraction (DI-SDME). The main drawbacks of this method were the use of a microsyringe for GC sampling after completion of the extraction process and the instability of extraction drop. In order to solve these problems, conventional a GC microsyringe as a micro separation funnel was used by He and Lee in 1997 [109]. The authors referred to the procedure as dynamic LPME. In this method, the configuration of the extractant phase is in the form of a plug rather than a drop. This method has been developed to solve the instability of extraction drop, which is a significant problem in SDME extraction methods. To speed up the extraction process, the sample phase is repeatedly drawn into the syringe and removed again [109]. The introduction of these applications into the literature has been an important milestone for the future of liquid liquid extraction based methods, and different modes of SDME were introduced to the literature in a

very short period of time. These SDME methods can be classified by considering the application of extractor phase as follows: Three-phase SDME: In 1999 Ma and Cantwell introduced three-phase SDME as a new mode of LPME for cleanup and preconcentration of trace analytes [110]. In this method, the 30 μL n-octane liquid membrane was held inside the a Teflon ring above the 1.60 mL of sample solution. A microdrop of receiving aqueous phase is left suspended inside the organic liquid membrane by using a microsyringe, and sample solution is stirred for extraction of analytes from the sample solution into the organic membrane phase and back-extracted simultaneously into the microdrop. After extracting for a certain time, a syringe needle was used to take back the microdrop and put it into an HPLC for quantification. Scientists used this new method for analysis of trace amounts of methamphetamine, methoxyphenamine, 2phenylethylamine and mephentermine. As the method provided a 160-fold enrichment factor for 2-phenylethylamine and 500-fold for methamphetamine, mephentermine, and methoxyphenamine with the use of microliter-level receiving drop, doubled preconcentration factors were obtained with the use of a 0.50 μL receiving drop [110]. Head space single-drop microextraction (HSSDME): The acceptor phase is suspended above the sample solution, and extraction of analytes from the sample solution into the acceptor phase is carried out by stirring the sample solution. Head space solvent microextraction (HSME), or more commonly head space single-drop microextraction (HSSDME), was introduced for the first time by Theis et al. in 2001 [111]. They used a 1-octanol drop at the microliter level as the extraction phase (acceptor phase) for the separation and preconcentration of volatile compounds including toluene, o-xylene benzene and ethylbenzene following GC or GC/MS detections. 1octanol was selected as the extraction phase

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

due to its low vapor pressure, which led to minimum evaporation during the extraction process. The HS-SDME method provided an inexpensive and convenient separation and preconcentration for the trace amounts of volatile organic compounds [111]. Continuous-flow microextraction/single-drop microextraction (CF-SD-LPME): In 2000 Liu and Lee introduced continuous-flow microextraction (CFME) as an LPME method. The method is similar to the DI-SDME method [112]. But in this mode of SDME, the sample solution flowing at a certain speed interacts with the organic drop. In this method, polyetheretherketone (PEEK) connecting tube in a 0.5 mL glass chamber is used to hold an organic drop at the outlet tip of PEEK and used as a fluid delivery duct. The connecting tube is immersed in a continuously flowing sample solution up to completion of the extraction process. They used this CFME method for the separation and preconcentration of trace chlorobenzenes and nitroaromatic compounds in environmental samples. After the microextraction process, analysis of analytes was carried out by gas chromatography electron capture detection. They obtained enrichment factors between 260to 1600-fold by applying 10 min of extraction. The CFME method provided a very low detection limit at femtogram-per-milliliter levels [112]. Membrane-based LPME: In 1999 membranebased LPME as a different mode of LPME was introduced by Pedersen-Bjergaard and Rasmussen [113]. In these applications, disposable and cheap hollow fibers, typically made of polypropylene, are used. In these methods, the analytes are transferred from the sample solution into the acceptor phase in the porous hollow lumen filled with a extraction solvent through the pores. If the solution in the hollow fiber is the same as the extraction solvent imprinted in the pores of the hollow fiber, this method is classified as two-phase HF-LPME. But if these solvents are different, this method

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is classified as three-phase HF-LLLME. Extraction is carried out by magnetic stirring or ultrasonic irritation. Pedersen-Bjergaard and Rasmussen extracted methamphetamine traces from aqueous sample solution (pH 13, 2.5 mL) in the 1octanol impregnated pores of an 8 cm piece of a porous polypropylene hollow fiber, followed into a 25 μL acidic acceptor solution inside the hollow fiber. Methamphetamine concentration in the last phase was measured with capillary zone electrophoresis (CE). The extraction process was carried out in a 4 mL sample vial and two needles for introduction and collection of the extraction phase. The preconcentration factor, detection limit, and relative standard deviation for methamphetamine were 75, 5 ng mL21, and 5.2%, respectively. The method developed was applied for analysis of methamphetamine in human urine and human plasma samples [113]. DLLME: In the 2000s, analytical chemists continued their search for new sample preparation techniques that were more environmentally friendly, easier and faster. This research was turned into products in a short time, and new-generation extraction methods were developed. In 2006 a new LPME method based on a ternary component solvent system, called dispersive liquid liquid microextraction (DLLME), was introduced to the scientific world by Assadi and colleagues [114]. In this method, the dispersing phase solution containing the extraction solution is rapidly injected into the sample solution containing the analytes. A cloudy extraction solvent phase is obtained. Obtaining a finely dispersed cloudy extraction phase allows the extraction phase and the analyte to interact more with each other. Thus the analytes in the sample solution are extracted into the finely dispersed cloudy extraction solvent phase. The most important point is that the dispersion phase can be mixed with both water and extraction phases [114].

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

Solidified floating organic drop microextraction: Efforts to develop greener extraction methods have led to a reduction in extraction and other organic solvents in microextraction methods. Scientists continued to concentrate on the extraction process with a single drop of microvolume. However, the tendency to break on the surface where the extraction drop is attached, the problems during the transfer of the drop to the analysis step after the extraction, and loss of the extraction liquid contacted with a surface can limit the usability of these methods. To solve these problems, in 2007 Zanjani et al. introduced solidified floating organic drop microextraction (SFODME) as a new mode of LPME [115]. The microvolume organic extraction solvent drop with a melting point close to room temperature (10 C 30 C) is left on the sample solution, and the sample solution is stirred on the magnetic stirrer at a certain rotational speed. At this stage, analytes are extracted from the aqueous sample solution phase into the extractor drop. Then the sample is cooled via an ice bath. In this way, the extraction solvent solidifies into a drop while the sample solution, having a low freezing point, remains liquid. The solidifying extraction phase is taken up in a vial with a spatula, melted, and analyzed [115]. Zanjani et al. used the SFODME method for the separation and preconcentration of some polycyclic aromatic hydrocarbons (PAHs) at trace levels. They used 8 μL of 1-undecanol as extraction solvent drop. After completion of the extraction step, 1-undecanol, solidified in an ice bath, was transferred into a vial and melted. In the last step, 2 μL of 1-undecanol was placed into a GC system for analysis of analytes. The values of detection limit, enrichment factor, and relative standard deviation for PAHs were 0.07 1.67 μg L21, 594 1940, and ,7%, respectively [115]. The amounts of organic extraction solvents used are considerably reduced in the microextraction methods described herein. According

to the commonly used liquid liquid extraction method, microextraction methods are classified as faster, easier and more environmentally friendly. However, in these methods, the use of organic solvents, even in microvolumes, disturbed scientists. Analytical chemists aimed to use new-generation environmentally friendly solvents. As a result, they began to use more environmentally friendly solvents such as ionic liquids, deep eutectic solvents, supramolecular solvents and switchable solvents in microextraction methods.

1.2.3 Historical development of cloudpoint extraction A different liquid liquid extraction method called CPE was first introduced by Watanabe et al. in 1978 [116]. Their method was based on the extraction of Zn(II) ions as 1-(2-pyridylazo)-2-naphthol (PAN) complex from aqueous phase into Triton X-100 micellar phase. Cloudpoint extraction is the newest separation and preconcentration method among the traditional methods. CPE is also called surfactant-based extraction [116 119]. CPE is based on the extraction of analytes in aqueous solutions into the micelle phase formed by nonionic, zwitterionic, cationic and anionic nonionic surfactants containing a nonpolar tail and a polar head group. These two sides are hydrophobic and hydrophilic in an aqueous sample solution, respectively. The hydrophobic tails gravitate to create aggregates called micelles. When the solution including aqueous sample and surfactants is heated to a particular temperature, referred to as cloudpoint temperature (CPT), micelle formation is started and a turbid solution is obtained. Above the CPT, the micellar solution separates into a surfactant-rich phase of a small volume and an aqueous sample phase. Concentrations of analytes in the surfactant-rich phase are measured by a suitable detection system.

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

CPE needs only a diminutive amount of relatively nonflammable, nonvolatile and ecofriendly surfactant; since the use of solvent is at a minimum level, the level of secondary wastes after extraction is significantly lower, and this method has the ability to be safely and easily applied in a short period of time [119 124]. Moreover, the toxic, volatile, and flammable organic solvents in large quantities used in conventional methods such as liquid liquid extraction, solid phase extraction and coprecipitation methods are eliminated by CPE. Hence CPE can be considered environmentally friendly. CPE has been used frequently for the separation and preconcentration of trace amounts of metal ions, bioactive compounds, organic compounds, persistent organic pollutants and drugs. Important parameters affecting CPE efficiency are the type and concentration of surfactants, pH and ionic strength of aqueous phase, incubation time and equilibrium temperature, and volume of the aqueous phase. The most commonly used surfactants in the CPE method are Triton X (polyoxyethylene-(n)octylphenyl ether), PONPE (polyoxyethylene(n)-nonylphenyl ether), Genapol X (oligoethylene glycol monoalkyl ether), polyethylene glycol 600 monooleate (PEG600MO), and Brij (polyoxyethylene-10-akyl ether) [117 128]. In 1991 Saitoh and Hinze synthesized 3[nonyl- (or decyl-) dlmethyl-ammonlojpropyl sulfate (C-APS04 or C10-APSO4 zwitterionic surfactants) for separation and preconcentration of hydrophobic species, some steroidal hormones and vitamin E prior to HPLC determination. They obtained high recovery results of more than 88% for analytes. When compared with other commercial surfactants such as polyoxyethylene (7.5) nonyl phenyl ether (PONPE-7.5), the new surfactant provided important superiority such as formation of two-phase system in lower temperatures, higher extraction efficiency, homogeneous and purer surfactant formation and minimum

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background absorbance at UV detection wavelengths [117]. Okada used poly(oxyethylene) (7.5) nonylphenyl ether as a surfactant for the cloud-point ion-pair extraction of SCN2 complexes of transition metal ions. The concentration of SCN2 has an effect on the cloud point of this surfactant. This mechanism can be explained by the repulsive interaction between the surfactant chains because of the partition of SCN2 into the micelle, which is experimentally proved with the analysis of SCN2 in the surfactantrich phase by ion chromatography [118]. Horvath and Huie investigated the saltingout effect on the separation of Triton X-100 as a nonionic surfactant from aqueous solutions and the extraction efficiency of the trace amounts of organic analytes. Improved extraction capabilities and enrichment factors were obtained for the separation and preconcentration of many hydrophobic and hydrophilic metalfree porphyrins (protoporphyrin, coproporphyrin, hematoporphyrin, and uroporphyrin,) and one metalloporphyrin (iron-protoporphyrin) at room temperature [119]. Laespada et al. developed a CPE method for the separation and preconcentration of uranium as 1-(2-pyridylazo)-2-naphthol hydrophobic chelate form. They used Triton X-114 as the nonionic extraction phase. The CPE method was used for analysis of trace amounts of uranium in tap and river waters [120]. Warner-Schmid et al. synthesized permethyl-hydroxypropyl-β-cyclodextrin (PMHPβ-CD) as a new surfactant and used it for the cloud-point extraction of many aromatic compounds (i.e., aniline, acetanilide, N-methylaniline, 2,2ʹ-dihydroxybiphenyl, 2-naphthol, o-nitroaniline, m-ni-troaniline, p-nitroaniline, o-nitrophenol, m-nitrophenol, p-nitro-phenol, nitrobenzene, 2-phenylbenzimidazole, 3-phenylphenol, and 4-phenazophenol) from aqueous solution [121]. In a different CPE application, napropamide and thiabendazole at trace levels in aqueous phase was extracted into Genapol X-80

New Generation Green Solvents for Separation and Preconcentration

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

surfactant phase with recovery rates of up to 95%. Concentrations of analytes in the surfactant-rich phase were measured by fluorescence. The method developed applied for determination of analytes in soil samples with detection limits below 0.2 μg L21 [122]. Akita and Takeuchi used PONPE10 surfactant for cloud-point extraction of trace amounts of phenol and three pyridines [123]. The same authors also searched the equilibrium distribution of aromatic compounds between an aqueous solution and a coacervate of polyoxyethylene nonyl phenyl ether nonionic surfactant. The results showed that aromatic compounds that lower the cloud point to greater extent can lead to higher extraction efficiency [124]. Ferrer et al. developed a CPE method to separate and preconcentrate polycyclic aromatic hydrocarbons in water samples. They used Triton X-114 as the extraction solvent phase. After CPE, HPLC with fluorimetric detection and wavelength programming was used for determination of analytes in the surfactant-rich phase. The detection changes from nanograms per liter to even subnanograms per liter were accomplished by this procedure [125]. Silva et al. used a CPE method for the separation and preconcentration of Er(III) traces in Er(III)-2-(3,5-dichloro-2-pyridylazo)-5dimethylaminophenol complex form prior to its spectrophotometric determination at 584 nm. Polyethyleneglycolmono-p-nonylphenylether (PONPE-7.5) was used as extraction agent. The molar absorptivity, linear range, and detection limit values were 27 3 105 L mol21 cm21, 0.02 2 mg L21, and 1.48 3 1027 mol L21, respectively [126]. Pourreza et al. used Triton X-100 surfactant as extraction solvent for the separation and preconcentration of malachite green at trace levels in river water and fish farming samples prior to UV visible spectrophotometer determination with recoveries in range of 95% 102% [127].

Tang et al. developed an easy CPE method for the separation and preconcentration of trace amounts of tricyclazole, diniconazole triadimefon, and tebuconazole triazole fungicides in environmental waters by using polyethylene glycol 600 monooleate (PEG600MO) nonionic surfactant. Analysis was carried out by HPLC/ UV [128]. Average recovery results for river water and tap water samples were between 82% and 92%, and RSDs were between 2.8% and 7.8% [128]. Wang et al. applied CPE for the separation and preconcentration of di-ethyl-phthalate (DEP), 2-ethylhexyl-phthalate (DEHP) and dicyclohexyl-phthalate (DCP) in spiked water samples following HPLC/UV analysis. The CPE method provided the preconcentration factors between 35 and 111 and recoveries between 85% and 103% [129].

1.2.4 Historical development of solid phase extraction/microextraction methods Solid phase extraction started with a process in which users were not aware of scientific facts and therefore used different names such as “adsorption,” “sorption,” “retained on solid materials” for thousands of years. Some scientists claim the first literature reference is to be found in the Bible, Ex. 15: 24 25 to be exact [130]. In the medieval period, in the city of Grasse in France, rose petals were placed in paraffin wax, and the extraction of the volatile fragrances of the rose petals is considered a solid phase extraction application [130]. The use of charcoal, diatomaceous earth, and zeolite to remove pigments from chemical reaction mixtures can be considered the first modern application of solid phase extraction. In such applications, the charcoal, diatomaceous earth, or zeolite was passed through the filter and discarded together with the compounds it absorbed. It should be noted that this is a bulk extraction rather than a solid phase extraction

New Generation Green Solvents for Separation and Preconcentration

1.2 Historical development of separation and preconcentration methods

method. The main goal is to collect but not to discard the compounds of interest, preferably by preconcentrating them from a sample in order to analyze and remove the unwanted compounds, that is, those we do not wish to analyze [130,131]. Solid phase extraction can be considered low-performance liquid chromatography, used in two extreme conditions: minimum and maximum retention during extraction (adsorption) and elution (desorption), respectively. In these systems, organic, inorganic or biological analytes are adsorbed on the sorbent in column, and the sorbent is washed with pure water to remove the matrix components. In this way, while analytes are adsorbed on the sorbent, unwanted matrix components are removed. Then analytes retained on the sorbent are eluted with a proper liquid phase. Elution reverses the adsorption process, leading to the analytes passing from the adsorbed layer into solution again. Concentrations of the analytes in the last phase are measured by a detection system. The mechanism of adsorption of analytes on active sites of the surface sorbent can be explained the dipole-induced dipole, dipole dipole, hydrogen bonding, ionic bonding, covalent bonding and dispersive interactions [130 144]. The US Public Health Service group (Cincinnati, Ohio, United States) published a pioneering study based on the column system for the enrichment of organic compounds [132]. They filled 1200 1500 g of granular activated carbon in an iron cylinder for the preconcentration of organic compounds in raw and filtered surface waters. Using these carbon filters, they sampled at six water plants along the Ohio River from Midland, Pennsylvania, United States, to Louisville, Kentucky, United States, during the spring of 1949. The carbon filters through which the known volume of water samples passed were removed and dried with air. The organic compounds on the surface of carbon filters were extracted with

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diethyl ether in the Soxhlet extractor. Five groups of organic residues were formed, and specific chemicals were identified within these groups [132]. Then the carbon filter method was used by Rosen and Middleton for the determination of the petroleum refinery wastes in surface waters. For this purpose, thousands of gallons of surface water are pumped into the solid phase sorbent system consisting of a carbon filter to enrich the petroleum components on the carbon filters. The compounds resting on the sorbent were then desorbed with chloroform and separated by column adsorption chromatography. Concentrations of these components were analyzed by infrared spectroscopy at the parts per million level [133]. The same working group combined the carbon filter system with adsorption chromatography and infrared spectrometry. This combined method was used to isolate, enrich, and detect insecticides commonly found in surface waters. As with the previous method, they pumped thousands of gallons of surface water into the solid phase sorbent system 1833 in ID (1 in 52.54 cm) inches consisting of a carbon filter to preconcentrate the insecticides on the carbon filters. These applications increased the popularity of activated carbon use for analytical applications [134]. The problems encountered due to the nonhomogeneous structure of activated carbon have seriously prevented the use of the carbon filter method in solid phase extraction applications. Problems in the use of activated carbon such as irreversible adsorption, chemical reactions during extraction and low recovery values have led scientists to investigate other sorbents. But it should be noted that activated carbon has an important role in the development of the solid phase extraction method. Moreover, the use of activated carbon in the enrichment of trace organic analytes has led to the interest of scientists. It should be noted that, even

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

though classic activated carbon is losing its popularity in the separation and enrichment of organic and inorganic analytes, it is still very popular in water treatment technologies [135 160]. In this sense, solid phase extraction only became a scientific technique in the 1970s. The process of development as an analytical practice progressed from initial latency (before 1968) through the next three stages. 1. 1960 77: The period of searching for the most suitable materials for SPE 2. 1977 89: The period of technical developments in SPE 3. 1989 present: The modern period of SPE In solid phase extraction methods, advancement has been stepped up in order to meet the needs of the time. This progress is closely linked to the development of new-generation technologies, the production of new solid phase materials, and the development of product diversity. Solid phase extraction methods can be divided into three basic groups based on the adsorbent used: (1) inorganic materials, (2) organic materials, and (3) organic/ inorganic hybrid materials. Up to now, many adsorbents have been used in SPE such as geltype, macroporous and hypercross-linked, and ion-exchange polymer resins, silica-based nano/microsized materials, carbon-based nano/microsized materials including activated carbon, graphitized carbon black (GCB), porous graphitic carbon (PGC), graphene, graphene oxide (GO), carbon nanotubes (CNTs), fullerenes (C60 or C70), metal oxide micro/ nanoparticles including TiO2, SiO2, Fe3O4, Fe2O3, Al2O3, restricted-access materials (RAM), monolithic materials, magnetic materials, metal organic frameworks (MOFs), among others [135 197]. For a sorbent to be used in SPE extraction methods, one or more of the following features must be present (Fig. 1.3).

But in the first applications of solid phase extraction methods, the following adsorbents were used: (1) porous polymeric sorbents categorized as gel-type, macroporous, and hypercross-linked sorbents, (2) ion-exchange resins, (3) silica-based sorbents, modified with C18, C8, phenyl, CH, CN, or NH2 groups, (4) carbon-based sorbents, including GCB and PGC [132 134]. Solid phase extraction was used from the 1940s to the 1970s, when synthetic polymers such as porous polymeric sorbents (primarily the macroporous polystyrene-divinylbenzene [PS-DVB]) were first reported in the literature [130,138]. As polymeric supports, the commercially available porous polymeric sorbents categorized as gel-type, macroporous, and hypercross-linked sorbents polymer-based resins are very promising solid phase extraction materials because of the their effective chemical and physical features such as high surface area, purity, strength, no solubility in aqueous and organic solvents, and improved pore structures and adsorption capacity, which is comparable with activated carbon around 1000 m2 g21. Moreover, they can be designed in many different forms to control their resin structure, pore size distribution, internal surface area, polarity and so on. For example, the hydrophobic character (apolar) of polystyrenedivinylbenzene resins is dominant; hence it can be used for solid phase extraction of hydrophobic analyte or analytes, while hydrophilic (polar) character of polyacrylate-divinyle benzene resins is dominant so it is suitable for solid phase extraction of hydrophilic analyte or analytes. They have been used frequently since the mid-1960s in the separation and preconcentration of trace organic, inorganic and bioactive species. Important improvements on separation and preconcentration methods were lived in the 1960s by production of the macroporous resins as adsorption material [136 139]. They are capable of effectively adsorbing organic,

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1.2 Historical development of separation and preconcentration methods

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FIGURE 1.3 Features of sorbents used in solid phase extraction/microextraction procedures.

inorganic and biological compounds because of their porous polymeric matrix. These procedures are generally called solid phase extraction (SPE), liquid solid extraction (LSE), liquid solid adsorption (LSA), or sorbent extraction. In this book, the most common name, solid phase extraction (SPE) will be used. Developments in the usage of resins has played an important role not only in solid phase extraction studies but also in the development of wastewater treatment methods and recovery of valuable metals (Au, Pt, Pd, etc.), minerals (Ca, Mg etc.), radioactive species (U, Th, Ac, etc.), organic compounds (antioxidant, azo dyes, pharmaceutical compounds) and biological materials (proteins, amino acids, DNA, RNA, etc.). In the 1960s, Amberlite XAD-1, a cross-linked polystyrene resin, was fabricated by Rohm and Haas [137]. By the end of the 1960s, polymer

materials were used first a first time by Riley and Taylor for the separation and preconcentration of organic compounds in water samples. They used a column system designed with a 1 cm diameter, Amberlite XAD-1 resin fastened to a column depth of 7 cm. After the SPE procedure, concentrations of organic analytes in seawater samples were measured by fluorimetry, photometry, 14C counting, and GLC detection systems. Moreover carbohydrates, amino acids, and humic acids were studied [137]. Many types of polymeric resins were produced in the 1970s, and they became a focus of intense interest for separation and preconcentration applications. In 1972 Burnham et al. used styrene divinylbenzene Amberlite XAD-2 and ethylene dimethacrylate-XAD-7 resins for solid phase extraction to extract trace organic contaminants in potable water. Particularly,

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

the resins have been used to preconcentrate neutral organic compounds, metal-ligand complex, weak organic acids, and bases from aqueous solutions at parts per billion levels [138]. In 1973 Harvey et al. used an SPE liquid liquid extraction (LLE) approach with XAD-2 in order to determine polychlorinated biphenyls (PCBs) in North Atlantic Ocean water [140]. In the same years, apart from Amberlite resins, other polymeric materials for preconcentration studies were employed for the first time. Gesser et al. used porous polyurethane foam for the solid phase extraction of polychlorinated biphenyls (PCB) in water samples prior to GC analysis [141]. Mieure and Dietrich used Chromosorb 102 filled a column in order to extract and preconcentrate organic compounds from water samples. After the SPE step, the Chromosorb 102 column was then coupled to the head of analytical column of a GC system, and organic compounds were thermally desorbed by the flow of the carrier gas [142]. In 1974 Junk et al. reported a comprehensive preconcentration strategy by using XAD-2 resin [143]. In this study, they used a small column of a macroreticular resin to preconcentrate and isolate the organic impurities from water with solid phase extraction. In this study, many model organic compounds between parts per billion and parts per trillion levels were added into water samples, and the organic compounds adsorbed was eluted with diethyl ether and analyzed by gas chromatography. Recovery studies for organic compounds proved the applicability of polymer-based adsorbents such as styrene divinylbenzene materials for trace analysis applications. After these important steps, hundreds of articles based on the use of polymers such as styrene divinylbenzene, ethylene dimethacrylate copolymers (Amberlite XAD-7 and Ambelite XAD-8), separon and spheron acrylate copolymers, porapaks, chromosorbs, polypropylene,

polytetrafluoroethylene, polyurethanes, polyurethane foam, tenax, ion-exchange resins, among others, have been published in the ensuing decade for the separation and preconcentration of organic, inorganic, and bioactive species [144 153]. A few examples of the first application of polymer-based solid phase extraction applications are described next. In 1978 Tateda and Fritz prepared a mini solid phase extraction column system (1.2 1.8 mm 3 25 mm) containing Amberlite XAD-4 resin or Spherocarb to preconcentrate a wide range of organic contaminants from water samples. After the SPE method, the adsorbed analytes were treated with a microliter volume of organic solvent and analyzed by gas chromatography. They obtained excellent recovery results for the studied organic compounds. The adsorption and desorption performances of Amberlite XAD-4 and Spherocarb adsorbents were compared. It was found that Amberlite XAD-4 and Spherocarb adsorbents can be used for solid phase extraction of organic compounds in wastewater samples [144]. In 1983 Zygmunt et al. used LC-grade styrene divinylbenzene polymer for the separation and preconcentration of 20 pollutants in industrial wastewater prior to LC determinations. With this developed procedure, it was possible to analyze 20 different organic pollutants at parts per billion levels [145]. In 1985 Tabor and Loper used a special column system containing Amberlite XAD-2 and Amberlite XAD-7 resins for the separation and preconcentration of mutagenic residue organics in drinking water samples. The organic residues adsorbed were eluted with organic solvents prior to bioassay for mutagenicity [146]. Richard and Junk reported a combination use of Amberlite XAD-4 resin based solid phase extraction and a GC-electron capture

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1.2 Historical development of separation and preconcentration methods

detection system to determine parts per billion levels of munitions in water samples. They tested some of nitrobenzene, nitrotoluene and triazine derivatives as model analytes. They used solid phase extraction in the field instead of the laboratory. Hence, the transportation cost of water samples to the laboratory was eliminated [147]. Pankow et al. developed an electronically controlled rain sampler and solid phase extraction system for the collection and preconcentration of organic compounds in rain water, such as naphthalene, hexachlorocyclohexane ( HCH), acenaphthylene, phenanthrene, and fluorene in 1984. They used this system for the in situ filtration of the collected sample and preconcentration of apolar organic species with cartridges of the sorbent Tenax GC. Moreover a ion-exchanging resin cartridge was used to preconcentrate organic acids in rain water. After the SPE procedure, gas chromatography mass spectrometry (GC MS) was used to analyze 27 compounds in the rain water [148]. In 1987 Bitteur and Rosset compared the trace enrichment performances of octadecylbonded silica and styrene divinylbenzene copolymer sorbents [149]. In 1988 Pankow et al. suggested a solid phase extraction and gas chromatography procedure for analysis of various semivolatile compounds in water samples. Semivolatile compounds adsorbed on the Tenax cartridges (0.68 cm3 of bed volume) were desorbed thermally into a fused-silica capillary gas chromatography column [150]. The first applications of the solid phase extraction method were carried out on the capillary columns, which were packed with gram levels of sorbent. Columns were fabricated from quartz, polyethylene, or polytetrafluoroethylene (PTFE) in 1977 and this step can be considered an important revolution in preparing a more suitable, simpler and more effective solid phase extraction system.

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This technique was introduced in 1978 on the cover of a catalog of laboratory equipment. In the same year, the first article in this area was published. The published article described the use of a C18 silica based solid phase extraction system as a commercial product (Sep Pak C18 “cell”) to remove histamine from wine samples. The commercial chromatographic sorbents and reverse phases capable of extracting the desired analytes from aqueous phases marked the start of solid phase extraction applications in the environmental, analytical, pharmaceutical, and clinical markets. These important developments led to the transformation of the solid phase extraction method from a laboratory innovation into a accepted and widely used form of chromatographic application [150,152,153]. At the end of the 1980s, the production of support materials called membrane and solid phase extraction discs led to an innovative period in solid phase extraction methods. Such apparatus consists typically of discs containing glass fiber pads, glass fibers, or a Teflon matrix with a sorbent stuck between them. As a result of these developments, a very short and very thick solid phase extraction cartridge was obtained [154 156]. Packaged cartridges, columns or discs are now used in virtually all laboratories in the world where sample preparation is needed. Designs for housing SPE sorbents, from “pipette tip” models to glass minicolumns or plastic with steel or Teflon or polymer frits have all been well established. Some solid phase extraction apparatuses are fabricated for vacuum use, facilitating the sample to be “pulled” through, while others are used for the sample to be “pushed” through the sorbent. However, for nearly 40 years, megacolumns containing several grams of sorbent, extraction membranes, or discs have become popular in solid phase extraction applications because of the increased market for SPE [150 156].

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

Many publications on the use of silica since 1978 do not express the widely accepted term “solid phase extraction.” Since this term has not been used in the main title of many studies based on sorption for so long, solid phase extraction has been given different names during its historical development (Fig. 1.4). Hence it is necessary to look at the details of literature

FIGURE 1.4 Tracking solid phase extraction synonyms: a list of terms used [130].

studies in order to understand the historical developments of SPE. Growth in the number of citations on solid phase extraction started with the first use of the SPE term by the employees of the J.T. Baker Chemical Company [130]. When the last half of the 1980s is examined, it is seen that SPE studies were used in clinical, pharmaceutical and analytical applications. In the 1990s, there is a rapid increase in the number of publications on the environmental applications of SPE. It has been seen that solid phase extraction has been used frequently in all applicable areas. Significant developments, important applications, and milestones in solid phase extraction methods for the preconcentration and separation of trace analytes from past years to the present will now be explained in detail in the literature studies [157 161]. In 1977 Tjaden et al. used methyl silica as the solid phase in the high-pressure liquid chromatography (HPLC) system for the separation of barbiturates. They obtained good results for the determination of barbiturates at trace levels in blood samples [157]. In 1985 Kubo et al. provided an accurate and simple solid phase extraction method for the separation of trace levels of procainamide (PA) and N-acetylprocainamide (NAPA) in breast milk and serum samples prior to their highperformance liquid chromatography determinations [158]. In 1986 Bardalaye and Wheeler developed a solid phase extraction method for preconcentration of trace amounts of triazine herbicides, prometryn, arnetryn and terbutryn in water. They used chromatographic-grade silica gel particles, chemically modified with a nonofunctional C8H17 group. In the modification procedure, the C8H17 group covalently bonded on the surface of silica gel particles. The triazine herbicides adsorbed on the silica gel particles were eluted by using 2-propanol. Concentrations of prometryn, arnetryn, and terbutryn in the last phase were analyzed by capillary gas chromatography with a

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1.2 Historical development of separation and preconcentration methods

nitrogen-phosphorus detector. The limits of detection values for analytes were found in the range of 0.1 10 μg L21 [159]. At this time, as a result of the developments in instrumental devices, the transition from offline to online solid phase extraction systems has found a lot of application areas and has gained momentum. These developments have led to new horizons in the minds of scientists: automatic sampling and detection, minimum sample manipulation, improved sensitivity and selectivity, completion of the preconcentration and analysis steps. The combined usability of online SPE methods with spectroscopic and chromatographic methods such as AAS, AFS, AES, UV VIS spectroscopy, GC, GC MS, LC, LC MS, HPLC, and the like, is one of the most important steps in the development of this method [160 168]. In the online solid phase extraction and detection systems, first, polymer-based and carbon-based sorbents were used. A few examples of the first online solid phase extraction and detections applications are described here. Liska et al. suggested an online solid phase extraction and column liquid chromatography procedure for 50 pesticides in surface water at trace levels. They accomplished online preconcentration of pesticides on a styrene divinylbenzene copolymer (PLRP-S) precolumn prior to liquid chromatography detection [160]. In an another study provided by Hennion and Coquart, solid phase extraction performers such as porous graphitic carbons, nonpolar styrene divinylbenzene copolymers, and alkyl-bonded silicas as reversed phase extraction sorbents were compared by the online mini column preconcentration and liquid chromatographic separation system for polar organic compounds in environmental water samples. The results showed that porous graphitic carbon was the most suitable sorbent for the preconcentration of trace levels of polar organic compounds [161].

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Liska et al. carried out a comprehensive study to compare the sorption features of 10 different sorbents used in preliminary preconcentration studies. They used online a solid phase extraction system to compare the adsorption features of sorbents, including three C18 bonded polymers with neutral, weak anion- and cation-exchange properties and two C18, a phenyl- and a diol-bonded silica, together with a styrene divinylbenzene copolymer and two carbon phases obtained from the controlled pyrolysis of saccharose (CF) and cellulose (CPP-50). The adsorption features of the selected sorbents were checked on the model solutions, including atrazine, aniline, 2nitrophenol, diuron, and 2-chloroaniline. The obtained results showed that a styrenedivinylbenzene copolymer with a C18 silicabonded analytical column was the optimum and most effective solid phase extraction system for preconcentration applications. This study also shed light on the solid phase extraction studies to be done later [162]. In 1994 a flow injection online SPE-AAS method was provided by Lancaster et al. in order to preconcentrate and analyze metal ions. They prepared ligand-adsorbed hydrophobic solid phase extraction material by using 4-(2pyridylazo)resorcinol, diethyldithiocarbamate (DDC), 1-(2-pyridylazo)-2-naphthol, quinolin-8ol, and dithizone and checked the adsorption efficiency of these new ligand-adsorbed SPE materials. The diethyldithiocarbamate- (DDC) and quinolin-8-ol-adsorbed SPE were selected to preconcentrate lead and copper ions. They obtained preconcentration factors in range of 50 and 100 with parts per billion levels of detection limits [151]. A comprehensive online solid phase extraction study, which compared SPE performance of different sorbents, was reported in 1995 by Naghmush et al. [163]. In this study, they checked the online SPE performances of commercial chelating sorbents (Spheron Oxin 1000 and Chelex 100), nonpolar sorbent Amberlite

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

XAD-2 modified with Pyrocatechol Violet and several cation-exchange resins, C18 sorbent nonmodified and modified with 8-quinolinol or Pyrocatechol Violet, cellulose sorbents with carboxymethyl groups, and phosphonic acid. Pb(II) was selected as a model analyte, and online analysis was carried out with FAAS. Functionalized cellulose sorbents were found as the best sorbent material in this study. The detection limit for Pb(II) was found as 0.17 μg L21 at a flow rate of 7 mL min21 [163]. A different online solid phase extraction thermospray tandem mass spectrometry (TSPMS-MS) combination was applied for the preconcentration and determination of β-agonists in urine of cattle. In this method, a sorbent having both hydrophobic and ionic properties were used [164]. Hollenbach et al. provided a flow injection (FI) analysis procedure consisting of SPE and ICP-MS steps in order to analyze 230Th, 240Pu, 239Pu, and 234U in soils. The elution solution was injected into the nebulizer of the ICP-MS. A 20 preconcentration factor was obtained in this method. The detection limits for 230Th, 240Pu, 239Pu, and 234U were found as 4, 0.3, 0.2, and 3 ng kg21, respectively [165]. In 1997 Daghbouche et al. combined a fully designed online solid phase extraction FT-IR methods to analyze caffeine in soft drinks. The samples, degasified, were directly passed through a C18 SPE cartridge by using a flow manifold. Caffeine adsorbed on the C18 was eluted with chloroform and analyzed at 1658 cm21 by using a flow injection FT-IR system. Limit of detection, relative standard deviation, and sampling frequency values were 10 μg mL21, 3.5%, and 30 h21, respectively [166]. The 1990s are an important turning point for solid phase extraction methods, since new extraction devices, new-generation sorbents, and microvolume systems were introduced for the first time in these years. One of the most important of these developments is the use of

membrane extraction discs. This system was first used by Hagen et al. in 1990 [167]. The researchers prepared membrane discs by modifying a network of PTFE fibrils with hydrophobic octyl and octadecyl-bound silica (47 or 25 mm diameters) and used these discs in the reverse phase solid extraction of environmental pollutants from aqueous media. Water samples were passed through the disc under optimum test conditions, and thus organic species were adsorbed on the disc. After the adsorption process, the organic species retained were eluted with a small volume of eluent and given to the chromatographic separation system. In last step, the new method was used for analysis of parts per billion levels of phthalates, pesticides and polychlorinated biphenyls in tap groundand surface water samples [167]. Membrane discs composed of the fibrilized PTFE matrix were modified with different nanoparticles, silicas, polymers, or ion exchangers. High recovery values can be obtained at a high sample flow rates because of the internal structure of the membrane discs. The SPE method based on membrane extraction discs can be applied in online and offline modes for sample solutions and can be combined with chromatographic and spectroscopic detection systems. Membrane discs are widely used for the separation and preconcentration of organic and inorganic analytes in different matrix media [168 174]. Antibodies have been used frequently in biosensors, affinity chromatography and very popular immunoanalysis studies for 50 years. By the end of the 1980s, researchers realized that the analyte antibody interaction can be used in the solid phase extraction method and thus a new SPE application, which is classified as immunoaffinity, has emerged. In these systems, immunosorbents are obtained by fixing the antibodies in monoploid or polyploid form produced against the target compounds onto a support material. Immunosorbents were first used by Farjam et al. in 1988 for the isolation

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1.2 Historical development of separation and preconcentration methods

and enrichment of 19-nortestosterone from biological samples [175]. In this study, scientists suggested an automated extraction and analysis procedure for the anabolic hormone β-19nortestosterone (β-19-NT) and its metabolite α-19-nortestosterone (19-norepitestosterone) in calf urine samples. In this method, the liquid chromatographic column-switching system was used. For this purpose, they prepared an immunoaffinity precolumn by modifying the sepharose with polyclonal antibodies against α-19-NT and used a C18-bonded silica-loaded precolumn as a second column and an analytical C18 column [175]. Twenty-five milliliters of urine sample were passed through the antibody-immobilized precolumn to allow the analytes to adsorb on the column. The analytes were then selectively desorbed with a solution containing an amount of the steroid hormone norgestrel that was cross-reacted with analytes and transferred to the analytical column via a second precolumn. The recovery of β-19-NT in spiked urine samples was over 95%. The detection limit was 50 ng L21 for a 25 mL urine injection. The system showed no loss of analytical performance over a 6-month period, during which about 100 samples were analyzed with the same immuno precolumn. Recovery values of more than 95% with 50 ng L21 of detection limit for analytes were obtained. The immunosorbent column was used over a 6-month period for about 100 samplings [175]. Until now, the immunosorbents obtained from different antibodies have been widely used as an effective solid phase extraction material for trace analytes such as pesticides, herbicides, active ingredient, PAHs, and the like in environmental, biological, and pharmaceutical samples [154,175 178]. The need for the development of analytical methods that provide improved selectivity and sensitivity has accelerated the studies on the development of molecularly imprinted polymers (MIPs) for solid phase extraction

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applications. In the molecular imprinting technique, a target molecule as a template is used to fabricate highly selective binding matrices by applying a casting methodology. MIPs are obtained by producing highly crosslinked polymers in the presence of a template molecule, leading to the formation of functional groups in a specific arrangement within the polymer. High selectivity is achieved for analyte or analytes since the MIPs show antibody-like affinities to specific analytes. Hence molecularly imprinted solid phase extraction (MISPE) applications eliminate the needs of a chromatographic separation of analytes, which lead to faster and simpler access to analytical results. Sellergren introduced a different MISPE method for the first time in 1994 [179]. Pentamidine (PAM) is used as a drug molecule for the treatment of AIDS-related pneumonia. In this study, scientists compared the solid phase extraction performances of PAM-selective polymer and benzamidine-(BAM-)imprinted reference polymer for the separation and preconcentration of PAM at trace levels. The enrichments factors for PAM-selective polymer and benzamidine-(BAM-)imprinted reference polymer were found as 54 and 14, respectively. The PAM concentration in eluent was directly analyzed in urine samples since the use of the high selectivity of polymer eliminated the second chromatographic separation step [179]. Nanotechnology has been a multidisciplinary discipline that has, in the last 35 years, brought innovation to all fields, from environmental science, medical science, engineering, pharmacy, science, and chemistry to veterinary science. Nanotechnology is a science that examines the production, characterization, and properties of new and revolutionary materials of 100 nm or less in size and paves the way for these materials to be used in different areas. One of the branches of science affected by developments in nanotechnology

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

is sample preparation methods in analytical chemistry [177,180 182]. The most important developments in the solid phase extraction method were experienced with nanotechnology. Nanotechnology began to affect solid phase extraction with the discovery of fullerene (C60) as a carbon allotrope (zero-dimensional) in 1985 [183]. Scientists noticed that, as the size of the material becomes smaller, most features of the material may change. The discovery of this new stable form of carbon, which differs from graphite and diamond, has led scientists to research other types of carbon. In 1990 when the C60 was found to be able to be produced in a simple arc-evaporation apparatus (available in many laboratories), research on this topic accelerated. This development was followed by the discovery of carbon nanotubes as one-dimensional material (single-walled, double-walled, and multiwalled CNTs) as another carbon allotrope in 1991. Iijima used arc-evaporation apparatus to fabricate CNTs [184]. CNTs are graphene sheet structures rounded into the shape of a cylinder. The discovery of the fullerene and carbon nanotubes has led to the idea that nanomaterials offering high surface area ( . 1000 m2 g21) can be effectively used in solid phase extraction. Transition from micro size to nano size has caused excitement over scientists working in solid phase extraction, as in all branches of science. Fullerenes and carbon nanotubes became very attractive materials after the discovery of their wonderful physical, chemical, and thermal stability, high surface area, and improved π π interactions. The fact that all adsorbents used up to 1990s could not be used in the extraction of polar and apolar analytes at the same time, which was the most important disadvantage limiting the applicability of the solid phase extraction method. But the usability of these carbon nanomaterials for either nonpolar analytes or polar analytes with the

functionalization of these nanomaterials led to a significant increase in the use of solid phase extractions in a wide range [185 187]. In these years, a race has started for the production of new nanomaterials and important nanomaterial production methods such as arcevaporation, vapor deposition, solvothermal, sol gel, in situ growth/polymerization, coprecipitation, electrospinning, and direct coating were introduced. These nanomaterial production methods have led to the discovery of nanosized materials based on carbon (CNT, fullerene, nanodiamond, carbon dot, etc.), nanofibers, metals (Cu, Au, Pd, Pt, etc.), metal oxides (SiO2, TiO2, Al2O3, etc.), magnetic nanoparticles (Fe3O4, γ-Fe2O3, ZnFe2O4, and ZnFe2O4), and polymers, which are commonly used in solid phase extraction [185 191]. Analytical chemists paid more interest to these nanomaterials than to other classic materials used in solid phase extraction because of the their high surface area, high adsorption capacity, ability to be modified with different organic and inorganic matrices, corrosion resistance, mechanical, and chemical and thermal stability. For 25 years, nanomaterials have been used in the solid phase extraction of almost all of the organic, inorganic and bioactive traces in environmental, food, drug and biological samples. In 2004 graphene (G) was introduced as one of the most important carbon materials with a hexagonal structure consisting of sp2 hybridized carbon atoms arranged in a honeycomb pattern. Graphene is characterized as the mother of all carbonaceous materials because it can be used not only in the production of carbon nanotubes by “rolling” but also as a building block of graphite by stacking together with strong Van der Waal forces [192]. Graphene provides some very good and unique features to users, such as high electrical conductivity, effective thermal stability, high Young’s modulus, high surface area (2630 m2 g21), zero band gap, and transparency for monolayer G sheets.

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1.2 Historical development of separation and preconcentration methods

Due to these unique features, graphene is one of the most commonly used materials in many fields such as electronics, medicine, pharmacy, engineering, physics, chemistry, biology and others. Perhaps there is no area left in which to use graphene [192]. After the discovery, graphene and graphene oxide are among the most frequently used new-generation materials used in the enrichment of almost all organic and inorganic species found in environmental samples. Graphene, mainly because it is a material with a theoretically large surface area (2630 m2 g21), is one of the most commonly used materials in adsorption-based methods, and it provides high selectivity and adsorption capacity for analytes by providing the analytes noncovalent interactions such as π π stacking, Van der Waals, hydrogen bonds, hydrophobic effect, dispersing forces, and electrostatic and dative bonds [193 195]. In 1990 an important revolution occurred with the introduction of the SPME, as one of the most popular green techniques, by Pawliszyn and Arthur [196,197]. Since then, the solid phase microextraction method has become one of the most widely used methods in the separation and enrichment of organic, inorganic and bioactive species found in various matrix environments. Conventional solid phase extraction procedures have some disadvantages such as slow extraction process; use of excessive amounts of sorbent, reagents, and solvents; formation of excess waste after the process; necessity of high volume or amount of samples; the need for complicated and expensive extraction apparatus; and the inability to obtain the desired sensitivity. SPME has proven itself as a successful method for eliminating most of these drawbacks. The fact that the solid phase microextraction method can be applied to all samples in different physical states—liquid, gas and solid—has made a significant contribution to its being one of the most important techniques available all over

35

the world. Hence SPME is a hot topic and taken its place as a separation and preconcentration method in sample preparation laboratories all over the world [196 201]. SPME consists of two main steps [11]: 1. Adsorption of analytes on the sorbent surface at the optimum conditions and 2. Desorption of analytes by applying high temperature or elution. In SPME, fine fibers made of molten silica coated with a suitable sorption material for the adsorption of the target analytes onto the solid phase are used. The analytes in the sample are dispersed between the coated fiber and the matrix. In this way, both the separation and the enrichment processes are performed. Then the desorption of analytes on the fiber are performed by applying high temperature, leading to the release of analytes in gaseous form or eluting with organic or inorganic solvents. Analytes in gas form are transported to the detection system, generally a GC column, or elution solutions are injected into the detection systems. According to the interaction of the fiber on the solid phase with the sample, the solid phase microextraction method can be applied in nine different ways: 1. 2. 3. 4. 5. 6. 7. 8. 9.

direct (direct immersion, DI); adsorption from the headspace (HS); in-tube SPM; solid phase dynamic extraction (SPDE); micro-SPE (μ-SPE); adsorptive microextraction (AμE); stir-cake sorptive extraction (SCSE); rotating-disc sorbent extraction (RDSE); and stir-rod sorptive extraction (SRSE).

As detailed explanations about these methods are made in Chapter 3, Historical background: milestones in the field of development of analytical instrumentation, the methods in this section have been mentioned only in headings.

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1. Historical backgrounds, milestones in the field of development of separation and preconcentration methods

1.3 Conclusions In a world where technology, industrialization and consumption are increasing day by day, there will be significant increases in the amount of organic, inorganic, and biological species in living areas, in living organisms and in the ecological environment. Accurate and sensitive analysis of these toxic species in all environmental samples, as well as in food, water, pharmaceutical, and similar consumer products directly related with living cells, is becoming an ever more important issue. Therefore as life goes on, separation and preconcentration-based sample preparation methods for trace organic and inorganic species will remain popular. Despite the rapid development in separation and preconcentration-based sample preparation methods the past 100 years and more, the ever increasing production and consumption of human beings are signs that this trend will continue rapidly with the contributions of other disciplines such as nanotechnology, material science, engineering, and others.

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New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

2 Historical background: milestones in the field of development of analytical instrumentation Nasrullah Shah1, Muhammad Balal Arain2 and Mustafa Soylak3 1

2

Department of Chemistry, Abdul Wali Khan University Mardan, Mardan, Pakistan Department of Chemistry, University of Karachi, Karachi, Pakistan 3Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey

2.1 Introduction

as instrumental methods. These methods include but are not limited to electroanalytical, spectroscopic, chromatography, thermal, and nuclear techniques of analysis. Voltmeter, ammeter, polarograph, spectrophotometer, and others are the instruments used to measure various properties for analytical purposes [1 3]. Instrumental methods are more sensitive, faster, and have a broad range of applications in industry. The instruments are usually interfaced with a microcomputer, which works as a readout device for digital data, titration curves and polarograms, and other output. In some cases, the instruments are fully automated, and they perform all the functions automatically from sampling to printing the results [1 3]. In chemistry much focus is placed on the theoretical background, applications, and interpretation of data of analytical techniques. In this chapter, the focus is on the historical background of common instrumental analytical

Quantitative analyses are mainly based on the measurement of (1) the chemical reaction, (2) the electrical property, (3) optical properties, (4) nuclear properties, and (5) thermal properties. Analytical methods are broadly classified as classic and instrumental methods of analysis. The classical methods of chemical analysis, such as gravimetry, titrimetry, and volumetry, are based on the quantitative completion of chemical reactions. Gravimetry is based on weight measurement, while in volumetry the volume needed for the completion of a reaction is measured. Gravimetry is largely classified as precipitation, volatilization, and electrogravimetry, and voltammetry is broadly consisted of neutralization, complexometric, precipitation, redox, and precipitation titration [1 3]. The methods based on measurement of a property by using an instrument are referred to

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00002-4

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© 2020 Elsevier Inc. All rights reserved.

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2. Historical background: milestones in the field of development of analytical instrumentation

techniques and the introduction of various types of hyphenated techniques such as HPLCAAS, HPLC-ICP-MS, HPLC-EC, HPLC-AFS.

2.2 Development in the field of chromatography Chromatography is an important branch of analytical chemistry. It is a separation technique in which the components of a mixture are separated in a system consisting of two phases: stationary and mobile. Although the term “chromatography” was first introduced by a Russian chemist and botanist Michael Tswett is 1906, the history of chromatographiclike separations is very old, dating back to ancient times. The extraction of natural dyes, food processing, and metal extraction have been done from the early ages of human history [4,5]. In 23 79 BCE, Pliny identified ferrous sulfate by using papyrus soaked with gall nuts, in a process resembling modern-day paper chromatography [6]. In 1834 and 1842 Runge reported a simple spot test for the analysis of bleaching solution using a dyed cotton fabric and a paper soaked with starch and potassium iodide, respectively [7]. In 1850 Runge laid the foundation of paper chromatography by separating the dyes obtained from coal tar using a special type of paper. Runge published his work in 1855 in which described his dye separations on paper [6]. In 1861 Groppelsroeder introduced the term “capillary analysis,” as he noticed that dyes became separated on strips of paper due to capillary movement of the water, which was used as a solvent for separation of the dyes. However, he was unable to explain the actual mechanism involved in the separation process in his paper on the chromatographic process [8]. Similarly, S. V. Heins reported in his paper that F. Feigle stated, “It seems not to be known

that L. Reed thirteen years before Tswett, discovered that it is possible to separate certain inorganic and organic [alkaloids] by column adsorption [on Kaolin]” [9]. A few other studies also reported that the concept of chromatography was applied by other scientists, such as Reed and Day before Tswett. Reed used a column for separation purposes and described some of his separation work using columns in 1893. In 1897 Day separated a petroleum fraction by using columns. Similarly, Engler and Albrecht also did fractionation while using columns [6]. Due to the introduction of more sophisticated chromatographic methods, the progress and use of paper chromatography declined after 1985 [6]. Beyerinck (1889) and Wijsman (1898), introduced thin layer chromatography (TLC) as they separated the strong acids and enzymes in malt extract using gelatin layers in place of paper. However, the current form of TLC was introduced by Izmailov and Shraiber, who in 1938 analyzed the pharmaceutical tinctures on the glass plates coated with alumina powder used as gelatine stationary phase. Meinhard and Hall (1949) developed their TLC plates by using microscope slides coated with celite and alumina containing starch as a binder. Further development in TLC was made by Kirchner, who in 1951 introduced the ascending TLC techniques. Stahl had compiled a book on TLC in which he described the techniques and various adsorbents used in TLC [5,8,10]. A breakthrough in TLC was observed in 1970s after the introduction of high-performance TLC having efficiency and speed. Heyns and Grutzmacher used a mass spectrometer coupled with TLC for analysis. Similarly, Hutzinger and Jamieson also used TLC coupled with a mass spectrometer (MS) for indole analysis in 1970. TLC coupled with other types of detectors, such as photoacoustic spectrometry and infrared spectroscopy, was also reported [8].

New Generation Green Solvents for Separation and Preconcentration

2.2 Development in the field of chromatography

The ion-exchange chromatography was first reported by Taylor and Urey in 1938 for the separation of isotopes of lithium and uranium using zeolite as an ion-exchanger bed. In 1939 Samuelson used synthetic ion-exchanger bed. The progress became much rapid during world war second for separation of transuranium elements. It was in 1980s when the high performance ion-exchange chromatography was introduced and it greatly enhanced the performance of ion-exchange chromatography [8,11]. Size exclusion chromatography was introduced in 1958 when Foldin and Porath produced a cross-linked gel by the reaction of dextrane and epichlorohydrin. More developments were made in size exclusion chromatography by introducing new stationary phases, and it became one of the mostly used chromatographic technique for polymers analysis [8,12]. In 1967 Porath developed affinity chromatography by using peptides and proteins as the stationary phase for the separation of biological molecules [8,13]. In 1903 Michael Tswett presented his work on the effect of different packing materials and their particle sizes on the separation performance of a column at the Warsaw Society of Natural Sciences. However, it did not get much attention until the work of Lederer and others in the field of plant pigments separation in 1930s and the publication of the first book on chromatography by Zechmeister in 1937. Chromatography gained interest among scientists, and Khun, Karrier, and Ruzika won the Nobel Prize in 1937, 1938, and 1939, respectively, for their contributions in chromatography. In 1940s ion-exchange partition and column chromatography led to the initial studies on gas solid chromatography. During this time, liquid adsorption chromatography was at its peak, and it was used as a main chromatographic technique for both analytical and preparative separation purposes. Tiselius (1940) and Claesson (1946) classified

47

chromatography in three broad classes: frontal, displacement, and elution chromatography. In 1948 Tiselius was awarded the Nobel Prize for his achievements in chromatography [6 8,10,14]. The concept of gradient chromatography was introduced in 1950s. In this progressive era of chromatography, Martin and Synge laid the foundation of liquid—liquid chromatography. They were working on the separation of acylated amino acids by using a series of 40 extraction funnels for the separation of different kinds of amino acids. They used water-chloroform as solvent mixture and observed that the amino acids were separated in the extraction funnels according to their distribution ratio and partition coefficients. This was tedious work, and soon they got the idea to utilize the column chromatography using water-containing silica gel as stationary phase with chloroform as a mobile phase for the separation of acylated amino acids. Martin and Synge replaced the silica gel and used cellulose to separate the amino acids without derivatization. They both were awarded the Nobel Prize in 1952. In the 1950s gas chromatography (GC) was developed, and the 1960s saw the development of high-performance liquid chromatography [6,8]. The diagrammatic representations of GC and HPLC are given as Figs. 2.1 and 2.2, respectively. GC laid the foundation for the modern instrumentation of chromatography. Martin and James were the pioneers in GC as they first used nitrogen gas as a mobile phase for the separation of C2 C4 fatty acids on stearic acid coated celite support as a stationary phase [8]. Although Martin and Synge described their work of gas liquid chromatography in 1941, the first paper on gas liquid chromatography was published by James and Martin in 1952. The first publication on gas solid chromatography was done by Hesse et al. Hesse and his coworkers separated hexanoic acid by using carbon dioxide as the mobile phase and silica gel as the stationary phase. Probably, it was

New Generation Green Solvents for Separation and Preconcentration

48

FIGURE 2.1

2. Historical background: milestones in the field of development of analytical instrumentation

Schematic diagram of GC.

Regulated helium source Mobile phase containers

Pump

Readout

Detector

Sample proportioning valve Column

Damp

Drain valve

Sample injection

Filter Regulator Pressure transducer

FIGURE 2.2

Schematic diagram of HPLC [15].

Cremer’s laboratory that developed the first complete gas chromatograph. Sweeley and Horning reported the use of film-coated inert support for use as the stationary phase. Touchstones reported the separation of estrogens and their detection by using an electron capture detector. Claesson and Ray worked the detector system for GC and reported the use of a thermal conductivity detector. In 1958 Lovlock used an electron capture detector. Harley, Nel, and Pretoriu introduced the flame ionization detector. Lovlock brought an argon

ionization detector, which was actually based on the research of Jesse and Sadankis. In 1955 Scott described the hydrogen flame detector. Holmes and Morrell reported the use of the modified mass spectrometer for detection purposes in GC. Similarly, Gohlki used a time-offlight mass spectrometer as a detector in GC. The use of GC/MS was in practice since 1957. Further, developments were reported in GC instrumentation and applications [6,16]. In 1958 Golay introduced the use of an open tubular column for increasing the efficiency of

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2.3 Development in the field of spectroscopy

gas chromatography. Improvements in GC columns were observed, when in the 1980s, the inner walls of the columns were coated with pure silica, made them sustainable to high temperatures. In the 1960s, Kirkland, Huber, and Horvath published their work on high-speed liquid chromatography, which is known today as high-performance liquid chromatography. Hamilton, Bogue, and Anderson had already reported their work regarding the separation of amino acid by using HPLC in the same year, but that was not much considered [6]. Kirkland had contributed much in terms of introducing new surface-coated porous stationary phases in HPLC. The use of enzymes and proteins as stationary phases in column for affinity HPLC was reported by Walters in 1985 [17]. Katz and Scott introduced the superspeed HPLC, which was able to separate the mixtures in a few seconds [18]. A great contribution was made by the DuPont in the establishment of practical instrumentation for HPLC. Various efforts were made from time to time to improve column efficiency and the detector system in HPLC. The detector used mostly was the UV detector; however, other detectors, such as the refractometer, fluorometer, and electrochemical detectors, were also introduced and used with the HPLC system for analysis [6]. The hyphenated techniques of HPLC such as HPLC-MS, HPLC-FTIR, HPLC-NMR were also reported, bringing tremendous development in the instrumentation and applications of HPLC. Supercritical fluid was used a mobile phase in chromatography in 1960s, which added a new type of chromatography known as supercritical fluid chromatography [8]. Klesper was the first who reported the use of supercritical fluid chromatography in 1962 [19]. The introduction of fused silica capillary columns in supercritical chromatography has brought much advancement to this technique [20].

49

Proper instrumentation was available since 1985, which made the supercritical fluid chromatography a practical technique for separation purposes [6]. Among several other techniques of chromatography, countercurrent chromatography was the first reported by Ito and Bauman in 1970 [21], which was actually based on the process of the countercurrent extraction process used by Craig in 1949 [22]. Likewise, the advancement of other chromatographic techniques in the instrumentation and applications of countercurrent chromatography is ongoing, reaching the stage of coupling with advanced detection systems such as the countercurrent mass spectrometer system, as reported in 1990 [23].

2.3 Development in the field of spectroscopy Spectroscopy is based on the measurement of absorbed or emitted electromagnetic radiation. EMR is divided into several types based on the range of wave length and energy, as well as the effect they cause. Table 2.1 represents different EMR sources along with their properties and effects. Absorption methods are classified as (1) visible spectrophotometry, (2) ultraviolet spectrophotometry, and (3) infrared spectrophotometry. Atomic spectroscopy involves the measurement of absorption or emission of electromagnetic radiations from atomic species [3]. The molecular spectroscopic techniques such as visible, ultraviolet (UV), infrared (IR), and nuclear magnetic resonance (NMR) spectrometry are well-known analytical techniques that measure, both quantitatively and qualitatively, the interaction of electromagnetic radiation with matter, contrary to mass spectrometry, which does not involve a similar interaction. However, in mass spectrometry, the data is presented in the same manner, and

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50

2. Historical background: milestones in the field of development of analytical instrumentation

TABLE 2.1 Different EMR sources with their properties and effects [24]. EMR Alpha rays Gamma rays X-rays UV Visible Infrared

Wavelength range λ (m)

Energy per mole

Molecular effect

# 1 3 10

6

$ 10 kcal

Ionization

212

6

B10 kcal

Ionization

210

B10 kcal

Ionization

28

B10 kcal

Ionization/electronic transitions

B10 kcal

Electronic transitions

B1 kcal

Molecular vibrations

212

1 3 10

1 3 10 1 3 10

26

0.5 3 10

25

1 3 10

22

Microwave

1 3 10

Radiowave

1 3 10

3

MS is therefore also considered a spectroscopic technique.

2.3.1 Development of ultraviolet visible spectrometry In ultraviolet visible (UV-Vis) spectroscopy, the iteration of UV-Vis radiation with molecules is studied for the purpose of interpreting quantitative and qualitative results. This techniques evolved from ancient observations of colored phenomena. The history of spectroscopy traces back to the study of various colors of the rainbow. The actual history of spectroscopy begins in the 17th century, when in 1666, Sir Isaac Newton attempted to study the nature of light, hoping to determine the origin of the colors of the rainbow that had been under observation for thousands of years. Newton passed a ray of sunlight through a prism and observed the splitting of light into a regular series of various colors, which were again converted into white light by passing it through a prism in the inverted position. From these experiments, Newton concluded that white light was made up of different colors fused together. The word “spectrum” was first coined by Sir Isaac Newton to illustrate the rainbow of colors that mingle to form white

4 2

22

B10

26

B10

kcal

Rotational motion

kcal

Nuclear spin transitions

light. Joseph von Fraunhofer carried on the experiments with dispersive spectrometers, which enabled spectroscopy to become a more precise and quantitative scientific technique in the early 19th century. The use of a prism by the Romans to generate a rainbow of colors and the works of various scientists such as Athanasius Kircher (1646), Jan Marek Marci (1648), Robert Boyle (1664), and Francesco Maria Grimaldi (1665) provided the basis for Sir Isaac Newton’s experiments [24 26]. In 1609 Galileo Galilei made the first telescopic discoveries and reported them in 1610 [27]. In 1802 William Hyde Wollaston improved Newton’s model. Wollaston built a spectrometer consisting of a lens and using a narrow slit in place of a round aperture. Wollaston observed that the focused sunlight was split into a series of colors with no uniformity and had dark bands acting as natural boundaries between the colors. However, a decade later, in 1815, this hypothesis was rejected by a German optician, Joseph von Fraunhofer, who studied the dark lines in more detail. Fraunhofer used a convex lens between the prism and slit and achieved a better defined series of images. To study the angular position of the lines precisely, Fraunhoper utilized a telescope to view the spectrum, and this resulted in the

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2.3 Development in the field of spectroscopy

development of the spectroscope. Fraunhoper used this spectroscope for observing the pattern of lines in the light coming from the sun and stars. He observed more than 500 dark lines in the solar spectrum and classified them as A to H for being in the red and in the violet regions, respectively. The work of Fraunhoper ˚ ngstro¨m, was further extended by Anders J. A who in 1868 measured the wavelength of 1000 Fraunhoper lines and represented them in units ˚ (A ˚ ngstrom) after of 10210 m—now known as 1 A his name [27,28]. Spectroscopic techniques were gaining more focus, and other scientists published their work [29]. In the 1820s, John Herschel and William H. F. Talbot did experiments to systematically observe salts using flame spectroscopy. In 1822 Sir John Herschel studied the visible spectra of colored flames and concluded that the color of the flames can be used to analyze different objects. This work formed the basis for the Kirchhoff and Bunsen studies. In 1835 Charles Wheatstone illustrated that in the emission spectra of various spark metals are bright lines that could easily distinguish the metals, thus introducing another mechanism for flame spectroscopy [30]. In 1849 J. B. L. Foucault reported that for the same materials, the absorption and emission lines appear ˚ ngstro¨m studied the at the same wavelength. A emission spectrum from hydrogen, later named Balmer lines [31,32]. In 1854 and 1855 David Alter reported his study on the observation of the Balmer lines of hydrogen as well as several metals and gases [33]. In 1859 Gustav Kirchhoff presented a theory to explain the Fraunhofer lines in the sun’s continuous spectrum. Kirchhoff drew a conclusion that a substance would absorb and emit light of the same wavelength. While explaining Fraunhofer’s lines, he stated that the dark lines in the solar spectrum were due to the absorption of lines matching the emission lines if the gases were otherwise excited [34]. In 1860s Bunsen and Kirchhoff recognized the relation between chemical elements and

51

their unique spectral patterns and hence established the technique of analytical spectroscopy. In 1860 they reported their findings on the spectra of eight elements and their presence in several natural compounds [34]. For instance, in 1861, Kirchhoff and Bunsen discovered cesium and rubidium, and Sir William Crookes discovered thallium. PierreJules-Cesar Janssen observed a new yellow line in the solar spectrum, which was identified as a new color line due to a new element, named helium by Sir Norman Lockyer and chemist Edward Frankland. In 1885 J. J. Balmer interpreted for the first time that the visible line spectrum of hydrogen has emission wavelengths at 6563, 4861, 4341, 4102, and 3970 A . In 1913 Niels Bohr proposed the idea of energy in the electronic states. He reported that electrons emit or absorb energy during transition that is equal to the energy difference between the two transition states. The worth of elucidating visible emission spectroscopy in the electronic structure of matter led to an important breakthrough in analysis. In 1913 August Beer presented his famous law, which defines the relationship between absorption and concentration. The unknown concentration of the colored solutions was derived from the transmitted light by comparing it with standard samples of the same nature. However, the human eye was not accurate enough and was replaced with a detector calorimeter or spectrophotometer in the 1930s [24,27]. In 1801 UV radiation was first observed by a German physicist J. W. Ritter. Ritter was working on the effect of the visible spectrum on silver chloride salt and noticed that violet light caused a darkening of the salt. He further observed that the darkening was more in the region beyond the visible region, and hence he named it the ultraviolet region. In 1947 Varian produced the first combined spectrophotometer, called Cary 11 [27]. In 1895 the X-ray was discovered by the German physicist W. C. Ro¨ntgen, which led to

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2. Historical background: milestones in the field of development of analytical instrumentation

FIGURE 2.3 Schematic diagram of UV-Vis spectroscopy.

Detector

Sample Light source

Entrance slit

Exit Dispersion slit device Monochromator

TABLE 2.2 The spectral regions of UV-Vis spectroscopy. Regions

λ(nm)

Absorbing compounds

Far ultraviolet (vacuum UV region)

, 190

Saturated and monounsaturated

(Near) ultraviolet

190 380

Polyunsaturated and aromatic

Visible light region

380 780

Colored

X-ray spectroscopy. In 1896 A. H. Becquerel discovered radioactivity, and P. Zeeman observed the splitting of spectral lines by a magnetic field [27]. In 1900 Frank Twyman developed the first commercial quartz prism spectrograph, and in the same year, time-resolved optical emission spectroscopy was reported. In 1947 48 the first commercially available optical emission spectrometers with photomultiplier tubes as detectors were produced. In 1937 the first fully automated spectrometer was developed by E. Lehrer. for more accurately measuring spectral lines. The introduction of more advanced instruments such as photodetectors brought accuracy in the measurement of the specific wavelength of the substances. In 1958 he invention of the laser contributed to the start of modern spectroscopy [27]. In 1963 the invention of annular inductively coupled plasma (ICP) by S. Greenfield and coworkers had an enormous impact on the progress of instrumental analysis. Spectrometers with ICP were commercially available in 1974 [27].

The schematic representation of UV-Vis spectroscopy is given in Fig. 2.3. The purpose of a radiation source is to provide the desired range of radiation necessary for electronic transition. UV-Vis EMR is classified into different regions shown in Table 2.2. Similarly, various types of transitions caused by UV-Vis EMR in different types of molecules are given in Table 2.3. Stable UV and visible radiation sources with different wavelength ranges have been introduced. Various UV radiation sources are deuterium lamp, hydrogen lamp, tungsten lamp, xenon discharge lamp, and mercury arc lamp. Examples of visible radiation sources are tungsten lamp, mercury vapor lamp, and carbonone lamp. Radiation sources usually emit polychromatic light from which the radiation of a specific wavelength is selected by a filter or monochromator. The monochromator contains entrance and exit slits, collimating and focusing lenses, and a dispersing device, which is usually a prism or grating.

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2.3 Development in the field of spectroscopy

TABLE 2.3 The spectral regions of UV-Vis spectroscopy. Transition

Molecules

σ-σ*

Alkanes

σ-π*

Carbonyls

π-π*

Unsaturated compounds

n-σ*

O, N, S, halogen-containing compounds

n-π*

Carbonyls

The sample is put into a cell made of material that is transparent to UV-Vis radiation. In visible-range glass, cuvettes made of plastic or quartz are used, whereas in UV, only quartz or fused silica is recommended as glass or plastic absorb radiation in the UV range. Although usually cells of rectangular shape with a 1-cm path length are used, they are available in various shapes and sizes. After passing through the sample container or cell, the radiations are directed toward detectors for measuring the transmittance and absorbance for data acquisition. Three types of detectors are used in UV-Vis spectroscopy, including photovoltaic cells, phototubes, or photoemissive tubes and photomultiplier tubes. The photomultiplier tube is a sensitive detector and is a commonly used detector in UV-Vis spectroscopy [2].

2.3.2 Development of infrared spectrometry Infrared (IR) spectroscopic techniques are based on the principle that the infrared region EMR (10,000 200 cm21) are passed through molecules, causing stretching, bending, or rotation of the bonds. This bond length or bond angle variation occurs in various functional groups of molecules at specific frequencies of IR radiation. The characteristic frequencies and the change in bond length and/or angle are

53

used for analytical purposes. The IR radiation lies near the visible range, and, on the basis of this relation, the IR range is divided into three groups: near IR (number ranges from 14,000 to 4000 cm21, and wavelength ranges from 0.8 to 2.5 mm); mid-IR (wave number 4000 to 400 cm21 and wavelength 2.5 to 25 mm); and far IR (wave number 400 to 10 cm21 and wavelength 25 to 1000 mm). All molecules are not IR active; the only molecules that are IR active are those containing polar bonds, composed of atoms of different elements, and organic compounds and inorganic compounds (H2O, HCl, salts, NO2, CO2) [35,36]. The IR region of EMR was discovered by Herschel in 1800. Herschel observed the presence of radiant heat ahead of the visible region of the solar spectrum. However, Herschel did not study this phenomenon further, and in 1882, Abney and Festing measured the IR absorption spectra for more than 50 compounds and assigned spectral bands to the presence of various organic groups in the molecules. Julius documented the spectra of 20 organic compounds and interpreted that methyl groups absorbed IR at their characteristic wavelengths. Over decades in 1903, W. W. Coblentz performed several measurements and analyzed the IR spectra of hundreds of compounds. However, there were many complications and hurdles in the measurements with IR spectroscopy, which were usually conducted at night due to presence of daylight, and the analysis was very time-consuming as well. This was why IR spectroscopy was not very applicable until the 1940s [35,37,38]. During the late 1930s, Richard S. Perkin and Charles W. Elmer established the Perkin-Elmer Corporation in the United States. In 1937 they constructed optical elements for a prototype IR. The Perkin-Elmer instrument was one of the first infrared spectrometers (Model 12). The Beckman Company also built their Model IR-1 instrument at the same time. Commercially available IR spectrophotometers give the

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54

2. Historical background: milestones in the field of development of analytical instrumentation

fingerprints of almost all molecules except for optical isomers. Different types of IR radiation sources are used based on their range of operation. Silicon carbide is used as a radiation source for measurement in the mid-IR region (5000 400 cm21). A tungsten halogen lamp is used for near IR radiation (10,000 4000 cm21). A mercury discharge lamp is used for measurement within the far IR range (200 cm21). Pyroelectric detectors are commonly employed in mid-IR spectrometers. Cooled photoelectric detectors are also used that have higher sensitivities and shortened response times. Liquid nitrogen—cooled mercury cadmium telluride detectors are the most widely used in the mid-IR range. Interferometer (Fig. 2.4) is used to obtain interferograms. In the near IR region, uncooled indium gallium arsenide photodiodes are utilized. In the far IR range, liquid helium—cooled silicon or germanium bolometers are the detectors of choice. Several types of beam splitters are used in IR spectrometers. The KBr-made beam splitter is useful up to 400 cm21. However, when it is coated with CsI, its range extends to about 200 cm21. ZnSe-based beam splitters are useful up to the range of 500 cm21, and these may be effected by water vapor. In the near IR region, the CaF2-made beam splitter is employed, but its range of use is only up to 1200 cm21. Far IR beam Fixed mirror Beam Splitter

IR source Moveable mirror Detector

FIGURE 2.4 Diagram of Michelson interferometer using IR spectrophotometer.

splitters are generally made of polymer films and are used in a limited wavelength range [35,36].

2.3.3 Development of nuclear magnetic resonance spectrometry Nuclear magnetic resonance (NMR) spectroscopy is based on the principle that the sample is placed in a magnetic field that causes excitation of the NMR active nuclei. The changes in the local magnetic field of the nuclei are detected for analytical purposes. The change in resonance frequency appears due the change in the intramolecular magnetic field around an atom in a molecule. These changes are detected for identification of functional groups and the electronic structures of molecules. Proton NMR and 13C NMR are common practices; however, it is applicable to any kind of molecule that has nuclei with spin. The discovery of the Zeeman effect in 1896 laid the foundation of NMR spectroscopy. The concept of NMR development spectroscopy originated in 1924, when Wolfgang Pauli first recognized the magnetic properties of nuclei. It was observed that atoms with nuclei possessing angular momentum had magnetic moment and that they could absorb specific radio frequency waves when kept in an external magnetic field. In 1946 Felix Block at Stanford and Edward Purcell at Harvard conducted the first successful NMR, and both were jointly awarded the Noble prize in 1952. Scientists also tried to determine resonant fieldfrequency relationships for the calculation of magnetic moments. In this regard, Yu and Proctor measured the magnetic moment of 14 N nuclei and expected the presence of single strong peak, but they observed two peaks of the same intensity. Similarly, Yu and Proctor also observed multiple peaks for antimony while studying its magnetic moment. Hahn and Alichter observed the same phenomenon and coined the term “spin interaction mechanism.”

New Generation Green Solvents for Separation and Preconcentration

2.3 Development in the field of spectroscopy

In 1951 the predicted chemical shift phenomenon was verified by Packard and coworkers. They recorded the chemical shift data of ethanol and its interpretation for its structural elucidation. James Shooley recognized the important applications of NMR in chemical analysis. In 1952 Shooley joined the Varian Corporation, and the first commercial 30-MHz NMR instrument HR-30 was produced by Varian Corporation in 1953. Within only five years, other models, such as 40 and 60 MHz, were also introduced. Currently, NMR instruments of various resolutions and natures are commercially available and are considered sophisticated instruments for chemical analysis. The resolution of NMR is dependent on the magnetic strength of the magnet used in the NMR spectrometer. Modern NMR spectrometers have a strong liquid helium—cooled superconducting magnet that is large and very expensive. There are two types of NMR instruments: the continuous wave NMR (CW-NMR) and Fourier transform NMR (FTNMR). Earlier, the CW-NMR was mostly used; however, after the introduction of the Fourier transform NMR in 1970s, it dominated the market due to its high sensitivity. In CW-NMR, the sample is held in a strong magnetic field, the frequency of the source or the strength of the magnetic field is scanned, and its effect on nuclei spin is noted and the data is generated. FT-NMR records many spectra at a time and transforms them into a single data. This decreases the noise ratio and increases the sensitivity [24,39,40]. A typical NMR instrument consists of a superconducting magnet, sample cell, sweep coil, radio frequency transmitter, radio frequency receiver and amplifier, and readout device.

2.3.4 Development of mass spectrometry Mass spectrometry (MS) ionizes chemical species and analyzes them by measuring their mass-to-charge ratio. MS is basically used to measure the masses of the analyte species,

55

which are then used for their qualitative analysis. This has a broad history; however, a brief description is given here. Following the cathode ray experiments conducted by Julius Plucker in 1858 and the discovery of electrons in 1886, Eugen Goldstein conducted similar experiments using a perforated evacuated discharge tube. Goldstein noticed a second beam passed straight through the perforated discharge tube. A few years later, Wilhelm Wein clarified the nature of these rays as positively charged particles, which were further studied by J. J. Thomson in 1907. The mass spectrometer origin came in 1912, when Thomson made a positive ray analyzer, or parabola mass spectrograph. In the presence of parallel electric and magnetic fields, the depletion of positive ions was noticed, which was dependent on their mass-to-charge ratio. Thomson was the first to record a mass spectrum. F. W. Aston enhanced the performance of the mass spectrograph by commencing velocity focusing. This development improved resolution, and the spectrograph was able to make isotopic mass measurement more precisely. However, in 1918, Dempster used an entirely different design for his work, which was the first true mass spectrometer. Dempster used a heating filament for bombarding with electrons for ionization purposes, focusing the beam of ions at the detector. Further development was made in mass spectrometry instrumentation to achieve a broad range of analysis [24,41,42]. A typical MS consists of an ionization source, accelerating slits, deflection chamber surrounded by a magnetic field (analyzer), detector, amplifier, and a readout device. The diagrammatic representation of the MS system is given as Fig. 2.5. • Sample injection: HPLC, GC, syringe, plate, capillary • Ionization sources: The function of the ion source is to produce gas phase ions. Various ionization sources used are electron

New Generation Green Solvents for Separation and Preconcentration

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2. Historical background: milestones in the field of development of analytical instrumentation

FIGURE 2.5 Diagrammatic representation of a mass spectrometer.

Magnet Flight tube To vacuum Ionization source

Sample

Detector

Readout

ionization (EI), chemical (CI), spray ionization (APCI, APPI, ESI), desorption ionization (FAB, MALDI, SALDI), gas discharge ion sources (e.g., inductively couple plasma), ambient ionization (DESI, LAESI). • Analyzers: The function of the analyzer is to analyze, or separate, the ions according to their m/z (mass-to-charge) ratio. Commonly used analyzers are sector, quadrupole, TOF, Orbitrap, FTICR. • Detectors: To convert masses to signals, detectors are used. Photoplate, Faraday cup, electron multipliers (MCP), solid-state, image current are used as detectors in MS.

2.3.5 Development of luminescence spectroscopy A radiated material emits light either through incandescence (all atoms emit light) or through luminescence (only certain atoms emit light). Luminescence is of two types: fluorescence and phosphorescence. The spectroscopy that is based on type of luminescence is generally known as luminescence spectroscopy. Fig. 2.6 shows the general emission process responsible for the luminescence phenomenon. Phosphorescence is a form of luminescence that happens when excited electrons of a different multiplicity from those in their ground

Excited state Incident light

E

Emitted light

Ground state

FIGURE 2.6 Phenomenon of emission.

state come back to their ground state through the emission of a photon. It is a spin-forbidden process, but it has applications across several fields. “Phosphorus” was the ancient Greek term stand for “the light bearer,” The term “phosphorus” has been used since the Middle Ages to designate materials that glow after exposure to light. A singlet or a triplet state can be created when one couple of electrons in a molecule is excited to a greater energy state. So, in the excited singlet state, the rotation of that excited electron is still contrary to that of the remaining electrons, though the spins of the two electron become unpaired and are thus parallel in the triplet state. Electronic spin states involved in fluorescence and phosphorescence phenomena in molecules are shown as Fig. 2.7. In the ground state, the spins are always paired; thus it is the single state. In the excited level, if this spin remains paired in the excited state, then it is a excited singlet state, but if the spin becomes unpaired, the molecule is in an excited triplet state. The transition of

New Generation Green Solvents for Separation and Preconcentration

2.3 Development in the field of spectroscopy

T2 S1

Intersystem crossing

Triplet–triplet absorption

T1

So Phosphorescence

Fluorescence

FIGURE

2.7 Mechanisms

in

luminescence

spectroscopy.

electrons from an agitated triplet state to the grounded singlet state produces molecular phosphorescence. Because the triplet—singlet transition produces a change in electron spin, it is much less feasible. As a result, the triplet sate has a much longer lifetime. The long lifetime of phosphorescence is also one of its drawbacks. Because the excited state is relatively long-lived, nonradiational processes have time to compete with phosphorescence for deactivation. Therefore the efficiency of the phosphorescence process, as well as the corresponding phosphorescence intensity, is relatively low. So, of the many of the earliest studies of shining in dark minerals, the best known is that of Bolognian phosphorus (barium sulfide in impure form) studied in 1602 by a cobbler from Bologna, Vincenzo Cascariolo. Later in 1677, a similar designation was allotted to the element phosphorus, separated by Brandt, because, when exposed to air, it burns and releases a shining vapor. Historically, phosphorescence and fluorescence were distinguished by the amount of time after the radiation source was removed that luminescence remained. Fluorescence was defined as short-lived chemiluminescence, whereas phosphorescence was defined as longer-lived chemiluminescence. The instrument used for phosphorescence, called the phosphor scope, was devised in 1857 by Alexander Edmond Becquerel, a pioneer in the field of luminescence. By that time,

57

phosphorescence could persist for seconds through minutes or even longer. The spectrum of phosphorescence is situated at wavelengths greater than the spectrum of fluorescence since the energies of the lower vibrational state of the triplet level T1 is lower than that of singlet level. The basic instrumentation for phosphorescence is similar to that of fluorescence. Two types of phosphoroscrope are used for the measurement of phosphorescence. Rotating disk phosphorescence (RDP) involves two rotating disks with holes, into which the sample is placed to be analyzed. When a beam of light penetrates one of the disks, the sample is electronically excited and can phosphoresce, and a photomultiplier records the intensity of the phosphorescence. The rotating can phosphor scope (RCP) consists of a rotating cylinder with a window to allow the passage of light. The sample is placed at the outside edge of the can, and when the light pass through the window and the sample is excited electronically, the intensity is measure via the photomultiplier. The advantage of RCP or RDP is that, at high speeds, RCP can minimize other types of interferences such as fluorescence, and RDP can minimize Raman and Rayleigh scattering of photons, in a typical phosphorescence-intensityversus-emission-wavelength spectrum of fluorinated acetophenone compounds [2,43,44].

2.3.6 Development of atomic absorption spectroscopy The study of EMR interaction with atomic gaseous forms of elements is used for the analysis of numerous metals and scarce nonmetals. Nearly all metal elements can be quantitatively examined by utilizing the spectral absorption features of atoms. This is a very simple and reliable method that can analyze more than 60 elements. In 1860 with the effort of Bunsen and Kirchhoff, spectrochemical examination was invented, but it had comparatively few uses

New Generation Green Solvents for Separation and Preconcentration

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2. Historical background: milestones in the field of development of analytical instrumentation

until the 1930s. Arc and spark emissions and, to some degree, flame emission techniques then became well-known. Due to the efforts of Walsh in 1955, the modern period of atomic absorption spectroscopy started in Australia, due to the work of Alkemade and Miltz in Holland. From 1955, the period can be separated into seven-year periods: the induction time (1955 62) when atomic absorption received rare attention from the public; a growth time (1962 61) when most of what we see nowadays was established; comparative stability (1969 76) when the contribution of atomic absorption was great compared to other methods. So we are today in an era of ongoing change that was initiated around 1976, owing to the impact of computer technologies on laboratory instruments. Currently such technologies are extensively utilized due to their ease of use, efficiency, and relatively lower price. The initial atomic absorption spectrometer was constructed by CSIRO (Commonwealth Scientific and Industrial Research Organization) in 1954 by Alan. The initial marketable atomic absorption spectrometer was presented in 1959. The method used the basic phenomenon that free (gas) atoms are produced in an atomizer and can absorb radiations at precise frequencies. The method qualifies the absorption of the ground-level atoms in gaseous form. The particles absorb visible light or ultraviolet and produce transitions to greater electronic energy states. The concentration of analytes is examined by the quantity of absorption [2,3,27,45,46].

A typical atomic absorption spectrophotometer consists of a radiation source, nebulizer, atomizer, monochromator, detector, and readout device. Fig. 2.8 shows the general mechanism of atomic absorption spectroscopy. Atomic absorption methods are potentially very precise because atomic absorption lines are extraordinarily narrow (0.002 0.005 nm) and, for every element, electronic transition energies are specific. In atomic absorption, the most commonly used two line sources are hollow cathode lamps and electrodeless discharge lamps. The most often used emission of radiations source is the hollow cathode lamp inn atomic absorption spectroscopy. It contains a hollow cylindrical cathode and a tungsten anode consisting of the elements to be examined. These are enclosed in a glass tube occupied by an inactive gas (argon or neon). At a pressure of 1 5 torr. If a 300-V potential difference is applied through the electrodes, then argon ionizes, and the electrons and the cations of argon migrate to the two electrodes, and a current of 5 10 mA is generated. When the potential is great enough, the cathode is struck by the cations with adequate energies to free some of the metal atoms and to form an atomic cloud. This procedure is known as sputtering. These sputtered metal atoms are in agitated states and release their characteristic radiation as they come back to ground level. Eventually, the metal atoms are diffused back to the surface of the cathode or to the walls of the glass tubes and are redeposited. In addition, to hollow cathode lamps, electrodeless discharge FIGURE 2.8 Flow sheet diagram of

Wavelength selector

Radiation Source

Detector

Readout

atomic absorption spectroscopy.

Atomizer Nebulizer

Sample

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2.3 Development in the field of spectroscopy

lamps are valuable in atomic line spectra. A typical electrodeless discharge lamp is built from closed quartz tubes comprising an inactive gas such as argon at a few torr pressure and a lesser amount of analyte metals (or its salt). The lamps contain no electrodes; in their place, the lamp is energized by a penetrating field of microwave radiation or radio frequency. The argon ionizes in this area, so the ions are enhanced through the greater frequencies constituting the field until they achieve adequate energies to agitate the atoms of the analyte metals. Electrode discharge lamp are available commercially for several elements. They are particularly useful for elements such as, Se, and Te, where hollow cathode lamp intensities are low. Every element has its own advance lamp that should be utilized for the analysis. A special high-pressure xenon short arc lamp is also used as a continuous source of radiation. There are numerous significant features of the nebulizing part of the burner arrangement. In order to deliver effective nebulization for every kinds of sample solution, the nebulizer must be adaptable. Stainless steel has been the usual material utilized for the manufacture of the nebulizer. Stainless steel has the benefit of strength and low cost, and it resists corrosion from samples with a great constituent of acid or other corrosive substances. For these issues, vaporizers assembled of a corrosion-resistant material, such as an inactive platinum, plastic, or tantalum, would be used [2,3,27,45,46]. Various types of nebulizers have been introduced such as pneumatic nebulizers, impact bead nebulizers, ultrasonic nebulizers, pulse nebulizers, and Babington nebulizers. The two major types of nebulizer burners used in AAS are the premix nebulizer burner and total consumption burner. In the premix burner, liquid is sprayed into a mixing chamber where the droplets are mixed with the combustion gas and sent to the burner. In the total consumption burner, the nebulizer and burner are

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combined. This is also called turbulent flow burner. These burners are widely used for atomic emission measurements. The element to be examined needs to be in the atomized state. Atomization is the isolation of elements into separate particles and division of molecules into atoms. It is completed by exposing the analytes to higher temperatures in a graphite furnace or flame. The commonly used vaporizers are flame atomizers and graphite tube atomizers. However, other atomizers, such as electrochemical, hydride, cold vapor, and glow-discharge atomizers, might be used for special purposes. It is very significant portion in AA spectrometers and is used to isolate thousands of lines. The monochromator is utilized to choose the exact wavelength of light that is absorbed through these samples and to eliminate extra wavelengths. The examination of the designated elements in others is found by the selection of precise light. Most commercial AAS instruments use diffraction grating as monochromators. The light chosen through the monochromator is focused on the detector, which is normally a photomultiplier tube, the function of which is to change the light signals into an electrical signal in the direct proportion to the light intensities. The commonly used detector in AAS is the photomultiplier tube. It is a photovoltaic cell consisting of a series of cathodes called dynode and anode. The readout system includes meters, chart recorders, and digital display meters. Modern instruments provide a fast display of experimental conditions, absorbance data, statistical values, calibration curves, and the like [2,3,27,45,46].

2.3.7 Development of atomic emission spectroscopy When energies in the form of heat or light are applied, the molecules are motivated to high-energy states and move from lowestenergy states to the highest-energy states, so

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FIGURE 2.9 Flow sheet diagram of fluorescence spectroscopy.

Sample EMR source Monochromator Monochromator Detector

Readout

molecules are unstable at this level. Consequently, the agitated molecules jump from the highest-energy states to the lowestenergy states, releasing radiation. The energies are emitted in the form of photons. The radiations are noted in the emission spectrometer. The change among the constituents in the agitated and lowest level is the level of emissions of a substance. Every element has a distinct and specific level of emission that benefits the experts in identifying the elements. In the 20th century, Max plank decided that energies might be emitted or absorbed irregularly in the form of packs of energies called quantas. A photon of energy is released when the particle jumps down from the highest-energy state to the lowest-energy state. The spectra gained are named “emission spectra,” and the spectroscopy is called atomic emission spectroscopy (EAS). Fig. 2.9 shows the simplified mechanism of AES. AES is a method used to examine the component amounts in the samples by means of the intensities of light released by spark, flame, plasma, or arc. In AES, the samples are useful with light or heat energies. The sources of energies could be plasma, flame, or electric arc. Every component has dissimilar emission levels and provides the forecast of the dissimilar elements in the sample. Lines of emission from hot gases were initially studied by ˚ ngstrom, and the method was then advanced A

by Robert Bunsen and David Alter Gustav Kirchhoff [2,24,27]. Atomic emission spectroscopy has a long history. In 1550 qualitative applications of atomic emission spectroscopy produced in the color of flames were cast off for the first time in the smelting of raw material. They were then completely established with the studies of atomic spectra produced on spark emissions and flame emissions in 1830. Quantifiable uses of atomic emission spectroscopy based on the electric spark were established by Lockyer in 1870. Quantitative uses of flame emission established in 1930 were found by Lundegardh. Atomic emission established upon production from plasma was presented in 1964 [2,27,45]. Atomic emission has been used dependent only on flame arc or spark excitation sources. Improvement is made by the introduction of noncombustion plasma source. Instrumentation: Light source: DC arc, AC arc, spark, ICP Spectrometer: Monochromator optical-direct read spectrometer, polychromatic optical— direct read spectrometer Detector: Spectrograph, photomultiplier tube (PMT), segmented-array chargecoupled detector (SCD) Readout: Gives signals or peaks

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2.3 Development in the field of spectroscopy

The instrument used for recording a spectrum is known as a spectrometer or spectrophotometer. The first step is atomization or excitation. In this step, a solid liquid or solution is converted into gaseous atoms. The sample is excited by absorbing energy and then emits it by releasing radiation in the form of electromagnetic radiation, which may be thermal or electrical. It is necessary that only the emitted radiation is collected and analyzed and then recorded. In case of emission spectrometer no analyzer is necessary, the source being its own analyzer. A monochromator is employed to separate radiations into individual wavelengths. The dispersing element used is a prism. The detector is the device that converts spectral radiation into an electrical signal that is transmitted to a recording device, called a recorder. The recorder prints the chart. It is essential that the detector does not receive radiation directly from the exciting beam and that the two are placed at right angles. A modulator is placed between the source of excitation and the sample, its function being only that the emission that directly arises from the excitation is recorded [2,45,47].

2.3.8 Development of plasma emission spectroscopy This emission spectroscopy utilizes plasma as a source of atomization, and it is known as plasma emission spectroscopy. It has greatly enhanced the application of atomic emission spectroscopy. Plasma is a fog of extremely ionized gases, consisting of electrons, ions, and neutral species. Ions represent about 1% of the total proportion. Argon gases are commonly ionized by a sturdy electrical ground. The produced plasma may be inductively coupled plasma (ICP) or direct current plasma (DCP) depending on the source of the electric field. In DCP, the ionization is done in a discharge tube with a two- or three-electrode system. In ICP,

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three silica quartz tubes are utilized in which argon gas transmits the samples in the aerosol form. The radio frequency power is applied to the system to ionize the gas and produce plasma. ICP has more of a detection limit than DCP. Compared to flam emission spectroscopy, the plasma substance produces a large quantity of agitated released atoms in the UV range. Plasma emission spectroscopy results in better atomization conditions than arc and spark spectroscopy. Plasma spectroscopy can be used for multielement determinations on a broad concentration range. The sample solution is injected into the system through a nebulization system that is usually a cross-flow nebulizer or Babington-type nebulizer. Basically two types of spectrometers are utilized in plasma emission studies: the concurrent and the successive multielement spectrometers [2,3].

2.3.9 Development of atomic fluorescence spectrometry An atom comprises a set of quantized energy states that can be attained by electrons depending on their energies. When atoms in ground state absorb EMR, they are excited toward the higher-energy level, or excited state. Then, after excitation, these electrons seek to relax back toward ground state by the emission of emitted radiations. In AFS, both absorption and emission occur in the UV range. AFS occurs in two steps: absorption and emission. In AFS, the minimum amount of analysis can be detected by the detector, which is in the range of femtograms to attograms. AFS is based on fluorescence phenomena introduced by Wood in 1905. Later in the development of AFS, an analytical method is attributed to West and Wineforder, who did the initial work in this area. The intensity of emitted light is measured with the help of the detector, which is placed in a direction perpendicular to

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that of the radiation source. A spectrofluorometer or fluorimeter is used in AFS. In the spectrofluorometer, a monochromator is used (as wavelength selector) to quantify the intensities of released energy, whereas in the fluorimeter, a filter is used as a (wavelength selector) to quantify the intensities of released radiations. The sample solution (analyte) is thoroughly associated with electrogravimetry in coulometry, which is also founded on Faraday’s law; the initial uses include examination of atomic weight and of tinny metal coatings. The amount of electric charge is a very ancient, possibly the oldest measurable “electroanalytical” technique; originally, electrolytic deposition electrolysis was designed for the quantification of currents or electric charges by the measurement of the number of electrolysis product(s) according to Faraday’s law. A primary tool for this determination is using the electrolysis of water, as proposed by Michael Faraday himself and known as voltaelectrometer. A coulometer is a tool utilized for determining the amount of electricity required to carry out a chemical alteration of the analytes. The usual exercise in coulometry is to insert the ammeter (which quantifies the current in electrical trials) with a coulometer. Iodine coulometer is a type of a titration coulometer in which an anodic alloy produced iodine is titrated with arsenic (III) or thiosulphate solutions. This is used in the study of the Faraday constant. Another example is the colorimetric coulometer, which is built on the principle of dying species with a substance with a metal ion that should be stripped anodically. For example, a cobalt ion species dyed with nitroso-R-salt and the quantification of absorbance with a spectrophotometer. Coulometry has progressed extensively and is categorized as follows: controlled-current coulometry (amperostatic), primary source coulometry, and secondary source coulometrycontrolled potential (potentiostat) coulometric titration. See Fig. 2.10 for a schematic diagram of various kinds of cuolometric procedures. In

Coulometric method

Controlled cuurent coulometry (amperostatic)

Primary source coulometry

Secondary source coulometry

Controlled potential (potentiostate)

Coulommetric titration

FIGURE 2.10 Schematic diagram of the various types of cuolometric methods.

controlled potential coulometry, the potential is kept constant in order to get maximum current efficiency so that the analytes react completely without involving interfering species. With progress in electrolysis, the concentration of analyte and the current decrease with time. The curve of current time is plotted and integrated. A three-electrode potentiostat is utilized to make the potential in controlled-potential coulometry [2,48 50].

2.4 Development of electroanalytical techniques In 1801 William Cruikshank was doing electrolysis of aqueous solutions of copper salts and suggested the possibility of using current as a parameter for the analysis of metals. In 1830 A. C. Becquerel suggested the use of anodic deposition for the detection of lead and manganese. Buchner used galvanic electricity or electric discharge for analysis at almost the same time in the 19th century. In 1861 and 1865 Weyl developed quantitative electroanalytical procedures for the determination of carbon amounts in pig iron and steel. Jaroslav was awarded the Nobel

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2.4 Development of electroanalytical techniques

prize in 1959 for his discovery of and contributions to polarography. Faraday’s law, the pH scale by Sorensen, the work of Haber and Klemensiewicz on glass electrodes, and the introduction of the carbon paste electrode by Ralph Adams have contributed much in the development of electroanalytical techniques [51,52].

2.4.1 Electrogravimetry Elecrogravimetry is a quantitative electroanalytical technique. In electroanalytical techniques, the concept of quantitative analysis was started with the work of Wolcott Gibbs for the determination of copper and nickel using the electroanalytical precipitation method reported in 1865. This method was used for the determination of copper in copper nickel coins. This work was followed by Carl Luckow, who in 1865 separated and determined copper in the presence of Zn, Co, Ni, Mn, and Fe by the electrodeposition method. Although these were the initially reported methods for the quantitative determination of metals using electrogravimetry concepts, they were called electroanalysis, electrochemical analysis, or electrolytic analysis [51]. With the passage of time, modifications in the nature and construction of electrodes were made by different scientists. Nikolai Klobukov used the rotating electrode to save time. Heinrich Paweck and Clemens introduced the net-shaped platinum electrode. Gibbs suggested the mercury electrode, which was used by Luckow. The concepts of electrode potential for analytical purposes was studied by Hermann Freudenberg. In 1907 Henry Sand and Arthur Fischer introduced electrogravimetry with manually controlled potential. Alexander Claessens wrote the first book on electrogravimetry in 1882. Similarly, in 1890 E. F. Smith published a monograph with the name Electrochemical Analysis [51,53].

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2.4.2 Coulometry Coulometry is the name given to the group of analytical technique used to determine the amount of matter transferred during an electrolytic reaction by measuring the amount of current or electricity produced or consumed. Alternatively, the quantity of electrical charge to convert the sample analyte qualitatively to another oxidation state is measured. The coulometric method is usually rapid and does not require the product of the electrochemical reaction be a weighable solid. Closely related to electrogravimetry is coulometry, which is also based on Faraday’s law; early applications include determinations of atomic masses and of thin metal layers. The measurement of electric charges is a very old, perhaps the oldest quantitative “electroanalytical” method, but originally electrolytic deposition electrolysis was aimed at the quantification of electric charges or currents by the measurement of the amount of electrolysis product(s) according to Faraday’s law. A first instrument for this purpose utilizing the electrolysis of water was suggested by Michael Faraday himself, called volta-electrometer [51,52,54]. Michael Faraday introduced the first voltage measuring device, the volta-electrometer. Similarly, A. C. Becquerel and Johann Christian Poggendorff introduced the metal voltmeter for copper and silver, respectively. In mid-19th century, coulometry progressed when Hampe and Pfeiffer determined the atomic masses of elements by measuring their deposited masses as specific electric charges were applied. In 1893 Freudenberg, with the help of Max Le Blanc, introduced the electrolytic cell incorporated with silver voltmeter. Heinrich Danneel worked on the use of the coulometer for the determination of metals, but his work did not get much attention. Coulometric determination of the tin layer on copper wire was used by Grower in 1917. In this case, Grower used electrolytic cells,

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2. Historical background: milestones in the field of development of analytical instrumentation

coupled with a coulometer, for determination of free tin and alloyed tin on the surface of copper wire. This was followed by the work of Zbinden who in 1931 used stripping analysis while employing the electrolytic cell, coupled with a coulometer, to determine trace amounts of copper. In 1938 La´szlo Szebelledy and Zoltan Somogyi published their work of titration involving coulometric analysis. In 1942 Archie Hickling introduced the potentiostat, which resulted in rapid progress in the use of coulometry for analysis. In the 1960s, Claassen, Milner, and Philiphs worked on analytical coulometry and published the first monograph [51,54]. A coulometer is a device used for measuring the quantity of electricity required to bring about a chemical change in the analyte. It is usual practice in coulometry to substitute the ammeter (which measures current in electrical experiments) with a coulometer. The iodine coulometer is an example of a titration coulometer in which anodically generated iodine is titrated with thiosulphate or arsenic (III) solution. This has been used in the determination of the Faraday constant. Another example is the colorimetric coulometer, which is based on the principle of developing a colored species with a reagent with a metal ion that may be anodically stripped. For example, a colored species might be formed for a cobalt ion with nitroso-R-salt and measurement of absorbance with a spectrophotometer. Coulometry has progressed extensively and is classified by the categories shown in Fig. 2.10. In controlled potential coulometry, the potential is kept constant in order to achieve maximum current efficiency so that the analyte reacts completely without involving interfering species. With progress in electrolysis, the concentration of analyte, as well the current, decreases with time. The curve of current— time is plotted and integrated. A threeelectrode potentiostat is used to set the potential.

In controlled current coulometry, the measurement is performed at a constant current instead of a constant potential. The relationship is drawn as a curve between current and time. Controlled current coulometry is advantageous over controlled potential coulometry in terms of taking less time and not needing the integration of the current—time curve [2,51,52,54].

2.4.3 Conductometry Conductometry is used to analyze ionic species and to monitor a chemical reaction by studying the electrolytic conductivity of the reacting species or the resultant products. It has notable applications in analytical chemistry. Conductivity measurement can be performed directly by using a conductivity meter or by performing conductometric titration. Conductometric analysis of electrolytes is a long-time practice. Henry Cavendish and Andreas Baumgartner reported the analysis of mineral waters and salt solutions by using conductometric methods. Georg Quincke and Emil Warburg checked the water solubility of glasses. In the early stages, direct current conductometry was utilized, but that had the drawbacks of electrode polarization, and hence alternating current was used. Kohlrausch and Nippoldt used alternating current and took conductometric measurements without polarizing electrodes. Alternating current was applied for the determination of electrolytes in water, mineral waters, acids, and sugars. Kohlrausch and Berthelot used conductometric measurements to study chemical reactions. Whitney used conductometry to determine the end point in volumetric analysis. Kolthoff summarized the studies related to end point detection by using conductometric analysis. A special type of conductometric analysis, called telephone analysis was introduced by Bouty. In this type of conductometric analysis,

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2.4 Development of electroanalytical techniques

different electrolytic mixtures, including KCl, KI, K2SO4, among others, were studied using the telephone as the indicator. Kohlrausch, Holborn, and Kolthoff published early monographs on conductometric analysis [2,51,52,55].

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the concept of limiting current, which is very important for analysis in voltametry, polarography, and amperometry [51,56].

2.4.5 Voltammetry 2.4.4 Potentiometry Nernst used potentiometric analysis in 1889 based on his famous equation regarding potentiometry. Behrend used potentiometry for the detection of end points in his volumetric analysis, working the titration of chloride and bromide with mercury nitrate. Bottger and Crotogino used the potentiometric method for end point determination of acid base and redox titrations, respectively. Ostwald’s laboratory was mainly used for such experiments. The use of glass membrane electrodes led to much development to potentiometry. Cremer, Haber, and Klemenciewics studied the relation between the concentration of hydrogen ions and the potential across a glass membrane in 1909. This was followed by the introduction of the pH equation by Søren Peter Lauritz Sørensen in the same year. In 1937 Nikosky depicted the response of an ion-selective electrode for target ions in the presence of interfering ions. Michaelis, Kolthoff Clarke, Muller, Furman, and Jorgensen performed work on the determination of pH using potentiometry and reported their work in the first half of the 20th century. Jagner and Graneli introduced chronopotentiometric stripping analysis in 1976. Ernst Salomon studied and published the current voltage curve in 1896. The current voltage curve brought on much development in utilizing voltametry for analytical purposes. Salomon studied the relation between concentration and residual current. Nernst and Merriam described the theory of residual current and interpreted that the limiting current in the stirred solution corresponds to the diffusion current. Nernst and Brunner introduced

Voltammetry is a category of electroanalytical methods used in analytical chemistry and several industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is changed. The result comes from the voltametric experiment in the form of voltammogram, which is plot of the current versus the potential of the working electrode. Voltammetry experiments investigate the half-cell reactivity of an analyte. Voltammetry is the study of current as a function of applied potential. These curves, I 5 f(E), are called voltammograms. The potential is varied arbitrarily either step by step or continuously, or the actual current value is measured as the dependent variable. The shape of the curves depends on the speed of potential variation (nature of driving force) and on whether the solution is stirred or quiescent (mass transfer). Most experiments control the potential (volts) of an electrode in contact with the analyte while measuring the resulting current (amperes). A number of voltammetric electrodes or cells are introduced and are used in industry and research. These electrodes are referred to as sensors, which are used for the analysis of various types of analytes in different media. Glucose sensors and oxygen electrodes are examples. Voltametry has developed very rapidly, and several types have been introduced with high efficiency, sensitivity, and selectivities. Among several types, a few examples are linear sweep. cyclic, staircase, square wave, stripping, normal pulse, differential pulse, direct current, alternating current, polarography, and the like [2,51,57].

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2.4.6 Polarography and analytical voltammetry The voltametric technique uses droping mercury electrode (DME) as an indicator or a working electrode is known as polarography. It was first introduced by Jaroslav Heyrovsky in 1922 and earned the Nobel prize in chemistry in 1959. However, its development starts with the study of electrocapillary phenomena, where DME was used as the measurement. Jaroslav Heyrovsky and Masuro Skikata developed the first automated instrument, the polarograph, for analytical purposes. The polarograph was used for automatic recording of the current voltage curve. Matheson and Nichols used the oscillograph for recording the current voltage curve in 1938. Oscillograph was used for studying the potential time curve in polarography. Although the term “oscillographic polarography” was given by Heyrovsky and Forejt, later literature reported this as chronopotentiometry. With the passage of time, differential polarography and derivative polarography were introduced for better analysis of analytes in the presence of interfering species. Different other modern polarographic techniques, such as cyclic, square wave, pulse, and differential polarography, were developed for analytical purposes. The use of stripping voltametry employing stationary DME was used for trace element analysis, starting in the 1950s. Heinz Gerischer used stationary DME in 1953 for electroanalytical purposes. The hanging DME (Kemula type) was introduced by Kemula and Kublik in 1956. Metallic substrates with mercury film were also used as electrodes. The carbon paste electrode was introduced by Adams in 1958. Analytical voltametry was promoted with the introduction of wax graphite, pyrolytic graphite, and glassy carbon electrodes by Miller and Zittelin in 1963 and 1965. The development of square-wave and pulse voltametry increased the sensitivity of voltametric techniques up to

the nanomolar range. In these techniques, a two-step process is performed; in the first step, preconcentration of the analyte is done, followed by analysis. The preconcentration of methylene blue was performed by Kemula and his coworkers in 1961, and with this they determined its concentration in the range of 10 8 M while working with DME. The preconcentration process prior to voltametric analysis was practically done by several researchers for both organic and inorganic species. The use of modified surface electrodes for analytical purposes was started in the 1970s. Cheek and Nelson used the carbon paste electrode for the determination of Ag 1 , and Oyama and Anson utilized the platinum electrode, modified with a polymer film, for analysis. Ravichandran and Baldwin were the first to float the idea of carbon paste electrodes for analytical purposes. A modified glassy carbon electrode has been employed for preconcentration and analysis of uranium (VI) [2,51,52,58,59].

2.4.7 Amperometry In this type of electroanalytical technique, the current produced during a redox reaction is observed at a constant potential. Amperometry is conducted in a three-electrode system. Every analyte has a fixed potential for undergoing a redox activity. The potential required is applied, and the resultant current is measured. Amperometric titration is done in the same manner. At the fixed potential, the changes in current are measured as the titrant is added to the analyte solution. Sharp changes are observed at the end point. The concept of amperometry was strengthened after the work of Nernest and his coworkers on diffusion current and limiting current. Amperometry was used for oxygen determination in the 1930s and 1940s. With the passage of time, much progress has been made in the amperometric method of analysis. Different types of

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2.5 Hyphenated techniques

Chromatographic technique

Interface

Detection (spectroscopy/other)

FIGURE

2.11 Block diagram hyphenated technique [61].

of

a

dual-

) Analyte enrichment (optional)

Further detection/s (depends)

amperometric methods have been introduced, such as single-potential or DC amperometry, pulsed amperometric detection (PAD), integrated amperometry. For amperometric titration, drop mercury electrode (DME), rotating platinum electrode (RPE), or twin polarized microelectrode (TPME) is used as the indicator electrode, while usually the saturated calomal electrode is used as the reference electrode. Various types of commercially available amperometers are vintage amperometers (about 1950) and (mechanical gauge) amperometers. Two types of detection methods are used in amperometery: single-potential amperometry or direct current amperometry and pulsed amperometry [2,51,59,60].

hyphenated techniques is given as Fig. 2.11. The results are also mostly free from interference and are reproducible. Initially, doubleinstrument hyphenated techniques were introduced. However, over time, triple-hyphenated techniques were developed to get more reliable and accurate results for quantification and identification. Among the double-hyphenated techniques are LC-MS, LC-NMR, LC-IR, CEMS, GC-IR, GC-MS, HPLC-DAD, and GCFTIR, while triple- or multiple-hyphenated techniques include but not limited to LC-APIMS, APCI-MS-MS, ESI-MS-MS, LVI-GC-MS, LC-ESI-MS, LC-UV-NMR-MS-ESI, LC-MSTSPLC-UV-NMR-MS, LC-NMR-MS, LC-DADAPI-MS, LC-PDA-MS, LC-PDA-NMR-MS, and SPE-LC-MS [61 63,66].

2.5 Hyphenated techniques These techniques involve the coupling of chromatographic techniques with an online detection system, mostly spectroscopic methods, and they are called hyphenated techniques. Hirsch Feld in 1980 adapted the term “hyphenation” for two- or multiple-instrument techniques for analysis in a single run. The basic aim was to achieve purification, identification, and quantification simultaneously [2,61 65]. These techniques were developed to achieve quantification results and detection simultaneously. They have the advantage that, in a single run, separation as well as identification of the analyte is done. Hyphenated techniques are mostly automated, fast, and reliable compared to using chromatography followed by spectroscopy. A generalized diagram for

2.5.1 GC-NMR The GC-NMR technique was introduced in the 1960s. In its early stages, the separated components of the sample coming from GC (gas chromatography) were introduced into an NMR (nuclear magnetic resonance) glass microtube through a syringe. In the 1970s, GCNMR system was improved by flow cell NMR tubes for the introduction of separated sample components from GC into NMR. Although these two were not really hyphenated techniques, the first GC-NMR hyphenated technique was introduced in 1980 by Buddrus and Hertzog. In this attempt, the NMR tube was used in the form of a flow cell with both sides open, connecting GC with NMR. Over time, much development followed, and the on-flow and stop-flow modes were introduced [61,63].

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2.5.2 LC-NMR The LC-NMR system is used for the simultaneous separation and identification of NMRactive compounds present in complex mixtures of all types. LC-NMR has been recognized since the 1970s. Watanabe and Niki reported the first paper on LC-NMR in 1978. They used a stop-flow mode of LC-NMR for the qualitative analysis of a mixture of compounds. The first online LC-NMR was reported in the 1980s, and its implementation as a common laboratory technique of analysis was started in 1990s. The LC-NMR system works in two modes: continuous and stop-flow. Along with the NMR detection system, a UV-Vis detector is also used as a primary detector with the LC system for primary operations [61,63,67].

2.5.3 GPC-NMR The hyphenation of on-flow or online gel permeation chromatography (GPC) with NMR, an GPC-NMR system, has been practiced widely to study the molecular weight and structure of polymers. The molecular weight and polymer size of poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) copolymers were determined by Hatada et al. using on-flow GPC-NMR. Similarly, other polymers such as polystyrene, polybutadiene, and poly (butyl acrylate) (pBA) mixtures have been examined effectively via GPC-NMR. This technique is also useful in determining the tacticity of polymers. GPC-NMR is rapid in response; however, compared to other analytical techniques, the GPC-NMR has low sensitivity, and it requires several scans of analysis for obtaining data with a low signal-to-noise ratio [67].

2.5.4 CE-NMR Capillary electrophoresis (CE) is used to separate ions based on their electrophoretic

movement under the influence of applied voltage. The ionic mobility is dependent on the mass-to-charge ratio, viscosity, and pH. CE is carried out in the submillimeter-diameter capillaries and in micro- and nanofluidic channels. The hyphenation of CE with NMR makes for a highly sensitive detection method as the volume size is reduced from microliters to nanoliters. Special small NMR flow cells are used for CE-NMR. Wu et al. used CE-NMR for the detection of amino acids by using a fusedsilica capillary NMR flow cell with an RF microcoil directly around the cell. The sensitivity was below 50 ng. Both on-flow and stopflow experiments have been reported for CENMR. CE-NMR is a promising technique that presents a huge number of potential applications in analyzing the structure of compounds very sensitively in the micro- and nanogram ranges [67].

2.5.5 SFC-NMR The combination of supercritical fluid chromatography (SFC) with NMR is more advantageous than ordinary LC-NMR. The use of supercritical fluid as a mobile phase does not require the suppression of solvent, and when supercritical CO2 is used as the mobile phase, it does not interfere with 1HMR results. SFCNMR needs special flow cells to carry out the analysis because the SFC system creates high pressure that cannot be handled by ordinary NMR flow cells. Different studies have been reported using SFC-NMR. Studies of monomeric acrylates, hydrocarbons, and cis/trans isomers of vitamin A via on-flow SFC-NMR have already been reported. SFC-NMR has been used to perform on-flow data for the NMR analysis of ethylbenzene and of a mixture of dibutyl and diallyl phthalate. SFCNMR has its applications in food analysis as well [67].

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2.5.6 SFE-NMR

2.5.8 LC-MS

Similarly to SFC-NMR, the hyphenation of supercritical fluid extraction (SFE) with NMR is considered an ideal analytical technique in both on-flow and stop-flow modes. The use of proton-free CO2 as the eluent of extraction is very compatible with 1HNMR. The hyphenation of SFE with NMR (SFE-NMR) is more sensitive and effective compared to conventional LC-NMR with the only need being a high-pressure NMR flow cell, as with SFC-NMR. Various studies, such as the study of the composition of coffee and black pepper extract in the on-flow and stop-flow modes with 2D COSY NMR, have been reported. Similarly, plastifiers from poly (vinyl chloride) have also been studied using SFE-NMR [67].

The hyphenation of LC with MS has broad applicability and is used for the simultaneous separation and identification of compounds. Automated LC-MS assembly consists of a double three-way diverter connecting the autosampler, chromatographic system (LC), and MS. The diverter works automatically for controlling the sample volume and passage to the LCMS system. Various types of interfaces are used to connect the LC with the MS system. Interfaces in LC-MS are designed to perform nebulization, vaporization, ionization, and control of the delivery of ions into the MS system. Among various common interfaces, atmospheric pressure chemical ionization and electrospray ionization are usually used for natural products analysis. In case of LC-UV-MS thermospray and continuous-flow FAB interfaces are also used [61,64].

2.5.7 GC-MS Gas chromatography coupled with mass spectrometry (shown in Fig. 2.12) is used for the analysis of volatile compounds. The two techniques are highly compatible with each other. However, there is the pressure difference between the two. GC operates at 760 torr, while MS works in an inert environment at only 5 7 torr. The two techniques are interlinked through an interface such as a jet/orifice separator, effusion separator, or membrane separator [61,64].

2.5.9 CE-MS Capillary electrophoresis (CE) was developed in the early 1990s. In CE, separation is achieved under the influence of an electric field, which is used to separate charged particles and have them move toward respective electrodes according to their mass-to-charge (m/z) ratios. The separation is achieved due to a change in migration rate. In the CE-MS hyphenated system, CE works for the

FIGURE 2.12 GC-MS system [61].

Interface

Sample injection

Carrier gas

MS

Amplifier Readout Column

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2. Historical background: milestones in the field of development of analytical instrumentation

separation or purification of components, which are detected through an online MS detector. Hence the simultaneous purification and data acquisition are accomplished [61,64].

2.5.10 GC-ICP-MS The GC system is used mostly for volatile compounds. The detectors of GC need a sample to be in volatile or gaseous form. Nonvolatile compounds can also be analyzed by GC after making them volatile by derivatization or pyrolysis. Although GC has several detectors systems, the hyphenation of GC with ICP-MS enables it to analyze volatile organic or organometallic compounds with high specificity and sensitivity. IC-MS is very sensitive and specific in elemental analysis when coupled with GC [68 70].

2.5.11 HPLC-ICP-MS In this hyphenated technique, HPLC is used for separation purposes while ICP-MS is used as a detection system. HPLC may separate the components of a mixture through an adsorption, partition, ion-exchange, or size exclusion mechanism. HPLC is very useful for nonvolatile compounds. The mobile phase composition is gradient or isocratic. The eluted separated components are entered into an ICP-MS detection system connected through an interface with an HPLC system. ICP-MS acts as an universal, element-specific detector for HPLC with several applications. This system is useful in the analysis of organic, inorganic, and biological molecules [70 72].

2.5.12 CE-ICP-MS Capillary electrophores (CE) are coupled with ICP-MS to perform simultaneous separation and detection of the electrically active components of a mixture. CE is not a

chromatographic technique; however, it functions in the same manner as any good chromatographic method does. In CE, the separation of components occurs according to their m/z ratio under the influence of an electric field applied through electrodes. CE is applicable to ionic or charged species from small cations to large biomolecules. Once the separation is achieved, the components are detected through an ICP-MS detection system, which is connected through a special type of interface with CE [73 75].

2.6 Advancement in sampling systems for analytical instruments Sampling plays an important role in any kind of analysis. It is very difficult to achieve accurate results without proper sampling. As a sample is a representative part of some material under investigation, it should be given great care. Various types of treatments are available to prepare a sample for analysis. For example, for an organic sample to be analyzed through GC, HPLC, GC/MS, or LC/MS, various processes such as extraction, concentration, purification and sometimes derivatization are necessary. For metal metals analysis through atomic spectroscopy (AA), graphite furnace atomic spectroscopy (GFAA), ICP, ICP/MS, extraction, concentration, and speciation are conducted. For metals analysis through UVVis, molecular spectrophotometry and ion chromatography, extraction, derivatization, concentration, and speciation are performed. Ions are initially extracted, concentrated, and derivatized prior to ion chromatography (IC) and UV-Vis spectrophotometry. For DNA/ RNA, cell lysis and extraction are done to analyze through PCR electrophoresis, UV-Vis, and florescence spectrometry. For amino acids, fats, and carbohydrates, the extraction and cleanup processes are done to make them suitable for

New Generation Green Solvents for Separation and Preconcentration

References

analysis through GC, HPLC, and EC. For microstructure analysis through microscopy and surface spectroscopy, various sample preparation techniques such as, polishing, etching, ion bombardments, reactive ion techniques, and the like are done. Once the sample is ready, proper loading to the instrument is also very important. For this purpose, sampling loading systems are specially designed to load the proper amounts of sample with small or no loss and reproducible results. Sample loading systems are researched progressively, and they have shifted from manual to automated in many instrumental techniques [8,76,77].

2.7 Conclusion Various analytical techniques have been practiced since ancient times. Chromatography, spectroscopy, and electroanalytical techniques are commonly used for routine as well high priority research purposes. The analytical techniques discussed here have emerged as efficient after continuous development in the related methods and instrumentation. Chromatography is mainly used for separation, purification, and preconcentration, while electroanalytics is mostly and spectroscopy generally used for detection. Prior to any analysis, the separation or preconcentration of the target species is an important step that is usually performed via chromatography, extraction, or electrophorisis techniques. After separation and purification, the analytes or mixtures containing analytes are passed through a detection system. The combination of chromatography with the detection system, such as spectroscopy, has resulted in hyphenated techniques that perform separation and/or purification and analysis simultaneously in a single run. The historical background and development of chromatography,

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spectroscopy, electroanalytical techniques, hyphenated techniques, as well as the development in sampling systems for these techniques, have evolved through continuous research contributions. The era from less efficient classic to more efficient sophisticated modern instrumentation has seen enormous developments and has not ended in the search for further improvements.

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C H A P T E R

3 Type of new generation separation and preconcentration methods Erkan Yilmaz1,2,3 and Mustafa Soylak3,4 1

2

Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, Turkey ERNAM—Erciyes University Nanotechnology Application and Research Center, Kayseri, Turkey 3 Technology Research & Application Center (TAUM), Erciyes University, Kayseri, Turkey 4 Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey

3.1 Introduction

techniques. One of the most important efforts is the development of sustainable microsized sample preparation techniques that use less harmful or harmless chemicals, reduce energy consumption and working time, and are environmentally friendly [1
3]. Solid phase microextraction techniques (SPME) that miniaturize solid phase extraction methods [4
6] and liquid phase microextraction techniques (LPME) that miniaturize liquid phase extraction methods have emerged [7,8]. The first steps in the field of microextraction were taken in 1990 with the introduction of the solid phase microextraction (SPME) method developed by Liu and Ouyang [9]. The basis of the SPME technique involves the extraction of the analyte or analyte group in the sample phase by adsorption/absorption into the solid phase coated on a silica fiber or on some metallic support, followed by desorption of this analyte or analyte group resting on the solid phase using a suitable solvent or heat treatment prior to

The sample preparation process prior to analysis is a common step in trace analytical methods, including extraction from the original sample matrix to another known phase to allow a more precise and selective analysis of the analyte or analyte class. Conventional sample preparation techniques such as liquid
liquid extraction, cloud point extraction, soxhlet extraction, coprecipitation, and solid phase extraction, which have multistage experimental processes, were preferred for many years, but they have lost their popularity due to their disadvantages, such as the necessity for expensive laboratory equipment, timeconsuming processes, the use of chemicals that harm health and environment, and so on [1
3]. Analytical chemists are working hard to eliminate these disadvantages, fulfill the requirements of green analytical chemistry, and develop sustainable sample preparation

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00003-6

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analysis. The LPME technique is based on the extraction of the analyte or analyte group in the sample phase into a microvolume of secondary liquid phase, which does not interfere with the sample phase and instrumental analysis [1,4,5]. The different application variations of the SPME and LPME techniques, along with innovative approaches, are briefly discussed in the following sections.

3.2 Liquid phase microextraction Since 1995, when the first application of liquid phase extraction methods in microscale was made [10], many different LPME approaches, including single-drop microextraction (SDME), hollow-fiber liquid phase microextraction (HF-LPME), dispersive liquid
liquid microextraction (DLLME), solidified floating organic drop microextraction (SFODME), and homogeneous liquid phase microextraction, have been developed [11
14]. A schematic classification of the LPME methods was made by Yamini et al. in 2019, as shown in Fig. 3.1 [15].

3.2.1 Single-drop microextraction The SDME procedure, which is considered the basis of liquid phase microextraction methods, is one of the most important techniques used for the separation and preconcentration of analyte/analytes from matrix environments [10,15]. The LPME methods in which a single drop of extraction is used is generally called a single-drop microextraction. In this method, an extraction drop with a volume of 1
10 μL is allowed to drop into the liquid or gas phase sample medium with a syringe in such a way that the drop structure is not distorted and the mixing is carried out until the extraction is complete (Fig. 3.2) [16]. The organic extraction phase drops, held up from the tip of a

microsyringe needle, are illustrated in Fig. 3.2. After completion of the extraction of analyte or analytes, the organic drop is withdrawn again into the microinjector and analyzed by a suitable detection technique. The executive power is passive diffusion for the transition of the respective analytes/analytes in the aqueous phase into a single-drop extraction phase. The most important reasons why this technique is very common and frequently preferred are low cost, applicability for analytes with different chemical structures and polarities, no need for complicated laboratory equipment, easy application, minimum use of organic solvent, and openness to the possibility of in situ complexation or derivatization. Besides these important advantages, problems such as the facts that the stable drop structure is difficult to maintain and that the use of a limited drip surface causes slow extraction kinetics are disadvantages of this method [16
18]. SDME was introduced by Liu and Dasgupta as a first time in the mid-1990s [10]. They used this technique for the extraction of ammonia and sulfur dioxide in gas samples. In this technique, a droplet of water, supported by a silica capillary tube, was used as the extraction phase prior to spectrophotometric analysis of ammonia and sulfur dioxide. The same authors used a different SDME, called as drop-in-drop solvent extraction system, for the extraction and analysis of sodium dodecylsulfate. For this purpose, 1.3 μL of chloroform was suspended inside a flowing drop, and extraction was carried out in this system [19]. Subsequently, a different application of SDME, compatible with chromatographic analysis, was introduced by Jeannot and Cantwell [20]. In this application, a drop of 8 μL of noctane was located at the end of a Teflon rod and immersed in aqueous sample solution including 4-methylacetophenone as analyte. When the aqueous sample solution was stirred, 4-methylacetophenone was extracted into an n-

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3.2 Liquid phase microextraction

FIGURE 3.1

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Schematic illustration of the existing LPME methods [15].

octane drop phase and analyzed by gas chromatography (GC) [20]. Later, a three-phase drop-based technique was introduced by Ma and Cantwell [21]. In this technique, 30 μL of n-octane forming a liquid membrane was kept within a Teflon ring and immersed over the aqueous sample solution. Stimulant drug molecules were then extracted from the aqueous sample phase into the n-octane and reextracted into an aqueous

drop. The drop was withdrawn by an injector and analyzed with HPLC [21]. In 1997, He and Lee introduced a new SDME procedure called dynamic LPME. In this procedure, a conventional GC microsyringe was used as a small-volume liquid
liquid separation funnel. The extractor phase was not in a drop shape, although it was definitely speaking. In contrast, the solvent was in the form of a plug designed to address the

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3. Type of new generation separation and preconcentration methods

(A)

(B)

5-µL GC syringe

5-µL GC syringe

1–2 µL solvent drop

1–2 µL solvent drop

1–4 mL aqueous sample Magnetic stirring bar

Aqueous sample

FIGURE 3.2 Typical SDME apparatus showing a 1
2 μL drop of the organic extraction phase held up from the tip of a microsyringe needle. (A) Direct immersion SDME; (B) headspace SDME. The panel shown on the right illustrates the needle tip with the pendent drop. Circulation in the microdrop is induced by momentum transfer from the aqueous phase. The dashed arrow outside the drop represents local convection in the mixed aqueous phase, and the dashed arrow inside the drop represents circulation in the microdrop induced by momentum transfer from the aqueous phase [16].

Magnetic stirring bar

problem of decline instability initially found in SDME. The stability of the drop would be a critical feature in unattended automated applications [22]. At all events, the authors compared it to the method introduced by Jeannot and Cantwell, which He and Lee called static LPME. Unlike the original static LPME or solvent microextraction, in the dynamic LPME, the sample phase was repeatedly drawn into the syringe to expedite the extraction process and then expelled. After these developments in SDME, an important SDME application called continuous-flow microextraction (CFME) was introduced by Liu and Lee [23]. In this technique, a microvolume organic drop, kept at the exit end of polyetheretherketone tubing, was sunk into a continually flowing sample solution pumped by an HPLC pump. After that, all microliter-volume solventbased extraction methods were named LPME by the scientific community. The SDME method was used to describe methods using a single-drop extraction phase. In the literature, solvent microextraction, SDME, and static LPME have come to be used and are still used synonymously. Later, in order to solve the

possible matrix interferences in the sample medium and to extract the more volatile compounds in the direct immersion (DI) mode, Tankeviciute et al. [24], Przyjazny and Kokosa [25], and Theis et al. [26] have introduced a new SDME mode called headspace- (HS-) SDME. In the recent past, different modes of SDME have been developed. A new procedure called bubble-in-drop (BID) SDME was introduced by Williams et al. In this technique, an air bubble is incorporated into a microdrop of a solvent to increase the surface area of the droplet [27]. Different variations of SDME methods, including direct immersion SDME, headspace SDME, three-phase SDME, drop-to-drop microextraction, bubble-in-drop SDME, and continuous-flow microextraction, are shown in Fig. 3.3 [28]. Wijethunga et al. combined the digital microfluidic chip with LPME and named the method drop-to-drop liquid
liquid microextraction. They have used this technique to monitor real-time concentrations of analyte. In this application, two immiscible nanoliter volumes of liquid droplets were merged and

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3.2 Liquid phase microextraction

FIGURE 3.3 Different variations of SDME. (1) Direct immersion SDME, (2) headspace SDME, (3) three-phase SDME, (4) drop-to-drop microextraction, (5) bubble-in-drop SDME, (6) continuous-flow microextraction [28].

mixed by electrodes. The ionic liquid extractor droplet was used for extraction of dyes in the sample droplet. Then the extractor droplet was analyzed in the imaging mode [29].

Recently, seven different versions of SDME have emerged. SDME methods can be examined as either two-phase or three-phase by considering the number of phases coexisting at

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3. Type of new generation separation and preconcentration methods

equilibrium conditions. Whereas direct immersion (DI), directly suspended droplet (DSD), continuous-flow (CF) and drop-to-drop (DD) can be classified under the two-phase modes, headspace (HS), liquid
liquid
liquid (LLL), and a combination of DSD and LLL can be considered under the three-phase modes. This classification is shown in Fig. 3.4. More details for the different modes of SDME, such as direct immersion (DI)-SDME, headspace (HS)-SDME, three-phase SDME, and continuous-flow (CF)-SDME, are mentioned in next sections. 3.2.1.1 Direct immersion single-drop microextraction In the first studies in the field of DI-SDME, a nonpolar organic solvent that is immiscible

in aqueous phase interacted with the aqueous sample solution phase by immersing it in the aqueous sample solution or by attaching it to the end of a rod made of Teflon and suspended in a continuously stirred sample solution. A disadvantage of DI-SDME, also known as static-SDME, is that extraction and injection must be done separately by different apparatuses [22]. To solve this drawback, Jeannot and Cantwell suggested the using of a microsyringe to hold the organic solvent drop. The microliter volume of the organic drop was first drawn into the microsyringe and immersed in the sample solution by the microsyringe needle passed through the septum of the sample vial. Aqueous sample solution was stirred, and at this stage the organic droplet held at the tip of the syringe needle was suspended. FIGURE 3.4 Classification of SDME Direct immersion SDME

methods in two- and three-phase modes.

Continuous-flow SDME Two-phase SDME Drop-to-drop SDME

Directly suspended droplet SDME SDME

Headspace SDME

Three-phase SDME

Liquid–liquid–liquid SDME

Combination of directly suspended droplet and liquid – liquid –liquid SDME

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3.2 Liquid phase microextraction

After completion of the extraction process, the organic extraction drop was withdrawn back into the microsyringe and subjected to analysis directly. A new technique, known as dynamicLPME, was described by He and Lee to develop a more effective SDME method with higher extraction efficiency. However, since this method does not have a drop configuration, it should be noted that it is wrong to put this method into the SDME class. In this procedure, the aqueous sample phase was drawn into the preloaded microsyringe with an organic extraction solvent phase. It was then allowed to sit for a few seconds to allow the analytes to be extracted into a thin organic extraction solvent phase film formed along the barrel wall, while the organic extraction solvent phase was withdrawn toward the back of the barrel. Finally, the organic thin film and bulk solvent are recombined. This cycle is repeated many times within a few minutes. The enriched organic phase is then used for quantization of the analytes. In dynamic LPME, as compared with the static mode, the mass transfer of analytes from the sample is faster and provides a higher enrichment factor; it is also claimed that extraction efficiency is better and reproducibility is improved [22]. Though SDME can be considered a rapid, simple, and cheap sample preparation technique, the main drawback is the instability of the used extraction droplets at high mixing speeds and complex matrix samples. In this case, technique requires very careful and attentive operation as well as continuous manual intervention in the process. This problem is mitigated by changing the 10-μL syringe with 1-μL one and replacing the needle tip [26], but the organic drop cannot withstand the mixing speed of 1700 rpm. In addition, when working on samples with a complex matrix, the sample solution must be filtered to alleviate the compromised stability of the extraction drop. Moreover, the precision and

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sensitivity of SDME procedures are very low and need to be improved. This is due to prolonged extraction times and faster mixing rates, which may cause the drop to dissolve and/or dislodge. 3.2.1.2 Headspace SDME (HS-SPME) In 2001, Theis et al. [26] presented a technique of sample preparation called headspacesolvent microextraction (HSME), or more generally headspace- single-drop microextraction (HS-SDME). In this technique, extraction of the analytes is carried out by suspending a microliter extraction solvent drop from the end of a microsyringe placed in the head cavity of a sample thermostated at a given temperature for a predetermined extraction time. In this technique, the organic extraction solvent drop takes place at the tip of the microsyringe during the extraction time to interact with the sample solution. After completion of the extraction of the analyte/analytes from the aqueous sample phase into this organic drop, the drop is retracted back into the microsyringe, and the analyte/analytes in the drop phase are analyzed by an appropriate method. In this system, the analytes are distributed among three phases: the aqueous sample, headspace, and organic extraction drop. Mass transfer from the aqueous sample phase to the organic extraction drop is the rate-determining stage; therefore mixing the sample solution at high speed increases the extraction rate as well as facilitating mass transfer. The usability of the HSSPME techniques for volatile species obtained by suitable derivatization procedures from food, environmental, forensic, and pharmaceutical samples is an important advantage. Further extract cleansing is possible because the nonvolatile and high-molecular-weight matrix interferences are reduced, if not eliminated [24
26]. In HS-SPME applications, due to the preference of extraction solvents with relatively low

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vapor pressures, it is often necessary for extraction solvents to have the required viscosity and vapor pressure; hence this important problem restricts the use of these techniques. More research and studies are needed to demonstrate their reproducibility. However, extraction solvents with high boiling points can be used for the extraction of nonmetals, organometals, and metalloids from different matrix media [24
26].

3.2.1.3 Three-phase single-drop microextraction Three-phase SDME is a new mode of SDME with simultaneous back extraction into a microvolume of a single drop for preconcentration and sample cleanup. This procedure was used as a first time by Ma and Cantwell in 1999 [21]. In this procedure, the organic liquid membrane is placed inside the Teflon ring positioned over the aqueous sample solution phase; then a microvolume of a single drop is suspended inside the organic liquid membrane by using a microsyringe. The new organic membrane configuration is stable for very high stirring rates. Direct mixing of the aqueous sample results in indirectly induced convection in the other two phases resulting from the momentum transfer in the liquid
liquid interface. Neutral or lipophilic forms of the analytes in the aqueous sample phase are obtained by adjusting pH or adding a complexing agent to the aqueous sample phase and extracting it once the organic phase is completed. At the last step, the back extraction of the analytes of interest into the receiving phase is performed by adjusting the aqueous microdrop condition. Unlike other methods, the final extract is in an aqueous phase. Further, the final analysis of analytes by different techniques, such as atomic spectroscopy (AS), HPLC, and capillary electrophoresis (CE), is possible.

3.2.1.4 Continuous-flow microextraction In 2000, a different mode of LPME, called continuous-flow microextraction (CFME), was introduced first by Liu and Lee [30]. In this application, in a 0.5 mL glass chamber, an organic extraction solvent drop is held at the outlet end of a polyetheretherketone (PEEK) connecting tube immersed in a continuously flowing aqueous sample solution and acting as a solvent holder and a fluid distribution channel. Since the extraction solvent drop is in interaction with the continuously flowing sample solution, the extraction proceeds until the sample solution flow stops or the extraction process is completed. Molecular and diffusion momentum emerging from mechanical forces contribute to the extraction efficiency of the CFME method. Because the extraction solvent drop comes into contact with the sample solution completely and continuously, this procedure can provide a higher preconcentration factor than static LPME procedures. To eliminate the risk of complex matrix samples encountered in other SDME applications disrupting the stability of the solvent drop during extraction, the sample solution is usually filtered before CFME application. 3.2.1.5 Applications of single-drop-based liquid phase microextraction methods in analysis of organic and inorganic species In the following section, the applications of the different SDME approaches previously mentioned are discussed for the analysis of organic and inorganic analytes such as aromatic compounds, polycyclic aromatic hydrocarbons (PAH), drug molecules pesticides, herbicides, fungicides, dyes and metals, nonmetals, metalloids and organometals, and so on. As discussed earlier, SDME was introduced by Liu and Dasgupta for the first time in the

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mid-1990s for the extraction of ammonia and sulfur dioxide in gas samples. In this technique, a droplet of water was supported by a silica capillary tube and used as an extraction drop before spectrophotometric determination of ammonia and sulfur dioxide. The same research group used a different version of SDME called drop-in-drop solvent extraction in the analysis of sodium dodecylsulfate. For this purpose, 1.3 μL of chloroform was suspended inside a flowing drop, and extraction was carried out in this system [10]. As previously mentioned, later a three-phase drop-based technique was presented by Ma and Cantwell. In this technique, 30 μL of noctane forming a liquid membrane was kept within a Teflon ring and immersed over the aqueous sample solution. Then stimulant drug molecules were extracted from the aqueous sample phase into the n-octane and reextracted into an aqueous drop. The drop was withdrawn by an injector and analyzed with HPLC [21]. In 1997, He and Lee introduced a new SDME procedure called dynamic LPME, in which a conventional GC microsyringe was used as a small-volume liquid
liquid separation funnel. This SDME application is also called static LPME [22], but unlike the original static LPME or solvent microextraction, in the dynamic LPME, the sample phase is repeatedly drawn into the syringe to expedite the extraction process and then expelled. After these developments in SDME, an important SDME application called continuous-flow microextraction (CFME) was introduced by Liu and Lee [23]. To solve the possible matrix interferences in the sample medium and to extract the more volatile compounds in the direct immersion (DI) mode, Tankeviciute et al. [24], Przyjazny and Kokosa [25], and Theis et al. [26] introduced a new SDME mode called headspace (HS)-SDME. In the recent past, different modes of SDME have been developed. A new

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procedure called bubble-in-drop (BID) SDME was introduced by Williams et al. In this technique, an air bubble is incorporated into a microdrop of a solvent to increase the surface area of the droplet [27]. Wijethunga et al. have combined the digital microfluidic chip with LPME and named their method drop-to-drop liquid
liquid microextraction. They have been using this technique to monitor real-time concentrations of analytes [29]. The first report on the usage of LPME for the separation and preconcentration of inorganic species was published in 2003 by Chamsaz et al. [30]. They have employed the HS-SDME method for the separation and preconcentration of trace arsenic prior to ETAAS determination. In this method, As(III) species were formed by converting all arsenic species in the presence of sodium tetrahydroborate, and As(III) species were extracted in a 4 μL drop of benzyl alcohol:pyridine containing silver diethyldithiocarbamate and Ni21 as a chemical modifier [30]. To simplify the experimental operation and improve reproducibility in sample extraction, in 2005, Saraji suggested a semiautomatic dynamic HS-LPME technique. The sample extraction step was automated by using a variable-speed stirring motor [31]. In this technique, a screw top/silicone septum was used to introduce the sample solution in a 4 mL vial. The sample vial was located in a waterjacketed container on a magnetic stirrer adjusted to 1500 rpm. The temperature of the sample bottle was maintained by the waterjacketed container for 10 min. at 60 C before and during extraction. Then 0.8 μL volume of the organic solvent was withdrawn into the microsyringe, the syringe needle was immersed through the silicone septum, and the end of the needle was fitted approximately 1 cm up from the solution surface. During extraction, the piston moves in and out of the

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syringe barrel at a constant rate ranging from 0.7 to 4 μL s21. In this way, the gaseous sample was drawn back into the syringe barrel and emptied. The process was then repeated 80 times. After completion of the microextraction, the syringe needle was taken for GC analysis. The suggested semiautomatic dynamic HSLPME is illustrated in Fig. 3.5. A fully automatic HS-LPME for dynamic methods was proposed by Ouyang et al. [32]. They controlled all operational parameters via a CTC CombiPal autosampler. A kinetic calibration procedure was applied for correction of the matrix. The developed new method was applied to determine BTEX in orange juice. Deng et al. [33] combined microwave energy and the HS-SDME method for the extraction and determination of paeonol as a bioactive compound in traditional Chinese medicines. Microwaves are combined with the species in the sample matrix, causing instantaneous, localized superheating [33]. Extraction of bioactive compounds from Chinese medicines was accomplished by a microwave-assisted extraction procedure prior to the HS-SDME

6

5 4 Water outlet 3 Water inlet

2 1

FIGURE 3.5 Schematic illustration of the semiautomatic dynamic HS-LPME system. (1) Water bath for adjusting to desired extraction temperature; (2) magnetic stirrer bar; (3) sample solution; (4) syringe needle tip; (5) microsyringe; (6) circular plate coupled to stirring motor [31].

method. The devices for the microwaveassisted extraction and HS-SDME for the extraction of the active compound of paeonol from the Chinese medicines are illustrated in Fig. 3.6. A combination usage of multiple headspace extraction and SDME was reported by Hansson and Hakkarainen [34]. In this technique, the extraction was continued until all of the analytes were extracted from the sample matrix, which led to the complete recovery and elimination of effects of matrix species [34]. In 2005, an innovative headspace microextraction method called headspace waterbased LPME (HS-WB-LPME) was introduced by Zhang et al. Unlike conventional HSLPME, water was used as the extraction solvent for the separation and preconcentration of volatile or semivolatile ionizable species prior to CE determinations. Hence the usage of high-boiling-point toxic organic solvent was eliminated and an environmentally friendly procedure was gained [35]. Pano-Farias et al. have developed DI-SDME for the separation and preconcentration of more than 20 pesticides prior to their GC-MS. The developed DI-SDME/GC-MS procedure provided satisfactory recoveries (69%
119%), high preconcentration factors between 20 and 722, and low LODs in the range of 0.14
169.20 μg kg21 [36]. Li et al. have suggested an SD-LLLME method for the separation and preconcentration of patulin before LC-MS analysis [37]. The suggested procedure provides a linear range of 2
2000 μg L21 and an LOD of 0.5 μg L21. The obtained results proved that the SD-LLLME/LC-MS procedure can directly apply to samples having complex and high sugar matrices [37]. The SD-LLLME apparatus used is illustrated in Fig. 3.7. An apple juice sample and 0.5 g NaCl were taken in a 10-mL volumetric flask. Using a micropipette, 1.5 mL of ethyl acetate was left on the sample solution. The mixture was subjected to manual shaking for primary extraction and

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FIGURE 3.6

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Devices used in microwave-assisted extraction of paeonol and HS-SDME [33].

then magnetic stirring to facilitate the mass transfer. A 5 μL microdrop in the organic phase was suspended with the help of a 25 μL flat-cut HPLC syringe for 20 min. After completion of the extraction, the drop was retracted back into the syringe and analyzed by UPLC-MS/MS. A SDME/GC-MS procedure was developed for the extraction and analysis of the residue of the natural anesthetic, menthol, in fish. The developed method had high recovery (94%), a low LOD of 0.021 μg L21, and a linear range of 1.56
120 μg L21 [38]. Generally, organic solvents are utilized as the extraction solvent drop in conventional SDME. To fulfill the requirements of green chemistry and extend the applicability of conventional SDME techniques, more green and nonconventional solvents, such as ionic liquids (ILs), magnetic solvents, supramolecular assembly-based coacervates, deep eutectic solvents (DESs), or

even sorbents dispersed in the extraction droplet in a combined liquid-solid version, have been suggested by scientists. The first application of ionic liquids in SDME was reported in 2003 [39]. The IL-based SDME method was used for the separation and preconcentration of PAH analytes. When compared with an organic solvent-based SDME (1octanol), the IL-based SDME method provided a threefold increase in the preconcentration coefficient. Different modes of IL-based SDME methods have garnered interest and have been used for the extraction of many organic and inorganic analytes from different matrix media. Some of the analytes are benzene, phenols, PAH, toluene, ethylbenzene, xylene (BTEX), aromatic amines, phthalates, pesticides, herbicides, trihalomethanes, as well as inorganic species such as mercury, lead, nickel, cobalt, copper, and the like.

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FIGURE 3.7 Schematic illustration of SD-LLLME apparatus [37].

Some of these applications are mentioned here. An IL-based HS-SDME procedure, combined with HPLC, was developed for the extraction and analysis of trace levels of chlorobenzenes in environmental water samples by Vidal et al. [40]. Optimization of the HS-SDME procedure was carried out by using

Plackett
Burman and central composite design programs. They have extracted chlorobenzenes from 10 mL of aqueous sample containing 30% (w/v) NaCl into a 5 μL microdrop of 1-butyl-3-methylimidazolium hexafluorophosphate by applying 37 min of the headspace and stirring at 1580 rpm. The developed

New Generation Green Solvents for Separation and Preconcentration

3.2 Liquid phase microextraction

IL-based HS-SDME/HPLC procedure provided low RSD in the range of 1.6%
5.1% and low LOD between 0.102 and 0.203 μg L21. The developed method was successfully applied to water samples [40]. Pena-Pereiara et al. have used 1-hexyl-3methylimidazolium hexafluorophosphate ([C6MIM][PF6]) ionic liquid as the extraction drop in an SDME application for the extraction of mercury species (MeHg1, EtHg1, PhHg1, and Hg21). The method is based on the extraction of these mercury species as neutral dithizonates complexes into 4 μL of IL drop at pH 11 by applying 20 min of microextraction time and 900 rpm of stirring rate. LOD values for analytes were found between 1.0 and 22.8 μg L21 with RSDs (3.7%
11.6%). After the optimization stage, the developed method was used for the extraction and analysis of trace amounts of mercury species in water samples [41]. Aguilera-Herrador et al. have combined ILbased SDME with GC/MS for the extraction and analysis of p-xylene, n-undecane, and dichloromethane. They have developed an innovative removable interface that provides the introduction of the extracted analytes into the GC/MS, preventing the IL from entering the column. Analytes in the aqueous sample phase were extracted into a 2-μL drop of 1butyl-3-methylimidazolium hexaflourophosphate, and then the syringe was utilized to ensure that the SDME was delivered directly into the interface, which was held at 140 C in order to completely achieve volatilization of the extracted analytes. After the injection, as the IL was trapped in the interface, the volatilized analytes were transferred into the GC inlet via a carrier gas. LOD with ng mL21 level was accomplished with low RSDs (3.3%
4.4%) [42]. Xia et al. have suggested a new IL-based cycle flow single-drop microextraction coupled to electrothermal vaporization and inductively coupled plasma mass spectrometry (ETV-ICPMS) for the extraction and analysis of trace Pb,

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Hg, and Co as 1-(2-pyridylazo)- -2-naphthol (PAN) complex. In this method, the PAN complex of analytes was extracted into the 1-butyl3-methylimidazolium hexafluorophosphate single-drop extraction phase at 10 min of extraction time. LODs of the developed method were between 1.5 and 9 pg mL21 with high EFs in the range of 50 and 350 and low RSDs between 5.2% and 12.0%. After optimization, the developed SDME application was successfully used to analyze trace Pb, Co, and Hg in environmental water and human serum samples [43]. Vidal et al. have introduced an IL-based SDME for the extraction of ultratrace levels of benzophenone-3 (BZ3) in human urine samples. Analyses were carried out by LC. Optimization of the suggested IL-based SDME was carried out by using Plackett
Burman and central composite design programs. They have extracted benzophenone-3 from 10 mL of aqueous sample containing 13% (w/v) NaCl into a 5-μL microdrop of 1-hexyl-3methylimidazolium hexafluorophosphate single-drop phase at pH 2 by applying 37 min of extraction time and stirring at 900 rpm [44]. Use of the magnetic solvents as single-drop extraction solvents began once a stable magnetic extraction drop was assured on the bottom of the magnet. A important related application was reported by Ferna´ndez et al. They used a hydrophilic magnetic ionic liquid (MIL), 1-ethyl-3-methylimidazolium tetraisothiocyanatocobaltate(II) as the extraction drop in HS-SDME to extract chlorobenzene species [45]. In a similar application, tetrachloromanganate-based MIL was used for the separation and preconcentration of aromatic compounds via HS-SDME [46]. The used HS-SDME apparatus is illustrated in Fig. 3.8. Yousefi et al. have prepared deep eutectic solvent-based magnetic Bucky gel as an innovative extraction medium in HS-SDME for GC analysis of volatile aromatic hydrocarbons in urine and water samples. They have fabricated

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FIGURE 3.8

3. Type of new generation separation and preconcentration methods

Schematic illustration of HS-SDME application for chlorobenzene species [46].

hydrophobic magnetic Bucky gel by magnetic multiwalled carbon nanotubes and choline chloride/chlorophenol deep eutectic solvent [47]. Noble metal nanoparticles, such as Ag, Au, and the like, show unique colorimetric or fluorescent features. Hence their dispersion into extraction drops is a good way to analyze extracted analytes by observing their colorimetric or fluorescent changes in connection with these nanoparticles. In an application, Ag nanoclusters (NCs) in HS-SDME were used for the extraction and analysis of dissolved ammonia. The method is based on the extraction of ammonia in the extraction droplet, agglomeration of Ag NCs via increased pH, and changes in the colorimetric/fluorescent features of Ag NCs. The analytical signals were observed and correlated to the ammonia concentration [48]. The developed HS-SDME is shown in Fig. 3.9.

Pena-Pereira et al. have used the HS-SDME system, including citrate-protected colloidal Au nanoparticles (NPs), to analyze bromine in polymer electronic waste materials. The method is based on the oxidation of Au NPs in the presence of the extracted bromine and signal generation for microvolume spectrophotometer analysis [49]. Similar applications have been developed by other researchers for the analysis of organic and inorganic analytes such as thiomersal and mercury [50,51]. Tolessa et al. have combined gold nanoparticles with HS-SDME for the colorimetric assay of mercury (II) in environmental waters [50] (Fig. 3.10). Automation of the separation and preconcentration procedures have an important place in analytical applications, and hence SDME procedures have gone through important automation stages. In order to develop automatic

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3.2 Liquid phase microextraction

FIGURE 3.9 Sensing device of the proposed HS-SDME for sensing dissolved ammonia [48].

FIGURE 3.10 Schematic illustration of the suggested procedure. (A) Mechanism for Hg(II)-induced colorimetric response of TGAAuNPs-based headspace nanosensors; (B) experimental setup [50].

three-phase SDME-CE, two different CE instruments were used by Choi et al. [52]. The formation, withdrawal, and injection of the organic single drop were controlled with adjustable forward and backward pressure modes in the instruments. This automatic three-phase SDME-CE procedure was used for the extraction of acidic analytes in aqueous solution with a 2000-fold preconcentration factor [52]. Mitani et al. developed an automated SDME method by using a lab-in-syringe platform for the separation and preconcentration of mercury prior to in situ vapor generationETAAS determination. In this procedure, two microsyringe pumps and a sequential injection system were used for the formation and

transfer of the single solvent drop [53]. Similar automated HS-SDME procedures have been developed by many research groups and used for different analytes, such as ethanol and ˇ ´ mkova´ and coworkers ammonia [54,55]. Sra developed an automated in-syringe singledrop headspace microextraction method for the microextraction of ethanol in wine samples. For the first time in literature, the syringe of an automated syringe pump was designed as an extraction chamber for a volatile analyte. This innovative application applies negative pressure during the extraction stage, which favors analyte evaporation. Putting a slowly spinning magnetic stirring bar inside the syringe, in addition, to effective syringe

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cleaning, the sample was mixed with the buffer solution to suppress the introduction of acetic acid. The determination of ethanol was based on the reduction of a single drop of potassium dichromate dissolved in sulfuric acid. The extraction drop was placed into the syringe inlet in the headspace above the sample with posterior spectrophotometric analysis. All stages of the method were carried out automatically by managing a sequential injection analyzer system (Figs. 3.11 and 3.12) [54]. In classical SDME, commercial syringes as the device/platform are generally used to hold

the extraction drop. However, to eliminate the drawbacks of the commercial syringes and to improve these procedures, many innovative SDME devices or platforms have been introduced in recent years [56,57]. For example, in an HS-SDME application, an optical probe was used as the microdrop holder. The optical probe had a stainless steel tube and an optical window to hold the drop at the bottom and was coupled to two optical fibers. As the first fiber was connected to a radiation source, the second fiber was linked to a spectrophotometer detector. In this way,

FIGURE 3.11 Schematic illustration of analyzer system and process for headspace extraction. (A) Holding coil (0.8 mm id, 25 cm) between valve and syringe pump; (B) PTFE tube for detection of flow cell (0.5 mm id, 7 cm); (C) PEEK tube for waste management (0.5 mm id, 10 cm); (D) detection flow cell: M 5 DC motor with magnets, SP syringe pump, SV valve for selection of rotary, V rotary syringe head valve, B management of buffer solution, R management of chromate reagent, S management of sample solution, W management of waste. Suggested automatic procedure (A) Injection of sample; (B) aspiration of air; (C) injection of chromic acid (R); (D) filling of water into the holding coil and droplet generation for headspace extraction; (E) negative pressure application; (F) preconcentration time; (G) release of negative pressure; (H) aspiration for spectrophotometric measurement and then discharge syringe with detection flow cell to waste [54].

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3.2 Liquid phase microextraction

SDME was applied more simply, and the transfer of the solvent drop was eliminated. This novel approach was used for the analysis of sulfite in food samples [56]. Later, a similar apparatus was applied to DI-SDME to extract and analyze thiocyanate in human saliva samples [57]. However, analysis of only one analyte at a time is the main disadvantage of these applications. A different version of the HS-SDME, called in-vial temperature gradient HS-SDME was developed for the analysis of volatile organic compounds. In this technique, the sample solution was heated in the sample vial, and simultaneously the extraction droplet of antifreeze solution was cooled in a homemade inner vial cap. After completion of the extraction, the

enriched extraction solvent drop was retracted into the microsyringe and delivered into LC-UV for determination. The new apparatus was successfully used to collect volatile compounds [58]. An effective solvent holder made up of a solvent-impregnated agarose gel disc (2 3 2 mm internal diameter) was introduced by Chong et al. [59]. This new apparatus was classified as an environmentally friendly solvent holder. This new apparatus was successfully used for the electromediated microextraction of phenols in water samples prior to microHPLC-UV detection (Fig. 3.13) [59]. Ma and Ma provided a membranesupported HS-SDME apparatus to solve the drop instability problem. They have used this new apparatus for the separation and FIGURE 3.12 Photos of drop exposure with stirring assembly (left) and detection system (right) [54].

Electromediated microextraction: Simple Efficient Microscale Green solvent holder

FIGURE 3.13 Schematic illustration of electromediated microextraction apparatus [59].

Power supply +

–

Platinum electrode

Solvent-impregnated agarose gel disc

Sample solution

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preconcentration of chlorobenzenes before GCMS analysis. The membrane, made of plastic, served as the extraction solvent holder during the extraction [60]. An innovative SDME approach was introduced by Mafra et al. They combined a 96-well plate system with SDME and used magnetic ionic liquid [P6,6,6,141]2[MnCl422] as the extraction phase in the high-throughput parallelsingle-drop microextraction (Pa-SDME) method. The innovative SDME approach was used for analysis of ethylparaben, methylparaben, bisphenol A, propylparaben, butylparaben triclocarban, and benzophenone in environmental aqueous samples. This test apparatus consists of a 96-well plate system with a set of magnetic pins that help compensate for MIL drops and that allow for the simultaneous extraction of up to 96 samples (Fig. 3.14) [17].

3.2.2 Hollow-fiber liquid phase microextraction The HF-LPME method was introduced as an innovative mode of LPME by Pedersen-

FIGURE 3.14

Bjergaard and Rasmussen. The method was based on the use of cheap and disposable porous polypropylene hollow fibers [61]. A cross-section of the fiber wall is shown in Fig. 3.15 [62]. Fig. 3.16 shows the main principle of hollow-fiber-based LPME [63]. In the HFLPME, because the microvolume of the extraction solvent phase is present in the lumen of a microporous hollow fiber, the extraction solvent and the sample solution are not in direct contact. In this technique, there is no loss of the volume of the extraction solvent even if the sample solution under mechanical protection is subjected to high-speed mixing and vibration. In HF-LPME, the hollow fiber is immersed in the water-immiscible extraction solvent prior to the extraction process. In this way, the extraction solvent is immobilized in the pores of the hollow fiber. Once the organic extraction solvent has a volume of about 10
20 μL and has formed a thin layer in the wall of the hollow fiber, the hollow fiber is placed in a sample bottle filled with aqueous sample solution. The aqueous sample phase is stirred or mixed at

Overview of the Pa-SDME/MIL-based extraction system [17].

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3.2 Liquid phase microextraction

FIGURE 3.15 Cross-section of LPME hollow fiber [62].

FIGURE 3.16

Acceptor solution

Basic principle of HF-LPME [63].

Porous hollow fibre

Sample solution Immobilized organic solvent

Analytes

higher speeds than other LPME procedures. The analytes of interest in the aqueous sample phase are extracted into the organic phase in the pores of the hollow fiber and then into a recipient solution in the lumen. The single-use nature of the HF eliminates the sample transport possibility and provides improved reproducibility, and the extraction of high molecular

weight materials are prevented by the pores in the hollow fiber walls, which provide selectivity [61
64]. HF-LPME can be applied in both a twophase and a three-phase mode [61
65]. In twophase HF-LPME, the acceptor solution and organic extraction solvent phase, immobilized in the pores of the hollow fiber, are the same,

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and the analytes in the aqueous sample phase are collected in the extraction phase [34
38]. In a three-phase HF-LPME, the acceptor phase is another aqueous solution, and the extraction of analytes from an aqueous sample phase into an aqueous acceptor solution is achieved through the thin film of organic extraction solvent. Whereas the two-phase HF-LPME can be combined with GC, the three-phase HF-LPME can be combined with AS, HPLC, and CE [61
65]. Fig. 3.17 shows the main principles of two-phase and three-phase hollow-fiber-based LPME [65]. In two-phase and three-phase HF-LPME applications, the extraction bases are the diffusion in which high partition coefficients promote the extraction. These extraction modes are more suitable for hydrophobic analytes than hydrophilic ones such as metal ions. Hence the extraction efficiency of metal ions based on diffusion is lower, leading to poor partition coefficients. To solve this limitation, the active transport mode can be applied by adding a carrier in the sample solution [61
65]. Ion-pair formation or complexation applications are effective ways to form hydrophobic forms of analytes, which cause the high-yield extraction of analytes from the aqueous sample phase into the pores of hollow-fiber-loaded organic extraction phase. The analytes then can be transferred into the acceptor phase by changing the

Hollow fiber Supported liquid membrane

Acceptor phase (organic solvent)

extraction conditions (i.e., pH adjustment or addition of a suitable acceptor phase). The HF-LPME works in the static or the dynamic mode. The static mode is explained in the preceding sections. For dynamic mode applications [63,65,66], several microliters of the same organic solvent, immobilized in the hollow fiber, are filled into a microsyringe. The hollow fiber piece is linked to the needle of the microsyringe and then to the sample phase. During extraction, the aqueous sample phase with low volume is repeatedly drawn through the hollow fiber by using the syringe plunger. When the aqueous sample phase is taken up, a thin organic solvent film is formed in the hollow fiber, and extraction of analytes from the aqueous sample segment is accomplished. During sample extraction, recombination of the thin film with the bulk organic extraction phase is performed in the syringe, and the organic extraction phase firmly holds the extracted analytes. After repetition of the extraction for a known cycle, the concentration of analytes in the bulk organic extraction solvent is carried out by different measurement techniques (Fig. 3.18) [63]. The dynamic mode can also be applied with three-phase HF-LPME in a procedure similar to that used in two-phase HF-LPME. The dynamic mode is faster than the static mode [63,65,66]; however, the dynamic mode process is more difficult and complicated.

Hollow fiber Supported liquid membrane

Acceptor phase (aqueous solution)

Sample

Sample 2-phase LPME

FIGURE 3.17

3-phase LPME

Basic principles of two-phase and three-phase HF-LPME [62].

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Sample solution solution

Liquid membrane

pH = 7 R-COO– + AH+

R-COO– + H+

Acceptor

95

FIGURE 3.18 Basic principle of active transport in HF-LPME.

pH < 3 R-COOH

AH+

R-COO–AH+

H+

Flux of H+ Flux of AH+

A = analyte, R-COOH = carboxylic acid

The two and three modes of HF-LPME can be applied for difficult matrices such as biological and environmental mediums with excellent sample cleanup effectivity and high preconcentration factor, and lately they have been completely automated with robotic systems [61
66]. Compared with other SDME methods, HF-LPME with different application modes provide improved organic extraction solvent stability and tolerance for high temperature and sampling time. Further, HF-LPME is cheap and suitable for miniaturization and automation. Its main drawbacks are the necessity of conditioning the membrane and the probability of memory influences after similar membranes are used again. 3.2.2.1 Applications of hollow-fiber liquid phase microextraction methods in analysis of organic and inorganic species HF-LPME has been generally used for environmental and bioanalytical applications; however, different sample usages, such as food and beverages, have been reported in the literature. Jiang et al. have used two-phase HF-LPME and three-phase HF-LPME methods for the

separation and preconcentration of methylmercury in human hair and sludge samples prior to ETAAS and ICP-MS. In both HF-LPME procedures, toluene was used as the organic solvent. In the three-phase application, 4% thiourea in 1 M HCl was used as the acceptor phase. Selective extraction of organic and inorganic mercury is the main advantages of this method. The extraction of methylmercury into the organic phase was possible as inorganic mercury remained in the sample solution as a free species. The three-phase HF-LPME provided a higher enrichment factor and lower LOD than two-phase HF-LPME [67]. Meng et al. have developed a homemade hollow-fiber-protected headspace liquid phase microextraction (HF-HS-LPME) for the separation and preconcentration of free cyanide in saliva and human urine samples prior to capillary electrophoresis (CE) analysis. The acceptor phase, containing Ni(II)-NH3 (as the derivatization agent), ammonium pyromellitate (as the internal standard), and sodium carbonate, is held within a hollow fiber membrane attached to a needle of syringe and immersed in the headspace of sample solution. Cyanide formed

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a stable Ni(CN)422 complex after extraction from the neutral samples and analyzed with CE (Fig. 3.18). A linear calibration curve was obtained between 0.1 and 20 μmol L21 with R250.9987. The LOD and RSD values of the developed method were 0.01 μmol L21 and 5.6%, respectively [68]. Fabrication of the hollow fiber membrane is schematized in Fig. 3.19 and 3.20. A different three-phase HF-LPME method was developed for the separation and preconcentration of trace gabapentin (GBP) in 1-fluoro-2,4-dinitrobenzene form before HPLCUV determination. GBP was derivatized with 1-fluoro-2,4-dinitrobenzene in borate buffer (pH 8.2) and extracted from the acidic sample solution into the dihexyl ether organic phase impregnated in the pores of an HF. In the last step, back-extraction was accomplished into

24 μL of the basic solution (pH 9.1) fitted inside a hollow-fiber lumen as the receiving phase. LOD and PF for the developed method were 0.2 μg L21 and 95. The developed three-phase HF-LPME/HPLC-UV procedure was successfully applied for analysis of GBP in human urine and plasma samples [69]. Pantalea˜o provided a three-phase HFLPME/GC-MS procedure for the extraction, identification, and analysis of methamphetamine, amphetamine, fenproporex, 3,4methylenedioxyamphetamine, and 3,4-methylene dioxymethamphetamine. The method involved three steps: (1) decontamination of hair samples with dichloromethane, (2) alkaline hydrolysis, and (3) three-phase HF-LPME of analytes. The LOQ values were given around 0.05 ng mg21 for all amphetamines. The intraday and interday RSDs were around 10.6% and 11.4%.

FIGURE 3.19 Schematic illustration of HF-HS-LPME [68].

Microsyringe

Hollow-fiber membrane Acceptor phase Sample solution Magnetic stirrer

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3.2 Liquid phase microextraction

Capillary Tip Clamp Polyethersulfone Hollow-fiber membrane on capillary

Task Water

FIGURE 3.20 Schematic illustration of the production of hollow fiber membrane [68].

The developed HF-LPME/GC-MS procedure was applied to hair samples with accuracy better than 87% [70]. Many innovative approaches and apparatuses, including ultrasonic irritation, vortex mixing, microwave irradiation, magnetic stirrer, and the like, have been adopted for HFLPME applications to accelerate the extraction procedure and improve extraction efficiency in recent years. Shrivas and Patel have introduced a rapid and simple ultrasound-assisted hollowfiber liquid microextraction (UA-HF-LPME) for the separation and preconcentration of selenium at trace levels prior to GF-AAS. Selenium in sample solution was extracted into 3.5 μL of organic solvent containing an N-octyl acetamide as an extracting agent located inside the hollow fiber by applying ultrasonication. Selenium in the sample solution was extracted at pH between 0.8 and 3.0 by applying 500 rpm of agitation rate and 15 min of extraction time.

97

The developed method was successfully used to analyze selenium in vegetable and fruit samples [71]. A different ultrasound-assisted HFLPME/GC-FID procedure was introduced for the extraction and analysis of benzene and toluene at extra trace levels in beverages trace analysis. The developed procedure provided high recoveries in the range of 98.2% to 99.6%, low RSD between 0.11% and 1.07%, low LOQ between 0.34 and 0.18 μg L21, and high EF between 105 and 308 [72]. Wang and coworkers provided an environmentally friendly vortex-assisted HF-LPME procedure for the separation and preconcentration of estrogens (diethylstilbestrol, 17β-estradiol, and estrone) in milk samples. Analyses were carried out with HPLC. Analytes in sample solution were extracted into 15 μL of nonanoic acid located the inside the hollow fiber by vortex mixing. Vortex mixing caused effective mixing of the sample solution, which leads to improved interaction between boundary layers of the hollow fiber and analytes, therefore enhancing the extraction of analytes with high recoveries (Fig. 3.21). The extraction equilibrium was reached within 2 min. The method provided high EF (330), good RSD in range of 2.56 and 4.38, and low LODs between 0.06 and 0.17 ng mL21 [73]. Li et al. have suggested a vortex-assisted three-phase HF-LPME combined with HPLC for the extraction and analysis of bisphenol-A (BPA), bisphenol-AF (BPAF), and tetrabromobisphenolA (TBBPA) in milk samples. The developed method provided good RSD (1.3%
3.7%), low LODs (0.16
0.35 μg L21), and LOQs (0.51
1.12 μg L21) [74]. Similar to other liquid phase microextraction methods, hydrophobic organic solvents such as isooctane, toluene, undecane, hexane, tetrachloromethane, or dihexylether are generally utilized as extraction solvents. These organic solvents are located inside the hollow fiber. But in order to meet the requirements of green chemistry and to extend the applicability of

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FIGURE 3.21 Schematic illustration of the VA-HFLPME method [73].

conventional HF-LPME techniques, more green extraction solvents such as ionic liquids (ILs), supramolecular solvents, deep eutectic solvents (DESs), and the like have been used by researchers. Loss of the extraction solvent during the extraction procedure is an important drawback in HF-LPME methods that can be eliminated by using high-viscosity ILs, moreover increasing the reproducibility of the extraction method. Consecutive modes of HF-LPME are also applied for sample preparation applications. An innovative approach called hollow-fiber solid
liquid phase microextraction (HFSLPME) was introduced to the literature by Es’haghi et al. [75]. In this method, multiwalled carbon nanotubes (MWCNT) were dispersed in the extraction solvent, and then the obtained liquid
solid phase was filled in the membrane pores. The analytes desired in the aqueous sample solution diffuse through the membrane and are simultaneously extracted by both an organic extraction solvent and a sorptive solid phase, that is carbon nanotraps. Afterward, back-extraction of the analytes into an aqueous acceptor phase inside the HF lumen is performed. SEM images of (a) polypropylene hollow fiber and (b) hollow fiber containing the dispersed functionalized MWCNTs solution in

1-octanol are shown in Fig. 3.22. In this way, high extraction efficiency with improved selectivity is obtained for organic analytes in an aqueous sample solution. It is characterized by high selectivity and good extraction efficiency in the case of extraction from aqueous samples [75]. A photograph for the dispersion of the functionalized MWCNTs solution in 1-octanol is shown in Figs. 3.22 and 3.23. In another similar application, the CNTs suspension fills the wall pores and HF lumen. In the provided solution, a hollow fiber, with magnetic stoppers enclosed to both ends, was applied as a pseudo stirring system [76]. This method, hollow-fiber solid
liquid phase microextraction (HF-SLPME) was used for the analysis of brilliant green. The basic scheme of the pseudo stir-bar HF-SLPME apparatus is shown in Fig. 3.24. Another dynamic HF-LPME method, known as solid phase membrane tip extraction (SPMTE), is applied by incorporating MWCNTs into a cone-shaped hollow fiber. In the SPMTE method, the membrane is coupled to a pipette tip, the aqueous sample is manually withdrawn through the membrane tip filled with MWCNTs, and then this is released back into the sample, and extraction is completed. After completion of the extraction, adsorbed analytes

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99

FIGURE 3.22 SEM images of (A) polypropylene hollow fiber and (B) hollow fiber containing the dispersed functionalized MWCNTs solution in 1octanol [75].

are removed by applying ultrasonic irradiation in acetonitrile (Fig. 3.25) [77]. In 2004, Jiang and Lee introduced an innovative method called solvent bar microextraction (SBME), based on the main guidelines of HFLPME [78]. In this method, an extraction phase (1-octanol) is immobilized inside the pores of a membrane (polypropylene tube). Both ends of the membrane are sealed and filled with an acceptor phase (liquid
liquid
liquid system). The membrane was located in a stirred aqueous sample solution. The new microextraction method can be applicable for extraction from “dirty” samples such as soil slurries because the hollow fiber membrane is sealed. The

developed SBME method was used for the analysis of pentachlorobenzene and hexachlorobenzene (HCB) at trace levels [78]. In another study, dual-solvent stir-bar microextraction (DSSBME) and U-shaped hollow-fiber liquid phase microextraction (U-shaped HF-LPME) were introduced by Yu et al. for the separation and preconcentration of Sudan dyes. In the DSSBME, the organic extraction solvent is imprisoned in a pair of HF membranes located on a stir-bar, which can stir by itself [79]. Upon completion of the extraction, the acceptor phase is removed from the membrane system with a microsyringe and then given into an HPLC or GC (Fig. 3.26) [79].

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FIGURE 3.23 Dispersion of the functionalized MWCNTs in 1-octanol [75].

FIGURE 3.24 Simple schematization of the pseudo stir-bar HF-SLPME apparatus. (A) Magnetic stoppers (iron pins; 1.5 3 0.6 mm); (B) Accurel Q3/2 polypropylene hollow fiber membrane (1-cm length, 200-μm wall thickness, 0.2-μm pore size, and 600-μm ID); (C) MWCNTs reinforced 1-octanol [76].

In 2007, Huang and Huang have introduced a new approach named solvent coolingassisted dynamic hollow-fiber-supported headspace liquid phase microextraction (SC-DHFHS-LPME) [80]. The method is based on the main guidelines of HF-LPME. In the SC-DHFHS-LPME, the extraction solvent phase is cooled about 21 C and pumped through a porous polymeric membrane. In this way, the extraction solvent loss born of lowered vapor

pressure is reduced (Fig. 3.27). The innovative method extends the extraction time, which leads to improved extraction yield. For the first time, it was applied for the separation and preconcentration of organochlorine pesticides prior to GC-MS analysis [80]. HF-LPME procedures can be driven by electrical fields to simplify the extraction of the analytes through the hollow fiber [81,82]. In 2006, Pedersen-Bjergaard and Rasmussen

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3.2 Liquid phase microextraction

FIGURE 3.25

Schematic illustration of (A) the SPMTE setup and (B) expanded view of dynamic SPMTE [77].

(A)

(B) Microsyringe needle Aqueous solution

Organic solvent Hollow fiber Steel wire Magnetic stirrer

applied 300 V dc of electrical field in the HFLPME to transport basic drug substances through a thin artificial organic liquid membrane. The new technique goes by two names: electromembrane extraction (EME) and electromembrane isolation (EMI). Moreover, its nano version reduces the acceptor phase volume from the microliters level to a few nanoliter levels.

FIGURE 3.26 Schematic illustration of (A) DSSBME and (B) Ushaped HF
LPME [79].

Aqueous solution

Organic solvent Hollow fiber Stir bar Magnetic stirrer

The principles of EME are the same as those of the three-phase HF-LPME in that they have involve the use of a donor phase, an extraction phase, and an acceptor phase. The difference from conventional HF-LPME is that the driving force in EME is an electrical potential over the SLM, maintained using an external power supply [81]. During the determination of basic analytes, the negative and positive electrodes are

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3. Type of new generation separation and preconcentration methods

3.2.3 Dispersive liquid
liquid microextraction Pump

Syringe

Cooling system

Hollow fiber

Sample Aluminum block Stir bar

FIGURE 3.27

Experimental setup of SC-DHF-HS-

LPME [80].

located in the acceptor phase and the donor phase, respectively. Neutral or acidic conditions are required to ensure protonation of the analytes and to achieve electrokinetic migration across the SLM. For acidic analytes, the direction of the electrical field is reversed, and the pH should be neutral or alkaline [81]. The electrical field-assisted HF-LPME equipment for electromembrane isolation (EMI) is shown in Figs. 3.28 and 3.29.

DLLME has garnered attention since it was introduced by Assadi and coworkers in 2006 [83]. The main working principle of the DLLME is the formation of a ternary solvent system such as cloud point extraction (CPE) and homogeneous liquid
liquid extraction (HLLE). The first applicability of the DLLME technique was checked on the separation and preconcentration of organic species such as organophosphorus pesticides, chlorobenzenes, and polycyclic aromatic hydrocarbons (PAH). However, soon it was used for inorganic analytes [83
86]. DLLME is a miniaturized solvent extraction procedure in which the ratio of the acceptor phase to donor phase is greatly reduced. In this technique, the microvolume of extraction and disperser solvents is rapidly injected into an aqueous sample solution containing the analytes of interest. The extracting solvent volume is generally about 1%
3% of the total volume of the aqueous sample phase. Therefore the injection of the extraction solvent, together with a suitable dispersive solvent, into the aqueous sample solution led to well dispersion and the formation of micro- or nanosized fine droplets of extraction solvent. At this stage, a cloudy mixture is obtained, and the formation of fine droplets of extraction solvent in the aqueous sample solution creates a larger surface area, quick equilibrium, and high extraction efficiency. After extraction of the analytes of interest from the sample solution phase into extraction solvent drops, the cloudy mixture is subjected to centrifugation, and the extraction solvent phase is collected at the bottom of the conical tube. Then analysis of enriched analytes in the extraction solvent phase is carried out with a suitable instrumental method. Highdensity water-immiscible extraction solvents such as carbon tetrachloride, chloroform, chlorobenzene, tetrachloroethylene, and carbon

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103

FIGURE 3.28 Schematic illustration of the equipment for electromembrane isolation (EMI) [81].

FIGURE 3.29

Schematic illustration of devices used for (A) extracting analytes by EME and (B) on-chip EME [82].

disulfide are used, as well as water-miscible polar dispersive solvents such as methanol, ethanol, acetone, and acetonitrile [84
87]. The minimized extraction solvent volume, quick and simple extraction, high extraction efficiency, and improved enrichment factors

because of the high ratio of the donor phase to acceptor phase are the main advantages of DLLME. Moreover, the technique meets most of the green analytical chemistry aspects, including using microvolumes of the solvent, selection of green extraction and dispersive

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3. Type of new generation separation and preconcentration methods

solvents, lower energy consumption, and formation of less wastes [84
89]. But DLLME also has limitations, such as the requirements for high-density extraction solvents, mainly toxic halogenated solvents, and for specially designed extraction devices. Over a period of time, DLLME has undergone an extensive evolution in terms of the development of special extraction apparatus and usage of more green solvents, leading to the development of more effective, simpler, cheaper, and energy-saving procedures [90,91]. In DLLME methods, the use of special extraction apparatus, such as the vortex mixer, microwave, ultrasound generator, manual shaker, magnetic stirrer, and the like, leads to high extraction efficiencies, simple and fast operations, and well dispersion of the extraction solvents in the sample solution through the aid of various processes. The formation of fine extraction droplets properly leads to increases in the interfacial area available for the transfer of analytes, reducing the diffusion distance, and improvements in the extraction rates so that partition equilibrium can be reached within a few minutes [92
94]. The usability of ultrasonic irritation to disperse extraction solvent into the aqueous sample phase was reported for the first time in 2008 by Regueiro et al. [95]. The new procedure, called ultrasound-assisted emulsification microextraction (USAEME), was used for the separation and preconcentration of synthetic musk fragrances, phthalateesters, and lindane in water samples prior to GC-MS determinations. The authors claimed that the developed USAEME method can be used as a cheap and effective alternative to other extraction techniques, such as SPE, SPME, and LPME [95]. From that point, ultrasonic irritation, which provides more efficient distribution of the extraction phase in sample solution, has gained in importance in liquid phase microextraction techniques, and its usage is increasing day by day. The authors have proposed many

ultrasound-assisted DLLME methods for almost all of the organic and inorganic analytes in the literature. Thanks to ultrasonic irritation technology, extractions can be completed in a few minutes, at the same time obtaining high extraction efficiency, consuming extraction solvents at low volumes, and using simple experimental apparatus. Wang et al. have combined the ultrasoundassisted DLLME method with the HPLC detection system for the extraction of and analysis of polybrominated biphenyls (PBBs) in water samples. They have extracted PBBs in aqueous sample solutions by using 40.0 μL of CCl4 and 0.8 mL of acetonitrile. They applied 2 min of ultrasonic irritation to samples for the extraction of PBBs from the aqueous sample phase to the CCl4 phase. The developed procedure was applied to real water samples with acceptable recoveries ranging from 75.8% to 105%. A schematic diagram of the UADLLME/HPLC procedure is shown in Fig. 3.30 [96]. Yan et al. have combined ultrasonic irritation with DLLME for the extraction of four fluoroquinolones (norfloxacin, ofloxacin, lomefloxacin and enrofloxacin) in pharmaceutical wastewater samples. Analysis was carried out by LC-MS. The developed procedure provided LODs between 0.14 and 0.81 μg L21, recoveries changed from 82.7% to 110.9%, and enrichment factors between 32- and 134-fold [97]. A different ultrasound-assisted DLLME method was provided for the separation and preconcentration of six pyrethroids in river water samples. In this method, tetrachloromethane as the extraction solvent phase and acetone as the dispersive solvent were used. The developed method was used for analysis of six pyrethroids with recoveries ranging from 86.2% to 109.3% [98]. Stanisz et al. have used ionic liquid (methyltrioctylammonium thiosalicylate) as an extraction solvent in an ultrasoundassisted dispersive liquid
liquid microextraction method for the separation and

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3.2 Liquid phase microextraction

FIGURE 3.30

105

Schematic illustration of UA-DLLME/HPLC procedure [96].

preconcentration of mercury species before cold vapor atomic absorption spectrometer (CV AAS) determination. In this method, no dispersive solvent or complexing agent was used. Successful extractions were carried out using 30 μL of ionic liquid. The enrichment factors of the developed method were 310 for Hg21 and 200 for CH3Hg1. The accuracy of the developed procedure was checked by analysis of the NRCC DOLT-2 and NIST 1643e Certified Reference Materials and addition-recovery experiments. The quantitative recoveries, ranging from 95% to 103%, were obtained for spiked samples and reference materials [99]. Ghoraba et al. have introduced a combination use of ultrasound-assisted DLLME and ion mobility spectrometry for the separation, preconcentration, and analysis of bendiocarb and azinphos-ethyl. Extraction studies were conducted at pH 9.0 using 150 μL of CHCl3 as

extraction solvent. Extraction solvent drops having high surface area were acquired by ultrasonic irradiation. The LOD values for bendiocarb and azinphos-ethyl were found as 1.04 and 1.31 ng mL21. The suggested procedure was successfully applied to water, food, soil, and beverage samples [100]. A schematic diagram of the developed procedure is shown in Fig. 3.31 [100]. For the first time, the usability of vortex agitation in liquid
liquid microextraction was researched in 2010 by Yiantzi et al [101]. In this method, called vortex-assisted liquid
liquid microextraction (VALLME), dispersion of 50 μL of octanol as a low-density extraction solvent into the aqueous sample phase was achieved by applying 2 min vortex mixing at 2500 rpm: in other words, a mild emulsification procedure. Researchers have used this new technique for the separation and

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FIGURE 3.31

3. Type of new generation separation and preconcentration methods

Schematic illustration of the UA-DLLME/IMS procedure [100].

preconcentration of bisphenol-A, nonylphenol, and octylphenol prior to HPLC analysis. The developed VALLME/HPLC procedure is schematized in Fig. 3.32 [101]. Altunay and coworkers have applied vortex agitation for ionic liquid-based dispersive liquid
liquid microextraction (VA-IL-DLLME) of nickel and cobalt at trace levels. 1-hexyl-3methylimidazolium tris(pentafluoroethyl)trifluorophosphate was used as extraction solvent. Extraction of Ni(II) and Co(II) ions as ninhydrin (2,2-dihydroxyindane-1,3-dione) chelates from the aqueous sample phase to IL extraction phase were accomplished at pH 9.0. FAAS was used in the analysis step. The suggested VA-IL-DLLME/FAAS procedure was successfully applied to chocolate-based real samples [102]. Microwave-assisted extraction (MAE) techniques are used in the rapid and high-yield extraction of organic and inorganic species from different environmental samples, as well

as facilitating the passage of analytes from the aqueous sample phase to extraction phase in liquid phase and solid phase microextractionbased methods. Microwave-based techniques have lower extraction time and solvent consumption than classical sample preparation techniques [103
105]. After the first use of sample preparation techniques in analytical chemistry in 1975, interest in microwaveassisted sample preparation techniques has increased rapidly [105]. Particularly, usage of microwave irritation power in liquid phase microextraction methods has an important place [106]. Li et al. have introduced a combined procedure including stable isotope labeling (SIL), microwave-assisted DLLME, and the UPLCMS/MS for the accurate analysis of hydroxyl UV filters in water samples. The pretreatment of water samples using microwave-assisted DLLME and SIL was conducted as follows: 1 mL of water sample, a mixture containing

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3.2 Liquid phase microextraction

500 μL acetone, 200 μL D0-/D3-MIAA, 100 μL DMAP, 60 μL EDC, and 100 μL chloroform was injected with a syringe. The centrifugal sample tube was then subjected to 240 W of microwave irritation for 300 s. After centrifugation of the sample tube, the analyte-enriched CHCl3 phase was settled in the bottom of the centrifugal

107

tube. A schematic diagram of the developed MADLLME-SIL-LC-MS/MS procedure is shown in Fig. 3.33 [107]. Zhong and coworkers have introduced a microwave-assisted dispersive liquid
liquid microextraction (MADLLME) using the solidification of the floating organic droplet (SFOD) as a cleanup step. The

FIGURE 3.32

Schematic illustration of the VALLME/HPLC procedure [101].

FIGURE 3.33

Schematic illustration of the MADLLME-SIL-LC-MS/MS procedure [107].

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3. Type of new generation separation and preconcentration methods

developed method was used for the analysis of 14 colorants in cosmetic products. Microwave irritation was used in DLLME for facilitating rapid extraction equilibrium and reducing manual operations, leading to good extraction efficiency and high sample throughput. The suggested microwave-assisted microextraction procedure provided good recoveries (90.2%
106.1%) and low RSDs (0.30%
3.1%) [106]. Automation of the DLLME procedures have an important place in analytical applications [108,109]. Hence important automation stages have emerged in DLLME procedures. Clavijo et al. have introduced an innovative online application involving in-syringe magnetic stirring-assisted DLLME and GC-MS analysis for the extraction and determination of UV filters [110]. In this study, extraction, derivatization, and enrichment were simultaneously carried out by using trichloroethylene as the extraction solvent, acetone as the dispersive solvent, and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) as derivatization agent. In this system, the mixture containing the sample solution, trichloroethylene, and acetone were loaded into S1. The magnetic stirring was run to acquire effective extraction for the desired analytes. After this step, completely dispersion of the trichloroethylene in aqueous phase caused the formation of a cloudy phase inside S1 and then an accumulation of enriched organic droplets at the head of the syringe. Afterward, the organic extraction phase was transferred at 0.5 mL min21 to the MIV. In last step, the extract was driven to the MIV in load status. The injection valve was adjusted to injection, and 3 μL was delivered to the GC by a gentle stream of air provided by S2. The developed in-syringe-MSA-DLLME-GC
MS procedure is shown in Fig. 3.34. Andruch et al. have used a sequential injection system (SI) to form an automated online DLLME method. In this new design, a sample and all used aqueous reagents were aspirated and mixed in the holding coil of a sequential

injection analysis system and then transferred into a conical tube. A solution including amyl acetate as auxiliary solvent, CCl4 as extraction solvent, and acetonitrile as dispersive solvent was added at high flow rate. At this stage, the formation of a cloudy solution was observed, which led to extraction of the analytes. The prepared solution including amyl acetate and CCl4 was immiscible with water, and its density is importantly higher than that of water. As a result, self-sedimentation of the extraction solvent phase at the bottom of the conical tube took place in a short time. Hence, use of centrifugation for phase separation was eliminated. Finally, the extracted analyte was given to a microvolume Z-flow cell, and the absorbance values were measured [108]. The developed SIDLLME procedure is schematized in Fig. 3.35. Guo et al. have introduced an innovative automated DLLME procedure called fast automated dual-syringe-based dispersive liquid
liquid microextraction. This automatic DLLME system was illustrated in Fig. 3.36. This new technique combined solvent demulsification DLLME with GC-MS for extraction and analysis of PAHs in environmental water samples. Utilizing a commercial two-rail automatic sampling device, rapid solvent transfer with the help of a large-volume syringe devoted to the DLLME, and appropriate collection of the extraction phase by using a small-volume microsyringe for better GC performance was achieved. 1-octanol was used as a low-density extraction solvent [109]. Different modes of DLLME stay popular by using innovative extraction apparatus in microextraction systems. An innovative DLLME approach was reported by Wang et al [11]. The developed MSA-DLLME procedure is illustrated in Fig. 3.37. In this approach, a simple device was fabricated by combining a sample vial and a cut plastic dropper (Fig. 3.36a). The bulb tip of the cut plastic dropper was placed into the neck of the sample bottle, and the open-end tip of the plastic dropper was

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109

FIGURE 3.34 Schematic illustration of the suggested in-syringe-MSA-DLLME-GC
MS system for online extraction, preconcentration, derivatization, and chromatographic separation of seven UV filters. Multisyringe modules (MSM 1
2), syringes (S1 and S2) with a magnetic stirring system on S1, multiposition valve (MPV), and microinjection valve (MIV) [110].

then cut to a suitable length (Fig. 3.36a). 1octanol as the extraction solvent was dispersed in the tea drink sample solution, and magnetic agitation was applied to accelerate the extraction process (Fig. 3.36b). Then the sample solution turned clear, and two layers formed after leaving it alone for a while. The cut plastic dropper was carefully placed in the sample vial, and then the liquid level of the sample solution was raised to the tip of the plastic dropper to collect the extraction solvent phase on the surface of the sample solution (Fig. 3.37c). In the last step, the collected extraction solvent phase was taken with the help of a microsyringe and delivered for HPLC-DAD analysis (Fig. 3.37d). The developed method

was applied to analysis of organophosphorus and carbamate pesticides in tea drinks [111]. Generally, hydrophobic organic solvents are used as the extraction solvent phase in conventional DLLME. To fulfill the requirements of green chemistry and expand the applicability of conventional DLLME techniques, more green and nonconventional solvents, such as ionic liquids (ILs), supramolecular assemblybased coacervates, deep eutectic solvents (DESs), magnetic solvents, or even nano- or microsized particles dispersed in the extraction phase in a combined liquid
solid version, have been developed by researchers [112
117]. Ionic liquids (ILs) are one of the most commonly used extraction solvents in the DLLME

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FIGURE 3.35

3. Type of new generation separation and preconcentration methods

Schematic illustration of the SI-DLLME procedure [108].

FIGURE 3.36 Schematic illustration of automated DLLME method. (A) Injection of mixture of extraction and dispersive solvent by using a large-volume syringe; (B) emulsion stage; (C) injection of demulsification solvent to obtain clear emulsion; (D) raising of upper extraction solvent phase to the vial neck and collection by using a small-volume microsyringe [109].

New Generation Green Solvents for Separation and Preconcentration

111

3.2 Liquid phase microextraction

Extractant collection Add extractant

7 Put down the dropper into the sample vial

6 5

Sample solution

Stir

Stand for several minutes

Emulification

Phase separation

4

Liquid level was elevated

3 2 1

(A)

(B)

(C)

(D)

FIGURE 3.37 The new combining devices and schematic presentation of MSA-DLLME. (1) Magnetic stirrer; (2) sample solution; (3) sample vial; (4) bottleneck; (5) the cut dropper; (6) collected extractant; (7) a microsyringe [111].

methods. Abujaber et al. have used ionic liquid in DLLME for the separation and preconcentration of cortisol and cortisone in human saliva samples. They used 90 mg of 1-butyl-3methylimidazolium hexafluorophosphate IL [C4MIM][PF6] as the extraction solvent and 150 μL of methanol as the dispersive solvent. After completion of the extraction, LC-UV/Vis system was used for analysis. The schematic procedure of the IL-DLLME is shown in Fig. 3.38 [112]. LOD values for cortisone and cortisol were 0.11 and 0.16 μg L21, respectively. EFs for cortisone and cortisol were 5.0 and 6.3, respectively [112]. Despite ILs being considered green solvents, controversies over the toxic effects of ionic liquids are still warm. Considering these controversies, some researchers checked the cytotoxic or genotoxic effects of ILs before using them in sample preparation applications. For this purpose, Pacheco-Ferna´ndez and coworkers have controlled the cytotoxic effects of some ILs before using them for DLLME application. They have synthesized IL-based surfactant octylguanidinium chloride (C8Gu-Cl) to reach a less harmful surfactant by using guanidinium core cation and

a relatively short alkyl chain. Its aggregation and interfacial features were checked by fluorescence and conductivity measurements (critical micelle concentration values were 42.5 and 44.6 mmol L21, respectively). Cytotoxicity experiments were conducted on the C8Gu-Cl, other ILs, and conventional surfactants, especially 1octyl-3-methylimidazolium chloride (C8MIm-Cl), and other imidazolium- (C16MIm-Br) and pyridinium- (C16Py-Cl) based surfactants, together with the conventional cationic cetyltrimethylammonium bromide and anionic sodium dodecyl sulfate surfactants. Cytotoxicity experiments showed that C8Gu-Cl has the only low cytotoxicity. After cytotoxicity test, an in situ DLLME method, based on transforming the watersoluble C8Gu-Cl into a water-insoluble IL microdroplet via addition of Li-NTf2 as anion exchange reagent, was proposed for the separation and preconcentration of a group of six personal care products in cosmetic samples. After extraction, analysis was carried out by HPLCDAD. The optimum in situ DLLME/HPLCDAD procedure takes B32 min for completion of the extraction and chromatographic separation stages [113] (Fig. 3.39).

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FIGURE 3.38

Scheme of the IL-DLLME of cortisol and cortisone in human saliva samples [112].

FIGURE 3.39

Scheme of the in situ DLLME/HPLC-DAD procedure [113].

Recently, supramolecular solvents (SUPRAS), which appeared as environmentally friendly, high-extraction-yield, hydrophobic solvents containing nano- or microscale supramolecular aggregates, have gained a good position in liquid phase microextraction techniques. Zong et al. have prepared hexafluoroisopropanol-alkyl carboxylic acid high-density supramolecular

solvent to use in the DLLME of steroid sex hormones in human urine samples. As ocatanoic acid was used as the extraction solvent, hexafluroisopropanol (HFIP) was used as the coacervation-inducer, disperser in DLLME, and density-regulator for octanoic acid because of its unique features, such as having high hydrophobicity and high density and being a strong

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3.2 Liquid phase microextraction

hydrogen bond donor. A solution prepared by mixing 20 μL octanoic acid (2%, v/v) and 70 μL HFIP (7%, v/v) was syringed speedily into the urine sample hydrolyzed with the help of a syringe. Then the mixed solution was subjected to vortex agitation for 10 s and waited for 10 min for effective extraction of the analytes. After that, the SUPRAS phase (38.5 μL) was separated from the urine phase by centrifugation and analyzed with LC-MS/MS. The whole SUPRAS-based DLLME procedure is illustrated in Fig. 3.40 [114]. Ali et al. have introduced a supramolecular solvent-based DLLME method for the separation and preconcentration of Hg(II) as dithizone (DTz) complex prior to its cold vapor atomic absorption spectrometer determination. 1-undecanol and tetrahydrofuran were used to obtain SUPRAS. After addition of the SUPRAS to the acidic aqueous solution, the micelles

FIGURE 3.40

were formed by vortex agitation, and extraction of the Hg-DTz complex from the aqueous sample phase to extraction phase was completed. LOD and EF for the Hg were found as 5.61 and 77.8 ng L21, respectively. Accuracy tests were carried out on the Certified Reference Materials. The developed method was used for the analysis of claystone and sandstone samples [115]. Liu et al. have used hydrophobic deep eutectic solvent (DES) in an ultrasoundassisted DLLME procedure for the separation and preconcentration of pyrethroid insecticides (fenvalerate, deltamethrin, bifenthrin, etofenprox, and permethrin) prior to HPLC-UVD detection [116]. They have synthesized DESs by using phosphonium salts and straight-chain monobasic acids by means of FT-IR and TGA methods. The DES synthesis procedure is illustrated in Fig. 3.41.

Scheme of the SUPRAS-based DLLME/LC-MS/MS procedure [114].

O

C6H13

C14H29 + P C6H13 C6H13

O Cl

–

+ HO

CH3 stir and heat 80°C C6H13 (CH2)10

C14H29 + P C6H13 C6H13

Cl

H

O

CH3 (CH2)10

H

O

(CH2)10

–

CH3 O

FIGURE 3.41

Chemical structure of the produced DESs [116].

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FIGURE 3.42

3. Type of new generation separation and preconcentration methods

Schematic illustration of the UA-DLLME-DES/HPLC procedure [116].

The DLLME method starts with the addition of 30 mg of the prepared DES and 80 mg of sodium chloride to the water sample. Then, the solution is subjected to ultrasonication (40 kHz, 150 W) for the dispersion of the DES droplets in the aqueous phase and eventual extraction of analytes from aqueous sample phase to DES phase. After completion of the phase separation, analytes in the DES phase were analyzed by HPLC (Fig. 3.42). The developed procedure showed good RSDs ranging from 1.45% to 4.86% and low LODs between 0.30 and 0.60 μg L21. In last stage, the developed procedure was applied to environmental water samples with acceptable recoveries (80.93%
109.88%). In recent years, favorable novel magnetic extraction solvents have been used due to the excellent extraction features of magnetic extraction solvents used directly or modified with magnetic particles. These features lead to more valuable and potential application prospects for magnetic extraction solvents than for conventional solvents in microextraction studies [117,118]. Cao et al. have introduced an innovative method based on in situ derivatization combined with magnetic ionic liquid (MIL)DLLME for the extraction of six biogenic amines (tyramine phenylethylamine, tryptamine, histamine, spermine, and spermidine). In this application, dansyl chloride was used

for the in situ derivatization of biogenic amines. Afterward, biogenic amines were extracted with the MIL-DLLME procedure. Analysis was carried out by means of HPLCUV (Fig. 3.43). Trihexyltetradecylphosphonium tetrachlorocobalt (II) [P6,6,6,141]2[CoCl422] was used for the extraction of analytes due to its unique advantages such as hydrophobicity, magnetic susceptibility, and mobile phase suitability. The developed MIL-DLLME/ HPLC-UV procedure was successfully used to analyze biogenic amines in wine and fish samples with high recoveries (93.2%
103.1% and 94.5%
102.3%) [117]. Fiorentini and coworkers used magnetic ionic liquid as the extraction phase in DLLME of arsenic before its ETAAS determination. This work is the first application of the MIL [P6,6,6,14] FeCl4 together with the DLLME technique for the extraction and analysis of As in honey samples. The As(III) species was complexed with ammonium diethyldithiophosphate under acidic pH and extracted by using the trihexyl(tetradecyl)phosphonium tetrachloroferrate (III) ([P6,6,6,14]FeCl4) MIL as the extraction solvent phase and acetonitrile as the dispersive solvent. After completion of the extraction stage, the MIL phase was isolated from the sample solution by applying a magnet separation and analyzed with ETAAS. Schematic illustration of the MIL-DLLME/ ETAAS is shown in Fig. 3.13. LOD, EF, and

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3.2 Liquid phase microextraction

FIGURE 3.43

115

Schematic illustration of the MIL-DLLME/HPLC-UV procedure [117].

RSD% values were 12 ng L21, 110, and 3.9%, respectively [118].

3.2.4 Solidified floating organic drop microextraction The requirements for greener liquid phase microextraction methods have brought important reductions in the volumes of organic solvent so that the microvolume of a single drop is enough for effective extraction in applications such as single-drop microextraction. However, problems, such as the fact that the stable drop structure is difficult to maintain and that the use of a limited drip surface causes slow extraction kinetics, have limited the applicability of this method. These limitations were eliminated by the introduction of SFODME. In the

SFODME method, a droplet of an immiscible extraction solvent phase is left on the surface of the aqueous sample solution and then floated by agitation of the sample solution to maximize the interactions between the extraction solvent and aqueous sample phases. The sample tube is then cooled via an ice bath in order to solidify the extraction droplet, which is taken simply by using a spatula and melted for analysis of extracted analytes [119
121] (see Fig. 3.44). In SFODME, known as an equilibrium extraction method, the analyte concentration in the extraction solvent phase is increased to a certain level, and consequently the system reaches equilibrium, and the concentration of analyte in the extraction solvent remains constant versus time. The melting point of the organic extraction solvent drop (immiscible

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water) must be between 10 C and 30 C. The first applicability of the SFODME technique was checked in the extraction of polycyclic aromatic hydrocarbons (PAHS) prior to GC-FID analysis [119
122]. Then innovative SFODME applications were carried out for analysis of different organic and inorganic species. In 2008, an innovative variation of SFODME was reported by Leong and Huang [123]. They injected a mixed solution containing the

extraction and dispersive solvents instead of maintaining one droplet of extraction solvent in the sample. In this way, a dispersion of fine extraction droplets, which lead to faster mass transfer and high extraction efficiency, was obtained. These two SFODME methods provide fast and simple operation while consuming only microvolumes of extraction solvent in a green process. The proposed DLLME-SFO is schematized in Fig. 3.45. FIGURE 3.44 Schematic illustration of example SFODME method [119].

FIGURE 3.45 Schematic illustration of the suggested DLLME-SFO devices [123].

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3.3 New-generation solid phase extraction methods

Both applications of SFODME are rapid, but the dispersive type is completed in extraction times even lower than those of nondispersive ones. Although these techniques are very attractive and effective, it should be mentioned that the matrix problems, which have also occurred with the LPME methods, have to be dealt with, so a primary cleanup step is necessary for samples with complex matrix. Simple and quick operation, the use of simple and cheap laboratory apparatus, minimized extraction solvent consumption, and good accuracy are the main advantages of SFODME methods. Over the period of time, scientists have attempted to find microextraction techniques using greener solvents, and important developments have emerged for liquid phase microextraction. Most important of them is the discovery of ionic liquids, supramolecular solvents, switchable solvents, deep eutectic solvents, ferrofluids, and supercritical solvents. As the microextraction techniques using these solvents are explained in detail in the following sections, only the SDME, HF-LPME, SFODME, and DLLME methods are discussed in this chapter.

3.3 New-generation solid phase extraction methods 3.3.1 Solid phase microextraction In 1990, Pawliszyn and Arthur aided in important revolutions in sorption-based separation and preconcentration methods. They introduced one of the most popular green techniques, the solid phase microextraction method (SPME) [4]. Since then, SPME has become one of the most widely used methods in the separation and enrichment of organic, inorganic, and bioactive species found in different matrix environments. For many years, researchers have worked on solutions for problems in conventional solid phase extraction

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methods such as using excessive amounts of sorbent, reagents, and solvents, slow extraction processes, the formation of excess waste after the process, the necessity of high volumes or amounts of samples, the necessity of complicated and expensive extraction apparatus, and low sensitivity. SPME has proven itself as a successful method for eliminating most of these drawbacks. The solid phase microextraction method can be applied to all samples in different physical states, liquid, gas, and solid, and SPME has made a significant contribution and has become one of the most important techniques available all over the world. Hence SPME is a hot topic and has taken its place as a separation and preconcentration method in sample preparation laboratories all over the world [124
129]. Basically, SPME is based on the extraction of the analyte or analyte group in the sample phase by adsorption/absorption into the solid phase coated on the silica fiber or on some metallic support, followed by desorption of this analyte or analyte group resting on the solid phase using a suitable solvent or heat treatment prior to analysis. So SPME consists of two main steps [4]: (1) adsorption of analytes on the sorbent surface at the optimum conditions and (2) desorption of analytes by applying high temperature or elution. In SPME, fine fibers made of molten silica coated with a suitable sorption material for the adsorption of the target analytes onto the solid phase are used. The analytes in the sample are dispersed between the coated fiber and the matrix. In this way, both the separation and the enrichment processes are performed. Then desorption of analytes on the fiber are performed by applying high temperature, which leads to releasing analytes in gaseous form or eluting with organic or inorganic solvents. Analytes in gas form are transported to the detection system, generally a column of GC system or elution solutions injected into the detection system. According to the interaction

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3. Type of new generation separation and preconcentration methods

of the fiber on the solid phase with the sample, the solid phase microextraction method can be applied in nine different ways: 1. 2. 3. 4. 5. 6. 7. 8. 9.

Direct (direct immersion, DI) Adsorption from the headspace (HS) In-tube-SPM Solid phase dynamic extraction (SPDE) Micro-SPE (μ-SPE) Adsorptive microextraction (AμE) Stir-cake sorptive extraction (SCSE) Rotating-disc sorbent extraction (RDSE) Stir-rod sorptive extraction (SRSE)

As in other solid phase extraction modes, in the solid phase microextraction method, the choice of the suitable stationary phase by considering the type of analytes studied is a very important step in the development of an effective method. Nowadays, it is possible to reach a wide range of commercial stationary phases such as divinylbenzene (DVB), polydimethylsiloxane (PDMS), polyethylene glycol (PEG), carbowax (CW), and carboxen (CAR). These adsorbents can be effectively used in the simultaneous extraction of analytes with similar chemical properties in a sample matrix, but they cannot be used in the simultaneous extraction of analytes with different chemical features such as polarity and solubility. To solve this problem, the composite stationary phase (sorbent) consists of polar and nonpolar materials that have been produced. Some of them are CW/DVB, PDMS/DVB, and PDMS/ CAR. Scientists realized that these commercial products are not sufficient to work in different matrix environments and that these commercial products do not meet their desires because of their disadvantages such as low thermal stability, low selectivity, and short expiration date. Analytical chemists have always been able to overcome the challenges they face and have always taken innovative steps in their fields. These adversities have led analytical chemists to discover and use new sorbents with the desired properties.

The performance of SPME for the separation and preconcentration of analytes depends on many different variables, such as: 1. 2. 3. 4. 5. 6.

Type and length of fiber, Mode of extraction, Thickness of the stationary phase, Medium of sample matrix, pH and volume of sample, and Temperature of extraction medium and contact time of sorbent with sample.

Some of the most important and widely used new-generation solid phase microextraction sorbents are carbon materials, molecularly imprinted polymers (MIPs), mesoporous and nanoporous silicates, aniline-silica nanocomposites, metal nanoparticles, immunosorbents (ISs), metal complex-imprinted polymers, ILs and polymeric ILs (PILs), conductive polymers, and materials obtained by the sol
gel method. These nine solid phase microextraction applications are described next in some of the studies in the literature. In the DI-SPME procedure, the fiber is allowed to interact with the sample solution by immersion. In this stage, the analytes are extracted directly from the matrix medium into the stationary phase immobilized on the fiber [130]. In HS-SPME application, analytes are not in direct contact with the sample matrix. The analytes are transferred from the sample matrix to the gas phase, which is in direct contact with the sample and analytes attached to the fiber located in the headspace (HS). In this way, the coating of the fiber is unaffected and undamaged by the nongaseous impurities from the sample matrix and the solvents [131]. The most important steps in the development of solid phase microextraction were taken in the 1990s by the Pawliszyn group [4], the inventors of this method. In the first application, they used fused silica optical fibers as solid phase extraction material to separate and preconcentrate chlorinated hydrocarbons from the aqueous phase. In this study, commercially

New Generation Green Solvents for Separation and Preconcentration

3.3 New-generation solid phase extraction methods

fused silica fibers coated with polyimide had a 171 6 5 μm outer diameter. The polyimide film was activated by burning at 350 C for 4 h. After polyimide burning process, fragile fibers were obtained, which must be handled carefully. A prepared fiber had 5
6 weeks of lifetime for regular use. The fiber burned was placed in a Hamilton 7000 series syringe and set to the correct length. In order to fix polyimide fiber in the syringe, a drop of 5 min epoxy was added to the end of the fiber. The SPME is quite cheap since polyimide cost of the 1-m fiber is $2. Chlorinated hydrocarbons preconcentrated on the sorbent were thermally desorbed and directly fused to the silica column of GC, which had an electron capture detector [4]. In another study published by the same research group in 1992, a similar solid phase microextraction (SPME) method was used to separate and preconcentrate toluene, benzene, ethylbenzene, and the xylene isomers from aqueous solutions. In this method, a fused silica fiber coated with a 56- or 100-μ poly(dimethylsiloxane) stationary phase was immersed in an aqueous solution containing organic contaminants and was left until completion of the adsorption of organic compounds or equilibrium was achieved. Then the fiber was taken out of the solution, and thermal desorption was used to transfer the organic analytes from the fiber into the injector of a gas chromatograph. Concentrations of analytes were analyzed via a gas chromatography
flame ionization detector system (GCFID) [132]. In the same year, Arthur et al. used 56-μm methyl silicone film
modified silicone fiber for the headspace SPME (HS-SPME) of toluene, xylenes, benzene, and ethyl benzene in groundwater samples [133]. In this SPME application, SPME apparatus was placed either in a fused-silica capillary with an outer diameter of 300 μ and inner diameter of 200 μ and/or in a 30-gauge stainless steel tube. Organic analytes were adsorbed on the sorbent and were thermally desorbed and analyzed directly with

119

a gas chromatography
flame ionization detector system. When compared to trap and purge applications, the HS-SPME developed increased the SPME time by three- to sevenfold. Limits of detection obtained with the use of fiber coated with 56-μm methyl silicone were found between 1 and 3 ppb levels [133]. The same research group members used an uncoated fused-silica fiber as the solid phase extraction material for the separation and preconcentration of caffeine. They have added isotopically labeled (trimethyl 13C) caffeine in a beverage sample, and the SPME apparatus was immersed in the beverage sample for 5 min. to achieve extraction. Then the preconcentrated caffeine on the sorbent was thermally desorbed in a conventional split/splitless injection port, and caffeine analysis was carried out with the gas chromatography
mass spectrometry (GCMS) method. The whole analysis was completed within 15 min per sample [134]. The first application of SPME for the separation and preconcentration of metal ions was reported by Otu and Pawliszyn in 1993 [135]. In this study, a fused silica fiber coated with poly(dimethylsiloxane) was modified with the di-(2-ethylhexyl)phosphoric acid (HDEHP) (liquid ion exchanger) to fabricate an ionexchanging microprobe. The probe prepared was applied to extract Bi(III) ions from an aqueous HNO3 solution. The adsorbed Bi(III) ions were eluted with an aqueous solution consisting 1% hypophosphorus acid, 0.4% KI, and 1 M H2SO4, In this stage, yellow-colored BiI42 complex formed and absorbance values of the complex were measured with UV-Vis spectrophotometry at 460 nm [135]. A different solid phase microextraction application was used for the preconcentration of volatile chlorinated hydrocarbons in the air and water samples. It is the first report for the application of SPME for gas samples. While the limits of detection were in the range of 1 and 130 ng L21 for liquid phase application, the limits of detection in parts per trillion range

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3. Type of new generation separation and preconcentration methods

were obtained for the gaseous phase with an electron-capture detector (relative standard deviation of 1%
5%) [136]. Motlagh and Pawliszyn have provided an online analysis method for organic analytes in a flowing stream based on solid phase microextraction and gas chromatography. They used a sonication process for the extraction of organic analytes from a flowing stream into the sorbent phase. They have claimed that the method developed could be combined with a flow-injection analysis system [137]. An important application was carried out by Hirata and Pawliszyn in 1994 [138]. Polydimethylsiloxane or polyacrylate coated fused-silica fibers as the SPME phase was used for the preconcentration of nonpolar and polar analytes prior to supercritical fluid chromatographic analysis. In this method, the polymeric coating absorbs analytes set on a piece of tubing system coupled to the supercritical fluid chromatograph column. Desorption of analytes from the sorbent into the column was carried out with the supercritical fluid carrier [138]. In a different study, 15μm poly(dimethylsiloxane) or a Carbopack B was immobilized onto a fused-silica fiber and the sorbent obtained was used for the microextraction of anthracene, naphthalene, benz[α] pyrene, benz[α]anthracene, 2,20 ,3,4,50 -pentachlorbiphenyl, and 2,20 ,5-trichlorbiphenyl in water samples prior to their GC-MS determinations. Detection limits for analytes were between 1 and 20 pg mL21 [139]. In 1994, Cisper et al. provided an important application of SPME. They used disposable fused silica optical fibers for two purposes: (1) microextraction of pyrene and (2) sample support for laser desorption of pyrene. The sample preparation step in the traditional methods was eliminated with the development of SPME
laser desorption ion trap mass spectrometry. The authors claimed that the new methodology is also useful for other organic compounds such as polycyclic aromatic hydrocarbons, pesticides, peptides, and laser dyes

[140]. Eisert et al. have used fused-silica fiber coated with a polymer (polydimethylsiloxane) for the solid phase microextraction of pesticides in environmental water samples following GC-AES determinations. Adsorbed species on the sorbent were transferred into a GC injector by means of thermal desorption [141]. Poly(dimethylsiloxane)-coated silica fibers are the most used solid phase microextraction sorbent. Research on the development of different materials that can be used in solid phase microextraction has paved the way for the production of different materials in this field. Wan et al. have used pencil lead as an alternative sorbent for solid phase microextraction of methyl parathion, lindane, and 2chlorophenol with different polarities prior to gas chromatography with electron capture detector [142]. Mangani and Cenciarine have used graphitized carbon black modified with fused silica fibers for SPME of organic micropollutants in gaseous and aqueous samples. GC and GC-MS were used for the analysis of analytes [143]. Rastkari et al. have investigated the usability of carbon nanotubes (CNTs) as the sorbent in headspace solid phase microextraction (HSSPME) applications. They prepared the new SPME apparatus by attaching SWCNTs onto a stainless steel wire with organic binder and used the new SPME apparatus for the separation and preconcentration of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) from human urine. A thermal desorption procedure was applied to transfer the analytes from the SWCNTs sorbent to the GC analysis system [144]. SEM images of commercial fiber and SWCNT-coated stainless steel wire are shown in Fig. 3.46. Mehdinia and Mousavi have compared the sorption efficiency of nano- and microstructured polyaniline (PANI) coatings on support material in solid phase microextraction. They have used polychlorinated biphenyls (PCBs) as

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121

FIGURE 3.46 SEM images of (A) commercial fiber and (B) SWCNT-coated stainless steel wire [144].

a model analyte in the HS-SPME application. The results obtained showed that nanostructured PANI coating provided higher extraction capacity and shorter desorption time than microstructured coating due to the larger surface area [145]. Cao et al. have fabricated nanostructured titania fibers as the sorbent in the HS-SPME application for the preconcentration and separation of dichlorodiphenyltrichloroethane (DDT) and its degradation products. In the fiber production process, titanium wires were oxidized with H2O2 at 80  C for 24 h to obtain nanostructured titania fibers with a B1.2-μm-

thick nanostructured coating consisting of B100-nm titania walls and 100
200-nm pores. As the nanostructured titanium on the surface of the titanium wire was homogeneously formed, the coating process on the titanium wire was made very regularly and strongly. This innovative SPME material was used at least 150 times due to mechanical stability of the titanium wire substrate and the chemical durability of titania coating. After HS-SPME application, the concentration of analytes was analyzed by using gas chromatography with electron capture detection (GC
ECD) [146]. SEM images of the titania SPME fiber prepared

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by oxidization of titanium wire in H2O2 (30%, w/w) solution at various conditions are shown in Fig. 3.47. Mehdinia et al. have produced and used nanosized lead dioxide (PbO2) fiber in a solid phase microextraction (SPME) application for the first time in the literature. The electrochemical deposition method was used to produce PbO2 nanofibers between 34 and 136 nm on a platinum wire. The nanosized fibers were used for toluene, benzene, xylenes, and ethylbenzene in environmental samples by headspace solid phase microextraction (HS-SPME), coupled to gas chromatography
flame ionization detection (GC-FID). The new nanostructured fiber provided high extraction capacity, reusability more than 50 times, and improved stability for high temperatures around 300 C. These features are the most important advantages of lead oxide fibers over commercially obtained SPME fibers [147] (see Fig. 3.48). Yousefi et al. have produced a graphenebased bucky gel-coated stainless steel fiber for headspace solid phase microextraction of volatile organic compounds. A bucky gel was obtained by mixing graphene with an ionic liquid. An etched stainless steel wire was directly deposited with the bucky gel to obtain fiber. The SPME sorbent prepared was characterized by FT-IR spectroscopy, thermogravimetric analysis, and field emission scanning the gelcoated analysis of toluene, benzene, ethylbenzene, and xylene isomers. Modification with graphene led to an increase in the π-interaction between the aromatic analytes and sorbent. The limits of detection were found in the range of 0.03 and 0.06 μg L21. The HS-SPME method was effectively used for the separation and preconcentration of xylene isomers in spiked urine samples with recoveries between 88% and 105% [148]. Internally coated capillary or needle are alternatives to the use of coated fibers in intube solid phase microextraction (in-tubeSPME); instead, open-tubular capillary

columns are used for analyte retention. In-tube systems can be classified as static and dynamic. In these systems, analytes are flowed from the sample phase through needles or tubes by the power of diffusion, pumping, or gravitational flow. In this way, the extraction process is completed. The in-tube solid phase microextraction method was initially developed to suggest an automation mode for fiber SPME-HPLC. The main drawbacks of conventional fiber SPME, such as thick-film coatings of fiber, low adsorption capacity, and fragility, can be solved by using in tube-SPME [149
151]. In the 1990s, the solid phase microextraction of very polar analytes was an important problem due to the limited selection of commercially available fiber coatings since these fibers were not durable for aggressive solvent conditions in the elution step. Eisert and Pawliszyn have provided an automated in-tube-SPMEHPLC method for the extraction and analysis of phenylurea pesticides from the aqueous phase for the first time in literature. In this system, Omegawax 250 sorbent was filled in a piece of an ordinary capillary GC column to adsorb the phenylurea pesticides from the aqueous phase (in-tube-solid phase microextraction). The capillary was accommodated in a needle when it is pierced through the vial septum containing the spiked aqueous sample. The sample solution was kept in 2-mL vials on a commercial autosampler. A syringe was used to aspirate and dispense 25 μL of the sample solution into the capillary many times to ensure the adsorption of analytes. Then the absorbed analytes were eluted from the sorbent by aspiring methanol into the column, and the methanol phase was injected into the injector loop of HPLC. In contrast to other solid phase microextraction methods, this innovative method allows the analysis of very polar analytes by using more polar column coatings instead of poly(dimethylsiloxane)-coated columns [149]. Mester and Pawliszyn have reported a different application consisting of

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3.3 New-generation solid phase extraction methods

123

FIGURE 3.47 SEM images of the titania SPME fiber prepared by oxidization of titanium wire in H2O2 (30%, w/w) solution at various conditions. (A) 55 C, 24 h; (B) 80 C, 12 h; (D) 80 C, 24 h; (D) 80 C, 36 h; (E) 80 C, 48 h; (F) 80 C, 72 h; (G) longitudinal image (80 C, 12 h); (H) image of part of the transect (80 C, 12 h) [146]. New Generation Green Solvents for Separation and Preconcentration

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3. Type of new generation separation and preconcentration methods

(A) SEM image of PbO2-coated Pt wire; (B) 20 μA cm22 for 60 min; (C) 200 μA cm22 for 30 min; (D) for 15 min; (E, F) 10 mA cm22 for 10 min; (G, H) higher magnification SEM images of PbO2 [147].

FIGURE 3.48 22

2 mA cm

New Generation Green Solvents for Separation and Preconcentration

3.3 New-generation solid phase extraction methods

in-tube-SPME, coupled directly to a positive ionization electrospray mass spectrometer (ESMS) for trimethyllead (TML) and triethyllead (TEL) species [150]. Kataoka et al. have provided an automated in-tube-SPME combined with LC-ESI-MS for the determination of ranitidine. An Omegawax 250 capillary column (60 cm 3 0.25 mm ID, 0.25-μm film thickness) was used as the stationary phase. The maximum extraction efficiency was obtained at pH 8.5 by applying 10 times the aspirate/dispense number of steps for 30 μL of sample. The desorption of ranitidine adsorbed on the sorbent was simply carried out with methanol. The automatic application of in-tube-SPME/LC-ESI-MS procedure was carried using the HP 1100 autosampler (Fig. 3.49). The method was used for the determination of ranitidine in water, urine, and tablet samples [151]. Asiabi et al. have provided a “packed intube” configuration for packed in-tube-SPME application. They have produced plate-like

cobalt/chromium-layered double hydroxide nanosheets (Co/Cr(NO32)-LDH) with a coprecipitation method and have used it as a packed in-tube-SPME application. They have characterized the produced nanomaterial with XRD, SEM, and FT-IR. The in-tube-SPME/HPLC method developed was used to determine two different groups of acidic pesticides and insecticides in water samples [152]. Ji et al. have modified stainless steel wires by coating with diamond nanoparticles as extraction material. The prepared extraction material then was placed into a poly(ether ether ketone) tube to obtain a new in-tube-SPME apparatus. The new in-tube-SPME apparatus was used for the extraction and preconcentration of polycyclic aromatic hydrocarbons, estrogens, and plasticizers, followed by HPLC determinations. Detection limits for the analytes studied were between 0.005 and 0.020 μg L21 with inter- and intraday RSD of 8.4% and 2.4% [153]. ˙ a different in-tube-SPME application, In scientists prepared polythiophene/graphene

FIGURE 3.49 Schematic illustration of the intube-SPME system for LC
MS [151].

PEEK tubing

Capillary

Injection needle

Column connectors

Ferrule Injection loop

Autosampler

125

Metering pump In-tube SPME capillary Six-port valve

From pump To column

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oxide (PTh/GO) nanostructured coated tube using a simple in situ electrodeposition procedure for the separation and preconcentration of doxepin (DOX) and amitriptyline (AMI) as antidepressant drugs. Their system was based on the electrochemical control of in-tubeSPME. GO (graphene oxide) was used in this study as a sorbent and anion dopant. When compared with the use of PTh and GO coatings, separately, use of them together led to improved surface area, mechanical stability, and long lifetime. The schematic illustration of the electropolymerization of PTh-GO in the inner surface of the tube is shown in Fig. 3.50 [154]. The complete assembly and operation mode of the instrument are shown in Fig. 3.51.

SPDE is a different mode of headspace solid phase microextraction: A convenient sorbent is used to cover the internal surface of the needle, which leads to improvements for the interphase contact [155
157]. In 2001, this application was introduced to the literature for the first time to analyze pesticides in water samples. Thereafter, many studies have been carried out for the analysis of organic, inorganic, and bioactive species. Musshoff et al. have developed an automated headspace SPDE for the microextraction of synthetic designer drugs and amphetamines in hair samples prior to GC-MS determinations. In this system, the inside of the hollow needle was coated with polydimethylsiloxane to prepare the capillary

FIGURE 3.50

Production method for (A) PTh/ GO nanostructured electrodeposited coating and (B) structure of PTh/GO after coating onto the internal surface of stainless steel tube [154].

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3.3 New-generation solid phase extraction methods

FIGURE 3.51

127

Schematic illustration of the EC-IT-SPME, followed by online HPLC analysis [154].

absorption trap. Extraction was carried out on the solution headspace by passing the gas through the device actively with a syringe, and analytes in the aqueous phase were collected onto the sorbent phase. The metal syringe needle located in the GC injection port was heated to desorp analytes [155]. A different solid phase dynamic extraction/gas chromatography tandem mass spectrometry (HS-SPDE/GC/ MS/MS) procedure was developed to analyze the trimethylsilyl derivatives of cannabinoids, trifluoroacetyl derivatives of amphetamines, methadone, and designer drugs of abuse. The analytes were extracted from the sample headspace directly into an internal coating of polydimethylsiloxane in the hollow needle by repeated aspirate/dispense cycles. The developed HS-SPDE/GC/MS/MS application provided improved detection limits (6
52 pg mg21) with precision (0.4%
7.8%) [156]. Torri and Fabbri have provided a pyrolysis-dynamic solid phase microextraction (Py-SPME) method to

determine volatile compounds with GC-MS. A microscale offline pyrolysis reactor was combined with dynamic solid phase microextraction equipment in order to analyze 12 main volatile pyrolysis products [157]. Micro-SPE (μ-SPE), also known as porous membrane-protected μ-SPE, has been used to extract and preconcentrate analytes in complex matrix. In this method, a small amount of sorbent is filled in small sorbent bags (1
4 cm2), producing a porous membrane (polypropylene or composite materials of polyamide and nylon fibers) [158,159]. When compared with the conventional solid phase extraction, micro-SPE provided important advantages. (1) It can be used in semisolid/ solid or suspension matrices since contamination of the sorbent is prevented by the porous membrane. Hence micro-SPE can eliminate the matrix effect, and the blockage problem usually encountered in other SPE applications is reduced. (2) High preconcentration factors are

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obtained. (3) It is cheaper, and minimum amounts of organic solvent re used. (4) Each apparatus can be used many times (B 20 times). (4) The operation process is simple, and it is faster than conventional SPME [158,159]. These important advantages have proved that the micro-SPE procedure is more suitable for routine analysis applications. An innovative and effective multiwalled carbon nanotube- (MWCNT-) supported microsolid phase extraction (μ-SPE) procedure was developed by Basheer et al. in 2006. A sheet of porous polypropylene membrane (2 3 1.5 cm) was used as a bag to cover 6 mg of MWCNTs. The prepared μ-SPE apparatus was soaked with dichloromethane and then was immersed in a solution of sewage sludge sample. The sample solution phase was stirred to extract organophosporous pesticides from the sample phase to the WMCNT phase. Extraction of the extraneous materials was blocked via the porous membrane filter, which eliminated further cleanup for analytes. Analytes adsorbed on the sorbent were eluted with hexane and analyzed by GS-MS. The μ-SPE apparatus was reused for 30 extractions [158]. A different μ-SPE apparatus was prepared by using C18 sorbent and a polypropylene membrane cover. The new μ-SPE apparatus was used for the microextraction of acidic drugs in wastewater samples prior to HPLC analysis [159]. The same research group used the same membrane-protected μ-SPE apparatus and HPLC detection system for the analysis of carbamate pesticides in soil samples [159]. Lee et al. have used a molecularly imprinted polymer (MIP) as a sorbent in a porous membrane for the microsolid phase extraction (μ-SPE) of ochratoxin A (OTA) in grape juice, coffee, and urine samples. After the extraction, an ultrasonic irritation power was used to desorb analytes followed by HPLC analysis [160]. Ge and Lee have combined the sonication-assisted emulsification microextraction and vortex-assisted μ-SPE methods for the

separation and preconcentration of acidic drugs in environmental water samples. GC-MS was used to measure the concentration of analytes in the last phase. They have used the zeolite imidazolate framework 8 (ZIF-8) as a sorbent for μ-SPE and 1-octanol as the extraction phase for emulsification microextraction. ZIF-8 exhibited very effective chemical and thermal stability for the aqueous matrix [161]. The same authors used the vortex-assisted porous membrane-protected microsolid phase extraction (SAE-VA-μ-SPE) method for the separation and preconcentration of polycyclic aromatic hydrocarbons (PAHs) in water samples. They have synthesized and used the mixed zeolitic imidazolate framework 8 (ZIF-8) (nanometer- and micron-sized) material as adsorbent in the SAE-VA-μ-SPE method. The schematic of the preparation and fabrication of a μ-SPE device is illustrated in Fig. 3.52 [162]. In a different study, 1 mg of reduced graphene oxide, an effective, mechanical, and thermal stable sorbent, was loaded into a polypropylene bag for the microsolid phase extraction of estrogens including estrone, 17βestradiol, 17α-ethynylestradiol, and diethylstilbestrol in water samples. Amounts of analytes in the eluent phase were measured by using the HPLC-UV detection system [163]. When the literature studies in recent years are examined, it is seen that there is rapidly increasing interest in AμE applications, which are considered to fulfill the requirements of green analytical chemistry [164]. New nanomaterials are commonly used in this method. As the diversity in nanomaterials with different physical and chemical properties increases, AμE methods become preferred in the determination of polar analytes and their metabolites, especially in biological samples. AμE can be applied by applying two geometrical variants: (1) bar AμE (BAμE) and (2) multisphere AμE (MSAμE). These new methods can be used with small analytical apparatuses having the appropriate geometry. In these applications,

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Edge folded over

Heat scaled Individual rectangular pieces are cut off

Polypropylene membrane

0.5 cm

5 mg of the sorbant is introduced into membrane envelope, and open end is heat scaled.

Sealed folded-over section is cut off from main membrane.

0.8 cm 0.5 cm

FIGURE 3.52

One of the open ends is heat sealed.

Schematic illustration of the production of a μ-SPE device [162].

sticking-based technologies are used to modify the substrate surface with sorbents [164]. In 2010, Neng et al. have introduced a adsorptive-extraction (AE) as a novel preconcentration method for the determination of polar analytes in the aqueous phase. They have used bar AμE and multisphere AμE methods as two different geometrical modes to compare the extraction efficiencies, mechanic stability, and robustness of microextraction apparatus, prepared using 20 different sorbents ranging from organic sorbents to metal oxides. In multisphere AμE, the apparatus first covered the polystyrene spherical substrates, followed by fixation with thermal supporting. In the bar AμE apparatus, adhesive films were used to fix the sorbent phases on polypropylene, hollow cylindrical substrates. The results obtained showed that, among the 20 sorbent materials tested, polystyrene divinylbenzene and activated carbons

were the most suitable sorbents and have the best robustness and stability and phases. They have used bar AμE and multisphere AμE apparatus successfully for the microextraction of polar analytes and metabolites such as drugs of abuse, pharmaceuticals, pesticides, and disinfection by-products in water and biological fluids [164]. In 2014, Ahmad et al. carried out a comparison study for different types of sorbent coatings, including styrene-divinylbenzene, five types of activated carbons, two types of modified pyrrolidone, n-vinylpyrrolidone, and ciano polymers. They used the BAμE/HPLC-DAD procedure to analyze trace levels of epitestosterone and testosterone in urine. It was reported that n-vinylpyrrolidone was the most suitable sorbent to obtain good recovery results (between 92.1% and 93.4%) [165]. SCSE is an advanced mode of stir-bar sorptive extraction (SBSE). First application of

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stir-cake sorptive extraction was reported by Huang et al. in 2011 [166]. In this extraction system, a specially prepared holder is used for the stationary phase. A mixture prepared from iron, coated with a glass protection layer, is located in the lower part of the cake holder. The extraction process is importantly longer than stir-bar sorptive extraction since interaction of the sorptive element with the bottom of the vessel is blocked. They have synthesized poly(vinylimidazole-divinylbenzene) by the in situ polymerization of monolith and used as the extractive cake. The developed SCSEHPLC-DAD procedure was used to preconcentrate and analyze steroid hormones in milk samples [166]. The same research group prepared a new polymeric ionic liquid-based monolith as the extractive cake used for the separation and preconcentration of PO432, NO22, NO32, SO422, Cl2, Br2, and F2 ions from water samples prior to ion chromatography with conductivity detection. The limits of detection and limits of quantification for the suggested procedure were in the range of 0.11
2.08 and 0.37
6.88 μg/L, respectively [167]. In 2013, a similar SCSE method was used for the extraction of benzoic acid, cinnamic acid, and sorbic acid from soft drinks and juices prior to HPLC-DAD detection [168]. Huang et al. have produced an innovative porous monolith as an SCSE sorbent by using in situ copolymerization of divinylbenzene and allyl thiourea. They have developed an analysis procedure including SCSE and HPLC-DAD stages for phenolic compounds in water samples [169]. A poly(ethylene glycol dimethacrylate/graphene oxide) (EDMA/GO) monolith was fabricated as a SCSE sorbent in a different application. The sorbent phase was used to preconcentrate strongly polar aromatic amines in waters. After the SCSE step, the HPLC-DAD detection system was used for measurements [170]. RDSE, a different mode of solid phase microextraction, was introduced by Richter

and coworkers in 2011 [171]. Rotating-disc sorbent extraction is a very effective application for the preconcentration and separation of lowpolarity analytes. In this system, the extraction process is conducted on the rotating Teflon disc modified with the stationary phase. The sol
gel method is used for the modification of the rotating disc. When the extraction process is completed, the disks are dried, and a small volume of solvent is added on the sorbent for the desorption of analytes. The reusability of disks is one of the most important advantages of RDSE applications. In this mode of SPME, a Teflon disc filled with polydimethylsiloxane (PDMS) is used for the microextraction of malachite green. After the RDSE step, the polydimethylsiloxane with the concentrated malachite green is plucked from the Teflon disk and used directly for determination of MG with solid phase spectrophotometry at 624 nm [171]. The extraction device used in this study is shown in Fig. 3.53. In a different RDSE application, Can˜as and coworkers have prepared a Teflon rotating disc apparatus filled with a copolymer of divinylbenzene and N-vinylpyrrolidone for the separation and preconcentration of florfenicol in plasma samples, followed by detection with HPLC-DAD. The whole extraction process was completed in 90 min. They obtained a recovery of 91.5% for florfenicol by using the developed RDSE/HPLC-DAD procedure [172]. Donato et al. have used polymeric sorbent Oasis HLB as a sorbent to prepare a rotating-disc sorbent extraction apparatus. They have combined this RDSE method with ultra-high-performance liquid chromatography with a tandem mass spectrometer (UHPLC
MS/MS) in order to extract and analyze the multiresidues of 62 pesticides in surface water [173]. SRSE is also considered as an advanced stirbar sorptive extraction like rotating-disc sorbent extraction and stir-cake sorptive extraction. This method was introduced for first time

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3.3 New-generation solid phase extraction methods

by Luo and coworkers in order to analyze fluoroquinolones in honey samples. In this method, surface of a metal rod is coated with a magnet and a monolithic polymer-based adsorbent. The extraction process is performed on this rod (Fig. 3.54) [174]. A different SRSE/GC-MS procedure was provided by Luo and coworkers for the extraction and analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples. They have used poly(ethylene glycol dimethacrylate)/graphene composite as the sorbent phase synthesized with an in situ polymerization method. The limit of detection (LOD) values for 16 PAHs were between 0.005 and 0.429 ng mL21 [175]. Ma and coworkers used a poly-

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(methacrylic acid-co-ethylene dimethacrylate) polymer as the sorbent in the stir-rod sorptive extraction of four sulfonamides prior to their liquid chromatography and electrospray ionization mass spectrometer (LC-ESI-MS) determinations [176]. In 2011, poly(4-vinylpyridineco-ethylene glycol dimethacrylate) (poly[VPco-EDMA]) monolithic polymer was used in an anionic exchange, SRSE coating material. The new material was used for the separation and preconcentration of three nonsteroidal antiinflammatory drugs in environmental waters. After the SRSE step, analysis of these three nonsteroidal antiinflammatory drugs was carried out with an HPLC/UV detection system [177].

FIGURE 3.53 Photograph of the Teflon rotating disk containing the PDMS phase. (A) Before and (B) after extraction of a 1-L water sample containing 40 μg L21 MG [171].

FIGURE 3.54

Schematic illustration for stir-rod sorptive extraction [174].

Metal rod

Rubber plug

Glass insert

Vessel Magnet

Magnetic stirrer

Monolithic polymer coating

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3.3.2 Stir-bar sorptive extraction SBSE is considered a green analytical application since the use of solvents can be eliminated. Complex and time-consuming sample preparation steps are made easier. In 1999, stirbar sorptive extraction was provided for the first time by Baltussen et al. They have used polydimethylsiloxane (PDMS) coating polymer as the sorbent in this new application. The principles of stir-bar sorptive extraction are the same as with solid phase microextraction. But the difference between these two methods is that the coating sorbent used is different. Whereas in SPME polymer-based sorbents are used as coating materials, a nonpolar polymeric phase such as polydimethylsiloxane is used as the coating sorbent to modify stir-bars in SBSE. The main interactions between sorbent and analytes are the hydrogen bonds and Van der Waals forces [177,178]. In this method, while sample stirring, SBSE apparatus is immersed into the samples for extraction of analytes by a bar, previously coated with a suitable sorbent material. After completion of the adsorption stage, the bar is taken out of the sample phase, washed with ultrapure water, and dried. Thermal desorption for analytes that are not degrading at high temperatures is applied to carry from the sorbent phase into the injection port for GC or LC. Other cases, liquid desorption is used for analytes. The applicability of SBSE in a wide range of analytes for liquid, solid, and gaseous sample media, its automation, and the achievement of high preconcentration factors are the most important advantages. Silicone materials, molecularly imprinted polymers, sorbents obtained with sol
gel methods, polyacrylate, poly(ethylene glycol)-modified silicone, polyurethane foams, poly(phthalazine ether sulfone ketone), poly(dimethylsiloxane)/polypyrrole, alkyl-diol-silica (ADS) restricted access materials, monolithic materials, carbon nanotubepoly(dimethylsiloxane), cyclodextrin, and

polyvinyl alcohol are the most used sorbents to cover the bar [177,178]. In 2000, Tredoux et al. introduced a SBSE for the separation and preconcentration of benzoic acid in lemon-flavored beverages. They covered a stir-bar with 50 mg polydimethylsiloxane (PDMS) and used this new extraction material like similar extraction mechanisms insolid phase microextraction. But the SBSE developed method provided a 100 times higher enrichment factor than SPME. After the adsorption step, benzoic acid was desorbed thermally to capillary gas chromatography (CGC)
mass spectroscopy (MS). A lineer calibration curve was obtained in the range of 1 to 1000 ppm [178]. In a different application, a stir-bar of 1-cm length was coated with poly(dimethylsiloxane) (PDMS) as a new stir-bar sorptive extraction sorbent to separate and preconcentrate the organotin compounds tributyltin (TBuT) and triphenyltin (TPhT), followed by ICP-MS detections. After completion of the adsorption process, thermal desorption at 290 C was applied for the analytes on the sorbent. Analytes in gas form were collected on a precolumn at 240 C. Flash heating was applied to quickly carry the analytes to the capillary column of GC coated with PDMS in order to separate the analytes. In the last stage, the analytes were delivered to an ICP-MS detection system by using a handmade heated (270 C) transfer system. The method was applied to water, mussels, and harbor water samples at the parts per quadrillion level [179]. In 2001, Wennrich et al. have suggested a combined extraction procedure consisting of accelerated solvent extraction (ASE) and stirbar sorptive extraction for several organochlorine pesticides and chlorobenzenes in strawberries prior to thermal desorption-GC-MS analysis. They have used a 65-μm polydimethylsiloxane/divinylbenzene fiber as the sorbent phase [180]. Sandra et al. have introduced a SBSE-thermal desorption-capillary GC-MS (TD-cGC-MS) procedure for extraction and analysis of the dicarboximide fungicides

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3.3 New-generation solid phase extraction methods

vinclozolin, procymidone, and prodione in wine samples [181]. An effective SBSE/GC-MS was suggested by Nakamura et al. for the preconcentration and determination of geosmin and 2-methylisoborneol in water samples. In this study, a 100-μm PDMS fiber was selected as the sorbent. The SBSE method provided 0.15 and 0.33 ng L21 of detection limits for geosmin and 2-methylisoborneol with 3.7% and 9.2% RSD [182]. An automatic solid phase extraction system for GC detections was introduced in the form of a high-capacity sorption device for GC determination of polycyclic aromatic hydrocarbons at trace levels in urban snow. In this system, the SPME method was combined with the SBSE. The SBSE system was prepared from polydimethylsiloxane (PDMS) rubber tubing (120 μL) covering a glass rod. A robotic autoinjector was used for the sampling. The system was applicable for 44 environmentally hazardous compounds with sub
parts per trillion detection limits [183]. Magnetic nanomaterials have found an important place in various SBSE applications. ´ lvarez et al. have modified a polymer Dı´az-A monolith with imprinted magnetic nanoparticles (MNPs) and used this material as a new SBSE apparatus. In the synthesis procedure of sorbent material, oleic acid-modified MNPs were encapsulated inside a silica network. Then, the surfaces of particles were modified with vinyl groups to start the copolymerization step with the imprinting polymerization phase. The final imprinted monolith sorbent had magnetic features allowing its applicability as a magnetic stir-bar. The new SBSE apparatus was used for the separation and preconcentration of triazines from soil sample extracts prior to HPLC-UV detection [184].

3.3.3 Magnetic solid phase extraction technique In the last two decades, magnetic solid phase extraction (MSPE) methods using

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magnetic adsorbents have become one of the most commonly used methods for the separation and enrichment of organic, inorganic, and bioactive species at the matrix level. In 1973, Robinson and coworkers proposed the first ˇ rikova magnetic separation device [185]. Safaˇ ˇ and Safaˇrik used magnetic solid phase extraction as an analytical application in 1999 [186]. They prepared a magnetic charcoal sorbent for the magnetic solid phase extraction of safranin O and crystal violet in water samples [186]. About a 460-fold preconcentration factor was obtained for the analytes. The MSPE method is based on the adsorption and desorption of analytes on magnetic adsorbents that are added to the sample solution containing the analytes. In this method, different type of polymers, nanomaterials, metals, and metal oxides that can be used as adsorbents are modified by magnetic particles, such as nanosized Fe3O4, γ-Fe2O3, ZnFe2O4, and ZnFe2O4. In this way, adsorbents that do not show magnetic properties are given magnetic properties [186
188]. Magnetic nanoparticles such as Fe3O4 and γ-Fe2O3 have low stability in solution medium, especially in acidic conditions, which cause the decomposition of materials in a short time and the loss of their magnetic properties. To prevent this drawback, the materials obtained are modified by silica, alumina oxides, or different groups resistant to harsh working conditions [189]. In this method, the magnetic sorbent is added to the sample solution containing the analyte or analytes of interest. Then, in order to adsorb the analytes on the sorbent, the sorbent with the sample solution is allowed to interact for a certain period of time. To make this interaction more effective, faster, and simpler, the resulting mixture consists of sample solution, and the magnetic sorbent is mixed for a certain time by means of devices such as vortex, magnetic stirrer, and shaker. After completion of the adsorption process, sorbent is isolated from the sample solution by an

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external magnetic field. Next, an eluent is added to the sorbent for elution of the target analytes, and the sorbent is isolated from the eluent phase by an external magnetic field. The concentration of target analytes in the eluent phase was analyzed by a suitable detection system. The main interactions between sorbent and analytes are dipole
dipole, dipoleinduced dipole, hydrogen bonding, dispersion forces, and ionic [187
189]. Selection of the suitable sorbent used MSPE is the most important step in this method, which affects the extraction efficiency as in other methods. Some of the most often used new-generation solid phase microextraction sorbents in MSPE applications are [187
198]: 1. Carbon nanoparticles (carbon nanotubes, fullerenes, nanodiamonds, graphene, graphene oxide, carbon dots, and modified carbon nanoparticles), 2. Metal oxides (SiO2, Al2O3, TiO2, etc.), 3. Polymers (cyclodextrine, polypyrrole, polyanyline, gelatin, chitosan, poly (divinylbenzene-co-methacrylic acid, etc.), 4. Metal-organic frameworks, 5. Molecularly imprinted polymers (MIPs), 6. Mesoporous and nanoporous silicates, and 7. Graphene-like materials (MoS2, MoSe2, WS2, C3N4, etc.). The SPME is used to separate and preconcentrate a wide range of trace analytes in different matrix mediums, including: 1. Food, drug, and biological sample analysis: Extraction and preconcentration of metals, dyes, pesticides, pharmaceutical active ingredients, and so on. 2. Biomedicine: Isolation, extraction, and preconcentration of different bioactive species such as DNA, RNA, enzymes, proteins, peptides, and cells. 3. Environmental analysis: Extraction and preconcentration of metals, dyes, pesticides, pharmaceutical active ingredients,

surfactants, PAHs, mutagenic, and carcinogenic analytes in water and sewage samples. 4. Earth and mineral science: Extraction and preconcentration of valuable metals and radioactive species. Some MSPE applications in the literature on the separation and preconcentration of trace organic and inorganic analytes are summarized here. ˇ rikova and Safaˇ ˇ rik tested the In 2002, Safaˇ applicability of the magnetic solid phase extraction procedure for high volumes of urine samples. For this purpose, they have fabricated a reactive copper phthalocyanine dyeimmobilized magnetite particles for the separation and preconcentration of crystal violet dye as a model analyte in high volumes of urine samples since crystal violet leads to an increased risk of cancer for living cells [187]. In 2005, the same research group used the MSPE method to separate and preconcentrate nonionic surfactants based on aliphatic alcohols, hydrogenated fatty acid methyl esters, and oxyethylated nonylphenol in water samples [187]. Huang and Hu fabricated, characterized, and used γ-mercaptopropyltrimethoxysilane(γ-MPTMS-) modified silica-coated magnetic nanoparticles (SCMNPs) as an innovative SPME sorbent for the separation and preconcentration of Pb, Hg, Cu, and Cd at trace levels in environmental and biological samples. In this method, 50 mg of magnetic sorbent was added to the sample solution including metal ions (pH 6.0), and the mixture obtained was ultrasonicated for 10 min to ensure the adsorption of analytes on the magnetic sorbent. Then the sorbent was isolated from the sample solution phase by applying an external magnetic field, and analytes on the sorbent were eluted with 1.0 mol L21 HCl and 2% (m/v) thiourea elution solution by using ultrasonication power. Analytes concentrations in the eluent

New Generation Green Solvents for Separation and Preconcentration

3.3 New-generation solid phase extraction methods

phase were measured by ICP-MS. The limits of detection for analytes were between 24 and 56 pg L21 [189]. Suleiman et al. have used bismuthiol-II-immobilized silica-coated magnetic nanoparticles for the separation and preconcentration of trace amounts of Pb, Cu, and Cr in lake and river water samples. Analytes in the aqueous phase were extracted to 100 mg of the magnetic nanosorbent phase at pH 7.0 by using an ultrasonic irritation source. A solution of 1.0 mol L21 HNO3 was used to desorp analytes from the sorbent. Concentrations of analytes were measured by ICP-OES [190]. A important application of the magnetic sorbents—on-chip, online solid phase extraction— was reported by Li et al. in 2009. The authors fabricated a poly(dimethylsiloxane)(PDMS)/ glass hybrid microchip for online solid phase extraction (SPE) and electrophoresis separation of the trace amount of fluorescence isothiocyanate (FITC)-labeled phenylalanine (Phe). The extraction phase was prepared by modifying the magnetic microspheres with hydroxylterminated poly-dimethylsiloxane (PDMS-OH). The extraction phase was conveniently immobilized into the solid phase extraction channel by magnetic field. In this system, injection of the sample solution into the SPE channel (PDMS-OH microspheres bed), and the desorption of analyte from the sorbent phase into the electrophoresis channel was electrically driven [191]. Cheng et al. have used 1-hexadecyl-3methylimidazolium bromide (C16mimBr)coated Fe3O4 magnetic nanoparticles (NPs) as a magnetic adsorbent for mixed hemimicelles solid phase extraction of trace amounts of 2,4dichlorophenol and 2,4,6-trichlorophenol compounds in environmental waters, followed by HPLC-UV analysis. The new nanosized sorbent provided a high surface area that led to high adsorption capacity and high extraction efficiencies (74%
90%) at a minimum level of sorbent (40 mg) [192]. Jiang et al. have used zincon-immobilized silica-coated magnetic Fe3O4 nanoparticles for the magnetic solid

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phase extraction of trace amounts of lead in water samples prior to graphite furnace atomic absorption spectrometric (GFAAS) determination. The detection limit (LOD), enrichment factor (EF), and recovery results of the proposed method were found as 10 ng L21, 200, and 84%
104%, respectively [193]. Cui et al. have prepared chitosan-modified magnetic nanoparticles by an emulsion method for the magnetic separation and preconcentration of Cr(III) and Cr(VI) in lake and tap water samples prior to ICP-OES detection. The LOD, PF, and RSD% for Cr(III) and Cr(total) were found as 100, 0.02, and 0.03 ng mL21 and as 4.8% and 5.6%, respectively [194]. Ferrofluid-based SPME method is another important application of solid phase extraction. Ferrrofluid is a magnetic fluid that is prepared by dispersing magnetic nanoparticles in the ionic liquids or surfactants homogeneously. The fluids obtained in this way show magnetic features and can be controlled by an external magnetic field. Hence ferrofluids are used in many applications such as SPE, magnetic resonance imaging (MRI), magnetophoretic control, drug delivery, and the like. Gharehbaghi et al. have prepared an ionic liquid ferrofluid and have used it as the extraction phase for dispersive magnetic solid phase extraction of Cd(II) ions in water samples, followed by FAAS detection. In this procedure, prepared ferrofluid was added to the sample solution, and the mixture obtained was shaken to ensure the dispersion of the ferrofluid phase into the sample solution. At this stage, the hydrophobic analyte complex was adsorbed/extracted to magnetic sorbent particles. After completion of the extraction stage, magnetic particles were collected by applying an external magnetic field, and analyte was eluted for FAAS analysis. When compared with other MSPE procedures, this method is faster, and its applicability and usability are simpler for opaque/dark samples, in which observation and separation of the extraction phase are difficult [199].

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Wang et al. have used a hydrothermal reaction procedure to synthesize a Fe3O4-functionalized metal-organic framework (m-MOF) composite as a MSPE sorbent. They have synthesized the metal-organic framework from Zn (II) and 2-aminoterephthalic acid. X-ray diffraction, FT-IR, TGA, SEM, and magnetization methods were used for the characterization of m-MOF composite. The new magnetic sorbent was used for the separation and preconcentration of trace amounts of copper, followed by ETAAS detection [195]. Azodi-deilami has used magnetic molecularly imprinted polymer nanoparticles (m-MIPs) as a magnetic solid phase extraction sorbent for trace amounts of paracetamol in human blood plasma samples. In the synthesis of the m-MIPs, magnetite (Fe3O4) as the magnetic component, 2-(methacrylamido) ethyl methacrylate as a cross-linker and methacrylic acid as a functional monomer were used. The m-MIPs synthesized were characterized by TEM, FT-IR, XRD, and vibrating sample magnetometry methods. Analysis of paracetamol in the last phase was measured with HPLC. The LOD, LOQ, PF, and RSD% recoveries for paracetamol were 0.17 μg L21, 0.4 μg L21, 40, and 4.5%, respectively [196]. Pan et al. have prepared a planar-structure amine-functional magnetic polymer-modified graphene oxide nanocomposite sorbent (NH2MP@GO) for the magnetic solid phase extraction of trace amounts of pentachlorophenol (PCP), 2-chlorophenol (2-CP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,4-dichlorophenol (2,4DCP), and 2,3,4,6-tetrachlorophenol (2,3,4,6TeCP). Concentrations of analytes were measured by LC-MS/MS. The MSPE method provided a very high preconcentration factor (1000) and good recovery results between 86.4% and 99.8% [197]. In a different MSPE application, scientists used magnetic multiwalled carbon nanotube composites (MMWCNTs) for the separation and preconcentration of trace amounts of linear alkylbenzene sulfonates from environmental water

samples. They have prepared MMWCNTs by using a one-pot chemical coprecipitation procedure. In this procedure, analytes in 500 mL of water sample were extracted with 100 mg of sorbent into 1.0 mL of eluent, and analysis of trace amounts of linear alkylbenzene sulfonates in eluent was carried out by HPLC [198].

3.3.4 Immunoaffinity solid phase extraction The need for the development of analytical methods that provide improved selectivity and sensitivity has accelerated studies on the development of antibodies that can be used in the detection of trace-level antigen-target analytes. Antibodies have been used frequently in environmental studies since the early 1970s. Antibodies are used in biosensors, affinity chromatography, and, very popularly, immunoanalysis such as the ELISA method (enzyme-linked IS [immunosorbent] assay). Scientists have come up with the idea that antibodies with high specificity and selectivity can be used in solid phase extraction studies and have developed a new sample preparation method called immunoaffinity solid phase extraction (IASPE) [124]. ISs are obtained by attaching relatively matched antibodies in monoploid or polyploid form onto a solid support material. In order for the antibodies to be able to function actively after this procedure, the physicochemical properties of both the antibody and the support material must be compatible with each other, and the experimental conditions must be strictly controlled. Although agarose gel and silica beads are used most often as support material, the usability of alumina, glass, or polystyrenedivinylbenzene polymers and the like have been searched and compared to silica, the desired performance could not be achieved [125,126]. The online or offline mode of immunoextraction procedures is applicable for trace

New Generation Green Solvents for Separation and Preconcentration

3.3 New-generation solid phase extraction methods

analytes. The determination of analytes in the last phase is usually performed with chromatography techniques (HPLC, GC) or capillary electrophoresis (CE). Imprinted antibodies show high specificity for analytes. Hence the immunoextraction procedure is a very effective application for the preconcentration and extraction of trace analytes in a biological and environmental sample matrix. The first extensive report explaining the advantages of the combination use of immunoextraction methods with a separation technique (HPLC) was published by Farjam et al. In this study, ISs were used for the separation and preconcentration of aflatoxin in milk samples and of testosterone and estrogen hormones in urine and plasma samples [127].

3.3.5 Microextraction in a packed syringe Microextraction in a packed syringe (MEPS) is an effective sample preparation technique resulting from the miniaturization of conventional SPE. In this method, the amount of sorbent in grams levels is reduced to milligrams levels. In the MEPS method, effective separation and enrichment are achieved despite the use of a milligram sorbent. MEPS apparatus is a microsyringe with a volume ranging from 100 to 250 μL. Approximately 1 mg of the sorbent is placed between the injector and a plug or barrier. The sample solution containing the relevant analytes is drawn into this syringe system, during which the analytes are adsorbed on the sorbent [128,129]. After the adsorption process is completed, the analytes are desorbed with a suitable eluent and analyzed. Similar sorbents used in conventional SPE are used in the MEPS method. When compared with other separation and preconcentration techniques, the MEPS method offers users significant advantages such as quick and simple operation steps, higher enrichment factors, lower consumption of sample and solvent

137

(about 10 μL), and the reuse of the MEPS devices multiple times. Due to these important advantages, MEPS can be used in the determination of a wide range of analytes such as organic pollutions, pesticides, azo dyes, drugs and their metabolites, and flavanoids in different types of sample matrices [128,129,200,201].

3.3.6 Molecularly imprinted solid phase extraction Sellergren has introduced the molecularly imprinted solid phase extraction (MISPE) for the first time in 1994 [202]. Since that time, MISPE has been improved and has found an important place in the separation and preconcentration of different trace analyte types because of their unique advantages, including (1) applicability for a wide range of analytes, (2) high chemical and mechanical stability, (3) simple and cheap preparation, (4) predetermined recognition capability, among others [203,204]. MIPs are synthetic polymers used in SPE procedures because of their predetermined selectivity toward a particular analyte or set of analytes [203
206]. In the most commonly used production method, the monomers form a complex with a template by covalent or noncovalent interactions and are joined by the addition of a cross-linking agent to the production medium. MIPs that used as sorbents in SPE methods can be produced with three different imprinting methods: 1. Covalent imprinting 2. Noncovalent imprinting 3. Semicovalent imprinting Online and offline modes of MISPE are applicable for trace analytes. The two applications are similar with conventional SPE methods. An extraction cartridge, including a small amount of imprinting polymer (15
500 mg), is

New Generation Green Solvents for Separation and Preconcentration

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3. Type of new generation separation and preconcentration methods

used in the MISPE system. After conditioning the solid phase, the sample solution is passed through the imprinting polymer in the cartridge. Analytes adsorbed on the imprinting polymer are eluted and analyzed with a suitable detection system. The major disadvantage of these methods, despite the significant advantages just discussed, is that they are time-consuming [204
208].

3.3.7 Dispersive micro-SPE The basis of the dispersive micro-SPE (DMSPE) method is to distribute the sorbent at the microgram level in the solution in which the analyte is contained, thereby forming a high surface area and accordingly increasing extraction efficiency and selectivity. DMSPE was first used in 2003 and has made significant progress since then [209]. In this method, the microgram level of the sorbent is injected into the sample solution by means of a dispersing liquid phase. In this method, the microgram level of the sorbent is injected into the sample solution by means of a dispersing liquid phase. To obtain the maximum surface area of the sorbent in the solution for better distribution, the resulting mixture is subjected to ultrasonic vibration, vortex mixing, and so on. After completion of the adsorption process, the solid phase particles in the suspension are separated by centrifugation or filtration. After completion of the adsorption process, the solid phase particles in the suspension are separated by centrifugation or filtration. The analytes of interest on the sorbent are eluted by a suitable solvent or thermally and analyzed by an appropriate detection system. Since the surface area of the sorbent is maximized in this method, when compared with conventional SPE methods, faster equilibrium is achieved, and the equilibrium ratio is increased, resulting in a higher extraction yield and faster sample preparation time [209
213].

As in all other SPE methods, the efficiency of the extraction, the extraction time, and the ease of the system studied in DMSPE depend on the type of sorbent used in the first order. The sorbents used in DMSPE must meet certain requirements, such as high adsorption capacity and large surface area, to ensure rapid, quantitative adsorption and desorption, and high dispersibility in liquid samples. Carbon-based nanomaterials such as CNTs, graphene, fullerene, metal oxide nanomaterials such as SiO2, TiO2, Al2O3, among others, magnetic nanomaterials such asFe3O4, γ-Fe2O3, ZnFe2O4, ZnFe2O4, and the like, and nanofibers have the characteristics that can meet most of these requirements. Moreover, the functionalization of these nanomaterials with polymers, complexing agents, organic compounds, bioactive species such as DNA, RNA, enzymes, and so on is a sound and effective way to ensure selective sample extraction [209
213].

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119. [193] H.M. Jiang, Z.P. Yan, Y. Zhao, X. Hu, H.Z. Lian, Zincon-immobilized silica-coated magnetic Fe3O4 nanoparticles for solid-phase extraction and determination of trace lead in natural and drinking waters

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256. C. Cui, M. He, B. Chen, B. Hu, Chitosan modified magnetic nanoparticles based solid phase extraction combined with ICP-OES for the speciation of Cr (III) and Cr (VI), Anal. Methods 6 (21) (2014) 8577
8583. Y. Wang, J. Xie, Y. Wu, X. Hu, A magnetic metalorganic framework as a new sorbent for solid-phase extraction of copper (II), and its determination by electrothermal AAS, Microchimica Acta 181 (9-10) (2014) 949
956. S. Azodi-Deilami, A.H. Najafabadi, E. Asadi, M. Abdouss, D. Kordestani, Magnetic molecularly imprinted polymer nanoparticles for the solid-phase extraction of paracetamol from plasma samples, followed its determination by HPLC, Microchimica Acta 181 (15-16) (2014) 1823
1832. S.D. Pan, L.X. Zhou, Y.G. Zhao, X.H. Chen, H.Y. Shen, M.Q. Cai, et al., Amine-functional magnetic polymer modified graphene oxide as magnetic solidphase extraction materials combined with liquid chromatography
tandem mass spectrometry for chlorophenols analysis in environmental water, J. Chromatogr. A 1362 (2014) 34
42. B. Chen, S. Wang, Q. Zhang, Y. Huang, Highly stable magnetic multiwalled carbon nanotube composites for solid-phase extraction of linear alkylbenzene sulfonates in environmental water samples prior to high-performance liquid chromatography analysis, Analyst 137 (5) (2012) 1232
1240. M. Gharehbaghi, M.D. Farahani, F. Shemirani, Dispersive magnetic solid phase extraction based on an ionic liquid ferrofluid, Anal. Methods 6 (23) (2014) 9258
9266. Z. Altun, L.G. Blomberg, E. Jagerdeo, M. AbdelRehim, Drug screening using microextraction in a packed syringe (MEPS)/mass spectrometry utilizing monolithic-, polymer-, and silica-based sorbents, J. Liq. Chromatogr. Relat. Technol. 29 (6) (2006) 829
839. M. Abdel-Rehim, Recent advances in microextraction by packed sorbent for bioanalysis, J. Chromatogr. A 1217 (16) (2010) 2569
2580. B. Sellergren, Polymer-and template-related factors influencing the efficiency in molecularly imprinted solid-phase extractions, Trends Anal. Chem. 18 (3) (1999) 164
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[204] N. Masque, R.M. Marce, F. Borrull, Molecularly imprinted polymers: new tailor-made materials for selective solid-phase extraction, Trends Anal. Chem. 20 (9) (2001) 477
486. [205] A. Martin-Esteban, Molecularly imprinted polymers: new molecular recognition materials for selective solid-phase extraction of organic compounds, Fresenius’ J. Anal. Chem. 370 (7) (2001) 795
802. [206] C. Schirmer, H. Meisel, Synthesis of a molecularly imprinted polymer for the selective solid-phase extraction of chloramphenicol from honey, J. Chromatogr. A 1132 (1-2) (2006) 325
328. [207] E.C. Figueiredo, C.R.T. Tarley, L.T. Kubota, S. Rath, M.A.Z. Arruda, On-line molecularly imprinted solid phase extraction for the selective spectrophotometric determination of catechol, Microchemical J. 85 (2) (2007) 290
296. [208] E.C. Figueiredo, D.M. de Oliveira, M.E.P.B. de Siqueira, M.A.Z. Arruda, On-line molecularly imprinted solid-phase extraction for the selective spectrophotometric determination of nicotine in the urine of smokers, Anal. Chim. Acta 635 (1) (2009) 102
107. [209] K. Kocot, B. Zawisza, E. Margui, I. Queralt, M. Hidalgo, R. Sitko, Dispersive micro solid-phase extraction using multiwalled carbon nanotubes combined with portable total-reflection X-ray fluorescence spectrometry for the determination of trace

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742. M. Abbasghorbani, A. Attaran, M. Payehghadr, Solvent-assisted dispersive micro-SPE by using aminopropyl-functionalized magnetite nanoparticle followed by GC-PID for quantification of parabens in aqueous matrices, J. Sep. Sci. 36 (2) (2013) 311
319. M.C. Huang, H.C. Chen, S.C. Fu, W.H. Ding, Determination of volatile N-nitrosamines in meat products by microwave-assisted extraction coupled with dispersive micro solid-phase extraction and gas chromatography
Chemical ionisation mass spectrometry, Food Chem. 138 (1) (2013) 227
233. S. Mahpishanian, H. Sereshti, Graphene oxide-based dispersive micro-solid phase extraction for separation and preconcentration of nicotine from biological and environmental water samples followed by gas chromatography-flame ionization detection, Talanta 130 (2014) 71
77. F. Gala´n-Cano, R. Lucena, S. Ca´rdenas, M. Valca´rcel, Dispersive micro-solid phase extraction with ionic liquid-modified silica for the determination of organophosphate pesticides in water by ultra performance liquid chromatography, Microchemical J. 106 (2013) 311
317.

New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

4 New methodologies and equipment used in new-generation separation and preconcentration methods Mohammad Hossein Ahmadi Azqhandi1, Tahere Khezeli2, Mehrorang Ghaedi3 and Ali Daneshfar2 1

Applied Chemistry Department, Faculty of Gas and Petroleum (Gachsaran), Yasouj University, Gachsaran, Iran 2Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, Iran 3 Department of Chemistry, Yasouj University, Yasouj, Iran

4.1 The historical development and overview of these preconcentration and separation methodologies Separation, purification and preconcentration of different components from their complicated matrices by immiscible solvents and/or different source of receiving phase is vital task. These goals is possible by liquid
liquid extraction (LLE) and/or solid phase extraction (SPE) or their combination candidate. These protocols are the most commonly applicable techniques for such purposes. LLE suffers from points like being time-consuming and tedious and requiring the consumption of huge amounts of potentially toxic organic solvents [1,2]. The scientific knowledge corresponding to the separation process was studied extensively while it been

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00004-8

completely unknown [3]. Among the various extraction methods, most attention and interest were devoted to SPE owing to its advantages like low cost, simplicity, convenience, and time savings, while it has the capacity to combine with different detection procedures that can done online and/or offline [4
8]. Solid phase extraction from 1750 to 1970, despite its extensive applications, suffers from certain limitations including long procedure time, solvent loss, large secondary wastes, and so on [9,10]. The most popular sorbents used in the solid phase extraction technique are cellulose, silica, activated carbon, and polymer foams [11]. The first separation guidebooks defining basic elements was written by Baker [3]. Subsequently, more detailed and inclusive

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

phenomena were explained by Varian, Thurman, and Mills, specifically their findings on SPE, its design, optimization, and modification, as well as the investigation of properties of silicas as the solid phase [12]. Analytes monitoring and quantification in complicated matrices such as environmental, food, or biomedical samples, in which direct determination is not possible or which yield lower accuracy, are significantly improved via a preconcentration step prior to appropriate detection systems. Recently, a huge amount of research has been devoted to the improvement of the efficient and cost-effective miniaturized sample preparation approach associated with a significant reduction in solvents and other chemicals, such as the solid phase microextraction (SPME), stir-bar sorptive extraction (SBSE), single-drop microextraction (SDME), liquid phase microextraction (LPME), dispersive microsolid phase extraction (D-μ-SPE), and aqueous two-phase system (ATPS).

4.2 Hyphenated and nonhyphenated chromatographic techniques for extraction and/or separation of target compounds Hyphenated techniques (HPT) benefit from the advantages of the chromatography and spectroscopy methods Chromatography-based techniques supply pure or almost pure fractions of any target chemical from their mixtures. Spectroscopy, commonly combined with the separation technique, enables the quantitative monitoring of separated and/or extracted species. Hyphenated instrument applications started in 1960 [13] and generally are based on the connection between gas chromatography (GC) and mass spectroscopy (MS). The first report for coupling GC and MS was by Karasek [14]. In such a device, open tubular glass traps capture

the target species via a chromatography instrument for later analysis by a mass spectrometer [14]. Another innovation of this research group on this topic is the application of the slash separator. The “hyphenation” expression, coined initially by Hirschfeld, is based on the combination of chromatography (as a separation technique) and spectroscopy (as a detection technique). These techniques, due to the simultaneous benefits from both approaches, led to higher selectivity and improvement of results. [15]. HPT have the remarkable ability to solve and/or diminish problems with cost, toxicity, and time, in addition to other associated complex analytical problems. HPTs are based on the preliminary extraction and/or separation of the target by HPLC (high-performance liquid chromatography), GC (gas chromatography), or CE (capillary electrophoresis) and their subsequent characterization by spectroscopic methods, such as the Fourier-transform infrared (FT-IR), photodiode array UV-Vis absorbance or fluorescence emission, MS, and nuclear magnetic resonance spectroscopy (NMR) (Fig. 4.1). All attempts in the last decade by researchers and engineers led to the construction of high-technology hyphenated instruments like CE-MS, GC-MS, LC-MS, and LC-NMR, while HPLC is the most popular and widely tool and protocol for qualitative and quantitative purposes. On the other hand, MS and NMR are exceptional complementary tools for qualitative analysis. In recent years, the hyphenated LC-MS and LC-NMR techniques have gathered interest for the previously mentioned purposes, and accordingly LC-MS is highly recommended due to its greater sensitivity and selectivity toward LC-NMR. Recently, the new coupling between separation and spectroscopy has shown up in a number of techniques, including LC-PDAMS, LC-MS-MS, LC-NMR-MS, and LCPDANMR-MS.

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4.3 Ultrasound-assisted emulsification microextraction

SPE LVI Analytical preconcentration

FIGURE 4.1

Separation technique

Detection technique

GC or HPLC or CE

PDA or IR MS or NMR or TLS

Hypentation

Further detection technique Optional multiple hypentation

Hyphenated technique.

4.3 Ultrasound-assisted emulsification microextraction Ultrasound radiation is an acceptable and highly influential approach owing to its intensification the mass transfer of lead to the induction of dispersion phenomena, especially in liquid-based microextraction methods. The ultrasound-assisted emulsification microextraction (USAEME) procedure is based on the extraction solvent with the aid of ultrasound waves and its complex mixing with aqueous solution. The USAEME procedure was first reported by Wood and Loomis in 1927 [16] and continued until 2008, when the transfer predication of synthetic musk fragrances, phthalate esters, and lindane from their liquid samples was presented [17]. The USAEME procedure is usually based on the application of frequencies between 16 and 450 kHz [18]. Sonication leads to the generation of periodic acoustic pressure, which in turn leads to a rising temperature and the generation of microstream, consequently accelerating the extraction process. The role of sonication is based on cavitation, which is created via the formation and collapse of bubbles and friction at the interface, leading to intensive shock waves in the surrounding liquid and causing respective (high-speed) waves that disrupt droplets in the vicinity of the collapsing bubbles [19
21].

These events, in combination with elevated temperatures owing to cavitation and friction, lead to higher diffusion coefficients and enhanced mass transfer. Sonication is applicable because baths and/ or probes act as corresponding sonic radiation sources, especially due to the greater accessibility of ultrasonic baths that are homogeneous in their ultrasonic energy output and because a minimum ratio of liquid can be used very close to the source (sonication and cavitation decline in power over time). Furthermore, the heat owing to sonication easily evaporates tiny extractive solvents and enables the extraction of solvents with lower pressure. The volume lost destroys the performance of characteristic research procedures like repeatability and reproducibility. Ultrasonic probes may be operated in continuous-wave mode (CWM) or pulsed-wave mode (PWM), while the latter case is recommended for situations requiring longer sonication times. As previously mentioned, during sonication, sample temperatures rise with time and permit more temperature handling at fixed and/or internal values [22,23]. The ultrasound-assisted surfactant-enhanced mode is another type of USAEME, starting in 2010 for carbamate pesticides extraction and preconcentration from liquid samples [17]. Due to the amphiphilic nature of surfactants and possible presence of both hydrophobic and hydrophilic groups, they can exert a dual role

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

leading to the contribution and interaction of different forces, like Van der Waals, and in some situations admicelle and/or hemimicelle effects following trapping. Surfactants are soluble in organic solvents and water, and consequently they especially lead to significant reductions in the surface tension of water via adsorption at the liquid
gas interface. Surfactants are also able to diminish the interfacial tension between oil and water by adsorbing at the liquid
liquid interface. Based on their unique properties, surfactants are able to act as emulsifiers to thoroughly disperse a water-immiscible phase with the aqueous phase. This consequently, via the construction of fine droplets of extraction solvent in the aqueous sample following ultrasound irradiation, enhances contact interface and mass transfer and reduces extraction time. An ultrasound-assisted polymer surfactant
(sodium alginate
) enhanced emulsification microextraction was designed that was able to simultaneously preconcentrate and consequently determine 2,4,5-trimethylaniline (TMA), 4-chloroo-toluidine (CT), 4-aminoazobenzene (AAB), 3,30 -dimethyl-4,40 -diaminobiphenylmethane (DMDAB), 3,30 -dimethylbenzidine (DMB), 3,30 -

FIGURE 4.2

dichlorobenzidine (DCB), 4,40 -methylene-bis-(2chloroaniline) (MBCA), and 3,30 -dimethoxybenzidine (DMOB) in water samples [22]. USAEME based on deep eutectic solvent (DES) has exhibited high efficiency in the extraction of Patent Blue V in syrup and water samples. Herein, choline chloride/phenol DES and tetrahydrofuran were applied to represent the role of extraction and emulsifier solvents, respectively. As is well-known, generally sonocavitation may be associated with the degradation of organic molecules, which avoids, prior to the microextraction step and in all stages, the degradation risk of Patent Blue V controlled in the ultrasonic bath for 1 h. Absorbance of Patent Blue V as a signal of the procedure was monitored sequentially by using UV-Vis spectrometry at 627.5 nm (λmax), and the experimental results revealed the least degradation. The schematic procedure is shown in Fig. 4.2 [24,25]. A creative centrifuge-less USAEME followed by HPLC-UV is applied for the separation, preconcentration, and quantification of some phthalate esters in aqueous samples. An extraction solvent of 1-undecanol is mixed completely with a solution of analytes and

Schematic of USAEME procedure utilized by Ghaedi et al. [24] (License Number 4662450649566).

New Generation Green Solvents for Separation and Preconcentration

4.4 Cloud point extraction

immersed in an ultrasonic bath to intensify the mass transfer processes. After sonication, the emulsion formed is passed through a small column filled with NaCl as a separation reagent, which consequently, owing to salting-out phenomena, leads to the flotation of droplets of 1undecanol on the surface of the mixture. In a later stage, these are easily collected as a separate layer [26]. Practical applications of USAEME for analyte extraction from samples with a different matrix are shown in (Table 4.1).

4.4 Cloud point extraction Cloud point extraction (CPE) is an alternative suitable separation approach that is undoubtedly an adaptable and simple route based on the unique properties of each surfactant to form a cloudy state following its heating until reaching a certain temperature and then subsequently cooling. It is notable that, during these stages, the surfactant reach phase at the bottom of vessels, owing to the appearance of interior cores, is able to trap or accumulate analytes. CPE uses the nonionic, zwitterionic surfactants or even a mixture of surfactants in aqueous solutions that depend on experimental conditions like pH, temperature, and ionic strength to produce micelles and that turn turbid after heating to a cloud point temperature (CPT), an event that is accelerated in the presence of a salting-out agent. At temperatures beyond CPT, as mentioned, the solution converts into two phases: (1) the dilute phase with surfactant and (2) the surfactant concentrated phase, namely the coacervate phase (containing the micelles). However, above the CPT, sometimes more than two phases may be achieved and formed, owing to the polydisperse nature of surfactants in an aqueous environment and showing deviation from the Gibbs phase rule (Fig. 4.3).

153

The first CPE application was done by Watanabe and coworkers in 1972 [42], which suggested it to be a promising and exceptionally high enrichment and preconcentration approach for the preconcentration of metals [42
48]. The theoretical background, processing extraction, and preconcentration of inorganic and organic components were accomplished by this simple and low-cost approach, especially by replacement of toxic organic solvents with cheaper and environmentally friendly surfactants. A summary of the power of CPE was accessible in 1982 [49], and a huge effort was put into evaluating the CPE technique in 1985. Accordingly, several modifications of classic CPE have been suggested. In the recent years, the development of CPE method was successfully progressed by several scientific groups by coupling this method with different techniques. For example, the coupling of CPE with ultrasound irradiation and magnetite SPME was optimized by Ghaedi et al. In this work, the CS-GO-Zn:Fe2O4 nanocomposite was fabricated and characterized, and subsequently the effect of the CS-GO-Zn:Fe2O4 dose, sonication time, pH, temperature, and Cr (III) on the extraction rate of chromium ion were examined by experimental design and optimized by the desirability function approach (DFA) [50] (see Fig. 4.4). In similar work, Ghaedi et al. applied ultrasound irradiation, CPE, and magnetite solid phase extraction to generate a new procedure for the simultaneous removal of Cu21, Ni21, Cd21, and Pb21 ions. In this work, the bismuth (III) phosphate/iron (III) phosphate nanoparticles trapped in chitosan gel was hydrothermally synthesized, characterized, and used as the solid phase. Subsequently the influential parameters such as temperature of sample, initial metal ions concentration, solid phase dose, and sonication time were explored by central composite design (CCD) and optimized by DFA [51] (see Fig. 4.5).

New Generation Green Solvents for Separation and Preconcentration

TABLE 4.1 Some applications of the USAME method. Matrix

Extraction solvent

Emulsifier

Analytes

Traditional Chinese medicine, Xianhui

deep eutectic solvent

Tetrahydrofuran- triadimenol, fipronil, tebuconazole, hexaconazole, and diniconazole assisted ultrasonic wave

[27]

Honey samples

1,2-dibromoethane

Ultrasonic wave

chlorthalonil, chlorpyrifos, dicofol, o,pʹ 2 2- (2-chlorophenyl) 2 2-(4chlorophenyl) 2 1,1-dichloroethene, p,pʹ-DDE, o,pʹdichlorodiphenyltrichloroethane, and p,pʹdichlorodiphenyldichloroethane

[28]

Urine samples

ethyl acetate,

Ultrasonic wave

methylparaben, ethylparaben, propylparaben, and butylparaben

[29]

Hookah water

chloroform, 1,2-dichloroethane, and Ultrasonic wave 1,2-dichlorobenzene

naphthalene, fluorene, anthracene, chrysene, and benzo[a]pyrene, biphenyl

[30]

Herbal medicines

toluene

Ultrasonic wave

Pb and Cr, Cd

[31]

Water and wastewater samples

chloroform, bromoform, 1,2dichlorobenzene, dichloromethane, and1,2,4-tichlorobenzene

Ultrasonic wave

2-chlorophenol, 2,6-dichlorophenol, 2,4,5-trichlorophenol, 2,3,4,6tetrachlorophenol, and pentachlorophenol

[32]

Wastewater, well water, and tap water

carbon tetrachloride

Ultrasonic wave

uranium and thorium

[33]

Spirits samples

carbon tetrachloride

Ultrasonic wave

acenaphthene, fluorene, phenanthrene, anthracene, pyrene, benz[a] anthracene, chrysene, benzo[k]fluoranthene, benzo[a]pyrene, benzo [ghi]perylene, dibenz[ah]anthracene, indeno[1,2,3-cd] pyrene

[34]

Tap and hookah water

tetrachloroethylene

Ultrasonic wave

acenaphthylene, anthracene, benz[a]anthracene, benzo[b]fluoranthene, [35] benzo[k]fluoranthene, benzo[ghi]perylene, benzo[a]pyrene, chrysene, dibenz[a,h]anthracene, fluorene, indeno[1,2,3-cd]pyrene, phenanthrene, and pyrene

Urin

1
heptanol

Ultrasonic wave

Methylmalonic Acid

[36]

Tap, sea, river water

1-octanol

Aliquat-336 assisted by ultrasonic wave

metsulfuron-methyl, chlorsulfuron and bensulfuron-methyl

[37]

Milli-Q water, tap water, seawater, spa water, swimming pool water, and river water

chloroform

Ultrasonic wave

UV filters (2-ethylhexyl methoxycinnamate, 4- methylbencylidene camphor, benzyl salicylate, ethylhexyl dimethyl PABA, ethylhexyl salicylate, etocrylene, homosalate, isoamyl methoxycinnamate, menthyl anthranilate and octocrylene)

[38]

Mineral water samples bottled

tributylphosphate

Ultrasonic wave

Cr speciation

[39]

Fruits and vegetables

deep eutectic solvent

Tetrahydrofuran- quercetin assisted ultrasonic wave

[40]

Urine

carbon tetrachloride

Ultrasonic wave

[41]

celestolide, phantolide, traseolide, galaxolide, tonalide musk xylene, and musk ketone

References

4.5 High-diffusion liquids

4.5 High-diffusion liquids Classical LLE and SPE methods are based on separation and/or extraction of each substance from others according to their

FIGURE 4.3

Schematic of liquid-coacervate extraction.

155

distinguishing polarity and solubility characteristics. However, a solid-state sample must be preliminarily dissolved in the appropriate solvent. In these methods, the separation process typically lasts a few hours to several days depending on the temperature, type, and volume of the aqueous and organic phase volumes. Over time, these techniques were modified and replaced by more attractive approaches. The Soxhlet [52] (from 1879) and sonication-based extractions [53] (developed in 1960) are popular and widely applicable extraction techniques. Such traditional approaches and conventional protocol are known as multistep procedures, and each step before analysis is followed by successive cleanup steps. These pretreatments lead to the

FIGURE 4.4 Schematic of presentation of the coupling of CPE with ultrasound irradiation and magnetite SPME utilized by Ghaedi et al. [50] (License Number 4662450982888).

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

FIGURE 4.5 Schematic of presentation of proposed extraction utilized by Ghaedi et al. [51] (License Number 4662451225528).

consumption of large amounts of sorbents, samples, and organic solvents, owing to their high number of stages. In addition to the large consumption of toxic or hazardous solvents and chemicals, their lack of accuracy and precision limit their application. These drawbacks were eliminated and/or diminished using techniques employing highdiffusion liquids that have been successfully applied in the developed methods. The principle of such approaches is based on enhancement of the diffusion coefficient with temperature and pressure. Such a protocol is based on high diffusion at higher temperatures and pressures, namely microwave-assisted extraction (MAE) and pressurized liquid extraction (PLE). These methods use significantly less organic solvent and provide a very fast and rapid extraction process. It was mentioned that raising the temperature of liquids from 30 C to 150 C is proportional to a diffusion rate increase of about 2- to 20-fold [54]. Supercritical fluid extraction (SFE) is another related extraction technique that typically uses

carbon dioxide at pressures and temperatures above 74 atm and 31 C, respectively. Such an approach, owing to the closeness of carbon dioxide properties at such pressures and temperatures, is similar to a liquid phase and has liquid-like density and low viscosity.

4.6 Pressurized liquid extraction The intended green technology outcome is the reduction of environmental hazards and toxic materials and the limitation of their subsequent negative human and living impacts. This has led to efforts to create new designs and instruments to reduce or even eliminate the use of hazardous materials, including toxic metal ions. The green chemistry platform definition, started by Anastas and Warner, is to remove or reduce carcinogenic organic compounds and/or solvents [55]. Traditional extraction methods (e.g., Soxhlet and sonication extraction), however, came with disadvantages that made these methods tedious,

New Generation Green Solvents for Separation and Preconcentration

4.7 Microwave-assisted extraction

time-consuming, and consumers of large amounts of samples, sorbents, and organic solvents, with the associated costs of extraction, human health aspects, and negative environmental impacts [56]. PLE is based on the extraction of analytes using liquid solvents at elevated temperatures and pressures that are strongly superior to the same extractions at ambient temperature in terms of efficiency and selectivity. PLE via thermal pressure leads to higher mass transfer and improvement of solubility properties. The PLE technique introduced by the Dionex Company in 1995 and its complementary version is called accelerated solvent extraction technology (ASET). The PLE is also known as pressurized solvent extraction, pressurized liquid extraction, enhanced solvent extraction, and accelerated solvent extraction. The PLE technique is based on the application of water as a solvent under the nomenclature of pressurized hot water extraction, subcritical water extraction, or superheated water extraction [56]. PLE is applicable for a wide range of analytes with different polarities, and it can reveal involved influencing factors, including temperature, extraction time, type of solvent, water content, and sample particle size. The optimization of these factors has been examined by Camel [57], as exemplified in (Fig. 4.6).

157

4.7 Microwave-assisted extraction Microwave energy is applicable for the extraction of organic constituents from solid samples such as foods, seeds, and soil and was used as far back as 1986 for the extraction of crude fat, antinutritives, and organophosphate pesticides, as investigated by Ganzler et al. [58]. This technique is based on the insertion of a treated sample into a conventional household microwave oven for 30 s and the replication of this process several times. The sample is cooled and subsequently centrifuged, and its respective supernatant aqueous are analyzed by HPLC. Consequently, according to the experimental results, the MAE technique was more efficient than Soxhlet extraction. Salgo et al.’s research in 1987 [52] is based on the extraction of gossypol and pyrimidine-glucosides from raw meal and vicia faba by MAE. According to the Environmental Protection Agency (EPA) recommendation and based on operational conditions, MAE can be considered a green method, an idea based on its rapidity and lowered energy usage. The automated MAE has remarkable ability and possibility for the simultaneous extraction of multiple samples through simple and accessible routes. The Soxhlet and solvent extraction methods, most conventional and widely available approaches, FIGURE 4.6 Influential factors on the PLE by Mustafa et al. [56] (License Number 4662270284212).

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

suffer from essential restrictions. For example, Soxhlet extraction requires hours to days and high volumes of toxic organic solvents (hundreds of milliliters). In contrast, MAE can reduce the average extraction time to below 20 min, simultaneously diminishing solvent consumption to values less than 20 mL and having unique ability to simultaneously extract up to 12, 24, or even 50 species [59], and respective recoveries by MAE re comparable to and/or higher than those of the traditional methods. Microwaves are a form of electromagnetic radiation, constructed of two perpendicularly oscillating fields, including the magnetic and electrical fields, with frequencies between 300 MHz (1 m) and 300 GHz (1 mm) [60]. Microwaves are widely applied in professional instruments, such as radio astronomy, spectroscopy, wireless networks, radar, satellite, cancer treatment, remote, industrial foods, and cooking food.

FIGURE 4.7

The microwave radiation-based approach (MAE) requires preliminarily heating the mixture samples (solvents and solid samples) and liquid samples or solid samples (i.e., fresh tissues). Heating samples leads to the partition of the compounds from complicated matrices into the solvent. The microwave heat, in contrast to traditional methods, is accomplished with the lowest temperature gradients and the most direct heat transfer to the solution. Microwave energy causes molecular motion in two ways: movement of ions and rotation of dipoles. The influence of microwave radiation is forcefully dependent on the properties of the solvent and the matrix. Regularly, the applied solvent in the MAE has a high dielectric constant that makes it a candidate for powerfully absorbing the microwave rays. Rarely, the sample matrix may be heated by the microwaves so that the compounds are separated from the mixture and released into the cold solvent (e.g., in the apolar solvents like chloroform and/or hexane) (see Fig. 4.7).

(A) Experimental setup for MAE; (B) traditional extraction experiment [61] (License Number

4662270522006).

New Generation Green Solvents for Separation and Preconcentration

4.9 Supercritical fluid extraction

4.8 Vacuum microwave-assisted extraction The conduction of MAE in open mode (airMAE) is performed at a mixture temperature close to the solvent boiling point, but this temperature is usually too high for thermosensitive and oxygen-sensitive biological mixture. Compound degradation during MAE at high operating temperatures was inhibited by vacuum microwave-assisted extraction (VMAE), which has since been developed. The first report of the VMAE technique is devoted to the extraction of resveratrol and emodin from R.P. Cuspidati, myricetin, and quercetin from M. rubra leaves, and safflomin A from F. Carthami [62]. The extraction conditions, including solid:liquid ratio, extraction time, extraction temperature, and degree of vacuum, strongly affect performance of this procedure, and these parameters’ contribution to the signal must be investigated [62]. The other pioneering work in the VAME technique is based on the combination of the VMAE and magnetic molecular
imprinted polymer beads and its subsequent application for the extraction, enrichment, and cleanup of auxins in plants, while the determination and monitoring of analyte content were done by HPLC and fluorescence detection (FL) [63].

4.9 Supercritical fluid extraction Raising fluid temperatures and pressure to values beyond the critical point leads to the construction of SFE [64]. Beyond the critical point, the fluid physical properties significantly change as the fluid behaves as a solvent. The first experimental works with SFE started back in the 1822, when the gas
liquid boundary at a specific temperature and pressure was studied; experimental results confirmed that this boundary becomes extinct following the

159

raising of the temperature [65]. Forty-seven years later (1869), following the suggestion of a critical point by Thomas Andrews led to the first report on the application of SFE [66]. The solvating power of supercritical ethanol (Tc 5 243 C; Pc 5 63 atm) for some metal chlorides, including CoCl2 , FeCl3 , KBr, and KI; reveal that these salts’ content in supercritical fluid was much higher than in their vapor phase [65]. Supercritical fluid (SF) is a substance between gas and liquid that represents mixed properties and possesses both their benefits. The viscosity of SF is comparable to a gas, while SF density is similar and close to liquid values. Moreover, the diffusivity of SF is intermediate (i.e., between liquids and gases). The surface tension and solvent strength properties are altered in a SF. The properties of a SF at the critical point, their comparison to those of the parents’ phase, like gas and liquid, and their influence on extraction performance significantly contribute to the performance of SFE and has been reviewed comprehensively in literature [67,68]. The high densities of SF supply greater solubilization, whereas low viscosities are proportional to higher diffusion in solids. Adjusting the pressure and temperature around the critical points affects the properties of SF, increases the penetration of the SF, and strongly affects the extraction of targeted molecules from the mixture sample [69]. Conventional methods applicable at high temperatures suffer from such drawbacks as using a high amount of organic solvents and consequent product contamination with solvent residues. These limit and/or diminish SFE, which gets great attention for the fractionation of oils (plant and animal) in the medical and food industries [70]. Carbon dioxide, water, methanol, ethylene, ethane, n-butene, and n-pentane are some of the supercritical fluids mostly used [69]. These are superior to others in terms of lower cost,

New Generation Green Solvents for Separation and Preconcentration

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

availability, and better performance in most situations under mild conditions near to ambient temperature and pressure. Among the SCFs just mentioned, carbon dioxide is an ideal fluid for extraction and is considered a green and safe solvent for the food industry while being cheap and easily available. Also, carbon dioxide is an industrial by-product, and CO2 application in extraction processes avoids its hazards like household effects and facilitates its reuse. Another important factor about CO2 that makes this composition more attractive is that CO2 is a gas under room conditions. In an extraction process via a reduction in pressure, it is automatically evaporated, and a simple and economic phase separation occurs. CO2 has very low polarity, and this disadvantage makes it suitable for the extraction of highor medium-polarity compounds [71].

4.10 Dispersive liquid
liquid microextraction Dispersive liquid
liquid microextraction (DLLME), as Rezaee et al. suggested in 2006 based on miniaturized analytical techniques, is applied to the preconcentration of organic and inorganic analytes from aqueous matrices [72]. This method involves the application of a ternary solvent component consisting of the aqueous phase (a water-immiscible solvent or extraction solvent) and a polar water
miscible solvent (dispersive solvent) [72,73]. A mixture of the extraction (μL) and disperser solvent (mL) is injected into an aqueous sample to form a cloudy solution and, owing to the formation of the emulsified phase, generates a very extensive contact area between the aqueous phase and the extraction solvent that consequently enhances mass transfer, preconcentration factor, and detection limit and strongly diminishes extraction time [74,75]. The sample is then centrifuged to break down the emulsion, and subsequently the extracted

organic solvent, which generally includes (highly toxic) halogenated hydrocarbons and carcinogens, is separated. These solvents, due to their heavier nature and their higher-thanwater density, sink to the bottom of the centrifugation tube, so that the final separation is a significant problem. DLLME efficiency depends on various factors, such as types and volumes of extraction and disperser solvents, extraction time, sample volume, pH, and salt addition [76]. The general requirements and necessities assigned to extraction solvents in DLLME are as follows: 1. No and/or least immiscibility with water to allow simple and facile phase separation and proper analyte partitioning in order to achieve complete and the almost exhaustive separation and extraction of analytes: Therefore, the polar and hydrogen bonding ability of organic solvents such as methanol, acetonitrile, and acetone are excluded. 2. Density higher than water to collect sediment at the bottom of the centrifuge tube: Chloroform, methylene chloride, and carbon tetrachloride, despite their toxic nature and so on, are promising and talent materials to achieve such goals. 3. Lower volatility of organic solvents to avoid solvent loss by evaporation: The extraction process target is retrieving the analyte in the least and constant amount of organic solvent that leads to the exhaustive and/or equilibrium status of the reaction. Changing the volume can destroy and at least affect both equilibrium and preconcentration. 4. High partition coefficient to ensure preferential distribution in the organic droplet. 5. Miscible with disperser solvent, while having a higher tendency and ability to bind with and enrich analyte(s). 6. Compatible with analytical instrumental methods.

New Generation Green Solvents for Separation and Preconcentration

4.10 Dispersive liquid
liquid microextraction

The main and essential requirement of the disperser solvent is its acceptable solubility and miscibility with both organic and aqueous phases. Accordingly, solvents like methanol, ethanol, acetone, and acetonitrile are commonly applicable candidates for such purposes. One of the extensive goals of up-to-date chemistry is replacing toxic and environmentally incompatible solvents with lower-toxicity and economically feasible alternative solvents to prevent consequent pollution of the natural environment due to the noxious action of organic solvents and/or chemicals. Recently, different types of solvents, such as lighter-than-water organic solvents [77], ionic liquids (IL) [78], supramolecular solvents [79], deep eutectic solvents (DESs) [80], and switchable solvents [81,82], have been successfully applied as extraction solvents in DLLME. DLLME is a rapid and efficient extraction approach that provides high preconcentration factors, while suffering from very timeconsuming steps, including the extracting phase, but the time taken can be eliminated or diminished with the introduction of modern setups and procedures. The current DLLME limitation is the two-step extraction mechanism from the sample solution into the extracting phase, which tremendously decreases the sample cleanup and causes difficulty in the analysis of complicated samples [83]. A bio-DLLME method is devoted to the extraction of paracetamol from human urine samples. Rhamnolipid biosurfactants denote that the role of the extraction solvent is superior to that of conventional DLLME in terms of rapidity and greater environmental friendliness, making them candidates for current green chemistry trends. On the other hand, bioaggregates assigned to bio-DLLME are more stable than the colloidal phase in conventional DLLME, and this is attributed to the fact that rhamnolipid biosurfactants are active even at extreme temperatures, pH, and salinity [84
87].

161

SPE coupling with DLLME leads to higher sensitivities than that of each separate procedure. The experimental route is based on the preliminary extraction of species from the sample solution using the solid phase (C8-modified magnetic graphene oxide), and subsequently accumulated species were eluted and reserved for a later stage, that is, DLLME for further enrichment [88]. A binary solvent
based DLLME was applied for the extraction and preconcentration of eight hazardous aromatic amine products of azo dyes in wastewater and textile samples. The use of an extraction solvent, while under study, has diverse extraction efficiencies for simultaneous preconcentration and subsequent analysis. Binary solvents, as mentioned, enhance the extraction efficiencies of multiple analytes by combining two or more extraction solvents [89]. Cortisone and cortisol in human saliva have been simultaneously determined using IL-DLLME, followed by LC separation and UV-Vis detection. The IL, based on 1-butyl3-methylimidazolium hexafluorophosphate [C4MIM][PF6], and methanol were used as the extraction and dispersive solvents, respectively [90]. A novel hydrophobic DES, based on benzyltriethylammonium chloride/thymol mixture as the extracting solvent, has been suggested for vortex-assisted DLLME of the commonly used synthetic red dyes in food samples, including beverage, jelly, and chocolate samples. Experimental results confirm the successful application of the researched approach with related recoveries in the range of 94.2%
100.8% [91]. The in situ stir-bar DLLME approach has been suggested and proposed for the determination of a group of organic pollutants following their extraction and/or preconcentration of tetrabutylimidazolenickelate(II) chloride ([Ni(C4IM)421]2[Cl2]), tetraoctylimidazolenickelate (II) chloride ([Ni(C8IM)421]2[Cl2]), and tetraoctylimidazolecobaltate (II) chloride

New Generation Green Solvents for Separation and Preconcentration

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

([Co(C8IM)4 21]2[Cl2]). These ILs provided sufficient magnetic properties as extraction solvents, and acetone, acetonitrile, or tetrahydrofuran plays the role of dispersive solvent. The present ion-exchange reagent ([Li1][NTf22]), in combination with the magnetic ionic liquids (MIL) ([NTf22]), is able to generate the metathesis reaction and subsequently exhibit a high ability to disperse within the extraction vial. These solvents can be collected onto the NdFeB stir-bar, and consequently the coated stir-bar is transferred to a headspace vial and subjected to headspace sampling at 100 C
200 C for 10
40 min [92]. Magnetic effervescent tablet-assisted ILDLLME was developed for the extraction and preconcentration of polybrominated diphenyl ethers (PBDEs) in liquid matrix samples. In IL-DLLME, the extraction solvent, with the aid of a dispersive solvent mixed thoroughly with each other and an aqueous phase, is accelerated with additional energy, such as by

FIGURE 4.8

shaking, vortexing, ultrasound, or heating. The dispersive solvents (in mL scale), such as methanol or acetonitrile, lead to the creation and formation of a cloudy solution of the extraction solvent. The dispersive solvent helps in the distribution of analytes among phases and, in most situations, accelerates the mass transfer by providing more accessible reactive sites and surface area, which is due to its reasonable stability. Recently, effervescence-assisted DLLME that operates on the basis of an effervescent reaction is based on the thorough and complete dispersion of the extraction solvent into water through the carbon dioxide produced by the reaction of the glacial acetic acid solution with sodium carbonate (assigned to the sample) [93]. In the current method, a magnetic effervescent tablet, containing CO2 sources, ILs, and Fe3O4 magnetic nanoparticles, is synthesized and subsequently applied for the magnetic effervescent tabletassisted IL-DLLME procedure (Fig. 4.8) [94].

Schematic of a magnetic effervescent tablet-assisted IL-DLLME procedure [94] (License Number

4662271326713).

New Generation Green Solvents for Separation and Preconcentration

4.10 Dispersive liquid
liquid microextraction

163

FIGURE 4.9 Schematic of a pressure variation in-syringe DLLME (PV-IS-DLLME) [95] (License Number 4662460461360).

A novel approach is to perform DLLME based on rapid pressure variation in order to accelerate extraction solvent mixing and dispersion in an aqueous medium in which a glass syringe is the source environment subject to a rapid pressure difference. The nickel was applied, in an approach called pressure variation in-syringe DLLME (PV-IS-DLLME). The 1butyl-3-methylimidazolium hexafluorophosphate (IL), selected as the extraction solvent, and ammonium pyrrolidine dithiocarbamate (APDC) are applied as the complexing reagent. The schematic diagram of the approach is presented in Fig. 4.9 [95]. The combination of DLLME with spectrophotometry was examined to determine curcumin in water, wastewater, and food samples. For the first time, the CCD was used to optimize the main interaction of selected variables. The desirability function (DF) was used to identify optimum %ER through simultaneous variables optimization. Experiments were made as a function of different variables

(dispersive solvents and volume of extraction, ionic strength and pH of sample solution, and extraction time). It was found that the application of ethanol (disperser solvent) and chloroform (extraction solvent) in combination resulted in a possible achievement of 80.0% recovery and was selected for subsequent experiments. Finally, the combination of CCD and the DF helps us to achieve .98% extraction recovery of curcumin at optimum conditions (150 μL of chloroform, 900 μL of ethanol, pH 5 4, and 4 min of centrifugation time in the absence of any salt). The repeatability of DLLME was studied by extracting spiking water, wastewater, and food samples at a concentration of 100 ng mL21. The relative standard deviation (RSD) was 2.3%
1.2% (n 5 4). The method had a limit of detection (LOD) of 0.23 ng mL21 and a limit of quantification (LOQ) of 0.78 ng mL21 for curcumin. These results confirm the potential of the method for quantification of curcumin in water samples with adequate sensitivity and

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

repeatability. The recoveries for the addition of different concentrations of curcumin from samples are in the range of 91.8%
101% and indicate that the proposed method is suitable for the determination of trace amounts of curcumin in real samples [96]. Table 4.2 shows some applications of the DLLME method.

4.11 Solidified floating organic drop microextraction Solidified floating organic drop microextraction (SFODME), based on liquid
liquid microextraction, was developed in 2007 [109] and is composed of the consumption of a small volume of organic solvent whose melting point is close to room temperature (B10 C
30 C). A free microdrop of the organic solvent is floated and comes to the surface of the sample/standard solution in a vial during extraction, and mixing and agitation were undertaken by a magnetic stir-bar. The sample vial is then cooled by placing in an ice bath for up to 5 min. The organic phase is solidified and subsequently is transferred to another vial and dissolved in an appropriate organic solvent. Owing to its compatibility, this does not destroy or affect accuracy. Under the best operational conditions, the technique’s simplicity, short extraction time, low cost, the least organic solvent consumption, and achievement of high enrichment factor make this approach a candidate for trace analysis with excellent characteristic performance [110
113]. The low, acceptable, and reasonable melting and freezing points of the organic solvent assigned to SFOD lead to the feasibility of the freezing step using a simple ice bath, which reversibly allows the frozen droplet to melt at room temperature after separation from the extraction medium. This requirement is not fulfilled by most of the low-density organic solvents used in LLE, such as toluene, benzene, and amyl acetate [114]. Organic solvents

commonly employed in DLLME-SFOD are listed in Table 4.3. Different modes of SFODME, including disperser solvent (DLLME-SFO) [115], vortex mixing (VA-SFODME) [116], manual shaking [117], or using surfactants (SA-SFODME) [118], are presented to increase the mass transfer rate in classical SFOD. Ultrasound-assisted solidified floating organic drop microextraction (USSFODME) has been introduced to overcome this limitation by applying ultrasound wave as a dispersion force [119]. However, after applying these methods, the centrifugation step, as well as possibly further automation, is mandatory to collect the extraction phase that prolongs the overall extraction procedure duration [120]. An ultrasonic-assisted supramolecular SFOD has been suggested as a green method for the preconcentration of methadone prior to gas chromatography
mass spectrometry (GC-MS). Supramolecular nanostructured liquids, based on mixed amphiphiles with some aggregate, are produced via the self-assembly process. Such chemicals dispersed in a sustained phase can act as extractants with the unique ability to extract and/ or separate analytes. The supramolecular solvent aggregates based on reverse micelles of 1dodecanol in tetrahydrofuran (THF) are constructed in the presence of ultrasonication and are subsequently dispersed in the sample solution. Sonication owing to different mechanisms led to the quick formation of supramolecular solvent aggregates. The formation of reverse micelles of 1-dodecanol in THF and their subsequent dispersion (supramolecular solvent) in plasma or saliva samples were both accelerated by sonication. A schematic of the developed procedure is shown in Fig. 4.10 [121]. (See also Table 4.4.) LPME based on SFOD, followed by a novel solvent-assisted back extraction combined with liquid chromatography
tandem mass spectrometry, provides the best characteristic performance for nitrated-PAHs (nitro-PAHs) and oxygenated-PAHs (oxy-PAHs) from natural

New Generation Green Solvents for Separation and Preconcentration

TABLE 4.2 Some applications of the DLLME method. Matrix

Mode of DLLME

Extraction solvent

Dispersive solvent

Analytes

References

Brewed coffee samples

Conventional dichloromethane

acetonitrile

acrylamide

[97]

Honey samples

IL-DLLME

acetonitrile

As

[98]

Human saliva

Conventional trichlorometane

acetone

2,2-bis(4-hydroxyphenyl)propane; 4,40 -sulfonyldiphenol; 4,40 (hexafluoroisopropylidene)-diphenol; 4,40 -(1-phenylethylidene) bisphenol; 4,40 -(1,4-phenylenediisopropylidene)bisphenol; 4,40 -cyclohexylidenebisphenol, parabens (methyl-; ethyl-; propyl-; butyl-;benzyl-; methyl-protocatechuic acid, 2-hydroxy-4-methoxybenzophenone, 2,4dihydroxybenzophenone; 2,20 ,4,40 -tetrahydroxybenzophenone; 2,20 dihydroxy-4-methoxybenzophenone; and 4-hydroxybenzophenone; 1-(4chlorophenyl)-3-(3,4-dichlorophenyl) urea triclocarban)

[99]

Water samples

Ultrasoundassisted ILDLLME

—

speciation Cr(III) and Cr(VI)

[100]

Human plasma, pharmaceutical formulations

Conventional 1-undecanol

methanol

efavirenz (EFV), nelfinavir (NFV), and nevirapine (NVP)

[101]

Meat

Conventional chloroform

methanol

biogenic amines

[102]

Petroleum refinery samples

Conventional 1-octanol

acetone

phenol, cresols, 2
nitrophenol and 4-nitrophenol; o-cresol, m-cresol and p-cresol; 2,4-dichlorophenol and 2,6-dichlorophenol; 2,4,6trichlorophenol and 2,4,5-trichlorophenol

[103]

Urine

Ultrasoundassisted DLLME

acetonitrile

suvorexant

[104]

Vinegar

Conventional dichloromethan

ethanol

tetramethylpyrazine

[105]

Water matrices

Conventional 1,1,2-trichloroethane

2-propanol

synthetic musks and UV-filters

[106]

Tea beverages and fruit juices

Vortexassisted DLLME

hydrophobic DES

acetonitrile

transfluthrin, fenpropathrin, fenvalerate, ethofenprox, bifenthrin, L-carnitine, and betaine

[107]

Honey

Ultrasoundassisted DLLME

chloroform

acetonitrile

chloramphenicol

[108]

trihexyl(tetradecyl) phosphonium tetrachloroferrate (III) ([P6,6,6,14]FeCl4)

[Omim] [PF6]

1-undecanol

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

TABLE 4.3 Organic solvent commonly used in SFODME method. Solvent

Freezing point ( C)

Melting point ( C)

Density (g ml21)

1-bromohexadecane

17
18

190

0.99

1-decanol

6.4

233

0.83

1-dodecanol

22
24

259

0.83

1-undecanoic acid

28.6

284

0.89

1-undecanol

13
15

243

0.83

2-dodecanol

17
18

249

0.80

cyclohexanol

25.9

169

0.98

n-hexadecane

18

287

0.77

FIGURE 4.10

Ultrasonic-assisted supramolecular based on SFOD, developed by Ezoddin et al. [121] (License Number

4662280537800).

waters. Briefly, a mixture of the disperser solvent (methanol) and the extraction solvent (1dodecanol) are injected rapidly, and consequently centrifugation and solification of extraction solvent, after to the back-extraction following the addition of acetonitrile into the 1dodecanol, occurs. The settled separated phases are transferred into an ice bath again to remove the solidified solvent and the remaining acetonitrile phase (Fig. 4.11) [144].

A novel creative technique was designed to overcome the limitations of classical SFOD microextraction, such as the tedious and timeconsuming centrifuge step and the need to consume disperser solvent to facilitate participation of the solid and liquid phases. Accordingly, to achieve such a purpose, a magnetic carbon nanotube-nickel hybrid (MNiCNT), as a solid part of the extractor, is dispersed ultrasonically in the sample solution,

New Generation Green Solvents for Separation and Preconcentration

167

4.11 Solidified floating organic drop microextraction

TABLE 4.4 l0069st of application of SFODME method. Matrix

Mode of SFOD

Extraction solvent

Analytes

References

Pork, chicken, milk, and eggs

LPME-SFOD

1-undecanol

prednisone, betamethasone, dexamethasone, and cortisone acetate

[122]

Water and freshwater fish

SFOD

1-undecanol

mercury

[123]

Tap water, river water, seawater, and acid digests of rice flour and black tea samples

DLLME-SFOD

1-undecanol

copper

[124]

Chili products

UAEM-SFOD

1-dodecanol

Sudan I
IV

[125]

Breast milk

DLLME-SFOD

1-undecanol

uranium

[115]

Human urine

DLLME-SFOD

1-dodecanol

caffeine, levamisole, lidocaine, phenacetin, diltiazem, and hydroxyzine

[126]

Thai herb samples

SFOD

1-undecanol

cadmium

[113]

Natural water samples

DLLME-SFOD

1-dodecanol

3-amino-1,4-dimethyl-5H-pirido-[4,3-b]-indole (Trp-P-1), 3-amino-1-methyl-5H-pirido-[4,3-b]indole (Trp-P- 2), 2-amino-9H-pyrido-[2,3-b]indole (AαC), and 2-amino-3-methyl9Hpyrido-[2,3-b]-indole (MeAαC)

[127]

Egg

DLLME-SFOD

1-dodecanol

albendazole, chloramphenicol, trimethoprim, enrofloxacin, oxitetracycline, and nicarbazin

[128]

Environmental water samples and tea samples

DLLME-SFOD

1-dodecanol

bifenthrin, fenpropathrin, permethrin, and deltamethrin

[129]

Corn flour, UA-SFOD maize corn, bean, bean leaf, cabbage leaf, and water samples

dodecanol

cadmium

[130]

Reservoir and river water Samples

UA-SFOD

1-undecanol

α-BHC, β-BHC, γ-BHC, δ-BHC, heptachlor, aldrin, heptachlor epoxide, α-chlordane, endrin, β-endosulfan, p,p’-DDD, endrin aldehyde, and endrin ketone

[131]

Food and environmental samples

UA-SFOD

1-undecanol

lead and cadmium

[132]

Water samples

UA-SFOD

1-dodecanol

bismuth(III)

[133]

UA-SFOD

1-undecanol

[134] (Continued)

New Generation Green Solvents for Separation and Preconcentration

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

TABLE 4.4 (Continued) Matrix

Mode of SFOD

Extraction solvent

Hospital drainage and Gomti river water

1-undecanol

Analytes

References

metronidazole, sulfamethoxazole, trimethoprim, norfloxacin, chloramphenicol, cephalexin, ampicillin, levofloxacin, dexamethasone, amoxycillin, cefixime, tetramycin, betamethasone phosphate, gentamicin sulfate, erythromycin, penicillin, ofloxacin, doxycycline, and ciprofloxacin DLLME-SFOD

1-undecanol

Cu, Ni, Co, Pb, and Zn

[135]

Tap, well, spring, DLLME-SFOD river, and seawater

1-undecanol

Ni, Co, and Cu

[136]

Fruit juice

DLLME-SFOD

1-dodecanol

benzoylurea insecticides

[137]

River and well water

DLLME-SFOD

1-dodecanol

organochlorine pesticides

[138]

Human plasma

DLLME-SFOD

1-undecanol

duloxetine

[139]

Human urine

DLLME-SFOD

1-undecanol

cocaine adulterants

[126]

Human plasma

DLLME-SFOD

1-undecanol

Carvedilol

[140]

Human urine

DLLME-SFOD

1-undecanol

nicotine and cotinine

[138]

Human urine

DLLME-SFOD

1-undecanol

macrolide antibiotics

[141]

Human plasma

DLLME-SFOD

1-undecanol

atorvastatin

[142]

Human serum and urine

DLLME-SFOD

1-undecanol

thiamine and cobalamine

[143]

the ensuing dispersion of liquid phase (1-undecanol) undergoes high-rate stirring, and MNiCNT in the organic solvent droplets is easily collected through hydrophobic force. Decreasing the stirring rate causes a formation on top of the solution of MNi-CNT, which acts as both extractor and the coalescence helper between organic droplets for a facile recollection. MNi-CNT was prepared by spray pyrolysis of nickel oleate/toluene mixture at 1000 C (Fig. 4.12). The proposed SC-SF-SLDME procedure was applicable for the extraction and preconcentration of four tyrosine kinas inhibitors (as model

analytes) in human serum and cerebrospinal fluid samples; effecting parameters were investigated [145]. A new mode of liquid microextraction has been used for the determination and preconcentration of some pyrethroid insecticides from different samples. In this approach, the homogeneous solution is broken by controlling pH and in situ salt formation. The realized extraction solvent (pivalic acid) droplets are solidified on the top of the solution to facilitate their removal. This method is performed in a homemade extraction device (Fig. 4.13) [146]. Table 4.5 lists some applications of the SFODME method.

New Generation Green Solvents for Separation and Preconcentration

4.11 Solidified floating organic drop microextraction

FIGURE 4.11

Schematic of methodology of LPME based on SFOD [144] (License Number 4662280794348).

FIGURE 4.12

Schematic of SC-SF-SLDME procedure [145] (License Number 4662281013314).

New Generation Green Solvents for Separation and Preconcentration

169

170

FIGURE 4.13

4. New methodologies and equipment used in new-generation separation and preconcentration methods

Schematic of SFOD developed by Torbati et al. [146] (License Number 4662281264227).

4.12 Modern techniques of isolation and/ or preconcentration 4.12.1 Liquid phase microextraction LPME as a LLE method is based on the consumption of at least small amounts of solvents (usually a few microliters) and in conventional mode is classified as SDME and hollow fiber (HF). The latter one (HF-LPME) acts as the extraction carrier membrane [147]. In the mid-1990s, a single liquid drop of water was applied to extract ammonia and sulfur dioxide [148], and their first demonstration based on such a principle was termed SDME [149]. There are two SDME modes: two-liquid phase or three-liquid phase SDME. Two-phase SDME usually includes analyte extraction from aqueous solution to an organic solvent [150]. The two-phase SDME technique can be used in drop-to-drop and direct immersion (DI) geometrics. In drop-to-drop mode, the analyte from aqueous solution (about microliter in volume) is extracted to a drop of extraction phase, which meets the requirement of using the smallest volume of sample solution for the

accurate and precise monitoring analyte(s) from complicated matrices. The DI-SDME mode is based on the application of nanoliters to microliters of a water-immiscible organic droplet, which is created at the tip of a microsyringe and directly immersed in the sample solution [151,152]. Three-phase SDME involves two modes including liquid
liquid
liquid microextraction (LLLME) and headspace LPME (HSLPME) modes. The LLLME mode is based on analyte transfer from aqueous sample solution extract to an organic solvent and the subsequent transfer from the organic solvent to an aqueous drop (back-extraction) [150]. In the HS mode, the extraction system consists of a microsyringe, a vial containing the sample with a cap to avoid the loss of the analytes and solvent, and a stirrer bar. The vial containing the analytes is placed on a magnetic stirrer, and the needle tip of the microsyringe containing the organic solvent is passed through the septum of the vial and fixed about 0.5
1.0 cm above the sample solution. Afterward, the sample solution is continuously agitated. After extraction, the microsyringe

New Generation Green Solvents for Separation and Preconcentration

TABLE 4.5 Some applications of DLLME method. Matrix

Mode of DLLME

Extraction solvent

Dispersive solvent

Analytes

References

Brewed coffee samples

Conventional dichloromethane

acetonitrile

acrylamide

[97]

Honey samples

IL-DLLME

acetonitrile

As

[128]

Human saliva

Conventional trichlorometane

acetone

2,2-bis(4-hydroxyphenyl)propane; 4,40 -sulfonyldiphenol, 4,40 [129] (hexafluoroisopropylidene)-diphenol; 4,40 -(1-phenylethylidene) bisphenol; 4,40 -(1,4-phenylenediisopropylidene)bisphenol; 4,40 -cyclohexylidenebisphenol, parabens (methyl-, ethyl-, propyl-, butyl-, benzyl-,) methyl-protocatechuic acid; 2-hydroxy-4-methoxybenzophenone; 2,4dihydroxybenzophenone; 2,20 ,4,40 -tetrahydroxybenzophenone; 2,20 dihydroxy-4-methoxybenzophenone; and 4-hydroxybenzophenone; 1-(4chlorophenyl)-3-(3,4-dichlorophenyl) urea triclocarban

Water samples

Ultrasound assisted ILDLLME




speciation Cr(III) and Cr(VI)

[130]

Human plasma, pharmaceutical formulations

Conventional 1-undecanol

methanol

efavirenz (EFV), nelfinavir (NFV) and nevirapine (NVP) in

[131]

Meat

Conventional chloroform

methanol

biogenic amines

[132]

Petroleum refinery samples

Conventional 1-octanol

acetone

phenol, cresols, 2
nitrophenol and 4-nitrophenol; o-cresol, m-cresol and p-cresol; 2,4-dichlorophenol and 2,6-dichlorophenol; 2,4,6trichlorophenol and 2,4,5-trichlorophenol

[103]

Urine

Ultrasoundassisted DLLME

acetonitrile

suvorexant

[104]

Vinegar

Conventional dichloromethan

ethanol

tetramethylpyrazine

[105]

Water matrices

Conventional 1,1,2-trichloroethane

2-propanol

synthetic musks and UV filters

[106]

Tea beverages and fruit juices

Vortexassisted DLLME

hydrophobic DES

acetonitrile

Transfluthrin, Fenpropathrin, Fenvalerate, Ethofenprox, Bifenthrin, Lcarnitine, Betaine

[107]

Honey

Ultrasoundassisted DLLME

chloroform

acetonitrile

chloramphenicol

[138]

trihexyl(tetradecyl) phosphonium tetrachloroferrate (III) ([P6,6,6,14]FeCl4)

[Omim] [PF6]

1-undecanol

172

4. New methodologies and equipment used in new-generation separation and preconcentration methods

needle is removed from the vial and injected into the analysis system for quantitative analysis. The rate-determining step of the HS mode of LPME is removing analytes from the sample to the headspace because the diffusion rate in the headspace is faster than that in the sample. Its different branch is shown in Fig. 4.14 [154,155]. DI-SDEM is suitable for nonvolatile analytes, whereas HS-SDME is an appropriate choice for volatile and semivolatile compounds. Compared to the DI mode, the HS mode avoids possible interference from the sample matrix and is widely applied for the extraction of more volatile compounds [155]. The appropriate and best selection of this approach is made as a compromise among the advantages of SDME, that is, easy operation and simple equipment [151,152], and its drawbacks, including variation of the organic droplet volume [153] (especially at high temperatures or long extraction times), instability of hanging droplet (especially at high stirring speeds when the matrix contains many suspended particles) [156], and low contact surface area between the organic droplet and sample due to its submicrovolume leading to a low extraction kinetic [157]. HF-LPME supplies the configuration and conditions to overcome droplet instability by holding the solvent within the lumen and the pores of the HF (usually made of polypropylene and other polymers) as a protective sheath [147,158]. HF-LPME can be classified into two-phase HF-LPME and three-phase HF-LPME. In twophase HF-LPME (aqueous-organic), extraction solvent (commonly primary alcohols such as nhexanol, n-heptanol, and n-octanol) is immobilized in the HF wall micropores, and the filledin HF lumen and target analytes are extracted by passive diffusion from aqueous sample into the extraction solvent. The analytes with high solubility (uncharged hydrophobic analytes) in the extraction solvent can be extracted by the

two-phase system. In three-phase HF-LPME (aqueous-organic-aqueous), the extraction solvent is immobilized in and/or onto micropores of the HF wall, and the water-soluble acceptor phase is the filled-in HF lumen. Target analytes in the sample are first extracted by the extraction solvent and subsequently back-extracted into the acceptor phase. The analytes that are higher in the acceptor phase with respect to the extraction solvent are efficiently extracted and/or preconcentrated by the three-phase system [159]. In two-phase HF-LPME methods, only the partition coefficient determines the maximum enrichment, while in the three-phase mode, the efficiency, preconcentration, and enrichment factors depend on other degrees of freedom applicable for the extraction conditions, including the pH gradient between the sample solution and the aqueous phase. Three-phase HFLPME also provides much better cleanup in comparison to the two-phase mode [160,161]. Implementation of HF-LPME is the same as SDME in both the DI and the HS modes. The three most common configurations for HF-LPME are shown in Fig. 4.15. Most conventional and applicable configurations corresponding to such methods uses the rod-like setup in which the organic solvent is immobilized in the pores of the HF and the fiber is directly attached to the needle of a microsyringe containing a certain amount of the same organic solvent. Then the organic acceptor phase is introduced into the lumen of the HF, and the same microsyringe is used for the withdrawal of the obtained acceptor phase and subsequent injection into the analytical instrument. The bottom of the HF can be open or sealed manually, and the setup is immersed in the sample solution [160]. Another common technical configuration is a U-shaped one with both ends of the HF connected to the needles of two medical syringes to maintain the organic solvent throughout the extraction. After extraction is accomplished, one end of

New Generation Green Solvents for Separation and Preconcentration

173

4.12 Modern techniques of isolation and/or preconcentration

FIGURE 4.14 Different modes of SDME [153] (License Number 4662290290154).

the HF is disconnected to flush the final acceptor phase with excessive air, which is collected in a microtube. The U-shaped setup as simple configuration is dispensed with any clamp, stand, or even a microsyringe. Another configuration of HF-LPME, named solvent bar microextraction (SBME), is based on the

incorporation and/or immobilization of the organic acceptor phase in the HF with both ends of HF sealed and subsequently immersed in the sample solution. At the end of the process, the extraction solvent is drained from the lumen of the two-ended sealed HF and injected into the analysis instrument.

New Generation Green Solvents for Separation and Preconcentration

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

FIGURE 4.15 Three most common configurations for HF-LPME [162] (License Number 4662290539811).

The main drawback of HF-LPME is the formation of air bubbles on the surface of the HF, a situation that, if not handled carefully, can consequently affect its repeatability [162]. In LPME approaches, the extraction solvent has a significant effect on extraction efficiency, while, accordingly, conventional solvents such as 1-octanol, n-hexane, toluene, dodecane, and hexadecane exhibit drawbacks, mainly related to the extraction selectivity owing to their high volatility and consequently, and destroy and worsen extraction efficiency and precision [163,164]. Recently IL, MIL, surfactant-based approach switchable hydrophilicity solvent, supramolecular solvent (SUPRAS), and DES, owing to their remarkable advantages, have attained extensive attention in LPME. Their relative advantages correspond to their exceptional properties, like wide liquid range, low vapor pressure, hypotoxicity, safety, convenient phase separation as well as easy preparation, appropriate route, and easy and costeffective synthesis or commercial availability. Moreover, nanomaterials, as solid modifiers,

enhance the diffusion-based driving force of the extraction process in LPMEs. A novel SUPRAS approach based on hexafluoroisopropanol/Brij-35 was proposed for the LPME of parabens in water samples, pharmaceuticals, and personal care products. SUPRAS is a water-immiscible liquid composed of nano- or microsupramolecular aggregates generated through a self-assembly process of amphiphilic molecules in an aqueous solution with the aid of noncovalent interactions [165]. Experimental results reveal that small amounts of hexafluoroisopropanol (1%, v/v) can reduce the cloud point of Brij-35 to room temperature, and the LPME method was established without heating [166]. Switchable solvents are described as a system in which a nonionic liquid turns into an ionic liquid under the influence of carbon dioxide and is subsequently switched back to its nonionic form with exposure to inert gases or sodium hydroxide [167]. The switching procedure is based on the appropriate application of CO2 as a stimulus to convert the nonionic

New Generation Green Solvents for Separation and Preconcentration

4.12 Modern techniques of isolation and/or preconcentration

liquid into an ionic liquid by protonating the amine into a water-soluble carbonate salt [168]. A switchable solvent
based LPME has been proposed for the determination of cobalt in egg yolk and vitamin B12 at trace levels, while N,Ndimethylbenzylamide (DMBA) was used as a switchable extraction solvent and converted to protonated DMBA form by the addition of dry ice [169]. Ultrasound-assisted deep eutectic solvent LPME has been designed and applied for N,NDimethylbenzylamide preconcentration and speciation of Hg21 and CH3Hg1. Cholinephenol-based DES (1:3, molar ratio) was used as an extractant for the determination of species of mercury, Hg21 formed hydrophobic complexes with dithizone, and its consequence complexes were extracted using DES. CH3Hg1 determination was accomplished through its direct extraction into the DES phase because of its hydrophobic property [170]. One of the main challenges of analytical researchers is automation of analytical procedures that provide reduced analysis time, higher sample throughput, and greater reproducibility through the reduction of human error [171,172]. To continue this research, an innovative and

FIGURE 4.16

175

high-throughput parallel-single-drop microextraction (Pa-SDME) was developed using the [P6,6,6,141]2[MnCl422] MIL as the extraction phase, which was demonstrated and applied for the extraction and determination of parabens from environmental aqueous samples. This experimental setup was comprised of a 96-well plate system containing a set of magnetic pins that facilitate stabilizing the MIL drops and provide the simultaneous extraction of up to 96 analytes. This configuration is capable of performing a series of extraction and desorption/dilution steps using a relatively large amount of extraction solvent and maintaining microdrop stability, even with high stirring rates in direct-immersion mode. A scheme of the new configuration used in this study is shown in Fig. 4.16 [164]. A fully automatic HF-assisted LPME method combining the positive attributes of carbon nanofiber/polymer composite membranes (CNF@HF-LPME) has been demonstrated for the determination of acidic drugs (ketoprofen, ibuprofen, diclofenac, and naproxen) in urine [173]. Dispersed carbon nanofibers (CNF) are immobilized in the pores of a single-stranded polypropylene hollow fiber

Schematic of USAEME based on DES utilized by Kanberoglu et al. [164] (License Number

4662290290154).

New Generation Green Solvents for Separation and Preconcentration

176

4. New methodologies and equipment used in new-generation separation and preconcentration methods

(CNF@HF) membrane, which is thereafter accommodated in a stereolithographic 3Dprinted extraction chamber without glued components for ease of assembly. The analytical method involves continuous-flow extraction of the acidic drugs from a flowing stream donor (pH 1.7) into an alkaline stagnant acceptor (20 mmol L21 NaOH) containing 10% MeOH (v/v) across a dihexyl ether impregnated CNF@HF membrane (Fig. 4.17). The separation of extraction solvent in conventional LPME is still a problem. Recently, superwetting substrate named superhydrophobic materials [174,175] and underwater superoleophobic films [176,177] could be used to separate an organic extraction solvent in LPME. Based on wettability, the superwetting substrate can selectively extract waterimmiscible organic solvent or water easily in the oil-water mixture. Wang et al. developed a method to directly extract malachite green, verapamil, and methadone from complex samples on a superwetting PSi substrate based on

FIGURE 4.17

LPME and then directly analyzed the target compounds on PSi with surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) [178]. Table 4.6 summarizes some of the applications of LPME method.

4.12.2 Aqueous two-phase system The ATPE, a LLE technique, is a powerful technique for the simultaneous recovery and purification of different analytes from various matrixes. It is a single-step unit operation, which selectively partitions and purifies a specific solute by concentrating in any one of the phases [197]. In 1896, Martinus Willem Beijerinck accidently found ATPS while mixing an aqueous solution of starch and gelatin. However, its real application was discovered ˚ ke Albertsson [198
200]. ATPS is usuby Per-A ally formed by mixing two aqueous solutions with distinct physicochemical properties (e.g., a polymer and an electrolyte) under specific

Schematic of a fully automatic HF-assisted LPME method [173] (License Number 4662290933380).

New Generation Green Solvents for Separation and Preconcentration

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4.12 Modern techniques of isolation and/or preconcentration

TABLE 4.6 Application of LPME method. Matrix

Mode of LPME

Water samples

Extraction and/or acceptor solvent

Analytes

References

HF-LPME 1-octanol

phthalic acid esters

[179]

Water samples

HF-LPME aliquat 336

hexavalent chromium

[180]

Urine

HF-LPME 1-octanol and/ aliquat 336

trans,trans-muconic acid, hippuric acid, and mandelic

[181]

Dam lake, river and well water

Vortexassisted LPME

dichloromethane/ herbicides dichloroethane

[182]

Edible oil samples

SDME

acetonitrile/ ethanol

phenolic antioxidants

[183]

Water samples

HF-LPME methanol

speciation of chromium(III) and chromium(VI)

[184]

Traditional Chinese medicine

HF-LPME n-heptanol

hesperidin, honokiol, shikonin, magnolol, emodin, and β,β0 -dimethylacrylshikonin

[185]

Water

HF-LPME 1-octanol

sulfonamides

[186]

Environmental water, honey, and tomato

HF-LPME decane

riazine herbicides

[187]

Biological and environmental samples

HF-LPME DES

antiarrhythmic drugs

[188]

Water samples

HF-LPME 1-octanol

aniline, metformin, acetaminophen, carbazole, aldicarb, caffeine, thiabendazole, carbaryl, ibuprofen, atrazine, carbofuran, 2,4-dichlorophenoxyacetic acid, ametryn, bisphenol A, diuron, carbamazepine, methyl parathion, disulfoton, triclosan, diazinon, tebuconazole, malathion, chlorpyrifos, hydrocortisone, temephos, glibenclamide, and 4 nitrophenol

[189]

Environmental samples

HF-LPME o-xylene

2-methylisoborneol, 2-isopropyl-3-methoxy pyrazine, 2,4,6-trichloroanisole, and 2,3,6-trichloroanisole

[190]

Environmental samples

HF-LPME n-octanol

melamine

[191]

Food sample

HF-LPME reverse micelle

quercetin

[192]

Breast milk

HF-LPME HCl 10 mM

Paroxetine, Fluvoxamine, Mianserin, Citalopram

[193]

Urine, plasma

HF-LPME H3PO4 0.1 M

Imipramine, Amitriptyline, Setraline,

[194]

Urine, serum

HF-LPME HCl 0.01 M

Chlorpromazine

[195]

Plasma

HF-LPME HCl 5 mM

tetradrine fangchinoline

Urine, plasma

HF-LPME HCl 100 mM

Mebendazole

New Generation Green Solvents for Separation and Preconcentration

[196]

178

4. New methodologies and equipment used in new-generation separation and preconcentration methods

thermodynamic conditions of temperature, pressure, and concentration [201]. Traditional ATPS systems are comprised of polymer/polymer, polymer/salt, salt/salt mixtures. ATPS based on polymer/salt are preferred over the polymer/polymer systems because of larger differences in density, greater selectivity, lower viscosity, lower cost, and the larger relative size of the drops [202]. Recently, ATPSs based on ionic liquid (IL)/salt, IL/polymer, or IL/ carbohydrate combinations or on short chain alcohols/salt mixtures have been reported [203]. ATPSs have been based on polymer/ ionic liquids, which have low interfacial tension, high hydrophilic and hydrophobic range of the coexisting phases, fast and high-phase separation, and interesting properties relevant to ILs such as negligible vapor pressure, low flammability, large liquid range, and high thermal stability. Therefore, they are well documented for the specific and efficient separation of a wide diversity of molecules [204]. ATPS based on short-chain alcohols/salt mixtures are beneficial due to their moderation with efficient mass transfer, low viscosity and interfacial tension, biocompatibility, and nontoxicity [205]. Phosphates and sulfates salts are commonly used in ATPS. Phase separation in ATPS commonly requires high concentrations of the salts mentioned. Therefore, the use of these salts leads to effluent streams and hence presents an environmental concern. Nowadays, use of citrate salts as a phaseforming agent with polymers is preferred since citrate salts are biodegradable and nontoxic [206]. Another type of ATPS is the micellar two-phase system first introduced by Bordier for the separation of integral membrane proteins [207]. Commonly nonionic surfactants are used in these systems. The concentration and molecular weight of polymer, ionic liquid, and the like, the concentration and composition of salt, the pH of the system, and the temperature can affect phase separation and partitioning in ATPS. The higher

the molecular weight of the polymers, the lower is the polymer concentration required for phase separation [208]. The phase diagram of ATPS under specific conditions (e.g., temperature and pH) provides unique information about the concentration of the phase-forming components required to form a two-phase system, the concentration of phase components in the top and bottom phases, and the ratio of phase volumes. Fig. 4.18 shows the diagram of a binodal curve (TCB), which divides the region of component concentrations. This curve splits the concentrations that form two immiscible aqueous phases (above the binodal curve). The main advantages of ATPS over other purification and concentration protocols are attributed to their high water content, low interfacial tension, scalingup feasibility, and recycling capability [153,156]. The nodes that make up one phase (below the binodal curve), the line (TB) in the diagram (Fig. 4.18), is a tie line; it connects two nodes lying on the binodal curve. All the potential systems (e.g., S1, S2, S3) have the same top phase and bottom phase equilibrium composition due to their being on the same tie line. Point C on the bimodal is called a critical point; just above this point, the volumes of both phases are theoretically equal. At point C, the value tie line length (TLL) is equal to zero. The length of the tie line is related to the mass of the phases by the equation: Vt ρt SB 5 ST V b ρb where V and ρ stand for volume and density of the top (t) and bottom (b) phases while SB and ST are segment lengths. Binodal can be determined by three methods: turbidometric titration method, cloud point method, and node determination method [208,209]. ATPS has been successfully used in the purification, recovery, removal, and extraction of many materials like proteins, enzymes, amino acids,

New Generation Green Solvents for Separation and Preconcentration

179

4.12 Modern techniques of isolation and/or preconcentration

FIGURE 4.18

antibiotics, plasmids, DNA, and the like. All these applications are briefly discussed in the following sections. Wang et al. developed an extraction method based on the dispersive solid phase extraction (DSPE) procedure and cold-induced acetonitrile ATPS for the extraction of caffeine from tea [88]. Cold-induced acetonitrile ATPS was first used by Gu et al. [210] in protein purification. Compared with the salt-out-assisted acetonitrile ATPS method, cold-induced acetonitrile ATPS does not need to utilize any salts and consequently can decrease the cost of salt, and the subassembly prevents new impurities in the extracted materials. Furthermore, another special merit of cold-induced acetonitrile ATPS is that different concentrations of acetonitrile/water mixture can yield a different phase separation ratio (defined as a ratio of the volume of upper layer to the volume of lower layer) [211]. ATPS based on thermally separating UCON polymer was developed by Hernandez-Vargas and coworkers for the recovery of PEGylated

Diagram of a binodal curve (TCB).

lysozyme species [212]. UCON is a thermosensitive polymer. The recycling of phaseforming agents (commonly salts) in conventional ATPS is a difficult task that increases the high operational costs owing to the large number of operations required to remove the rest of the phase-forming components and that does not provide an attractive way to reuse the waste streams [213]. This drawback of the conventional ATPS method is solved by applying interpolymer complex or/and a combination of two polymers so that at least one of the polymers will be more thermosensitive than the other polymer. Subsequently, with a change in temperature, conformations in one polymer will be different from that of the other polymer. Consequently, beyond the cloud point or below the critical solution temperature, the separation phase occurs and leads to the separation phase, as in the two-phase system, including a polymer-rich phase and a water phase [214,215]. Lopes and coworkers have examined the influence of various electrolytes in the

New Generation Green Solvents for Separation and Preconcentration

180

4. New methodologies and equipment used in new-generation separation and preconcentration methods

increased formation of the polyethylene glycol/ polyacrylic acid ATPS. Herein, the simultaneous recovery of green fluorescent protein and lipopolysaccharide removal from an Escherichia coli cell lysate was planned. At first, they examined the effect of different electrolytes, including NaCl, Li2SO4, KI, and KNO3, on the separation phase and formation of binodal curves in each system. They found that the formation of ATPS is enhanced following the anion tendency: SO422 . Cl2 .. NO32 . I2. Then, green fluorescent protein partitioning and lipopolysaccharide removal in different types of ATPS, in both the presence and the absence of salts, was investigated. In addition, they studied the influence of high loads of lipopolysaccharide (104 and 106 EU mL21) on the pure green fluorescent protein partitioning using different polymer and salt concentrations. They found that the presence of high loads of lipopolysaccharide can affect (decrease) the Kgreen fluorescent protein values (Kgreen fluorescent protein without lipopolysaccharide . Kgreen fluorescent protein with 104 EU mL21 . Kgreen fluorescent protein with 106 EU mL21) [216]. An ATPS fabricated from PEG(1000) and (NH4)2SO4 was applied to a polysaccharides mixture (dextran and sulfateddextran). Consequently the extraction and preconcentration of sulfated polysaccharides were accessible by entering into the polymer-rich phase, and the ATPS obtained from PEG (1000) and/or sodium citrate, dipotassium hydrogen phosphate, sodium tartrate, and the like was used to back-extract sulfated polysaccharides to a salt phase. This process was further employed for the separation of the sulfated Enteromorpha polysaccharides (EPs) from crude EPs. Fig. 4.19 is a schematic based on the ATPS [217]. The aqueous micellar two-phase systems (AMTPS) was developed as an advanced ATPS method and employed for removing soy antinutritional factors (trypsin inhibitors), isoflavones, and raffinose family oligosaccharides from soy flour. This method is based on

solid
liquid and LLE and depends on the ability of some surfactants to form two immiscible aqueous phases, a micelle-rich phase and a micelle-poor phase, above a certain temperature defined as the cloud point [218]. Thereby, the physicochemical differences between both phases allow the separation of biomolecules present in a mixture [219]. Fig. 4.20 represents the use of AMTPS in real samples [220]. A recyclable ATPS was fabricated by two synthesized pH-responsive copolymers (PADB4.99 and PMDM7.08) and applied for purification of porcine circovirus type 2 Cap protein fermentation broth (PCV2 Cap protein). Fig. 4.21 explains the phase formation mechanism of PADB4.99/PMDM7.08 ATPS with the partition of PCV2 Cap protein. The results indicated that ATPS appeared when the concentration of both copolymers was 4%
6% (w/w) with pH 7.5
8.6. The main parameters, such as copolymer concentration, temperature, pH, type, and concentration of salts, were investigated. Moreover, two phase-forming copolymers were recycled by single-pH regulation, with over 97.5% recovery by adding certain concentration salts. In addition, the partition results attested that PCV2 Cap protein was extracted effectively from protein fermentation broth, and most impurities can be removed efficaciously after the addition of salt (Li2SO4 or KCl) to the ATPS [221]. Sixteen kinds of novel deep eutectic solvents (DESs), composed of polyethylene glycol (PEG) and quaternary ammonium salts such as tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), tetraethylammonium chloride (TEAC), and tetraethylammonium bromide (TEAB), were applied in aqueous biphasic systems (ABSs) to extract RNA. The results of extraction efficiency showed that the use of lower PEG content in DESs, smaller PEG molecular weights, longer carbon chains of quaternary ammonium salts, and more hydrophobic inorganic salts led

New Generation Green Solvents for Separation and Preconcentration

FIGURE 4.19 Schematic of an ATPS composed of PEG1000 and (NH4)2SO4 [217] (License Number 4662401226142).

FIGURE 4.20 Schematic representation of the selective removal of soy antinutritional factors by using AMTPS. TI, Trypsin inhibitor; NaCit, sodium citrate; RFOs, raffinose family oligosaccharides; IF, isoflavones; GX, Genapol x-080 [220] (License Number 4662420247010).

182

4. New methodologies and equipment used in new-generation separation and preconcentration methods

FIGURE 4.21

Phase formation mechanism of PADB4.99/PMDM7.08 ATPS with the partition of PCV2 Cap protein [221] (License Number 4662420953095).

FIGURE 4.22

DES-based ABSs for the extraction of RNA [222] (License Number 4662430109241).

to an increase in the extraction of RNA. DESs synthesized by PEG and TBAB were applied to form ABSs with salt solution. After the extraction of RNA, the two phases were separated,

and the top phase containing mostly RNA further formed new ABSs in the back-extraction procedure (Fig. 4.22) [222]. Table 4.7 summarizes other applications of ATPS.

New Generation Green Solvents for Separation and Preconcentration

183

4.12 Modern techniques of isolation and/or preconcentration

TABLE 4.7 Other application of ATPS. Real sample

Analyte

Extraction solvent

Phase separator agent

References

—

demeclocycline

polymers PADB4.0 and PADB4.6

pH

[223]

Garcinia indica

anthocyanin-kuromanin chloride (cyanidin-3-O-glucoside), garcinol, isogarcinol, hydroxycitric acid,

1-propanol, ethanol. PEG-4000

K2HPO4, (NH4)2HPO4, Na3C6H5O7, NaH2PO4, ZnSO4, MgSO4, Na2SO3, (NH4)2 HPO4

[224]

Integrated 6-aminopenicillanic acid microfluidic reactorsseparators

PEG 4000, PEG 8000 NaH2PO4 2H2O, K2HPO4, and MgSO4.7H2O



[225]

—

vanillic acid, eugenol, L-tryptophan, l-phenylalanine, nicotine, caffeine, l-tyrosine, gallic acid

PEG 4000

(NH4)2SO4

[226]

—

bovine serum albumin

PEGDME250

cholinium aminoate ionic- [204] liquids

—

antibiotics

PADB4.05 and PMDB3.36

pH

[227]

—

caffeine, codeine, vanillin

Propanol

sugar

[228]

Bixa orellana L. seeds

bixin and norbixin

PEG 1500, 4000, and NaH2C6H5O7 6000, L35 ((EO)13(PO)30(EO)13)

[229]

Radix Sophorae tonkinensis

polysaccharides

ethanol

Na2HPO4

[230]

Marigold (Tagetes erecta L.) flower

polyphenol and lutein

ethanol

ammonium sulfate

[231]

Vanilla planifolia, Vanilla tahitiensis, and Vanilla pompon

Vanillin

maltodextrin/ acetonitrile

dextrose

[232]

Nickel metal hydride cobalt and nickel batteries

L64 Na2SO4 ((EO)13(PO)30(EO)13)

[233]

Aspergillus tamarii URM4634

protease

PEG

NaH2C6H5O7

[234]

Aqueous samples

acetylcholinesterase (AChE) inhibitors
galantamine (gal), N-desmethyl galantamine (des), and ungiminorine (ung)

choline saccharinate and choline acesulfamate ionic liquids

Na2CO3, Na2SO4, MgSO4, (NH4)2SO4, KH2PO4, K2HPO4, K3PO4, and NaH2PO4

[235]

1,4-dioxane

Na2SO4

[236]

Synthetic solutions lactic acid and the mixture directly derived from corn stover

(Continued)

New Generation Green Solvents for Separation and Preconcentration

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

TABLE 4.7 (Continued) Real sample

Analyte

Extraction solvent

Phase separator agent

References

—

Tetracycline

PEG600, PEG600, cholinium chloride

cholinium chloride, cholinium bicarbonate, Na2SO4, K3PO4

[203]

—

molybdenum

L35, HO Na2SO4 (EO)11(PO)16(EO)11H

[237]

Radix Sophorae tonkinensis

alkaloids

ethanol

Na2HPO4

[205]

Fermented broth

1,3-propanediol

Isoproponal

K2CO3:K2HPO4

[238]

Crude extracts of ginseng roots

bioactive ginseng saponins

n-alkyl-tropinium and nalkylquinolinium bromide ionic liquids

K3PO4, K2CO3, NaH2PO4, K2HPO4, Na3C6H5O7, and K3C6H5O7

[239]

—

caffeine and catechin

ethyl lactate

trisodium citrate, disodium tartrate, and disodium succinate

[240]

—

penicillin-G

PEG 6000

K2HPO4

[241]

—

gallic acid, vanillic acid, eugenol, nicotine, caffeine, L-tryptophan, L-phenylalanine, and L-tyrosine

PEG 400,

citrate buffer at pH 7.0

[242]

Lilium davidii var. unicolor Salisb.

polysaccharides

ethanol

K2HPO4

[243]

—

Remazol Brilliant Blue R dye

1-propanol/2propanol/tertbutanol

(NH4)2SO4

[244]

—

caffeine, theobromine,2,6-amino purine

choline derivative ionic liquids

K3PO4, K3C6H5O7, or K2CO3

[245]

Cerrena unicolor and Pleurotus sapidus

laccases

PEG 400, 1500, 3000, phosphate buffer 6000 (pH 5 7.0)

[246]

Ziziphus Jujuba cv. Muzao

polysaccharides

ethanol

(NH4)2SO4

[247]

Fermentation broth of Lactobacillus plantarum ST16Pa

bacteriocin

PEG, sodium polyacrylate

Na2SO4 or choline chloride

[248]

—

tryptophan

benzyl trialkyl ammonium based ionic liquids

K3PO4, K2HPO4, K2CO3, and KOH

[249]

—

molybdate ion

PEG 4000

CuSO4

[250] (Continued)

New Generation Green Solvents for Separation and Preconcentration

185

4.12 Modern techniques of isolation and/or preconcentration

TABLE 4.7 (Continued) Real sample

Analyte

Extraction solvent

Phase separator agent

References

Escherichia coli

green fluorescent protein

1-propanol and ethanol

tripotassium citrate

[251]

—

cefprozil

PADB6.8

pH

[252]

—

gallic acid

deep eutectic solvent (choline chloride:sugars)

K2HPO4

[253]

Spent Ni
MH batteries

lanthanum

L64 or PEO1500

Li2SO4, Na2SO4, MgSO4, Na2C4H4O6, or Na3C6H5O7

[254]

Capsicum chinense var. cumari-do-Para´

capsaicin

ethanol

NaH2PO4, Na2S2O3, Na2SO4, and Na2CO3

[255]

Blueberry leaves

chlorogenic acid

ChCl-1,3-butanediol

K2HPO4

[256]

Feeds

mycotoxins

PEG with different NaH2PO4, K2HPO4, molecular weight NaHCO3, and sodium including 3.5, 8, and citrate tribasic dehydrate 20 kDa

[257]

—

H3PO4

PEG 1000

Na2SO4

[258]

Capsicum oleoresin

Capsaicin

ethylene oxidepropylene oxide (EOPO) copolymer

(NH4)2SO4, Na2HPO4, and [259] Na2CO3, Na3C6H5O7

Amauroderma rugosum (Blume & T. Nees) Torrend

lignin peroxidase

PEG 600

K2HPO4

[260]

—

cefazolin

PEG 6000, 8000

sodium sulfate, sodium tartrate, and sodium citrate

[261]

Food sample

bromelain

PEG113-b-PNIPAM14 Na2C4H4O6/ K2C4H4O6/ (NH4)2C4H4O6/ K3C6H5O7/ K2C2O4

[262]

—

mannan
protein mixtures

1-butyl-3methylimidazolium bromide

K2HPO4

[263]

Wastewater

Hg(II), Zn(II), and Co(II)

PEG-6000

Na2CO3

[264]

Lithiumion batteries

copper and cobalt

L64

Na2SO4

[265]

Penicillium sp. UCP 1286

collagenase

PEG 1500, 3350 and 8000

phosphate salt

[266]

—

linear alkylbenzene sulfonates

PEG 1500

(NH4)2SO4

[267]

ethanol

NaH2PO4

[268]

Gentiana scabra Bunge polysaccharides

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

4.12.3 Dispersive-µ-solid phase extraction Dispersive-μ-solid phase extraction (Dμ-SPE) is a miniaturized version of SPE, as reported by Tsai and his coworker [269]. It considerably reduces the time consumed and simplifies the extraction process. In this method, extraction is not carried out in a cartridge, column, or disk but in the bulk solution, which leads to greater rapidity and ease of operation compared with conventional SPE. Usually, DSPE is used for matrix cleanup purposes; that means, after the dispersion of micro- or nanosorbents in the bulk solution or matrix containing the target analytes, any possible matrix interferences are retained on the sorbents. The dispersion phenomenon enables the sorbent to interact rapidly and uniformly with all the target analytes, leading to the enhanced precision of the phase extraction method and reduced extraction time [270
274]. Then sorbents are separated from the bulk solution by centrifugation, and the target analytes are collected in the supernatant. In contrast, D-μ-SPE can be performed by trapping the target analytes in the sorbents. The adsorption of analytes is based on many different phenomena, including hydrogen bonding, dipole
dipole and π
π interactions. In D-μ-SPE, the nature and physicochemical properties of the solid sorbent are very important in order to achieve an accurate, sensitive, and selective determination of target analytes. In practice, the main requirements for a solid sorbent are (1) fast and quantitative adsorption and desorption, (2) high surface area and high capacity, and (3) high dispersibility in liquid samples [275]. After extraction, the sorbent containing the target analytes is isolated by centrifugation or filtration. The target analytes can then be eluted or desorbed by an appropriate desorption solvent [276,277]. So far, various adsorbents have been utilized to trap or adsorb target analytes in different real samples. Nowadays, several commercial

or synthetic nanomaterials, including functionalized silica, multiwalled carbon nanotubes, graphene, graphene oxide, and modified magnetic NPs (MNPs), have been applied as sorbents in D-μ-SPE. These nanomaterials can be used for the speciation, enrichment, and separation of various analytes from different matrices. The larger superficial area of nanomaterials (which enhances the extraction kinetic) and the variety of different chemical interactions (which widens the applicability to different problems) can be considered among the main reasons. Within the composites, the combination of MNPs with different materials such as metal-organic frameworks, zeolitic imidazolate frameworks, layered double hydroxides, and polymers is especially interesting. In this sense, the composite presents high extraction capabilities due to the porosity, existence of hydrogen bonding, dipole
dipole and π
π interaction, and/or polymeric network while maintaining magnetic behavior that simplifies the overall extraction procedure. Based on a review study by Castillo-Garcia and coworkers, the distribution percentages of different types of coated MNPs used in solid-based extraction methods in the period 2011
15 are as follows [278]: polymers (21.1%), molecularly imprinted polymers (MIPs) (17.2%), silica (13.2%), graphene (12.7%), surfactants (12.7%), carbon nanotubes (CNTs) (10.3%), ionic liquids (7.4%), and metal/metal oxides (5.4%). CNTs are novel and interesting carbonaceous materials, which are classified as single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) on the principle of the presence of carbon atom layers in the nanotube walls [279]. Due to their remarkable physical and chemical properties, MWCNTs have attracted increasing interest as sorbents for SPE methods. Barfi and coworkers developed a novel method, named syringe-assisted D-μ-SPE, based on repeatedly withdrawing and pushing out a mixture of an aqueous sample including some chelated potentially toxic metal ions

New Generation Green Solvents for Separation and Preconcentration

4.12 Modern techniques of isolation and/or preconcentration

(Pb21, Cd21, Co21, Ni21, and Cr31) with bis(acetylacetone) ethylenediimine and a low level of a suitable adsorbent (1.6 mg of MWCNTs) in a test tube using a syringe. Since the maximum contact surface areas were simply provided between the chelated ions and adsorbent with no need to essentially offline the accelerating mass transfer (including sonication and vortex) and centrifugation steps, maximum efficiency was achieved within a short period of time [280]. In recent years, layered double hydroxides (LDHs) have attracted considerable attention due to their versatility and potential application as anion exchangers, sorbents, catalysts and catalyst supports, drug delivery agents, molecular sieves, polymer composites, sensor materials, and electrode materials. Their composition can be represented by the general formula [M21 12xM31 x(OH)2]x1[An2]x/n.m. H2O, where M21, M31, and An2 are the divalent cation, trivalent cation, and interlayer anion, respectively [281
283]. Arghavani-Beydokhti have introduced a new mode of D-μ-SPE named syringe-to-syringe magnetic D-μ-SPE as an efficient, simple, rapid, and ecofriendly sample extraction method. Nickel-aluminum
layered double hydroxide
coated magnetic nanoparticles (Fe3O4@Ni-Al-CO3-LDH), as an efficient nanosorbent, were synthesized and successfully applied for the concurrent extraction of trace amounts of Cd21 and Pb21 ions in food and water samples prior to their determination using a microsampling-flame atomic absorption spectrometry technique. In this method, the dispersion is done by injection and back-injection of a mixture of nanosorbent and sample solution using two disposable connected syringes without the need for an ultrasonic bath or a vortex mixer [284]. Adlnasab produced a magnetic calcined LDH (CLDH(Zn-Fe)@Fe3O4) modified with the tannic acid (TA) as a biosorbent. Then supramolecular ferrofluid was obtained from the combination of CLDH(Zn-Fe)@Fe3O4@TA nanoparticles, along with the supramolecular

187

solvent (composed of 1-dodecanol and toluene) as the carrier liquid through ultrasonic energy. Coating magnetic nanoparticles with a suitable supramolecular solvent provided steric repulsions to prevent particle agglomeration. This method was successfully applied for the supramolecular preconcentration of diazinon and metalaxyl from various fruit juice samples [285]. Krawczyk and coworkers combined an ultrasound-assisted D-μ-SPE, with the use of silver nanoparticles (AgNPs) as a solid sorbent; with a high-resolution continuum source, electrothermal atomic absorption spectrometry has been proposed for the preconcentration and determination of Hg21 ions in water samples [286]. Krawczyk at al. also used dendrimermodified halloysite nanotubes as a new sorbent for ultrasound-assisted D-μ-SPE and sequential determination of cadmium and lead in water samples [287]. Halloysite is a natural kaolinite mineral, having rolled aluminosilicate sheets. Alumina octahedral sheets are at the inner surface, while the silica layer is at the outer surface of the tube. The outer surface is negatively charged, while the inner lumen surface is positively charged in the pH range 2
7. This enables selective modifications related to anionic species that can be trapped in the lumen, while cationic units can be immobilized on the surface [288
290]. Amine groups can be introduced to the surface of HNTs employing the unique materials called dendrimer. Dendrimers are a kind of polymers that possess notable properties and applications. These well-known polymers are defined as three-dimensional structures with versatile chemical properties due to the multifunctional end groups and hollow interiors between branches. Dendrimers have different functional end groups, whose number and type can be controlled by choosing a proper synthetic method and generation [291,292]. Graphene, a one-atom-thick sheet of sp SP2 hybridized carbon atoms arranged in a

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

honeycomb lattice, has emerged as an attractive two-dimensional nanomaterial owing to its outstanding properties like large surface area, unique electrical, thermal, mechanical, and optical properties. Unlike CNTs, both sides of the planar sheets of graphene are available for molecule adsorption. Hence, the ultrahigh specific surface area of graphene is responsible for its high adsorption capacity and high chemical activity [293]. However, the adsorption of metal ions on graphene nanosheets often requires formation of hydrophobic complexes using chelating agents. Herein, the development of functionalized graphene is recommended. Khaligh et al. used carboxylated nanoporous graphene as a nanoadsorbent in ultrasound-assisted D-μ-SPE for the rapid speciation of trace arsenic (V) and arsenic (III) ions in natural water and human biological samples prior to determination by flow injection
hydrid generation atomic absorption spectrometry [294]. Report of the use of chitosan as an adsorbent in D-μ-SPE are rare. Chitosan is obtained from partial N-deacetylation of chitin and is soluble in acidic solution [295]. The expansion of chitosan can be promoted by the repulsive force between cationic charges, which is favorable for the formation of hydrogen bonds between
OH groups in chitosan and target analytes. Shi et al. established a novel in-syringe chitosan-assisted D-μ-SPE method for the determination of anthraquinones in three kinds of traditional Chinese medicinal oral liquids containing rhubarb [296]. Silica is one of the most widely used sorbents due to its attractive properties, including high surface area, porosity property, low cost, and safety. In addition, silica can be easily functionalized via silylation [297,298]. As a sorbent, the interactions between silica and analytes are the result of hydrogen bonding, electrostatic attraction of the silanol groups, and porosity. For more selectivity, silica is often derivatized (or modified) with different

functional groups. Metarwiwinit and coworkers demonstrated a simplified D-μ-SPE using silica sol as the sorbent for the preconcentration of ferrous ions. Ferrous ions were prederivatized via complexation with 1,10phenanthroline (Phen) before being adsorbed by the silica sol. Silica sol was prepared via the hydrolysis and condensation of TEOS and L-arg [299]. MIPs have a high selectivity, affinity, and simplicity, and therefore many are used in Dμ-SPE procedures as sorbents for the cleanup and preconcentration of different target compounds from biological and environmental samples. MIPs are polymeric materials whose synthesis is done in connection with template correlation in template, functional monomer, and cross-linking agents. MIPs include specific recognition sites with the memory of shape, size, and functional groups of the template molecule [300
302]. A core-shell Fe3O4@SiO2@MIP has been synthesized and used by Asfaram and coworkers for the preconcentration and determination of quercetin residues in Apium graveolens, Brassica oleracea, Spinacia oleracea, watercress, onion, and apple matrices based on the D-μ-SPE procedure. A schematic procedure of a Fe3O4@SiO2@MIP
based D-μ-SPE is shown in Fig. 4.23 [303]. Liu et al. applied hyperbranched polyester (HBPE) as a D-μ-SPE sorbent for the determination of hexaflumuron, flufenoxuron, chlorfluazuron, and lufenuron in environmental water samples in combination with HPLC analysis [304]. Hyperbranched polymers are well-defined as polymer systems possessing a large number of branch points combined with relatively short chains in their molecular structures. Their structures are not consistent (as in the case of dendritic polymers), and the specific molecules can have different molecular weights and degrees of branching [305,306]. Metal-organic frameworks (MOFs), selfassembled directly from metal ions with

New Generation Green Solvents for Separation and Preconcentration

4.12 Modern techniques of isolation and/or preconcentration

FIGURE 4.23

A schematic procedure of Fe3O4@SiO2@MIP
based D-μ-SPE [303].

New Generation Green Solvents for Separation and Preconcentration

189

190

4. New methodologies and equipment used in new-generation separation and preconcentration methods

organic linkers via coordination bonds, are an intriguing class of hybrid inorganic
organic crystalline porous materials [307,308]. Because of their fascinating structures and unique properties, such as diverse structures and pore topologies, large surface-to-volume ratios, high surface areas, and good thermal stability, MOFs have great potential as sorbents in the D-μ-SPE method. Xia et al. used a Zr-based metal-organic framework with ligands of 2amino-benzenedicarboxylic acids (UiO-66NH2) as a special and efficient adsorbent for the pretreatment of chlorophenoxy acid herbicides (CPAHs) from biosamples. The assynthesized material not only possessed high porosity, large surface area, exceptional thermal and chemical stability in water, and organic solvents but also exhibited special adsorption for CPAHs, owing to the ionic bond between the amino groups of UiO-66-NH2 and the carboxyl groups of the CPAHs [309]. Vakh et al. developed an automated magnetic D-μ-SPE procedure in a fluidized reactor for the determination of fluoroquinolone antimicrobial drugs (fleroxacin, norfloxacin, and ofloxacin) in meat-based baby food samples. The developed approach involves the dispersion of the MNPs in a liquid sample phase by air-bubbling, followed by the collection of MNPs containing analytes in the fluidized reactor in a magnetic field, elution, and analytes detection (see Fig. 4.23) [310]. ILs have received attention because of their promising properties in terms of their great physicochemical characteristics such as low volatility, good thermal stability, high conductivity, and tunable miscibility. Some ILs, such as imidazolium-based ILs, have long alkyl chains, which enable them to aggregate and form a surfactant-like compound in aqueous solutions. This behavior has resulted in their successful application in different sample preparation procedures including magnetic mixed hemimicelles solid phase extraction [311]. This performance has attracted great attention

because of its several advantages such as high extraction efficiency, easy elution of analytes, and high flow rate for sample loading. Hamidi et al. designed an ionic liquid-based magnetic mixed hemimicelles D-μ-SPE using 1hexadecyl-3-methylimidazolium bromide
coated magnetic graphene oxide/polypyrrole as an adsorbent for extraction and preconcentration of methotrexate from urine samples [312]. A new strategy of D-μ-SPE is effervescentassisted D-μ-SPE. In this technique, sodium carbonate and citric acid are used as the source of gas production (carbon dioxide) and the effervescence precursor. Dispersion of the adsorbent particles in the sample solution is accomplished by means of a boiling process, and the particles are distributed uniformly in the solution. This technique is very simple, very fast, and effective [313,314]. Fahimirad et al. used this method for the extraction and preconcentration of the drugs Amitriptyline (AMT) and Nortriptyline (NRT). They synthesized Fe3O4@SiO2@N3 as a new and effective adsorbent and applied it in D-μ-SPE (see Fig. 4.24) [315]. Table 4.8 listed the many application of D-μ-SPE.

4.12.4 Stir-bar sorptive extraction SBSE as a solvent-less sample preparation technique was first offered by Baltussen et al. (1999). SBSE is based on the use of polydimethylsiloxane (PDMS) as a sorbent for SPE [347]. PDMS is coated (typically 0.5
1 mm thick) onto a glass-coated magnetic bar (socalled twisters). Sampling is done by directly introducing the SBSE device into the aqueous sample. During stirring, the bar adsorbs the organic compounds to be extracted. The bar is removed from the sample, rinsed with deionized water, and dried. After sorption, the compounds are chemically desorbed by a liquid or thermally [348]. Thermal desorption is

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4.12 Modern techniques of isolation and/or preconcentration

FIGURE 4.24 Schematic of an automated magnetic D-μ-SPE procedure developed by Vakh et al. [310] (License Number 4662431245371).

TABLE 4.8 Other application of D-μ-SPE. Matrix

Sorbent

Analytes

References

Tap water, milk, honey, and plasma

Fe3O4

sulfasalazine

[316]

Environmental water samples

poly(methyl methacrylate) grafted agarose

Cd, Ni, Cu, and Zn

[317]

Real water samples

Fe3O4

Cu

[318]

Human urine

cation exchange sorben

muscarine

[319]

Urine samples

S@SnO2-NPs-activated carbon

glibenclamide

[320]

Water samples

γ-Fe2O3-NPs- activated carbon

malachite green

[321]

Plasma, urine, and water samples

Ni:ZnS-MMWCNTs

Phenobarbital and phenytoin

[322]

Honey

polymer cation exchange

ametryn, atrazine, prometryn, simazine, and terbutryn

[323]

Seawater, river water, and mine water

halloysite nanotubes

gallium, indium, and thallium

[324]

Environmental and biological samples

titanium dioxide (TiO2)

ribonucleosides

[325]

Biological fluids and tap water samples

(Mg-Al-4-amino-5-hydroxyl-2,7naphthalendisulfonic acid monosodium salt interlayer anion DH)

Cd21, Cr61, Pb21, Co21, and [326] Ni21 (Continued)

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

TABLE 4.8 (Continued) Matrix

Sorbent

Analytes

References

Human plasma and urine samples

Cu@SnS/SnO2

atorvastatin

[327]

Aquaculture water

MIL-101(Cr)

chloramphenicol, thiamphenicol, and florfenicol

[328]

Biological matrices

polyaniline/sodium dodecyl benzene sulfonate/ TiO2 nanocomposite

amlodipine, diltiazem, and verapamil

[329]

Food samples

ZnO nanoparticles

germanium

[330]

Milk samples

magnetic-activated carbon

Bisphenol A

[331]

Propolis

microcrystalline cellulose

phenolic compounds

[332]

Human biological samples

nano LDH-ammonium pyrrolidine dithiocarbamate

chromium species

[333]

Nonalcoholic beer samples

Ni/Cu-Al LDH nanocomposites

carboxylic acids

[334]

Well water, Tap water, river water, human urine, milk

Fe3O4/NiO@SiO2-OP2O5H

meloxicam and piroxicam

[335]

Water and caprine blood samples

carboxyl-functionalized nanoporous graphene

mercury species

[336]

Commercial edible oils

polymer anion exchange

bisphenols

[337]

Water and urine samples

Mn@CuS/ZnS-NCs-activated carbon

sildenafil citrate (Viagra)

[338]

Milk samples

MIL-101(Cr)@graphite oxide

sulfonamides

[339]

Fruit juices

Ni/Co-NO3 LDH nanosheet

phenolic acids

[340]

Water samples

CoFe2O4-NPs-activated carbon

Maxilon Red GRL dye

[341]

Urine and plasma samples

Fe3O4@nSiO2@mSiO2-NH2

ofloxacin

[342]

Biological matrices

polypyrrole-sodium dodecylbenzenesulfonate/ ZnO nanocomposite

antihypertensive drugs

[343]

Water samples

MWCNTs/Fe3O4@Poly(1,8-diaminonaphtalen)

aromatic amines

[344]

Aqueous samples

Fe3O4@CuS@Ni2P-CNTs

Allura Red

[345]

Water samples

ZnO-ZrO2@activated carbon

thallium

[346]

performed at temperatures in the 150 C
300 C range for up to 15 min. However, the high sensitivity of the thermal desorption requires the use of an expensive unit in the GC setup, the thermal desorption unit (TDU). Liquid desorption is an alternative to thermal desorption

when thermally labile solutes are analyzed, when the separation is carried out using liquid chromatography or CE, or when a unit coupled to GC is not available. During the liquid desorption mode, the polymer-coated stir-bar is immersed in a stripping solvent or solvent

New Generation Green Solvents for Separation and Preconcentration

4.12 Modern techniques of isolation and/or preconcentration

mixture for the chemical desorption of the extracted solutes. Liquid desorption can also be more suitable than thermal desorption in order to minimize contamination from the PDMS phase that can interfere in the analysis of certain solutes (i.e., phthalate esters, PEs) [349]. Fig. 4.25 depicts an image of the SBSE analytical device, showing it to be constituted by a magnetic stir-bar incorporated into a glass jacket (10 or 20 mm in length), typically coated with 24
126 mL (0.5 or 1.0 mm in film thickness) of PDMS [350] (Fig. 4.26). The theory behind SBSE is the same as that of SPME, but, instead of a polymer-coated fiber, stir-bars are coated with PDMS, an apolar polymeric phase used for hydrophobic interactions

FIGURE 4.25

193

with target molecules. The retention process in the PDMS phase is based on Van der Waals forces and the hydrogen bonds that can be formed with the oxygen atoms of PDMS, depending on the molecular structure of the target analytes [351]. Only three coatings for SBSE are commercially available: PDMS, polyacrylate (PA), and ethylene glycol/silicone (EG/silicone). PDMS is a nonpolar phase, so it is not suitable for the extraction of polar compounds, especially those with log Kow values lower than 3 [352,353]. The EG/silicone coating degraded quickly, and each stir-bar could be used only about 20 times, but to solve this issue, the stirring of the sample was modified. The EGsilicone bar is placed on the wall of the

Schematic of D-μ-SPE procedure based on Fe3O4@SiO2@N3 [315] (License Number 4662440096465).

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194

FIGURE 4.26

4. New methodologies and equipment used in new-generation separation and preconcentration methods

Schematic of a SBSE device [350] (License Number 4662440560383).

extraction jacket while the sample is stirred by a magnetic stir-bar or a conventional PDMScoated sportive bar. The development of new coatings is the most relevant improvement to expand the applicability of SBSE, allowing the analysis of polar compounds. The new coatings are typically manufactured using two technologies: molecular imprinting technology (MIT) and sol
gel processes. MIT is a technique to create artificial receptors or ligands with a predetermined selectivity and specificity for a given analyte. The sol
gel process is a method for producing advanced solid materials from small molecules. The method is used for creating organic
inorganic hybrid materials, mainly metal oxides of silicon, titanium, and zirconium. In general, the sol
gel process involves the transition of a solution system from a liquid “sol” (mostly colloidal) to a solid “gel” phase. New coatings must have the following characteristics: 1. They should be physically stable and have good mechanical properties that ensure they do no break or degrade after their use. 2. Bonding of the coating to the cover of the magnetic rod must be strong enough to allow intense friction between the coating and the surface of the sample recipient without material losses.

3. The coatings must be also chemically inert. 4. New developed materials must be able to tolerate the high temperatures used in thermal desorption without degrading or losing extraction efficiency. Other materials used for coating magnetic stirrers are polyurethane foams, silicone materials, poly(ethylene glycol)-modified silicone (EG Silicone Twister), poly(dimethylsiloxane)/ polypyrrole, poly(phthalazine ether sulfone ketone), polyvinyl alcohol, carbon nanotubepoly(dimethylsiloxane) (CNT-PDMS), alkyldiol-silica (ADS) restricted access materials, zeolitic imidazole framework, monolithic materials, and/or cyclodextrin [354]. SBSE can be used in headspace (HS) or DI sampling mode (Fig. 4.27) [352]. In the immersion mode, which is usually abbreviated simply as SBSE, the polymer-coated stir-bar is added to a sample vial that contains the liquid sample, and the sample is stirred under controlled physical and chemical conditions. The use of SBSE was extended almost immediately to sampling in the vapor phase (headspace mode) by Bicchi et al. [355] and is known as headspace solvent extraction (HSSE). In HSSE, sampling is performed by suspending the coated stir-bar in the headspace vial, and the polymer is in static

New Generation Green Solvents for Separation and Preconcentration

4.13 The application of carbon nanotubes and nanoparticles in separation

195

FIGURE 4.27 Extraction mode of SBSE: (A) DI and (B) HS [352] (License Number 4662441025095).

contact with the vapor phase of a solid or liquid matrix. The sample is usually stirred in order to favor the presence of the solutes in the vapor phase. Some applications of SBSE are listed in Table 4.9.

4.13 The application of carbon nanotubes and nanoparticles in separation For the first time, Sumio Iijima described the synthesis of a new type of finite carbonaceous materials with needle-like tube shapes of graphitic sheets [382]. Since they have a cylindrical structure, nanometric diameter, and lengths up to several tens of micrometers and are made of carbon, they were termed carbon nanotubes. Carbon nanotubes (CNTs) are intermediate between graphene and bucky balls and have a two-dimensional hexagonal lattice of carbon atoms. CNTs are also known as one of the allotropes of carbon. The CNTs can be classified into two types: single-walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs) (Fig. 4.28). SWCNTs are fabricated by rolling a graphene sheet into a whole cylinder. MWCNTs are made up of two or more graphene sheets coaxially assembled around a central hollow core.

On the basis of the rolling angle of the graphene sheets, SWCNTs called chiral, armchair, and zigzag (Fig. 4.29). Given the unique properties of CNTs, such as thermal and electrical conductivity, strength, toughness, and stiffness, they have found different applications in science and engineering, including electronic devices [383], reinforced materials [384], drug delivery [385], removal [386
393], gas storage [394], or field emission materials [395]. In many of the applications, the modification surface of CNTs is crucial. The walls of the carbon nanotube are not reactive, but the fullerene-edges are more reactive. Hence, the end, tips, and defect area of the carbon nanotubes are used sometimes to produce functional groups (e.g.,
COOH,
OH, or
C 5 O). Moreover, the walls of CNTs can be functionalized via hydrogen bonding, electrostatic forces, hydrophobic interactions, Van der Waals forces, and p
p stacking by small molecules or biochemically active molecules [396] or to wrap macromolecule chains [397]. Since CNTs have large surface areas, thermal stability, and high mechanical surface, they recently have been extensively used as adsorbent materials. For example, some research approaches have focused to combine

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4. New methodologies and equipment used in new-generation separation and preconcentration methods

TABLE 4.9 Some application of SBSE. Matrix

SBSE mode SBSE-coating material

Type of desorption Analytes

References

Orange samples

DI

MIP

liquid

thiabendazole and carbendazim

[356]

Human urine

DI

PDMS

liquid

plastic additives

[357]

Surface and tap water samples

DI

PDMS, EG-silicone

liquid

48 polar and nonpolar pollutants

[358]

Human body fluids

DI

zeolitic imidazole framework

liquid

fluorouracil and phenobarbital

[359]

Coastal sand samples

DI

CoFe2O4@oleic acid

liquid

UV filters

[360]

Urine

DI

CoFe2O4@Strata-XTM-AW magnetic composite

liquid

triphenyl and diphenyl phosphate

[361]

Staphylococcus aureus

DI and HS

PDMS or EG-silicone

thermal

bacterial volatile and/or semivolatile metabolites

[362]

River water and rain water

DI

carbon-nanoparticle

liquid

PAHs

[363]

Water samples

DI

PEG
g-MWCNTs

liquid

PAHs

[364]

Human plasma

DI

acrylate monolithic polymer

liquid

losartan and valsartan

[365]

Beer

DI

PDMS

thermal

flavor compounds

[366]

Soil

DI

PDMS

liquid

soil fungal biomass

[367]

Fruit juice

DI or HS

PDMS

thermal

volatiles

[368]

Fruit juices and vegetables

DI

montmorillonite/polyaniline/ polyamide nanocomposite

liquid

organophosphorous pesticides

[369]

Wastewater samples

DI

PDMS

liquid

selected pharmaceuticals

[370]

Water samples

DI

PDMS

thermal

polychlorinated biphenyls and organochlorine pesticides

[371]

Beverage and urine

DI

zeolitic imidazole framework

liquid

caffeine

[372]

River water and DI agricultural wastewater samples

ZrO2-reduced GO

thermal

ethion

[373]

Air samples

—

PDMS

thermal

phosphorus flame retardants

[374]

Water and soil samples

DI

PDMS

thermal

nitrophenols

[375]

Water

DI

MIP

liquid

Bisphenol A

[376] (Continued)

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4.13 The application of carbon nanotubes and nanoparticles in separation

TABLE 4.9 (Continued) SBSE mode SBSE-coating material

Type of desorption Analytes

References

Environmental water samples

DI

polydimethylsiloxane/MIL-100 (Fe)

liquid

triazines

[377]

Water samples

DI

PDMS

liquid

N-nitrosamines

[378]

Tap and lake water

DI

etched poly(ether ether ketone)

liquid

Sudan dyes, triazines, PAHs, alkaloids, and flavonoid

[379]

Cucumbers and green bean sprouts

DI

C18

liquid

acidic phytohormones

[380]

Human plasma

DI

vinylpyrrolidone-ethylene glycol dimethacrylate monolithic polymer

liquid

diazepam and nordazepam [381]

Matrix

FIGURE 4.28

Graphical representations: graphene (left), SWCNT (middle), and MWCNT (right).

FIGURE 4.29 Carbon nanotubes are classified as armchair, chiral, or zigzag based on their structure.

a trace amount of CNTs with the porous bed as a new class of stationary phases. It is easy to find early examples about the use of CNTs in the literature for preconcentrating trace analytes. Yang and coworkers (2001) reported the

first data on MWNTs as a sorbent for dioxin removal. They used a temperatureprogrammed desorption technique for studying dioxin adsorption [398]. This group showed that dioxin adsorbed on a functionalized carbon nanotube is a thousand times bigger than dioxin adsorbed on the activated carbon. In another work, the applicability of MWNTs as packing adsorbents for SPE was explored for different endocrine disruptors, such as bisphenol, 4-nnonylphenol, and 4-tertoctylphenol. In this paper, Jiang et al. used MWCNTs as adsorbents in the form of the cartridge, and the mentioned analytes adsorbed on the MWNTs were eluted by an appropriate

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198

4. New methodologies and equipment used in new-generation separation and preconcentration methods

amount of methanol. Finally, the three analytes were determined by HPLC [399]. Also, Cai and coworkers extended the extractions of diethylphthalate, di-n-propyl-phthalate, di-iso-butylphthalate, and di-cyclohexyl-phthalate by a packed cartridge of the MWCNTs from aqueous solutions. Then the stated analytes adsorbed on the MWCNTs were eluted with 5 mL of acetonitrile and analyzed by HPLC. The adsorption capacities of organic compounds on the MWCNTs, graphitized carbon black and fullerene C60 by different solvents as eluents, were investigated by Liu [400]. In this work, the highest recoveries were obtained for MWCNTs. In another work, the extraction of inorganic ions (Pb21, Cd21, and F2) from aqueous solution was done via oxidized MWCNTs (OX-MWCNTs) [401]. The preconcentration of cadmium, magnesium and nickel on the OXMWCNTs as the solid phase has been investigated by Liang, and the determination was done with ICP-AES [402].

4.14 Conclusion The overview of the different extraction methodologies has indicated that some of these approaches get more attention among researchers because the use of harmful organic solvents and the volume of the studied sample have dropped considerably. This chapter focused on the application of environmentally friendly methods. Direct comparison of the methods introduced so far for a group of different analytes is simply not possible, since the methods for determining given analytes are usually specific, therefore preventing a rigorous discussion. Nonetheless, among preconcentration techniques, the properties of CNTs and the possible modification of carbon nanotube surfaces by chemical methods have led to developing new microseparation methods and techniques. On the other hand, all aspects of these

analytical techniques with respect to the progress of nanotechnology, in the near future, will lead to significant developments in the technology of preconcentration and extractions.

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1492.

New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

5 Type of green solvents used in separation and preconcentration methods Erkan Yilmaz1,2,3 and Mustafa Soylak3,4 1

Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, Turkey ERNAM—Erciyes University, Nanotechnology Research Center, Kayseri, Turkey 3Technology Research & Application Center (TAUM), Erciyes University, Kayseri, Turkey 4Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey

2

Abbreviations [C8mim][PF6] [Cnmim][PF6] [APMIM]Br [C16MIM]Br AµE ASE BaPy BPA BTEX C60 CE CF-SD-LPME ChCl CIAME CNTs COOH

1-octyl-3-methylimidazolium hexafluorophosphate 1-alkyl-3-methylimidazolium hexafluorophosphate 1-(3, aminopropyl)-3methylimidazolium bromide 1-hexadecyl-3-methylimidazolium bromide adsorptive microextraction accelerated solvent extraction benzo(a)pyrene bisphenol A benzene, toluene, ethylbenzene, and xylene fullerenes capillary electrophoresis continuous-flow microextraction/ single-drop microextraction choline chloride cold-induced aggregation microextraction carbon nanotubes carboxylic acid

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00005-X

CV-AFS CyNMe2 CPE CPT DBU DESs DESAAELLME DES-ELLME DES-UAELPME DI-SDME DMCA EPA ETAAS FAAS FIA FIP G GAC GAPI

207

cold-vapor atomic fluorescence spectrometry N,N-dimethylcyclohexylamine cloud point extraction cloud point temperature 1,8-diazabicyclo-[5.4.0]-undec-7-ene deep eutectic solvents DES-based air assisted emulsification liquid liquid microextraction DES-based emulsification liquid liquid microextraction DES-based ultrasound-assisted emulsification liquid phase microextraction direct immersion single-drop microextraction N,N-dimethylcyclohexylamine environmental protection agency electrothermal atomic absorption spectrometry flame atomic absorption spectrometry flow injection analysis international pharmaceutical federation Graphene green analytical chemistry green analytical procedure index

© 2020 Elsevier Inc. All rights reserved.

208 GC GC FID GC MS/MS GFAAS GO HF-VMME HGAAS HPLC HR-CSETAAS HS-SDME HWE ICH

ICP-AES ICP-OES ILs ISO LC-UV LCA LLE LLLME LPME MAE MALDI-MS MAE MCDA MIPs MISPE MOFs NADESs NEMI OH OTA PAHs PF6 PHWE PLE

5. Type of green solvents used in separation and preconcentration methods

gas chromatography gas chromatography flame ionization detection gas chromatography tandem mass spectrometry graphite furnace atomic absorption spectrometry graphene oxide hollow fiber vesicular-mediated microextraction hydride generation atomic absorption spectrometry high-performance liquid chromatography high-resolution continuum source electrothermal atomic absorption spectrometry headspace single-drop microextraction hot water extraction international council for harmonisation of technical requirements for pharmaceuticals for human use inductively coupled plasma atomic emission spectrometry inductively coupled plasma optical emission spectrometry ionic liquids International Organization for Standardization liquid chromatography ultraviolet spectrophotometry life cycle assessment liquid liquid Extraction liquid liquid liquid microextraction liquid phase microextraction microwave-assisted extraction matrix-assisted laser desorption/ ionization mass spectrometry micelle-assisted extraction multicriteria decision analysis molecularly imprinted polymers molecularly imprinted solid phase extraction metal organic frameworks natural deep eutectic solvents national environmental methods index hydroxyl ochratoxin A polycyclic aromatic hydrocarbons hexafluorophosphate pressurized hot water extraction pressurized liquid extraction

PROMETHEE QBD R1r2 Meim1PF62 R1r2 Meim1Tf2n2 RGO SDME SFE SFODME SHs SHWE SIA SPME SPE SRSE SUPRAs WCED SWE TMSPDETA TMSPEDa TOPSIS TSP-MS-MS UAE UNWFP USP WHO WPC

preference ranking organization method for enrichment evaluation quality-by-design 1-R1 2 2r2 2 3-methylimidazolium hexafluorophosphate 1-R1 2-R2 3-methylimidazolium bis [(Trifluoromethyl)sulfonyl]amide reduced graphene oxide single-drop microextraction supercritical fluid extraction solidified floating organic drop microextraction switchable hydrophilicity solvents superheated water extraction sequential flow injection analysis solid phase microextraction solid phase extraction stir-rod sorptive extraction SSs: switchable solvents supramolecular solvents World Environment and Development Commission subcritical hot water extraction N1-(3-trimethoxysilylpropyl) diethylenetriamine N-(3-trimethoxysilylpropyl) ethylenediamine technique for order of preference by similarity to ideal solution thermospray tandem mass spectrometry ultrasound extraction United Nations World Food Programme United States Pharmacopeial World Health Organization World Pharmacy Council

5.1 Introduction Direct analysis of untreated samples aims to score from a green analytical chemistry (GAC) perspective. One of the most desirable dreams for green analytical chemists is to gather as much information as possible about samples without any physical or chemical treatment and, if possible, to gain accurate information on samples by remote sensing [1]. However, problems, such as the complexity of the matrix medium in which the sample is being studied, the analyte concentration being below the lowest concentration a device can measure, make it

New Generation Green Solvents for Separation and Preconcentration

5.2 Green analytical chemistry

compulsory to use sample preparation methods before measurement [2,3]. In 2007 L. H. Keith and coworkers covered this idea in detail “Although an ideal green analysis would obviate preconcentration steps, the evolving understanding of the vanishingly low thresholds for the negative biological activity of environmental contaminants suggests that analytical chemists will continue to need sample pretreatment as a tool to take measurements from dilute samples at, or below, the limit of detection” [4]. In addition, it is recognized by the analytical chemistry community that most of the existing analytical tools/devices generally work better in liquid or previously dissolved samples and that it is easier to obtain accurate, and precise measurements in samples where the separation and preconcentration steps are applied to solve analytical problems. Namiesnik and Szefer published a report in 2008 based on information from 250 questionnaires answered by analytical chemistry laboratories in Central Europe. This report underlined that the extraction and sample preparation steps are the weakest links of the analytical chain and that both consume most of the laboratory study time and resources devoted to analytical procedures [5]. In 2009 Tobiszewski and coworkers reported that sample treatment is considered the most polluting step of analysis, as generally organic solvents are used [6]. In 2016 M. Koel stated that the usually discussed areas of GACrelated analytical chemistry are separation science and sample preparation due to the required high amount of solvent and energy [7]. Therefore taking into account all these arguments, it may be that sample preparation is one of the most challenging steps regarding both the main analytical properties and the green parameters, especially in the case of operator safety and environmental impacts. The sample treatment step in analytical chemistry can be considered as partial or total digestion, mineralization, extraction, filtration, and distillation, among other steps. In most cases, sample preparation

209

techniques, called separation and enrichment, are a labor-intensive step using toxic organic and inorganic solvents that harm the environment and laboratory workers. As Bizzi and coworkers stated in 2011 “[I]t is still usual to think that sample digestion (in elemental content determination) is just a question of adding huge volumes of concentrated acids to sample aliquots, followed by an increase of temperature.” [8]. On the other hand, analyte leaching or other mean partial dissolution of analyte/analytes, the direct extraction of analyte/analytes from sample matrix, and the separation and preconcentration of analyte/analytes generally needed to use high amounts of organic or inorganic solvents and laboratory extraction and digestion equipment that are complex and difficult. Hence, new digestion and extraction systems based on ultrasounds, high pressure, microwave heating, vortex mixing, and the like; new solvents such as ionic liquids (ILs), deep eutectic solvents (DESs), switchable solvents, supramolecular solvents, supercritical solvents, surfactants, and so on; and innovative separation and preconcentration methods such as liquid phase microextraction (LPME) and solid phase microextraction (SPME), among others, have replaced conventional ones and have led to a revolution in analytical chemistry [9 11]. The need to reduce solvent consumption, to decrease sample preparation time and cost, to use environmentally friendly solvents, to obtain reproducible analytical results, and to develop high extraction efficiency are the main reasons for this revolution and are born of green analytical chemistry.

5.2 Green analytical chemistry 5.2.1 History, principles, and recent trends in green analytical chemistry The introduction of the green chemistry idea is related to the widespread trend of the rules and principles of sustainable development and

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5. Type of green solvents used in separation and preconcentration methods

the application of these rules in laboratories and chemical plants. Actually, the principles of green chemistry were adopted in certain areas of chemistry, and several other principles were later published. Some of them are Principles of Green Chemical Technology, 12 Principles of Green Analytical Chemistry, and 12 Principles of Green Engineering [6,7]. The adverse impacts of performing analytical procedures can harm the environment and pose serious risks to operators. Hence, for these reasons, it is very important to think about the consequences and results of actions taken by researchers of analytical procedures. Respecting the perspective of those who care about the environment and also take into account the economic conditions of analytical procedures, exceptional attention should be paid to the inherent risk of certain types of samples, some of the reagents and solvents used, the energy consumption associated with advanced instrumentation, and, of course, laboratory wastes and emissions from many of the analytical procedure steps [10,12]. Taking into account all these natural risks, the analytical chemistry community has taken important steps in this sense long before the term GAC was used. In the mid-1970s, some innovative advances were introduced in sample preparation methods as well as in measurement and data processing [13]. It should be noted that the methodological milestones designed to enhance the green character of analytical procedures (Fig. 5.1) were obtained before the formulation or introduction of GAC concepts [13]. For example, usage of the term “clean waste” instead of the word “waste” can be considered one of the most important opinions and proposes an alternative way that includes an additional chemical attempt for the minimization of the environmental effects of flow injection analysis. This attempt can be considered the starting point of the clean analytical chemistry concept. In 1995 the opportunities born of the

contribution of degradation processes and flow injection analyses to develop analytical methods were verified [13]. In the same year, de la Guardia and Ruzicka published an article entitled “Towards Environmentally Conscientious Analytical Chemistry Through Miniaturization Containment and Reagent Replacement,” which is recognized as the first declaration of the so-called Green Analytical Chemistry [14]. In another important study, Green and coworkers used the term “waste minimization” for the analytical practice. Although the authors did not mention the green analytical chemistry term, the article is considered the pioneering work of GAC because the green idea is naturally present [15]. As can be seen in Fig. 5.1, since then, the development of green analytical applications has accelerated and evolved for the introduction of new methodologies and instruments. Today, green analytical chemistry is an idea whose rules every analytical chemist should learn and apply in their studies. Therefore it is not surprising that analytical chemistry studies have developed in different ways within the framework of chemical degrees in the world [10,13]. This is mainly due to advances in analytical chemistry but is also an increasing tendency to be environmentally friendly, which is often pointed out during chemical work. However, the teaching of analytical chemistry today is to develop basic analytical figures on the value of existing and common approaches in general, as well as to maintain knowledge from the past in order to improve them. In addition, questions and problems related to our social compromise need to be adequately answered in terms of the safety of operators and the environment. Therefore teaching analytical chemistry should involve two main phenomena: (1) the way of thinking about analytical problems and (2) solutions of these problems in terms of sustainability, the known background knowledge of

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5.2 Green analytical chemistry

2 0 0 0

2 0 0 3

2 0 0 4

2 0 0 6

2 0 0 7

2 0 1 1

2 0 1 2

2 0 1 3

2 0 1 8

Introduction of an in-needle SPME device for analysis of VOCs using a copolymer of methacrylic acid and ethylene glycol dimethacrylate miniaturiaztion and autimation of CCF

Patent of fiber packed needle for analyzing aldehydes and ketoues

Carbon nanotuves proposed as extracting agent, instead of a supported liquidmembrane for a micro extraction that hybridizes HF-LPME and SPME

The six principles of Green Extraction of Natural Products introduced

Supramoleculer solvent-based HP-LPME introduced to laboratory practise Parallel artificial liquid membrane extraction

Report on Green Analytical Procedure Index Report on ultrasound-assisted solvent extraction of porous membrane packed solid

1 9 9 9

Application of hollow fiber membrane–protectd solidphase microextraction of thiazine herbicides in bovine milk and sewage sludge samples

The concept of environmentally friendly analytical chemistry Report on cold fiber HS_SPME device(CCF)

1 9 9 6

Development of thin-film microextraction First report on microextraction in packed syringe (MEPS)

1 9 9 5

Introduction of an inside–needle technique for vapor and liquid sampling named solid phase dynamic extraction (SPDE)

1 9 9 4

The concept of green chemistry The concept of integrated approach in analytical chemistry The concept of green analytical chemistry First publication focused on SBSE application

1 9 9 3

Development of presurized solvent extraction–PSE Development of liquid phase micro extraction–LPME Development of single drop microextraction–SDME

1 9 9 0

Concept of clean analytical chemistry

Developmetn solid phase extraction-SPE

1 9 8 7

Development of head space-SPME Development of moleculer imprinted solid phase extraction

Application of microvawe ovens for sample digestions

1 9 8 5

First publication focused on the basic knowledge on SPME Development of micro total analysis system-μTAS Development of sequential injection analysis (SIA)

Devolopment and flow injection analysis–FIA Devolopment purge and trap technique– acronym in parentheses; e.g.,(P.T)

FIGURE 5.1

1 9 7 8

The concept of ecological chemistry The concept of sustainable developmet

1 9 7 6

Developmetn of microwave-assisted extraction–MAE Developmetn of supercritical fluid extraction–SFE

1 9 7 5

Developmetn cloud point extraction-CPE

1 9 7 4

Milestones of green analytical chemistry [7 13].

analytical figures of merit related to different approaches, and the directions to reduce or eliminate the use of toxic, hazardous, bioaccumulative, persistent, and corrosive solvents and their generation of waste [4,6,10,13]. Many efforts have been made to incorporate the principles of green chemistry into education, as well as in the analytical chemistry field, where the 12 Principles of Green Analytical Chemistry play a major role [13]. GAC education can balance both ethical and chemical aspects. Therefore the concept is to convince students that chemistry is not only a risk to the planet but indeed has a great commitment to a sustainable environment as well as to human health care. Now teachers have the obligation to communicate such information [13].

5.2.2 The 12 Principles of green analytical chemistry The concept and 12 Principles of Green Chemistry were defined by Anastas in 1998 [16]. The principles were formulated by considering guidelines and recommendations to the scientific community for greening chemical processes. The following 12 principles have been decided by focusing on issues involving many

aspects of chemical element economics, the use of catalytic methodologies, the use of renewable raw materials, and the control of environmental side effects of chemical activities [16,17]. 1. Direct analytical measurement techniques should be used instead of sample pretreatment. 2. The use of a minimal number of samples and minimal sample size are the aim. 3. In situ detections or determinations should be preferred. 4. The integration of analytical processes and operations saves energy and reduces reagent usage. 5. Miniaturized and automated methods should be preferred. 6. Derivatization should be avoided. 7. Generation of high amount of analytical waste should be avoided, and suitable management applications for analytical wastes should be suggested. 8. Multianalyte or multiparameter methods should be preferred over methods that use one analyte at a time. 9. Energy usage should be reduced to minimum levels. 10. Reagents from renewable sources should be preferred as much as possible.

New Generation Green Solvents for Separation and Preconcentration

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5. Type of green solvents used in separation and preconcentration methods

11. Toxic reagents should be eliminated or replaced. 12. The safety of the operator should be increased. Gałuszka and coworkers suggested the mnemonics “SIGNIFICANCE” for these principles and “IMPROVEMENTS PRODUCTIVELY” for the condensed 24 Principles of Green Chemistry and Green Engineering (Fig. 5.2) [17 19]. Modern analytical chemistry provides a variety of techniques and tools for the determination of a particular analyte or analyte group in different sample matrices. The main objectives to be achieved in greening analytical methods are: 1. Eliminating or reducing the use of reagents, solvents, preservatives, additives for pH adjustment, and others, 2. Minimizing energy consumption,

3. Appropriate analytical waste management, and 4. Increased safety for workers and operators. Many of these problems are diminished by reducing the number of samples studied, minimizing the amount of reagents used, designing energy-saving systems, minimizing or preventing waste generation, and eliminating vital risks. One of the problems encountered in greening laboratory applications is the need to compromise between GAC requirements and performance parameters. The analytical methods using the 12 Principles proposed by GAC are likely to face the problem of decreasing performance parameters such as accuracy, precision, and sensitivity. The practical consequences of GAC principles were associated with the selected parameters of analytical procedures by Gałuszka and coworkers [17]. This situation is shown in Table 5.1. FIGURE 5.2 The principles of green analytical chemistry expressed as the mnemonic SIGNIFICANCE [17 19].

New Generation Green Solvents for Separation and Preconcentration

213

5.2 Green analytical chemistry

TABLE 5.1 Practical consequences of GAC principles for selected parameters of analytical process [17]. Parameters of the analytical process Steps in analysis

Representativeness Accuracy Precision Selectivity Sensitivity Detectability

Sampling Minimal sample size

(Decrease)

Minimal sample number

0

0

0

0

0

Sample treatment Without derivatization

(Neutral effect)0

Minimal use of energy

0

Reagents from renewable source

0

Without toxic reagents

0

Safety for operator

0

Measurement Direct In situ

(Increase)

Integrated operations and processes 0 Automation

0

0

0

Miniaturized instruments Multianalyte and multiparameter

0

Minimal use of energy

0

The reliability of analytical methods can be easily called into question when applying direct methods, minimizing sample size, and using miniaturized instruments. However, quick technological advancement and information about

0

0

0

0

0

the existing problems will lead to improvements in GAC. Sometimes, overcoming these problems is made easier by small modifications such as changing standards to improve calibration by running standards between samples [17].

New Generation Green Solvents for Separation and Preconcentration

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5. Type of green solvents used in separation and preconcentration methods

5.2.3 Stages of analytical procedure description The first step of each analytical procedure is sample collection [20]. The elapsed time between sampling and obtaining analytical results is critical to characterizing an analytical procedure as green. Hence, the greenest approach to the sample collection step is inline sampling. A portable XRF device usage is a good way to do this. Other sample collection modes include online and at-line sampling, representing a midgreen approach, and Tobiszewski and coworkers claimed that offline sample collection should be avoided [20]. The second step for the analytical procedure is the protection of the samples from potential physical and chemical changes. This stage can be considered one of the most important for the overall quality of the assay, since it ensures the integrity of the sample [17], but it is not a green step as it requires the use of energy and/ or chemicals in any analytical procedure. Samples are protected from potential physical and chemical changes by applying chemical, physical, and physicochemical methods. Carrying a sample is another step that should be discussed in light of the GAC idea. Due to the energy consumption of the vehicle (fuel), time used, emissions pollutants from vehicles, and the like, the application of field analysis is not recommended and can be avoided. The stage of bringing samples to the laboratory depends on the capacity of the laboratory [17,20]. The sample preparation stage is generally at the center of any analytical procedure, given the green nature of a method, since it generally involves many processes where nongreen reagents such as strong acids or organic solvents are used. The use of direct methods is the best solution when sample preparation has no requirements. Unfortunately, the most used sample preparation methods are extraction, postextraction, or derivatization. Although the

ideal situation does not have to extract a sample, separation and preconcentration processes are usually required. The extensive exploration of the field of extraction and the discovery of new methods by analytical chemists are important steps to be taken in making this process greener [21 23]. Considering the 12 Principles of GAC, the best way is to use solvent-free extraction [24,25]; followed by the minimization of solvent and reagent amounts; the use of micro- or nanosized extraction methods such as LPME [21], SPME, [22] and the like; replacement of conventional organic solvents with more green solvents such as supercritical fluids [26], supercritical water [27], ionic liquids [28], deep eutectic solvents [29], switchable solvents [30], supramolecular solvents [31], surfactants [32], and so on; the use of new extraction apparatus (ultrasound or microwave vibration and vortex shaking) to enhance extraction efficiency. The last stage of the analytical procedure is to identify and quantify analytes using analytical techniques. As mentioned, the use of direct analysis techniques is the ideal choice. Otherwise, indirect methods that require sample preparation should be used. Some of the direct analysis techniques are electrothermal atomic absorption spectrometry (ETAAS), near-infrared spectroscopy, and laser ablation (with ICP-MS or inductively coupled plasma optical emission spectrometry (ICPOES)). However, even some improvements can be made here; for example, miniaturization of analytical methods can provide many valuable advantages over the principles of GAC, reducing the use of toxic solvents and chemicals and leading to a reduction in waste generation [33].

5.2.4 Application of the green analytical procedure index Analytical protocols have key roles to generate data in all application areas. The validity of

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215

5.2 Green analytical chemistry

these data is of paramount importance as it is mainly applied in decision making [34]. Therefore consistent quality of the data obtained with these analytical methods is mandatory. To ensure the quality of data, a tool named life cycle assessment can be used [35]. The transfer of the life cycle idea to analytical procedures is shown in Fig. 5.3. The life cycle for an analytical method involves quality-bydesign (QbD) approaches in method development, validation, and operational use and can be regarded as a connection between method development and method validation [34,36]. Moreover, the life cycle approach can be divided into three phases: method design, method qualification, and ongoing method validation. Nowadays, regulatory agencies have begun to focus more on life cycle management for analytical methods, and an awareness has been created. The United States Pharmacopeial Forum and the international council for harmonisation of technical requirements for pharmaceuticals for human use therefore discuss the registration of new rules including life cycle management of analytical methods [33]. This minimizes the risk of nonspecific results related to the method, as well as reducing the

effort required in method performance verification and postapproval changes, and in turn helps to reduce costs of method over its lifetime [34]. In order to assess the greenness of analytical procedures, the national environmental methods index (NEMI) is one of the oldest tools. In the NEMI, analytical procedures are evaluated by using the symbol of the greenness profile divided into four areas (Fig. 5.4) [33]. Though NEMI has advantages (easy to read by potential users) as a greenness assessment tool, it also has some disadvantages such as showing each threat below or above a certain value. Hence NEMI cannot be considered quantitative. Also, especially if many nontypical chemicals are used in the procedure, the preparation of a symbol takes time because the existence of each compound needs to be checked against one or more lists (environmental protection agency TRI list, Resource Conservation and Recovery Acts lists, etc.) [37,38]. To improve the NEMI tool, Guardia et al. introduced an additional pictogram to classify a three-level assessment of the greenness of a method using a color scale [39]. Another tool for evaluating chemical methods, including analytical

FIGURE 5.3 Life cycle management in analytical procedure [34].

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5. Type of green solvents used in separation and preconcentration methods

FIGURE 5.4 Assessment of analytical procedure by (A) NEMI tool and (B) additional pictogram proposed by Guardia et al. [33].

procedures based on green chemistry properties, was proposed by Raynie et al. In this assessment, risk potential is classified into five categories: health, environmental, safety, energy, and waste, based on toxicity, reactivity, bioaccumulation, corrosivity, waste generation, energy consumption, safety, and related factors (Fig. 5.5). All criteria are shown on a pentagram and painted as green, yellow, or red depending on their environmental impact. Another approach, based on penalty points subtracted from the 100 base, is the Analytical Eco-Scale [40]. In this approach, the higher the score, the more green and more economical the analytical procedure will be. Methods are classified into three categories according to the eco-scale as: • Methodologies having more than 75 points are classified as excellent green analysis.

• Methodologies having more than 50 points are classified as acceptable green analysis. • Methodologies having more than 50 points are classified as inadequate green analysis. A schematic illustration of the procedural penalties is provided in Table 5.2 [33]. Although the Analytical Eco-Scale has many advantages, it suffers from several drawbacks, such as a lack of information on the nature of hazards and insufficient data on the causes of the environmental impact of the analytical procedure, such as the solvent and other reagents usage, occupational hazard, or waste generation [33]. All of these tools are related to the assessment of the greenness of protocols. They have their own advantages and disadvantages, and the best solution is to use all of them as much as possible to reach information, but this means spending a lot of time. In order to solve this

New Generation Green Solvents for Separation and Preconcentration

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5.2 Green analytical chemistry

FIGURE 5.5 Green assessment profile proposed Raynie et al. [40].

problem, Płotka-Wasylka introduced a tool named green analytical procedure index (GAPI) that can evaluate the green character of an entire analytical methodology, from the sample collection step to the last detection step [33]. Using all the advantages of the Eco-Scale in addition to the pictograms of Fig. 5.5, GAPI provides not only general information but also qualitative information. Płotka-Wasylka explained how to use GAPI in the assessment of analytical procedures applied for the analysis of biogenic amines in wine samples. Moreover, it is applicable to develop different analytical

by

procedures for many analytes such as polycyclic aromatic hydrocarbons (PAHs) [33]. 5.2.4.1 Application of the green analytical procedure index It is recommended that analytical chemists use the multicriteria decision analysis when selecting a method from literature studies. Some of them are preference ranking organization method for enrichment evaluation (PROMETHEE) or technique for order of preference by similarity to ideal solution (TOPSIS). These applications allow the comparison and

New Generation Green Solvents for Separation and Preconcentration

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5. Type of green solvents used in separation and preconcentration methods

TABLE 5.2 The penalty points (PPs) to calculate Analytical Eco-Scale [33]. Category

Subtotal PPs

Total PPs

, 10 mL (,10 g)

1

10 100 mL (10 100 g)

2

. 100 mL ( . 100 g)

3

None

0

Less severe hazard

1

More severe hazard

2

, 0.1 kWh per sample

0

, 1.5 kWh per sample

1

. 1.5 kWh per sample

2

Hermetization of analytical process

0

Emission of vapors to the atmosphere

3

None

0

, 1 mL (,1 g)

1

1 10 mL (1 10 g)

3

Reagents Amount

Hazard

Amount PPs 3 hazard PPs

Instruments Energy

Occupational hazard

Waste

. 10 mL ( . 10 g)

5

Recycling

0

Degradation

1

Pasivation

2

No treatment

3

sequencing of 12 analytical methods by considering their greenness. However, if only two or three methods are compared for the greenness of the methodology, GAPI is an ideal application in presenting and evaluating all analytical procedures from sampling to final detection. In the GAPI tool, using a color scale, a pictogram is applied to categorize the greenness of each stage of the analytical procedure with three levels of assessment for each stage [41 43].

In the GAPI tool, a special five pentagram symbol (Fig. 5.6) can be applied to assess and quantify (starting from green and yellow to red) low, medium, and high environmental effect for every stage of the analytical method [33]. A different aspect of the described analytical procedure is reflected by these fields, and the field is painted green if certain requirements are met in terms of green analytical chemistry.

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5.2 Green analytical chemistry

FIGURE 5.6 Green analytical procedure index pictogram with description [33].

By using the visual presentation of the assessment tool, individual researchers are able to create their own value judgments about conflicting green criteria. Therefore this assessment tool can be considered the most valuable in comparison procedures. The description of the GAPI index is illustrated in Table 5.3 [33]. 5.2.4.2 Evaluated analytical procedures Płotka-Wasylka used [33] four reported analytical procedures for the determination of biogenic amines in wine samples [44 46]. The GAPI tool is used for the assessment of greenness [33]. Schematic illustrations of these procedures are shown in Fig. 5.7. NEMI pictograms about the evaluated procedures are shown in Fig. 5.8. The same pictograms obtain for Procedures 1, 2, and 3. It means that these methodologies have a very similar green character. The Procedure 4, based on high-performance liquid chromatography (HPLC) technique, appears to be the worst analytical procedure. The green assessment of these procedures was checked with a tool provided by Raynie et al. [40]. These assessments are illustrated in Fig. 5.9. This assessment approach gives more information, and hence more visible differences between evaluated procedures are reached. Procedures 1 and 2, having similar green properties, are placed in the middle.

When Procedures 4 and 3 are compared, Procedure 4 seems to be the worst in green nature. Although this tool provides more information than NEMI, the pictograms cannot be considered semiquantitative. To reach more qualitative information, Analytical Eco-Scale penalty points for each procedure’s evaluated (PPs) should be calculated (Table 5.4). Procedure 3 with 85 PPs and Procedure 2 with 69 PPs can be classified as green methods. Analytical Eco-Scale is in harmony with the results that Procedure 4 is the worst when evaluated in terms of green character. As a result, although the Analytical Eco-Scale is a good quantitative tool for comparing laboratory parameters, educational objectives, and different parameters and steps in the analytical process, it still has the disadvantage of not providing comprehensive information about the protocols being evaluated. GAPI has been provided to supplement this information. GAPI gives information on the entire procedure from sampling, through the transportation, storage, and preparation of sample to final determination. In addition, information is given whether the quantification is part of the procedure being assessed. Analytical chemists who are familiar with the GAPI tool can quickly and confidently choose the best analytical

New Generation Green Solvents for Separation and Preconcentration

TABLE 5.3 Green analytical procedure index parameters description [33]. Category

Green

Yellow

Red

Collection (1)

In-line

Online or at-line

Offline

Preservation (2)

None

Chemical or physical

Physicochemical

Transport (3)

None

Required

—

Storage (4)

None

Under normal conditions

Under special conditions

Type of method: direct or indirect (5)

No sample preparation

Simple procedures, that is, filtration, decantation

Extraction required

Scale of extraction (6)

Nanoextraction

Microextraction

Macroextraction

Solvents/reagents used (7) Solvent-free methods

Green solvents/reagents used

Nongreen solvents/reagents used

Additional treatments (8)

None

Simple treatments (clean up, solvent removal, etc.)

Advanced treatments (derivatization, mineralization, etc.)

Reagent and solvents amount (9)

,10 mL (,10 g)

10 100 mL (10 100 g)

.100 mL ( . 100 g)

Health hazard (10)

Slightly toxic, slight irritant; NFPA health hazard score 5 0 or 1.

Moderately toxic; could cause temporary incapacitation; NFPA 5 2 or 3.

Serious injury on short-term exposure; known or suspected small animal carcinogen; NFPA 5 4

Safety hazard (11)

Highest NFPA flammability or instability score of 0 or 1. No special hazards.

Highest NFPA flammability or instability score of 2 or 3, or a special hazard used

Highest NFPA flammability or instability score of 4.

Energy (12)

# 0.1 kWh per sample

# 1.5 kWh per sample

.1.5 kWh per sample

Occupational hazard (13)

Hermetic sealing of analytical process

Waste (14)

,1 mL (,1 g)

1 10 mL (1 10 g)

.10 mL (,10 g)

Waste treatment (15)

Recycling

Degradation, passivation

No treatment

Sample preparation

Instrumentation

Emission of vapors to the atmosphere

Additional mark: Quantification Circle in the middle of GAPI: Procedure for qualification and quantification NFPA, National Fire Protection Association.

No circle in the middle of GAPI: Procedure only for qualification

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5.2 Green analytical chemistry

FIGURE 5.7 Schematic representation of evaluated analytical procedures for determination of biogenic amines in wine: (A) Procedure 1; (B) Procedure 2 [47]; (C) Procedure 3 [34]; (D) Procedure 4 [35].

methodology for their purposes. The green evaluation profile for the procedures evaluated by using the GAPI tool is illustrated in Fig. 5.10. The GAPI pictograms gives results similar to those of Analytical Eco-Scale Analysis. The greenest procedure is Procedure 3, followed by Procedure 2, Procedure 1, and finally Procedure 4. However, more information can be reached by GAPI pictograms, indicating whether an extraction is required and, if

available, the type and scale of the extraction; knowledge on whether any extra process is required; and, finally, whether the procedure can be applied for both qualification and quantification [33]. Given examples of analytical procedures in this paper, the first method for identifying biogenic amines in wine samples should be Procedure 3 (CE-DAD), which is the greenest choice. This direct method can be applied

New Generation Green Solvents for Separation and Preconcentration

FIGURE 5.8 The NEMI pictograms for assessment of “greenness” of selected analytical procedures [33].

FIGURE 5.9 Assessment of the green profile of evaluated procedures for determining BAs in wine samples by the using tool reported by Raynie et al. [33,40].

TABLE 5.4 The penalty points (PPs) for evaluated procedures determining BAs in wine samples [33]. Procedure 1

Procedure 3

Reagents

PPs

Reagents

PPs

NaOH (150 μL)

1

Methanol

6

Phosphate buffer 0.5 M

0

Internal standard

4

Internal standard

4

Borate buffer (20 mM)

0

HCl (2 mL)

4

Sodium dodecyl sulfate

0

Acetonitrile (1 mL)

4

Toluene (350 μL)

6

Instruments

PPs

Isobutyl chloroformate (110 μL)

8

Transport

1

MeOH (75 μL)

6

CE-DAD

2

Σ 37

Waste

2

Instruments

PPs

Total PPs: 15

Σ5

Transport

1

Score: 85

GC-MS

2

Procedure 4

Occupational hazard

0

Reagents

PPs

Waste

3

Polyvinylpyrrolidine 0.5 g

0

Total PPs: 43

Σ6

Internal standard

8

Score: 57

HCl (10 mL)

6

Procedure 2

Na2CO3 (0.5 mL)

0

Σ 10

Reagents

PPs

Dansyl chloride (1.6 mL)

8

Pyridine

3

Acetone (. 10 mL)

8

Internal standard

4

Acetonitrile (. 5 mL)

8

HCl (55 μL)

3

Water

0

Chloroform (400 μL)

2

Isobutyl chloroformate (110 μL)

8

Instruments

PPs

MeOH (215 μL)

6

Transport

1

Σ 26

HPLC-fluorimetric detection

2

Instruments

PPs

Occupational hazard

0

Transport

1

SPE

2

GC-MS

2

Hot-plate

2

Occupational hazard

0

Drying instrument

2

Waste

1

Waste

5

Total PPs: 31

Σ4

Total PPs: 52

Σ 14

Score: 69

Σ 38

Score: 48

224

5. Type of green solvents used in separation and preconcentration methods

FIGURE 5.10

GAPI assessment of the green profile of the evaluated procedures for determining BAs in wine samples [33].

without an extraction process, consumes very low amounts of nontoxic compounds, and generates very low waste. However, this procedure is only useful for qualification. In this case, Procedure 2 should be used if quantity measurement is required. Fig. 5.8 shows the NEMI pictograms for the evaluated procedures. Three pictograms are the same for Procedures 1, 2, and 3, which suggest that the green character of these methodologies is very similar. The worst analytical procedure appears to be Procedure 4 (methodology based on HPLC technique).

5.2.5 New-generation solvents When studies in the literature on analytical sample preparation methods are examined, it is seen that most of the scientists use the new-

generation solvents in the methods used and continue to do so successfully. This active research on new ecofriendly solvents has been closely associated with the development of novel extraction methods, thereby improving the green properties of the entire analytical process. These novel extraction methods can be classified as follows: LPME approaches including single-drop microextraction (SDME), hollow fiber liquid phase microextraction (HF-LPME), dispersive liquid liquid microextraction (DLLME), solidified floating organic drop microextraction, and homogeneous liquid phase microextraction [48 51]. Solid phase microextraction approaches include direct immersion solid phase microextraction (DI-SPME), headspace solid phase microextraction (HS-SPME), in-tube solid phase microextraction (in-tube-SPME), solid phase dynamic extraction (SPDE), microsolid phase extraction

New Generation Green Solvents for Separation and Preconcentration

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5.2 Green analytical chemistry

FIGURE 5.11 The new-generation green solvents used in the sample preparation methods.

(μ-SPE), adsorptive microextraction, stir-cake sorptive extraction (SCSE), rotating-disc sorbent extraction (RDSE), and stir-rod sorptive extraction. Solid phase extraction approaches include stir-bar sorptive extraction (SBSE), magnetic solid phase extraction (MSPE), immunoaffinity solid phase extraction, molecularly imprinted solid phase extraction, dispersive microsolid phase extraction (DMSPE), and cloud point extraction (CPE) [52 56]. The newgeneration green solvents mostly used in these methods are shown in Fig. 5.11. 5.2.5.1 Solvent selection guides By understanding the roles of solvents used in the preceding sample preparation techniques, it is easier to understand how published solvent selection guidelines (SSGs) can be reinterpreted in the solvent selection in a green sample preparation method. Many

SSGs have been reported to assist in the selection of solvents used in industrial applications. Classification of solvents by SSGs is based on the same criteria, such as useable, preferred, substitution advisable, hazardous, undesirable, and banned [57]. Scientists collected data by using these SSGs [57 60] and created an algorithm consisting of criteria (some of these criteria are given in Table 5.5) for the classification of 151 traditional solvents into three numerically ranked groups by considering the principles of green analytical chemistry. The properties and environmental risk ranking of the mostly used conventional extraction solvents are given in Table 5.6. These three numerically ranked solvents are: (1) rather nonpolar and volatile solvents, (2) nonpolar and nonvolatile solvents, and (3) polar solvents. Chemicals in the nonpolar

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5. Type of green solvents used in separation and preconcentration methods

TABLE 5.5 Physicochemical properties important for selecting an extraction solvent. Properties

Descriptions

Melting point



C

Boiling point



C

Flashpoint



C

Density

g cm2 3

Water solubility

ML mL21

Vapor pressure

kPa

Surface tension

g s22

Viscosity

cP

Log Kow

Log of the octanol/water partition constant. A measure of the hydrophobicity (nonpolarity) of the solvent. Unitless

Log Koa

Log of the octanol/air partition constant. Unitless

K

The air/water partition coefficient. Unitless Henry’s constant (H)

aw

Oral LD50

The lethal oral dose for half of a population

Inhalation LD50

The lethal inhalation dose for half of a population

fish LC50

The lethal water concentration for half of the fish population

IARC cancer class

International Agency for Research on Cancer human carcinogenicity classification

LogBCF

Log of the bioconcentration factor (plants, animals)

BOD1/2

Half time for biodegradation

POCP

Photochemical tropospheric potential

Recycling by distillation

Energy requirements/azeotrope formation effect on recycling

Flammability

Relative flammability

Other specific effects Mutagenicity, teratogenicity, reproductive effects, neurotoxicology and other chronic effects

apolar classes include most of the conventional LPME extraction solvents, while those in the polar solvent class include solvents used as auxiliary solutions in methods such as DLLME, supramolecular-based LPME, homogeneous LPME, and so on. Polar solvents such as ethanol, 1-propanol, acetone, acetonitrile, 2propanol, and methanol are listed as environmentally safe in the industrial SSGs and are at the top of the list of green chemicals [57].

The nonpolar chemicals including pentane, dichloromethane, hexane, benzene, carbon tetrachloride, and chloroform are considered in the highly hazardous, undesirable, and banned chemicals groups. These classifications are particularly important to ensure the safety and environmental requirements needed for use on a large industrial scale. Even xylene, heptane, toluene, and chlorobenzene solvents are considered usable but problematic. In 2017 this data

New Generation Green Solvents for Separation and Preconcentration

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5.2 Green analytical chemistry

TABLE 5.6 Properties and environmental risk ranking of mostly used conventional extraction solvents. Surface tension (g s22 per 25 C)

Vapor pressure (kPa 20 C21)

Solubility (mL mL21 per 20 C21)

Log Kow

Risk ranking

Solvent Water

100 1.00

0.01

72.8

3.17

Miscible

1.38

1.0000

1-propanol

97

0.80

1.96

23.7

2.0

Miscible

0.25

0.9545

Ethanol

78

0.79

1.04

22.4

5.9

Miscible

0.81

0.9300

Acetone

56

0.79

0.32

22.8

30.8

Miscible

0.24

0.9545

7.13

0.8919

0.73

0.8868

5.98

0.8703

3.0

0.8689

Dodecane Ethyl acetate Decane

Density (g cm23)

Viscosity (cP 20 C21)

Bp (C)

216 0.75 77

0.90

174 0.73

1.82 

0.43 (25 C) 0.48 

25

0.028

4.0 10

23.6

12.1

87.8

22.4

0.17

1.2 10

6

5

1-octanol

195 0.83

6.49 (30 C)

26.4

0.011

0.65

Acetonitrile

82

0.35

29.0

9.73

Miscible

0.34

0.8687

6.6

0.8677

0.78

Undecane

196 0.74

1.08

19.2

0.075

5.4 3 10

Methanol

65

0.79

0.543

22.7

13.0

Miscible

0.77

0.8644

Pentane

36

0.63

0.222

16

68.5

0.061

3.39

0.8475

Heptane

98

0.68

0.408

20.2

6.1

0.0044

4.66

0.8021

2-propanol

82

0.785

2.1

23.3

4.4

Miscible

0.05

0.8698

Cyclohexane

81

0.78

0.98

25

13.1

0.070

4.15

0.7892

m-xylene

139 0.86

6



0.62

28.9

0.8

0.19 (25 C)

3.20

0.7594

Toluene

110 0.86

0.59

29.7

3.79

0.55

2.73

0.7344

Dichloromethane

40

1.33

0.41 (25 C)

27.4

46.5

12

1.25

0.7150

p-xylene

138 0.86

0.34 (30 C)

29.0

0.9

0.21 (25 C)

3.15

0.7072

Hexane

69

0.65

0.37

18.4

17

0.02

3.94

0.7057

Tetrachloroethene 121 1.63

0.89

31.7 (25 C)

2.46

0.37

3.40

0.6841

Chloroform

61

1.48

0.57

27.2

21.1

5.54

1.97

0.6862

o-xylene

144 0.88

0.81

30.1

0.7

0.19 (25 C)

3.12

0.6715

Carbon tetrachloride

77

1.59

0.97

26.9

11.9

0.50

2.64

0.6424

Benzene

80

0.88

0.60 (25 C)

28.2

12.7

2.0

2.13

0.6098

was reevaluated by Tobiezewski et al. to improve the environmental risk-based ranking of 78 of the mostly used solvents [61]. The main classification criteria were established using

environmental persistence, toxicological, carcinogenicity, photochemical ozone generation, and chronic effects data for each chemical. To decide whether hazardous wastes containing

New Generation Green Solvents for Separation and Preconcentration

228

5. Type of green solvents used in separation and preconcentration methods

these chemicals can be recycled by distillation or incineration, the ideal solvent score is 1.0000 for water, and rankings of these solvents were made by considering similarities to the ideal solvent score [57]. As expected, volatile hydrocarbons, potentially carcinogenic chemicals, and chlorinated solvents have low scores in this classification. The ionic liquids, supramolecular solvent components, deep eutectic solvent components, and other solvents listed in Table 5.6 are not similarly listed, but their controlled use has not found any toxic or environmental problems reported so far [57,62 64]. In two different reviews, Tobiszewski [47] and Plotka-Wasylka and coworkers [65] evaluated these GSS results in terms of analytical chemistry and extraction techniques. Tobiszeweski searched and evaluated the various ways to understand and characterize the green nature of analytical chemicals and solvents used in extraction and sample preparation methods [47]. It is noted that the analytical literature is full of publications claiming to be green, but there has been no confirmation for such claims. In fact, when many published analytical methods are examined, it is seen that methods that give the lowest possible detection limits (LODs) are generally developed by maximizing sample and extraction solvent amounts and then balancing the dilution effects by working with highly sensitive, very expensive detection systems. Plotka-Wasylka and coworkers also underline that GAC needs a holistic approach to the entire analytical procedure, which includes the complete life cycle of chemicals, including fabrication, use, and recycling or disposal [65]. In addition, consideration should be given to consider that new-generation solvents, including ionic liquids (ILS), deep eutectic solvents (DESs), switchable solvents, supercritical solvents and supramolecular solvents, are green until additional toxicological and environmental fate data is available. The selection of a suitable green solvent used in sample preparation methods cannot be

made by easily selecting from a list of solvents. The process of selecting a solvent is based on understanding several variables, including sample properties, type and concentration of analytes, presence of instrumentation, operator competence, whether the method is to be used on a limited scale or in several analytes, as well as the chemistry, features, and health fears of the extraction solvent. Some important issues are clearly visible in the selections of solvents using solvent-based extraction methods and are explained here [57]: 1. Limitation or elimination of the use of toxic or carcinogenic solvents such as benzene, CH2Cl2, CCl4, CHCl3, tetrachloroethene, and so on in solvent extraction-based sample preparation methods; 2. The use of highly volatile solvents such as pentane in all extraction methods should also be avoided; 3. To limit the contamination of water samples, the use of solvents’ limited solubility with water such as decane, cyclohexane, and xylenes; 4. The use of solvents with moderate boiling points, surface tensions, and viscosities like decane, 1-octanol, or m-xylene; 5. The use of solvents that melt at near room temperature, like 1-dodecanol, 1-undecanol, and hydrophobic DESs; 6. The use of minimized amounts of ILs as extraction solvents and avoiding the use of ILs containing the imidazole and hexafluorophosphate (PF6) groups because of their adverse effects on users; 7. To reach extraction equilibrium, the use of solvents with high viscosity in the extraction procedure by dispersing them with additional agitation apparatus, such as ultrasound or microwave vibration, vortex shaking, and the like; 8. It is best to develop the method assuming that there is not really a green solvent other than pure water.

New Generation Green Solvents for Separation and Preconcentration

5.2 Green analytical chemistry

With all the recommendations outlined so far in this section, it is simpler to make choices that reduce energy consumptions, instrumentation, analysis time, operator safety, and appropriate waste recycling or disposal for the environment. For this purpose, the American Chemical Society took an important step and found a website to select suitable solvents for studies by scientists. The suitable solvent is interactively selected among 272 solvents by considering their physical features based on the ACS 2011 SSG [60]. 5.2.5.2 Ionic liquids ILs were initially considered to be the answer to improving methods according to the principles of GAC by replacing conventional solvents, and they have attracted great attention in the 21st century [66,67]. Depending on the aim of their usage, they may be viewed both as solvents and/or as materials. Therefore ILs have been used with great excitement for most of the following analytical applications: 1. Sample preparation methods including different modes of liquid liquid extraction (LLE), liquid phase microextraction (LPME) [67], solid phase extraction (SPE) [68], solidphase microextraction (SPME) [69], and so on; 2. Stationary phases for chromatographic techniques such as LC and GC [70]; 3. Electrochemical sensors [71]; 4. Mass spectroscopy [72]; and 5. Capillary electrophoresis [73]. The common use of the ILs in sample preparation methods is based on their chemical composition due to their adjustable chemical and physical features, in particular their capability for the selective extraction of polar and apolar analytes from different sample matrices by choosing the desired ILs according to the chemical form of analytes and sample medium and the measurement method used in determinations. However, ILs with ionic characteristics

229

are not good candidates for direct measurement with GC, GC/MS, AAS, ICP-OES, and ICP-MS analysis due to their ionic character, very low volatility, and high decomposition temperatures (B400 C). However, they are well suited to UHPLC/MS analysis, which is a more sensitive instrument, although they are more expensive [74]. The majority of ILs generally have very large surface tensions, low viscosities, and high densities. The high surface tension and low volatility make an IL a good extraction solvent, especially for use in liquid phase microextrusion methods. For example, IL provides ease of use in SDME because it is possible to achieve high extraction yields by balancing the extraction solvent drop [75]. Besides this advantage, high viscosity may cause the decreasing on the extraction efficiency of the analyte, which requires longer extraction times for the extraction methods such as HF-LPME and SDME. These problems resulting from high viscosity offer significant advantages in the separation of aqueous sample and IL phases in different extraction methods such as DLLME. Although there is much effort in the application of ILs in sample preparation methods especially in LLE and LPME methods, caution in their use results in environmental persistence and bioaccumulation, with the understanding that they may have important environmental influences resulting from their unique features, including chemical stability and very low volatility [76,77]. In addition, it should be noted that, contrary to the initial speculation, ILs, in particular those containing imidazole and PF6 groups, may also have toxic effects depending on their chemical composition. The first use of ILs in extraction procedures was with the liquid liquid extraction of both the organic compounds [67] and the inorganic species at the very end of the 20th century [78,79]. These attempts may be considered a revolution for the applicability of ILs in the separation and preconcentration of trace

New Generation Green Solvents for Separation and Preconcentration

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5. Type of green solvents used in separation and preconcentration methods

analytes. In 1998 Huddleston et al. searched the partitioning behaviors of substitutedbenzene derivatives between water and the room-temperature ionic liquid, butylmethylimidazolium hexafluorophosphate [67]. In the same year, Dai et al. carried out the extraction of strontium nitrate with ILs, 1-R1 2-R2 3methylimidazolium bis[(trifluoromethyl)sulfonyl]amide (R1 R2 MeIm1Tf2N2) and 1-R1 2 2R2 2 3-methylimidazolium hexafluorophosphate (R1 R2 MeIm1PF62) [78]. Visser et al. used 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6], n 5 4, 6, 8) roomtemperature ILs (RTILs) for the extraction of Na1, Cs1, and Sr21 ions from aqueous solutions [79]. The first use of ILs for LPME applications was reported by Liu et al. in 2003 [80]. This study opens the window to the use of newgeneration green extraction solvents in microextraction studies. They used 1-octyl-3methylimidazolium hexafluorophosphate ([C8MIM][PF6]) IL as an innovative extraction solvent in direct immersion and headspace liquid phase microextraction of PAHs. In this study, PAHs in aqueous sample phase were extracted into a 3-μL drop of [C8MIM][PF6] suspended on the tip of a microsyringe prior to liquid chromatographic (LC) determination. They have claimed that when compared with 1-octanol as a conventional extraction solvent, a larger volume of [C8MIM][PF6] can be generated that can offer a longer extraction time and higher enrichment factor for PAHs. For lowvolatility PAHs, direct-immersion LPME provides higher enrichment factors than those of headspace LPME. By applying directionimmersion LPME for 30 min, enrichment factors are increased 42- to 166-fold, and reproducibility values between 2.8% and 12% RSD are achieved [80]. For the separation and preconcentration of metal ions by using ILs as an extraction solvent, in 2005 Liu et al. developed a direct immersion single-drop microextraction (DI-SDME)

method. In this work, [CnMIM][PF6] used DISDME of organomercury, organotin, and organic compounds including PAHs benzene, toluene, ethylbenzene, and xylene, phthalates, phenols, herbicides, and aromatic amines. After completion of the DI-SDME step, organotin and organomercury compounds were analyzed with AAS and cold-vapor atomic fluorescence spectrometry [81]. After these important steps, it has been realized that ILs can be used in different SDME applications including direct immersion SDME, headspace SDME, three-phase SDME, drop-to-drop microextraction, bubble-in-drop SDME, and continuous-flow microextraction SDME [63,82 84]. These SDME applications have gained popularity, and applications are expanding beyond analytical chemistry into biochemistry, chemical engineering, biology, genetics, medicine, environmental science, engineering, agriculture, pharmacology, pharmaceutics toxicology, social sciences, and so on. They have been used for the separation and preconcentration of many trace organic and inorganic analytes prior to detection systems. Knowledge obtained from these methods has shed light on these other scientific areas. Initially, the first attempts for the use of ILs in the DLLME technique were reported by Zhou et al. [85] and by Baghdadi and Shemirani [86]. This new method was called IL-DLLME. Liu et al. are the pioneers of the conventional ILDLLME application [87]. They used the ILDLLME method for the separation and preconcentration of heterocyclic insecticides in water before HPLC-DAD determination. Among these first studies, in 2008 Zhou and coworkers reported a new approach called temperature-controlled ionic liquid dispersive liquid phase microextraction for the separation and preconcentration of organophosphorus pesticides prior to HPLC-DAD determination. Phoxim and methylparathion, as two of the model organophosphorus pesticides, were selected to check the applicability of this new microextraction method. For this purpose, 50 μL

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of 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6] IL was added to an aqueous sample solution including pesticides, and the centrifuge tube was heated to 80 C to dissolve the IL completely in the aqueous phase. Then the sample solution was cooled in an ice bath, and the cloudy solution, which indicated reformation of the IL drops and extraction of pesticides from the aqueous phase to the IL phase, was obtained at this stage. Two phases were obtained with centrifugation for 20 min. The low-density aqueous phase was removed, and the volume of the IL phase was completed to 200 μL with methanol for subsequent HPLC analysis. The developed innovative method, which provided low LODs (0.17 0.29 ng mL21) and RSD percentages (2.5% 2.7%), was used for the analysis of phoxim and methylparathion in environmental water samples with high recoveries (88.2% 103.6%) [85]. In the same year, Baghdadi and Shemirani used ILs as the extraction solvent for a new microextraction method called cold-induced aggregation microextraction (CIAME). This method is based on the microextraction of Hg (II) ions as Hg(II)-michler thioketone complex. In this application, extractant solvents including 64 mg of 1-hexyl-3-methylimidazolium

hexafluorophosphate [Hmim][PF6], 5 mg of 1hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [Hmim][Tf2N], and Triton X-114 (0.033%, w/v) were dissolved in aqueous sample solution at pH 4. This mixture was kept at 35 C for 4 min, then cooled in the ice bath for the formation of IL droplets as a cloudy solution. After centrifuging, the fine droplets of ILs were settled to the bottom of the centrifuge tube with centrifugation and analyzed with a UV-Vis spectrophotometer at 570 nm wavelength [86]. Experimental stages of the provided CIAME method is shown as photography in Fig. 5.12 [86]. In 2009 a new method called ionic liquid dispersive liquid liquid microextraction (ILDLLME) was introduced by Liu and coworkers for a first time. Chlorfenapyr, fipronil, hexythiazox, and buprofezin as four of the model heterocyclic insecticides were selected to check the applicability of this new microextraction method. In this method, a solution consists of 0.052 g of 1hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6] as extraction solvent and 0.50 mL methanol as the dispersive solvent was quickly aspirated into a sample solution containing the insecticides. At this stage, the formation of a cloudy solution indicated the fine dispersion FIGURE 5.12 Photography of different stages of CIAME. (A) Addition of IL in the sample solution; (B) mixing the sample solution and dissolving the IL; (C) cooling and formation of cloudy solution; (D) centrifugation and phase separation; (E) removal of aqueous waste phase [86].

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FIGURE 5.13 Photography of different stages of IL-DLLME. (A) Formation of cloudy solution with addition of IL and methanol mixture; (B) after phase separation via centrifugation; (C) after removal of aqueous waste phase [87].

of the IL phase in the aqueous sample. Then the mixture was centrifuged at 4000 rpm to collect the IL phase in the bottom of the test tube and the aqueous waste phase was removed by a syringe. The sedimented IL phase with a 19 μL volume was diluted with 50 μL of methanol and analyzed with HPLC [87]. Experimental stages of the provided CIAME method are shown as photography in Fig. 5.13. The use of ILs in the HF-LPME as extraction solvents is also an important place for the separation and preconcentration of trace analytes. ILs are nonvolatile and polar. Previous literature studies have also proved that an IL in the pores of the supported membrane is quite stable under stirring conditions and cannot be displaced under harsh experimental conditions. Moreover, ILs show improved affinity for polar compounds, and the IL modified membranes can be used for the selective extraction of organic compounds. These specific characteristics of ILs opened a window for the separation and preconcentration of organic compounds in different matrix media such as environmental and biological samples. In the IL-based HF-LPME applications, the immobilization of IL within the pores of the membrane forms a liquid barrier between the sample solution as the donor phase and the injection solvent as the acceptor phase. The first

application on the use of ILs in the HF-LPME was reported by Feng-Peng et al. in 2007 [88]. For this purpose, authors immobilized [C8MIM][PF6] ionic liquid for hollow fiberbased liquid phase microextraction of chlorophenols including 3-chorophenol (3-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4DCP), and 2,4,6-trichlorophenol (2,4,6-TCP). The polypropylene hollow fiber with a 5.0 cm length was interacted with 20 mL [C8MIM] [PF6] IL for the immobilization of IL in the pores of the hollow fiber. The prepared hollow fiber was then placed on the needle tip of the microsyringe holding B10 μL acceptor solution, and then the microsyringe was depressed to flush out the B10 μL acceptor phase to clean and fill the hollow fiber lumen without any air bubbles. After the other end was covered with heated tweezers, the prepared IL-modified HF membrane (length of B4.5 cm and acceptor phase volume of B10 μL) was used for the extraction studies. In the extraction experiments, the prepared IL-modified HF membrane device was immersed into 15 mL of sample solution including analytes, stirred for a while, and taken out from the aqueous solution. The closed end was cut open, and the microsyringe was filled with the acceptor solution and injected directly into the HPLC for detection. Low LODs, changed from 0.5 to

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1.0 μg L21, were obtained with this developed IL-based HF-LPME method. The developed ILbased HF-LPME method was used for the analysis of the four chlorophenols in tap water, river water, groundwater, and wastewater samples with recoveries changed from 70% to 95.7% [88]. SEM images of the inner surface of the hollow fiber (1) before IL impregnation and (2) after IL impregnation are shown in Fig. 5.14.

In 2009 Tao et al. reported IL-based HFLPME as a second study in literature for the separation and preconcentration of sulfonamides in water samples. In this study, the hollow fiber with a 13 cm length was washed with acetone and dried prior to modification [89]. The lumen of fiber was filled with water and interacted with a solution consisting of [C8MIM][PF6] IL and 14% (w/v) n-octylphosphine oxide for the immobilization of IL in the pores of the hollow FIGURE 5.14 SEM images of the inner surface of the hollow fiber. (A) Before IL impregnation and (B) after IL impregnation [88].

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fiber. The prepared hollow fiber was then washed with water for removal of excess membrane liquid, and then the lumen was filled with pH 13 NaOH solution (acceptor phase) by a disposable syringe. After the two ends were covered with aluminum foil, the prepared ILmodified HF membrane (length of B12 cm, and acceptor phase volume of B25 μL) was used for the extraction studies. The optimum experimental conditions were donor phase: 4 mL, pH: 4.5, organic liquid membrane phase: [C8MIM][PF6] with 14% TOPO (w/v), acceptor phase: 25 μL of pH 13 NaOH solution, extraction time: 8 h. The developed IL-based HF-LPME method was applied to the water sample with high recoveries (82.2% 103.2%) [89]. For the adsorption-based separation and preconcentration studies including different modes of solid phase extraction, solid phase microextraction and stir-bar sorptive extraction applications, ILs are also used as effective and selective extraction media. In these studies, ILs are immobilized on the surface or within the pores of a solid support materials and the prepared solid materials are successfully used for the separation and preconcentration of organic and inorganic analytes in the food, environmental, and biological samples. ILs are mainly used for the effective modification of different materials such as silica [90,91], carbon-based materials (graphene, graphene oxide, carbon nanotubes, porous carbons) [92 94], biological materials (chitosan, chitin, etc.,) [95], polymers [96], metal oxides (Fe3O4, TiO2, α-Fe2O3 etc.) [97,98], metal hydroxides, metal organic frameworks [99], and so on. As a result of the interaction of ionic liquid with these porous materials, important physicochemical parameters such as rheological and thermophysical and conductivity can be changed. In such hybrid materials obtained as the final product, not only are thermal and mechanical stability achieved, but also a significant increase in the adsorption capacity and selectivity to certain analytes is observed [90 99].

There are many procedures for the fabrication of IL solid support hybrid materials. Based on the desirable effect, covalent or noncovalent modification of solid supports with ILs led to the enhancement of the extraction procedure and fulfillment of the principles of GAC [69,100 102]. Perhaps the most important and desired benefits of the use of ILs to obtain hybrid materials for adsorption-based extraction methods are low toxicity and biodegradability. Further, they can be applied as green extraction media for the separation and preconcentration of trace organic and inorganic species. ILs show a high affinity to some inorganic, organic, and bioactive species because of the presence of dipole dipole, electrostatic interactions, and hydrogen bonding along with the alkyl groups of cations in them [69,100 102]. In the case of the non-covalent modification of solid supports with ILs, two other means of physical modification are mainly used. The simplest approach is to immerse a solid support into the IL and filling the pores of a solid support with the IL. The modification approach is also known as postimpregnation. Being able to use a wide range of support materials from metal oxides to polymers, from carbon-based materials to biological materials, is the main advantage of the production of ILmodified support with the postimpregnation method. Another group of IL-modified support preparation method is the in situ impregnation. This method is based on the fabrication of porous material in the IL medium by using sol gel or solvothermal reactions. In these applications, the gelling reaction also cause the formation of spatial solid structures surrounding the IL and surrounding it in the formed pore. For both modification methods, excess of IL in the solid support is removed by applying various cleaning procedures. It is desired that the IL, strongly interacting with the surface of solid support, causes the formation of a

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monolayer resistant to treatment with solvent. The covalent bonding of IL on the surface of the support is a most effective way to achieve a more stable and resistant support material: for example, the formation of covalent bonds anions acting as Lewis acids between silanol groups. In many cases, the oxidation or amination is just a previous step to the immobilization of ILs on the support. Then this modified support is chemically bonded to IL via a coupling agent has a silane group such as (3-aminopropyl) triethoxysilane, (3-chloropropyl)-trimethoxysilane, N-(3-trimethoxysilylpropyl) ethylenediamine (TMSPEDA), N1-(3-trimethoxysilylpropyl) diethylenetriamine, and 3methacryloxypropyltrimethoxysilane [68,103]. Another approach is the preparative method. This method consist of two successive steps: (1) formation of the uncharged precursor of cation on the surface of the support (e.g., imidazole) and (2) formation of IL on the surface of the support with N-substituted with an alkyl chain [104]. The reported methods of the production of IL-based hybrid materials, together with relevant supporting material examples, are schematically shown in Fig. 5.15 [104]. The first combined use of ILs with solid phase sorbents were reported in 2005 [69]. In this study, solid phase microextraction

fiber was coated with disposable 3methylimidazolium hexafluorophosphate ([C8MIM][PF6]) IL prior to the extraction step. The fabricated new fiber was used as a solid support for the headspace solid phase microextraction of benzene, ethylbenzene, xylenes, and toluene in paint samples [69]. In the preparation of IL-modified fiber, a mixture consisting of 900 μL of [C8MIM][PF6] IL and 100 μL of dichloromethane was prepared in a vial for the coating of an SPME fiber. Upon completion of the coating of stainless steel wire, the 1 cm tip of the wire was cleaned by means of methanol and dichloromethane solutions and then conditioned at 200 C under nitrogen in the GC injection port. After the steel wire was taken out from the injector and cooled to room temperature. it was immersed vertically into the coating solution for 1 min and then kept in air for a while for the dichloromethane to evaporate. This procedure was repeated three times to obtain better repeatability of the coating and relatively thick coating. Schematic illustration of the home-made SPME apparatus is illustrated in Fig. 5.16 [69]. After this important step reported by Liu et al. in 2005 an important revolution took place in the fabrication of the IL-based support used in the sorption-based extraction methods. Some of these applications are summarized next.

IL—solid support hybrid materials Chemical immobilization

Physical confinement

Post impregnation (ILS—support materials) Support materials: -

Silica

-

Carbon nanotubes

-

Carbon nanotubes

- Metal organic frameworks

In-situ impregnation (lonogels—IL via sol-gel reactions)

FIGURE 5.15 IL-based hybrid material production methods with relevant supporting material examples [104].

Supported ionic liquids (SILs) (prepared by coating a thin layer of IL film onto and/or into the surface of desired solid support materials)

Organic ionogels - Low molecular weight organic gelators (LMWOGs) - Organic polymers: · PMMA, PDMS, PVDF, PU/PBDO, Nafion Inorganic ionogels - Silica nanoparticles - Carbon nanotubes - Oxide materices · SiO2 (TEOS, TMOS, MTMOS, BTSE, VTEOS) · SnO2 (β-diketonato stabilized tin)

-

Support materials: Mesoporous silica materials Zeolites Clays (e.g., montmorillonite) Carbon nanotubes Metal/metal oxide nanoparticles Graphenes Polymers

· TiO2 (TTIP, TiCI4) Hybrid ionogels (Inorganic + IL containing organic polymer)

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FIGURE 5.16 Schematic illustration of the home-made SPME apparatus. (1) IL-coated fiber tip; (2) stainless steel needle; (3) silicone rubber O-ring; (4) glass syringe body; (5) movable stainless steel tubing; (6) stainless steel fiber or polyimide coated fused-silica fiber; (7) localizer [69].

FIGURE 5.17 Schematic diagram of the one-step self-assembly formation of threedimensional porous materials (MWCNTs-rGO-IL) [100].

Li et al. prepared a headspace SPME apparatus consisting of carboxyl multiwall carbon nanotubes (MWCNTs-COOH), ionic liquid (IL, i.e., 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate), reduced graphene oxide (rGO), polyaniline (PANI), and stainless steel wires. The synthesis procedure includes two steps: (1) formation of three-dimensional porous materials (MWCNTs-rGO-IL) by a one-step selfassembly process and (2) coelectrodeposition of MWCNTs-rGO-IL with polyaniline (PANI) on stainless steel wires by cyclic voltammetry. For this purpose, the stainless steel wire was interacted, respectively, with the following solution for 5 min under ultrasonication: 1 mol L21 NaOH, 1 mol L21 H2SO4 and distilled water. The electrode system was then immersed in a cell containing 0.15 mg mL21 of MWCNTsrGO-IL, 1 mol L21 of HNO3 and 0.10 mol L21 of ANI. For coating, cyclic voltammetry was applied as electrodeposition. The new material was characterized by FT-IR and SEM methods,

used for the separation and preconcentration of octanol, nonanol, geraniol, decanol, undecanol, and dodecanol prior to gas chromatography analysis [100]. The one-step self-assembly formation of three-dimensional porous materials is illustrated in Fig. 5.17. Zhang et al. fabricated a three-dimensional ionic liquid ferrite functionalized graphene oxide nanosorbent (3D-IL-Fe3O4-GO) for the separation and preconcentration of 16 polycyclic aromatic hydrocarbons in human blood samples via pipette-tip solid phase extraction (PT-SPE). Determinations were carried out by GC-MS detections. When compared with conventional SPE applications, the PT-SPE method provided important applicable advantages including the use of low volumes of solvent (1.0 mL) and blood sample (0.2 mL) and usability for many times (at least 10 reuses). Analytes in the blood samples can be analyzed with the developed PT-SPE/GC-MS procedure, with good recoveries from 85.0% to 115%. The LOQs

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were found in the range of 0.007 0.013 μg L21 [101] (see Fig. 5.18). In a different application, IL-functionalized graphene was produced as pipette-tip solid phase extraction sorbent for the separation and preconcentration of auxins in soybean sprouts. In this procedure, thiol-ene click chemistry was used for the functional modification of pentafluorobenzyl imidazolium bromide IL with graphene. Modification of graphene with IL led to the prevention of the aggregation of graphene and improvements in the interactions between graphene and analytes by hydrogen bonding, π π interactions, electrostatic interactions, as well as ionic exchange [102].

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Hamidi et al. have fabricated an ILfunctionalized magnetic graphene oxide/polypyrrole composite for the mixed-hemimicelles, dispersive microsolid phase extraction of methotrexate from urine samples prior to spectrophotometric determination [105]. The suggested method was successfully applied to urine samples with high recoveries between 89% and 93%. 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) was used as the IL. They modeled interactions between methotrexate and sorbent by molecular docking, and the interaction energy was found to be 28.35 kcal mol21 [105]. SEM images of the prepared GO- and IL-coated magnetic GO/PPy are shown in Fig. 5.19. FIGURE 5.18 The schematic diagram. (A) The PT-SPE device; (B) extraction procedure [101].

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FIGURE 5.19 SEM images of the GO- and IL-coated magnetic GO/PPy materials [105].

FIGURE 5.20 The schematic illustration of 3D-IL@mGO fabrication procedure [106].

Zhang et al. fabricated a new threedimensional ionic liquid functionalized magnetic graphene oxide nanocomposite (3DIL@mGO) as MSPE sorbent for the separation and preconcentration of 16 PAHs in vegetable oil samples. Analysis was carried out with GC MS [106]. The fabrication method consisted of two successive steps: (1) IL@mGO was fabricated by solvothermal reaction under N2 gas. For this purpose, 1.0 g NaOH, 2.5 g FeCl3 6H2O, and 7.5 g sodium acetate were dissolved in 100 mL EG at 50 C. Then 50 mg 1(3-aminopropyl) 2 3-methylimidazolium bromide ([APMIM]Br) and 50 mg of GO were added and stirred vigorously at 80 C for 1 h before solvothermal reaction. The resulting




IL@mGO was washed several times and dried. In step 2, 3D-IL@mGO was fabricated by freeradical copolymerization. For this purpose, 100 mg of IL@mGO, 0.0143 mol of divinylbenzene and 0.020 mol of maleic anhydride were dissolved in tetrahydrofuran under the inert gas. Then 1.0 g of benzoyl peroxide was added to the obtained solution and refluxed at 80 C and under inert atmosphere for 2 h [106]. The schematic diagram of the synthesis procedure is illustrated in Fig. 5.20. Wu et al. prepared ionic liquid-coated magnetic graphene oxide nanoparticles as the extraction medium for the mixed-hemimicelles, solid-phase extraction of cephalosporins in biological samples prior to HPLC analysis [107].

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FIGURE 5.21 The schematic illustration of surfactants-coated Fe3O4/GO NPs and its SPE application for analytes [107].

FIGURE 5.22 TEM images. (A) GO; (B) Fe3O4/GO [107].

After modification of GO with 1-hexadecyl-3methylmidazoliumbromide(C16mimBr) IL, a high surface area and excellent adsorption capacity were reached. The synthesis method and extraction procedure are shown in Fig. 5.21. Formation of GO and magnetic graphene oxide was proved with TEM images (Fig. 5.22). Trujillo-Rodrı´guez and Anderson modified SPME fibers with silver-based polymeric IL sorbents to fabricate a new SPME apparatus. In the first step of fabrication procedure, IL monomers were formed by cations including the Ag1 coordinated with two 1-vinylimidazole ligands. As second step, polymeric IL sorbents were obtained on the commercial fibers by free-radical polymerization in the presence of either silver bis[(trifluoromethyl)sulfonyl] imide, and/or a dicationic ionic liquid crosslinker. They used this method to fabricate seven different types of SPME apparatus by using different combinations of ILs, crosslinkers, and their different mole ratios. The new SPME apparatus was used for the

separation and preconcentration of unsaturated compounds before their GC-FID analysis. Composition of silver-based polymeric ionic liquid sorbents, application of new devices for the SPME of analytes, and SEM images of the silver-based polymeric IL are shown in Fig. 5.23 [108]. 5.2.5.3 Deep eutectic solvents Deep eutectic solvents (DESs) were discovered by Abbot et al. in 2003 when they searched the solvent features of the eutectic mixtures of different types of ammonium salts and urea [109]. The DESs were originally developed for extraction and industrial processing. Hence they have been primarily preferred as extraction solvents for metal ions and polar species from plant matrix or oils [110 116]. (DESs) are simply prepared by the mixing of two or more components whose melting points are lower than all of the individual components. The main driving force in the formation of these solvents is the hydrogen bonds between the constituent components [112].

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FIGURE 5.23 Schematic representation of composition of silver-based polymeric ionic liquid sorbents, application of new device for SPME of analytes, and SEM images of the silver-based polymeric ionic liquid [108].

FIGURE 5.24 The DES formation mechanism [114]. 2

+

N+

OH

Cl–

N+

OH

H

O

H

O

Cl–

HO

Although many DES can be prepared by the self-association of hydrogen bond donors and acceptors, the most preferred DESs for separation and preconcentration applications are preparations made by mixing choline chloride (ChCl, Vitamin B4) with carboxylic acids (e.g., citric, succinic, and oxalic acids), with urea and glycerol as hydrogen bond donors (HBDs). Further, DESs can be prepared naturally, with available and cheap components such as alcohols, sugars, amino acids, and organic acids. These kinds of

DESs are called natural deep eutectic solvents (NADESs) [113]. An example of the DES formation mechanism is shown in Fig. 5.24 [112]. When literature studies are searched, it is shown that DESs and NADESs have been generally used as digestive solvents for the digestion of food and biological samples, as extraction solvents in liquid liquid extractions, or in liquid phase microextraction methods and as functionalization agents for solid supports used in solid phase extraction and

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5.2 Green analytical chemistry

solid phase microextraction studies because of their green properties, adjustable viscosity and high selectivity toward analytes [65,115 121]. DESs are also more suitable for instrumental analytical techniques, such as GC and GC/MS, which are frequently used because they decompose at lower temperatures than ILs. Moreover, DESs are classified as 21st-century solvents due to their green nature. The first application of DESs for extraction applications was reported on the solubility of metal oxides including ZnO, CuO, and Fe3O4. In 2006 Abbott et al. prepared different types of DESs and tested them for the solubility the metal oxides. For this purpose, they prepared three different DES: (1) DES-I prepared from malonic acid:ChCl at 1:1 mol ratio, (2) DES-II prepared from oxalic acid:ChCl at 1:1 mol ratio, and (3) DES-III prepared from 2 phenylpropionic acid:ChCl at 2:1 mol ratio. It was found that CuO was more soluble in the DESIII, Fe3O4 was more soluble in the DES-II, and ZnO was more soluble in the DES-I. The concentration of metals was analyzed with inductively coupled plasma atomic emission spectrometry [110]. After this report, DESs have been mainly used for the extraction of organic, inorganic, and bioactive materials prior to the analysis stage. However, it is seen that the advantages of using DES for extraction-based studies had not been realized until 2010. In 2010 Shahbaz et al. used DESs to remove glycerol from palm oil-based biodiesel and provided a liquid liquid extraction method for this process. For this purpose, eight different DES were prepared from ChCl as hydrogen-bonding acceptor and ethylene glycol or 2,2,2-trifluracetamide as hydrogenbonding donors. The optimum molar ratio of DES to biodiesel was found to be 1:1 for all DESs [111]. Dai et al. prepared many NADES, characterized them, and checked their solvent properties on some compounds including quercetin, cinnamic acid, rutin, and carthamin. The comprehensive study has an

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important place in the extraction capability of DES or NADES because more than 100 NADES had been prepared for these extraction tests [113]. Later, DESs or NADES were used for the extraction of metal ions, organic compounds, and bioactive materials from environmental, food, and biological samples. Their use especially in the direct extraction of metabolites or active ingredients from plants has attracted attention. Some of these applications are mentioned next. In 2013 Bi et al. used alcohol-based deep eutectic solvent for the extraction of flavonoids (myricetin and amentoflavone) as bioactive compounds. They prepared ChCl-based DESs by using any alcohols including ethyl glycol, glycerol, 1,2Butanediol, 1,3-Butanediol, 1,4-Butanediol, 2,3-Butanediol, and 1,6-Hexanediol. The most suitable extraction condition was obtained with a solid:liquid ratio of 1:1, 35 vol.% of water in ChCl/1,4-Butanediol (1/5) at 70.0 C for 40.0 min. This DES-based method allowed for the extraction of 0.031 and 0.518 mg g21 of myricetin and amentoflavone. After completion of the extraction stage, analysis was carried out by HPLC [115]. Dai et al. used NADES for the extraction of phenolic metabolites in Carthamus tinctorius L. Most major phenolic compounds were extracted from NADES with high extraction efficiencies ranging from 75% to 97%. In this study, many NADES were prepared and checked for the extraction of phenolic compounds. For this purpose, NADES including fructose-glucose-sucrose, lactic acid-glucose, glucose-choline chloride, sucrose-choline chloride, 1,2-propanediol-choline chloride, sorbitol-choline chloride, and proline-malic acid were prepared. The extraction capabilities of these NADES were checked in the extraction of phenolic compounds, including Hydroxysafflor Yellow A, carthamin, and cartormin from safflower. After the extraction step, determinations were carried out with HPLC-DAD [116].

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ChCL (1 mol) + Urea (2 mol)

Stirred at 100°C until DES formed

160 μL DES 40 μL HNO3

Added to edible oil and stirred for 5 min at 50°C

FIGURE 5.25 Schematic illustration of the DES-LPME method [118].

Phase separation by centrifuging

DES rich phase subjected to ETAAS

After understanding that deep eutectic solvents are good extraction liquids in extraction techniques, the idea that these solvents can be used in LPME methods has emerged, and many innovative applications have been made in this field. The first DES-based LPME application was reported by Gu and coworkers in 2014. In this study, DESs were used as extraction solvent for the liquid phase microextraction of phenolic compounds from a model oil sample [117]. In 2014 Tang et al. used DESs in the headspace-solvent microextraction (HS-SME) of terpenoids including linalool, α-terpineol, and 2 terpinyl acetate as bioactive compounds from Chamaecyparis obtusa (CO) leaves. The DESs used were obtained by mixing ChCl with ethylene glycol (EG) at different molar ratios. For this purpose, The CO leaves powdered with a grinder were placed in a sample vial sealed with a rubber stopper. The GC syringe containing 2 μL of DES was immersed through this rubber plug so that it remained on top of the sample. The sample was then placed on the heating plate and heated to the optimum temperature. At this time, the extraction of analytes was continued. After the extraction was completed, the extraction drop was redrawn into the GC syringe, and the DES phase containing

the extracted material was injected into the GC system for the analysis of analytes. LOD values for the analytes were between 2.006 and 3.150 ng mL21. Analytes were recovered from the CO leaves with acceptable recoveries ranging from 79.4% to 103% [122]. The first use of DES for the microextraction of metal ions was reported by Karimi et al. in 2015. They introduced a DES-based LPME method for the separation and preconcentration of lead and cadmium in edible oil samples prior to their ETAAS determinations. Researchers used DES consisting of ChCl and urea. In this procedure, 200 μL of a mixture of (4:1) of DES (ChCl-urea) and 2% nitric acid solution was injected into oil samples, and the obtained mixture was subjected to vortex agitation and then heating at 50 C in the water bath and finally to stirring for 5 min. The extraction of analytes was successfully completed after these stages. The DES-rich phase was separated by centrifugation, and 20 μL of DES-rich phase was analyzed by ETAAS. The schematic illustration of the developed extraction method is shown in Fig. 5.25 [118]. Later, new extraction apparatus, such as ultrasounds, high-pressure systems, microwave heating, vortex mixing, and the like, has been adopted to DES-based LPME methods to

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FIGURE 5.26 Schematic illustration of DES-based ELLME method [119].

improve extraction efficiencies of DESs in order to reach extraction equilibrium in short extraction times. The use of these systems in DES-based LPME methods holds an important place in the separation and preconcentration of organic and inorganic analytes before detection systems. DES-based emulsification liquid liquid microextraction is a different mode of the LPME method. This LPME mode was applied for the first time in 2015 by Khezeli et al [119]. Authors used DES as the extraction solvent in the emulsification liquid liquid microextraction of toluene, benzene, ethylbenzene, and seven polycyclic aromatic hydrocarbons from water samples prior to their HPLC analysis. The introduced new method is schematized in Fig. 5.26. In this method, 1.5 mL of aqueous sample solution containing target analytes (125 μg L21) and 100 μL of water-miscible DES, prepared from ChCl and phenol at a 1:2 mol ratio, was placed in a sample vial. Afterward, 100 μL of THF was injected into the homogeneous solution, the aggregation of DES molecules was started, and greater dispersion of DES droplets into the sample solution was acquired by ultrasonication of this mixture for 20 min. After separation of the DES-rich

phase from aqueous phase by centrifugation, about 20 μL of the DES-rich phase was given into the HPLC system for the quantitative analysis of analytes [119]. Lamei et al. introduced a DES-based airassisted emulsification liquid liquid microextraction method (DES-AAELLME) for the preconcentration of methadone in water and biological samples. DES was prepared by mixing ChCl and 5,6,7,8-Tetrahydro-5,5,8,8-tetramethylnaphthalen-2-ol (TNO) at a molar ratio of 1:2. THF was used as a demulsifier solvent. The LOD, LOQ, RSD, and PF values of the developed method were found as 0.7 μg L21, 2.3 μg L21, ,6%, and 270, respectively. The developed DES-AAELLME/GC-FID procedure was successfully used in the analysis of methadone in water and biological samples with high recoveries ranging from 98.4% to 101.2% [114]. DES formation is shown in Fig. 5.27. Nie et al. combined DES-based extraction with headspace solid-phase microextraction and reported microwave-assisted deep eutectic solvent extraction coupled with headspace solid phase microextraction method for the separation and preconcentration of volatile

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5. Type of green solvents used in separation and preconcentration methods

2

+

N+

OH

Cl–

N+

OH

H

O

H

O

Cl–

HO

FIGURE 5.27

The DES formation mechanism [114].

FIGURE 5.28

Schematic illustration of the developed DES-UA-ELPME method [121].

compounds from tobacco samples. Analysis of volatile compounds was carried out with GCMS [120]. A DES-based ultrasound-assisted emulsification liquid phase microextraction method (DES-UA-ELPME) was suggested by Aydin et al. Authors used this microextraction procedure to separate and preconcentrate Malachite Green in farmed and ornamental aquarium fish water samples. After microextraction, a concentration of Malachite Green in DES-rich phase was measured with a UV-Vis spectrophotometer [121]. The DES-UA-ELPME method is illustrated in the Fig. 5.28. At the same time, the preparation of different types of sorbents, modified with deep eutectic solvents and natural deep eutectic solvents, has attracted considerable attention in solid phase extraction applications [123 125].

Liu et al. modified graphene with a DES, prepared from choline chloride and ethylene glycol. In the modification procedure, 200 mg of GO was added in the solution including 200 mL of water 140 mg of ChCl and 120 mg of EG, and the obtained mixture was stirred and refluxed at 80 C for 12 h. In the last step, 2 g of hydrazine hydrate was added, and this mixture was stirred at 80 C for 24 h. The new SPE sorbent was applied to pipette-tip solid phase extraction of sulfamerazine traces before its HPLC determination [123]. Wang et al. reported different applications of DES-modified sorbents in 2016. Researchers fabricated GO-DES@silica by using DESs and GO-IL@silica by using ILs. In this procedure, GO was modified by DESs or ILs to obtain GODES and GO-IL, and then the obtained hybrids were coupled to the surface of silica by a

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5.2 Green analytical chemistry

covalent bonding between carboxylic acid (COOH) groups of GO and amino groups of silica. Subsequent reactions of these materials with hydrazine solution cause the formation of G-DES@silica and G-IL@silica materials. The obtained last products (G-DES@silica and GIL@silica) were used for solid phase extraction of chlorophenols in water samples before their HPLC-UV analysis. The results showed that GDES1@silica (ChCl:formic acid, 1:2), GODES4@silica (ChCl:urea, 1:2), G-IL3@silica ([HMIM][Tf2N]), and GO-IL4@silica ([EMIM] [Br]) have the better extraction performance than other sorbents for the extraction of chlorophenols [124]. Yousefi and coworkers fabricated DESmodified magnetic bucky gels by modifying magnetic MWCNTs with DES (choline chloride/urea). The noncovalent modification method was used to interact magnetic MWCNTs with DES. The new DES-modified magnetic bucky gels were used as the sorbent in the dispersive solid phase extraction of organochlorine pesticides in water samples with enrichment factors between 270 340 [125]. 5.2.5.4 Amphiphilic and supramolecular solvents Surfactants, which have the most important place among amphiphilic solvents, are in first place among the solvents that can be considered as replacements for the toxic organic solvents used in analytical chemistry applications, especially in sample preparation [126,127]. Surfactants, when added to the aqueous sample phase at a concentration higher than critical micelle concentrations, are self-assembled to form normal micelle aggregates having strong dissolution features, which enable them to interact with compounds having different polarity properties. Hence, for many years, different micelle-assisted extraction (MAE) methods have been used in the extraction-based separation and preconcentration methods replacing conventional extraction solvents. To

245

increase interactions and accelerate the extraction procedure, different apparatus, such as ultrasounds, high pressures systems, microwave heating, vortex mixing, and the like, have been adopted to MAE methods [127 129]. In MAE-based separation and preconcentration methods, a small amount of the surfactant is added to the sample solution, and phase separation of the surfactant-rich phase containing the analyte or analytes of interest is promoted by a change in the solution environment. After completion of the extraction stage, the surfactant-rich phase is isolated from the aqueous sample solution and analyzed with a suitable detection system. Formation of micelle aggregates is promoted by different experimental changes including change of sample solution medium temperature, pH, and ionic strength. Formation of micelles with different shapes are illustrated in Fig. 5.29 [65]. Amphiphilic solvent-based methods are classified in seven main groups given in Fig. 5.30. These techniques have important advantages including nontoxic extractant, low cost, simplicity, and high capacity for the separation and preconcentration of a wide range of analytes. CPE as the first coacervate-based extraction method or micellar extraction was first introduced in the 1970s and has maintained its popularity. Coacervate-based extraction methods are convenient alternatives to liquid liquid extraction [130]. Applications of amphiphilic solvent-based extraction methods are very broad. These methods can be applied in the separation and preconcentration of heavy metals, persistent organic pollutants, pesticides, pharmaceutical ingredients, azo dyes, and so on from different matrix media. The most commonly used surfactants for separation and preconcentration applications are Triton X-100, Triton X-114, PONPE 7.5, and SDS [65,130,131]. Some example applications are discussed next. Fang and coworkers have reported a micellemediated extraction and preconcentration

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FIGURE 5.29 Schematic illustration of (A) micellar shapes and (B) procedure steps and scheme of the micellarbased extraction [65].

FIGURE 5.30 Illustration of main novel applications of amphiphilic and supramolecular solvents in newgeneration separation and preconcentration methods.

method. They used micelles of Triton X-100 as extraction phase in the presence of high salt content [65,130,131]. Paleologos et al. have introduced a cloud-point extraction method for the separation and preconcentration of biogenic

amines from fish-tissue samples as their benzoyl derivatives. They used Triton X-114 micelles as the extraction agent, followed by separation with micellar LC and UV detection. LOD values for the nine biogenic amines were in the vicinity

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5.2 Green analytical chemistry

of 0.01 mg L21. The CPE method was applied for the extraction and determination of cadaverine, putrescine, tyramine, agmatine, tryptamine, phenylethylamine, histamine, spermine, and spermidine in trout samples with high recoveries ranging from 95% to 103.5% [132]. Sirimanne et al. used Triton X-100 micelles for the separation and preconcentration of PAHs and polychlorinated dibenzo-p-dioxins (PCDDs) in human serum prior to their HPLC determination [133]. Rukhadze et al. used Triton X-114 micelles in the CPE method to separate and preconcentrate henobarbital and carbamazepine asanti-epileptic drugs in biological fluids. This method was based on the extraction of free and protein-bound fractions of the drugs directly from saliva and blood plasma samples [134]. Montesdeoca-Esponda et al. introduced a dispersive liquid liquid micellar microextraction (DLLMME) method for the separation and preconcentration of five pharmaceutical compounds from wastewaters prior to UHPLC-DAD determination. In this procedure, a micellar solution of polidocanol surfactant and chloroform were used for the dispersive liquid liquid micellar microextraction of the target analytes. The temperature of sample solutions was increased above critical temperature, and the formation of the cloudy solution was observed. The cloudy solution was centrifuged, and after phase separation, chloroform was removed. In the last step, the surfactant-rich phase was injected into the

UHPLC-DAD system. Under the optimum conditions, the suggested procedure provided enrichment factors of up to 47-fold, LODs ranged from 0.1 to 2.0 μg L21, and RSDs were lower than 26% for all analytes [135]. Xu et al. introduced a new liquid liquid method based on coacervation and phase separation. In this method, salt-free cationic surfactant aqueous systems based on lauric acid (LA) and dodecyltrimethylammonium hydroxide (DTAOH), using hexafluoroisopropanol (HFIP) as a coacervate-inducing agent was used. Phase separation occurred over a range of LA/ DTAOH molar ratios (78:22 0:100 mol mol21) and total surfactant concentrations (5 200 mmol L21) upon adding a small amount of HFIP (,10%, v/v). HFIP-induced salt-containing sodium laurate/dodecyltrimethylammonium bromide system has a lower two-phase region than an HFIP-induced salt-free LA/ DTAOH cationic surfactant system. The developed HFIP-induced LA/DTAOH coacervate extraction method was used for the separation and preconcentration of fluoroquinolones (rufloxacin, ciprofloxacin, danofloxacin, enrofloxacin) in milk. After the liquid liquid extraction stage, analysis was carried out by HPLC-UV. The HFIP-induced LA/DTAOH coacervate extraction-HPLC-UV analysis procedure is illustrated in the Fig. 5.31 [136]. Later, new extraction apparatus such as ultrasounds, high pressures systems, microwave heating, vortex mixing, and the like has FIGURE 5.31 The HFIPinduced LA/DTAOH coacervate extraction-HPLC-UV analysis procedure [136].

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5. Type of green solvents used in separation and preconcentration methods

been adopted to micelle-assisted extraction methods to achieve the highest possible extraction efficiency and reach the fastest extraction equilibrium. Recently, the term “supramolecular solvent” (SUPRAS) has been used to refer to all amphiphilic solvents that can self-assemble in water in a suitable environment. Supramolecular solvents are the new generation of ecofriendly solvent systems that occur as an alternative to organic solvents in extraction studies [137,138]. Analytical chemists use supramolecular solvents in separation and preconcentration applications under different names, such as cloud-point extraction and coacervative extraction. The cloud point technique [137,138] refers to the temperature at which nonionic surfactants are subjected to phase separation in aqueous solutions, hence the formation of the cloudy solution; coacervative extraction refers to the phenomenon through which liquid liquid phase separation occurs. Supramolecular solvents (SUPRASs) are referred as nanostructured liquids produced from amphiphiles through a sequential, selfassembly process occurring on two scales: nano and molecular. These are solvents that do not mix with water and are dispersed in a

continuous phase consisting of colloidal solutions of surfactant clusters by effects such as pH, temperature, and electrolyte effect [137 139]. First, amphiphiles form threedimensional aggregates, generally aqueous/ reverse micelles or vesicles, above a critical aggregation concentration, and then these nanostructures form bigger aggregates via selfassembly. At this stage, aggregates are separated through a phenomenon known as coacervation, and a new liquid phase is obtained (i.e., the supramolecular solvent) [137]. This selfassembly processes are illustrated in Fig. 5.32. Supramolecular solvents formed in the aqueous phase in the nano- and molecularsized micelles have polar and apolar regions [140 142]. Supramolecular solvents have regions of varying polarity that can make many interactions for analytes. Such interactions can be adjusted by altering the hydrophobicity and polarity of the amphiphilic groups [140 142]. In extraction studies, high extraction efficiency is obtained by adding supramolecular solvents containing high-concentration amphiphilic groups in very small volume (50 1000 μL). The mechanism of the application of extraction studies based on supramolecular solvent FIGURE 5.32 Self-assembly processes in SUPRAS formation [137].

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5.2 Green analytical chemistry

formation appears to be similar to cloud point extraction [137]. It is noteworthy that the components used in micelle formation in cloudpoint extraction are also used in the formation of supramolecular solvents [137]. Supramolecular solvents in the structure of hydroxyl (OH) and COOH groups with long carbon chain species are obtained by mixing species such as tetrahydrofuran, tetrabutyl ammonium, ethanol, and so on [137]. When compared with cloud-point extraction studies, the most important properties of extraction methods based on supramolecular solvent formation are the minimization of the amount of organic solvents used, the need for the formation of supramolecular solvent in cloud-point studies, and, most importantly, the presence of supramolecular solvent in the environment. These nano or microscale micelles interact more with the analyte because of their larger surface area than normal micelles, resulting in higher extraction efficiency. SUPRASs termed nonionic surfactant-based

micellar aggregates have been used mainly for the extraction of hydrophobic organic compounds and metal ions from environmental, food, pharmaceutical, and biological liquid samples. Some of these analytes are PAHs, pesticides, bioactive compounds, dyes, endocrine disruptors, phenols, and other organic surfactants, humic and fulvic acids, pharmaceutical ingredients, and heavy metals [31,137 144]. Supramolecular solvent formation is carried out through three different mechanisms: aqueous micelle, reverse micelle, and vesicle formation (Fig. 5.33) [138]. Some new-generation example studies on the use of supramolecular solvents are given next. Ballesteros-Go´mez et al. have used SUPRAS for the extraction of contaminants in liquid foods [138]. They have used reversed micellebased SUPRAS prepared by means of the dispersion of decanoic acid in tetrahydrofuran (THF) water. The SUPRAS were used for the separation and preconcentration of some

FIGURE 5.33 Light microscopy (bright field) micrograph of a typical amphiphile-based SUPRAS and schematic picture of the aqueous micelle, reverse micelle, and vesicle aggregates that may constitute it [138].

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5. Type of green solvents used in separation and preconcentration methods

contaminants, including bisphenol A (BPA), benzo(a)pyrene (BaPy), and ochratoxin A (OTA). In this method, 80 mg of decanoic acid and different volumes of THF (0.8 1.7 mL) were added to the liquid food sample (15 mL), and the mixture was stirred for 5 min. At this stage, the extraction of analytes from the liquid food phase into decanoic acid drops was accomplished. After centrifugation for 10 min, 10 20 μL of the decanoic acid-rich phase was analyzed with liquid chromatography coupled to mass spectrometry for BPA or fluorimetry for OTA and BaPy. The developed procedure was applied to wine and wine-based products, beer, soft drinks, tea and coffee brews, and/or aqueous artificial solutions including specific food matrix components. Recoveries for OTA, BaPy, and BPA in food samples were in the ranges 79% 93%, 90% 96%, and 78% 82%, respectively [138]. Moral et al. developed a method for the supramolecular extraction of benzimidazolic fungicides (carbendazim, thiabendazole, and fuberidazole) from water samples prior to liquid chromatography/fluorimetric analysis [31]. They preferred reversed micelles-based SUPRAS prepared by means of the dispersion of decanoic acid in tetrabutylammonium (Bu4N1) water. In this application, 100 mg of decanoic acid, 185 mg of Bu4NOH (40%, w/v), and 1 mL of Bu4NCl (1 M) were added to the aqueous sample solution (pH 5.0). The mixture was centrifuged, followed by stirring to make the formation of the supramolecular solvent simpler. After centrifugation, the supramolecular solvent phase (100 μL), which was collected in the narrow neck of the centrifuge tube, was analyzed with an LC system. In recent years, with the adaptation of supramolecular solvents to microextraction techniques, a large window has been opened for the development of greener methods. Rezaei et al. developed a supramolecular solvent hollow fiber microextraction method for the determination of five benzodiazepine

drugs in water, fruit juices, urine, and blood plasma samples [140]. First, researchers obtained vesicular coacervate by mixing 10.3 g of decanoic acid and 7.8 g of tetrabutylammonium hydroxide in 400 mL distilled water at pH 7.0 ( 6 0.1) and then by separating the aqueous and vesicular coacervate solvent phases after centrifugation. To prepare hollow fiber, approximately 35 μL of the SUPRAS was drawn into the syringe. A piece of hollow fiber (10 cm long) was fixed to the tip of the syringe needle, and the assembly was immersed in the coacervate phase for 2 min. to impregnate the pores of the fiber wall. To remove the excess amount of SUPRAS, the fiber was immersed in ultrapure water for 10 s. The syringe plunger was then pressed to fill the hollow fibers with the vesicular coacervate phase. Finally, the end of the hollow fiber was covered with a piece of aluminum foil. The prepared SUPRASmodified hollow fiber was used for hollow fiber vesicular-mediated microextraction (HFVMME) of five benzodiazepine drugs from water, fruit juices, urine, and blood plasma samples (Fig. 5.34) [140]. Fonseca et al. have used a supramolecular microextraction technique and liquid chromatography/fluorescence method for the analysis of ochratoxin in wheat samples [145]. Costi et al. have used a supramolecular solvent microextraction technique for multiple residue analyses of sulfonamides in meat samples [146]. After proving the usability of supramolecular solvents for organic analytes, the usability of metal ions for microextraction was investigated, and important applications were reported in this area. Yilmaz and Soylak introduced a novel supramolecular solvent-based liquid liquid microextraction (SsLLME) procedure for the separation and preconcentration of Cu(II) ions as dimethyl dithiocarbamate (DMDC) complex from aqueous sample phase. SUPRAS were obtained with reverse micelles of 1-decanol in THF:water. After SsLLME, analysis was carried out by microsampling with a flame atomic

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5.3 Switchable hydrophilicity solvents

FIGURE 5.34 A schematic illustration of HF-VMME [140].

absorption spectrometric detection system. The suggested SsLLME procedure was applied to food and water samples with satisfactory results [143]. The same authors have developed a different SsLLME method for the separation and preconcentration of gold from environmental samples [147]. Alothman et al. have used similar SsLLME methods for the extraction and analysis of cobalt from water samples prior to microsampling flame atomic absorption spectrometric determination [148].

5.3 Switchable hydrophilicity solvents In addition, to meeting the requirements of green analytical chemistry, a separation and preconcentration method must extract the analyte from the real sample medium in high yield, be able to perform effective separation, be selective against the analyte to be extracted, and not be affected by matrix components present in the actual sample medium. Extraction techniques involve multiple steps. Different polarity solvents have to be used in each step. For example, the first step of extraction requires the use of a polar solvent, while the second step may require the use of an apolar solvent [149 152]. This results in disadvantages such as the formation of secondary waste and an increase in cost due to the use of excess solvent for the developed method. To solve

this problem, solutions are needed that can be used in different steps of a process by altering some of its physical properties by itself. It’s not science fiction. At first glance, these solvents might be thought to be costly and difficult to prepare, but a new-generation solvent system has been developed that fulfills the requirements of green chemistry and completely eliminates prejudices in this field. These solvents are called switchable hydrophilicity solvents (SHS) (polarity can be changed instantaneously) [151 153]. SHS are new-generation solvents with two forms that differ in their physical properties: polar and apolar. The switching of the SHS from the polar form to the apolar form or vice versa can be accomplished in a simple, fast, instantly reversible, and controlled manner. This feature of SHS is similar to being able to control the tools we use in daily life. Examples include using the on or off button to turn on a lamp, and using the heat or cool options to use the heating or cooling feature of an air conditioner [151 153]. Switchable solvents are based on the formation of secondary, tertiary amines having an apolar nature, that is, amine bicarbonate or alkyl carbonate salts protonated with water in the presence of CO2 at a pressure of 1 atmosphere. This reaction is based on protonation of amines and is exothermic. The ammonium bicarbonate and alkyl carbonate solvents formed at the end

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5. Type of green solvents used in separation and preconcentration methods

of the reaction are the polar form of SHS [154 156]. If nitrogen gas (N2) and/or air is passed through this polar switchable solvent medium, the solvent is heated, and a basic solution such as NaOH or an acidic solution such as HCl is added to this solvent, the CO2 is removed again. When the CO2 is removed, the SHS returns to its apolar form [154 156]. An example reaction of this transformation is shown in Fig. 5.35. In addition, to changing the polarity of this reaction instantaneously, the components of these solvents are easily available, inexpensive, and nontoxic, which are important advantages. After its introduction in the literature, SHS has gained importance in analytical chemistry, as it has in other fields of chemistry. Jessop et al. first examined the applicability of SHS for the industrial process. Thereafter, SHS was used mainly as the extraction solvent for the extraction of many species such as oils (vegetable, soybean oil, sludge oil, and the like), hydrocarbons, lipids, bitumen, phenol compounds, and so on and for the many liquid phase methods for the microextraction of trace analytes, including polyaromatic

hydrocarbons, pesticides, herbicides, insecticides, dyes, pharmaceutical ingredients, nitroaromatic compounds, bisphenols, alkaloids, amino acids, and heavy metals. Some literature studies on the use of SHS are summarized next [30,151 160]. Phan et al. used SHS for the extraction of soy oil from soybean flakes. Thus the disadvantages of hexane-based extraction methods that are generally used in oil extraction—such as high energy requirements in extraction and distillation processes and the toxicity of chemicals used—are eliminated [161]. Samorı` et al. used a switchable solvent prepared by mixing 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), CO2, and octanol to extract hydrocarbons from the microalga Botryococcus braunii. DBU/octanol and DBU/ethanol polarity solvents were checked for the extraction efficiency of lipids from freeze-dried microalga samples. As a result, the DBU/octanol switchable solvent system was further used to directly extract hydrocarbons from algal culture samples. Steps of the switchable solvent-based extraction method is illustrated in Fig. 5.36 [158].

FIGURE 5.35 Synthesis and formation mechanism of polar apolar forms of SHS.

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5.3 Switchable hydrophilicity solvents

FIGURE

N N

OH

+ ( ) 7

Alga

Alga

5.36 Schematic illustration of switchable solvent-based hydrocarbons extraction from freeze-dried samples of B. braunii [158].

Hydrocarbons N N

OH

N

+ ( ) 7

OH + ( ) 7

N

CO2 N2 Hydrocarbons N

N

⊕

O ( ) 7

–

O O

N

N

⊕

O ( ) 7

–

O O

Hydrocarbons

Boyd et al. used SHS for the extraction of microalgae to produce biofuel. For this purpose, a known amount of lyophilized B. braunii samples were taken, to which N,N-dimethylcyclohexylamine (CyNMe2) was added. The obtained mixtures were sonicated by means of a 130-W ultrasonication bath for 30 min and then stirred for 18 h at different temperatures ranging from room temperature to 80 C. The samples were filtered and washed with fresh CyNMe2. Then the filtrate was mixed with an equal volume of water, and the obtained CyNMe2/water biphasic mixture was subjected to CO2 bubbling until reaching a monophasic system. At this stage, the lipid layer floating at the surface was recovered. To recover CyNMe2 for the next process, the monophasic solvent was subjected to N2 bubbling and heating until it became a two-layer mixture consisting of water and CyNMe2. Fig. 5.37 shows the steps of the switchable solvent-based extraction method [162].

Holland et al. used a CyNMe2-based switchable hydrophilicity solvent for the extraction of bitumen from oil sands with high extraction efficiencies between 94% and 97% [163]. Sui et al. synthesized hydrophilic forms of switchable hydrophilicity tertiary amines and used them for the extraction and recovery of heavy hydrocarbons from oil sand ores. For this purpose, they checked triethylamine, N,Ndimethylbenzylamine, and N,N-dimethylcyclohexylamine [164]. The adaptation of switchable solvents to new-generation microextraction studies took place in a short period of time and gained an important place especially in the extraction and enrichment of trace organic compounds, heavy metals, and other inorganic species from the matrix medium. The first attempt in the usability of switchable solvents in microextraction applications was taken by Lasarte-Aragone´s and coworkers in 2015 [165]. They introduced a homogeneous liquid liquid microextraction for the separation and preconcentration of benz[a]

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FIGURE 5.37 Schematic illustration of the switchable solvent-based microalgae extraction from lyophilized B. braunii samples [162].

anthracene before its fluorimetric analysis. In this method, the hydrophilic switchable solvent phase as an extraction solvent was synthesized by adding CO2 to a N,N-dimethylcyclohexylamine-water mixture until a single phase was observed, corresponding to a 1:1 (v:v) water: N, N-dimethylcyclohexylamine (DMCA) solution (Fig. 5.38) [165]. In the microextraction method, 750 μL of the hydrophilic form of SHS was added to 10 mL of aqueous sample solution previously located in a glass test tube, and 1 mL of a 20 M NaOH solution was added to this homogeneous solution. At this stage, a cloudy solution formed. The solution was vortexed for 15 s and waited for 5 min to achieve phase separation. 300 μL of DMCA are recovered and analyzed. The suggested microextraction method is schematized in Fig. 5.39 [165]. In 2015 two different applications of the SHS-based liquid phase microextraction for the trace metal ions (Cd(II) and Cu(II)) were introduced by Yilmaz and Soylak [151,153]. These two studies are the first applications of SHS-based LPME for metal ions. In the first application, the authors used the triethylamineprotonated triethylamine carbonate SHS system for the separation and preconcentration of Cd

(II) ions as pyrrolidinedithiocarbamate chelates. Microextraction experiments were carried out at pH 4.0. In this study, Cd(II) ions were first complexed with pyrrolidinedithiocarbamate in an aqueous sample solution including 750 μL of protonated triethylamine carbonate. Then 2 mL of a 10 M NaOH solution was added to this homogeneous solution. At this stage, a cloudy solution formed, and an extraction of Cd(II)pyrrolidinedithiocarbamate chelates from the aqueous sample phase to the triethylamine phase was accomplished. After centrifugation processing at 4000 rpm for 6 min, the trimethylamine-rich phase was analyzed with microsampling flame atomic absorption spectrometer (FAAS). A schematic diagram of the SHS-based LPME and microsampling FAAS analysis stage is shown in Fig. 5.40 [153]. Since 2015, SHS was used in different LPME applications such as fully automated effervescence-assisted switchable solvent-based liquid phase microextraction, centrifuge-less dispersive liquid liquid microextraction, switchable liquid solid dispersive microextraction, switchable hydrophilicity solvent membranebased microextraction, ion-pair switchablehydrophilicity solvent-based homogeneous liquid liquid microextraction, effervescence

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5.3 Switchable hydrophilicity solvents

FIGURE 5.38 Stages of the DMCA dissolution in water. (A) Initial state where the two immiscible phases were obtained; (B) after the addition of 10 g of dry ice where three phases (DMCA, water, and CO2 phases) were obtained; (C) after the solubilization of the CO2; (D) obtaining of single phase after many additions of dry ice [165].

FIGURE

5.39 Schematic illustration of the SHS-based liquid phase microextraction [165].

tablet-assisted switchable solvent-based microextraction, and vortex-assisted switchable liquid liquid microextraction. All of these SHSbased LPME methods have been used for the

accurate and sensitive analysis of organic, inorganic, and bioactive materials. These applications are discussed in detail in the following chapters.

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5. Type of green solvents used in separation and preconcentration methods

FIGURE 5.40 Schematic diagram of the SHS-based LPME and microsampling FAAS analysis stages [153].

5.3.1 Supercritical fluids When a substance is forced to a pressure and temperature above the critical point, it enters the supercritical state [166]. The physicochemical features of the supercritical fluid are located between the liquid and the gas; hence it is defined as a condition when the liquid and the gas cannot be distinguished. A supercritical fluid has a liquid-like density, the viscosity of a gas emission between these two states [166]. Compared to conventional extraction techniques such as solid liquid extraction, classical solvent extraction, or Soxhlet extraction, supercritical fluid extraction (SFE) has the advantages explained next, as well as reduced consumption of toxic solvents and better selectivity [167,168]: More effective mass transfer resulting from low viscosity and high dispersion is desirable, especially if the target compounds are extracted from solid samples, Faster extraction is obtained because the supercritical fluid can be readily dispersed from a solid sample matrix. High extraction efficiency is achieved by using low amounts of solvents. Direct coupling of SFE with analytical instrumental techniques used in the analysis step, such as GC, is possible.

Physical conditions, such as density and fluidity, can be changed to obtain suitable extraction media for target compounds. No production of toxic wastes after SFE are generated [26,169 171]. With these advantages, SFE has an important place in both industrial applications (pharmaceutical, food and cosmetic industries) and small laboratory applications. It is an important process in such fields as the food, pharmaceutical, and cosmetic industries [26,169 171]. The SFE method is a powerful technique for the extraction of natural compounds from food products. The SFE method has been used in many different applications, including extraction of drug and essential oils from natural matrices, extraction of bioactive compounds and lipids, extraction of persistent organic pollutants (PAHs, PCBs) from environmental samples, enzymatic reactions, and enantiomeric separation [172 175]. SFE methods consist of two main steps: [176,177]. First, when the solid sample absorbs the supercritical solvent, the soluble compounds are extracted from the matrix. As a result, the analytes in the matrix are dissolved by the solvent. The isolated analytes from the supercritical solvent after the analytes are transferred and then removed.

New Generation Green Solvents for Separation and Preconcentration

5.3 Switchable hydrophilicity solvents

The step of selecting the appropriate solvent is very important. In fact, any solvent can be brought into the supercritical state, but some factors need to be considered. These factors include solvent toxicity, physicochemical properties affecting the conditions of the supercritical state, technical applicability, and cost. Although carbon dioxide is most commonly used for this purpose due to moderate critical temperature and pressure, other solvents have also been investigated. For example, ethane-based supercritical fluid extraction was used to extract caffeine, cocoa butter, and theobromine from cocoa beans. The critical-point features of ethane are similar to those of CO2, but pressure is required to achieve a supercritical state to reduce energy consumption in the extraction process. Higher extraction efficiencies were obtained compared to those of supercritical carbon dioxide. The main disadvantage of ethane as SC solvent is its high cost, but the choice of this solvent should be taken into account by considering the lowered amount of energy required [178]. Other alternatives to commonly used CO2 are propane and dimethyl ether. Catchpole et al. checked the extraction performance of nearcritical carbon dioxide, propane, and dimethyl ether on ginger, chili powder, and black pepper. The results showed that, although subcritical dimethyl ether was effective in extracting the pungent principles from spices as supercritical CO2, a significant amount of water was also extracted with the analytes. The lowest extraction efficiency was obtained with subcritical propane. All solvents were successful in extracting gingerols from ginger. Similar results were obtained in the extraction of capsaicin using supercritical CO2 and dimethyl ether, while the yield of extraction was about twice that obtained with propane. The piperine yield extracted from black pepper by propane was 10% lower than that obtained with dimethyl ether and CO2, but it improved with increasing extraction

257

temperature [179]. One of the disadvantages of SFE, which uses CO2 as a solvent, is the use of an organic modifier (cosolvent). Extraction efficiency is, importantly, increased by the addition of the modifier because of the increase in the solubility of the analytes desired in CO2 especially in high polar species. Generally, the amount of the modifier added changes from 1% and 15%, but this factor is changed by considering extraction conditions, type of the matrix, type of the solute and type of cosolvent. Ethanol and methanol are frequently preferred as the cosolvents, but the choice of the appropriate substance is not always easy, and different factors (e.g., type of the target compounds, affinity of the analytes to modifier) have to be taken under consideration [179,180]. The addition of the organic modifier clearly reduces the greenness of the SFE method, but the volume of cosolvents is generally relatively low. Furthermore, some attempts have been made to utilize nontoxic substances of natural origin such as vegetable oils as cosolvent. Canola oil was used as a cosolvent for the extraction of carotenoids from carrots by applying subcritical CO2 extraction methods, increasing the extraction efficiency from 7% to 10% [181]. 5.3.1.1 Superheated water (subcritical water) Water, one of the cornerstones of life, is a special substance as the most widely used solvent because of its hydrogen-bonding capacity, high boiling point temperature, and polarity. Water can be heated to temperatures between 100 C and 374 C, can be increased to values above atmospheric pressure, and can cause changes in physicochemical properties to maintain the liquid state [182,183]. Superheated (subcritical) water becomes less polar, and its viscosity, surface tension, and permeability decrease as the diffusion rate increases. The decreasing dielectric constant at high temperature is a very significant factor. It

New Generation Green Solvents for Separation and Preconcentration

258

5. Type of green solvents used in separation and preconcentration methods

is 80 at room temperature, but it drops to 27 at 250 C, which is close to the dielectric constant of ethanol at room temperature. These unique features of water make the group of polar and nonpolar species water soluble [184,185]. A superheated water-based extraction method provides several advantages. It can be an effective alternative to conventional organic solvents. It is nontoxic, easy to find, and inexpensive. Therefore superheated waterbased extraction methods provide a fast, selective, and green extraction medium for the extraction of polar and medium polar analytes from solid samples [184 186]. It should be noted, however, that the extraction capacity of water is restricted and that the isolation of the analytes from the aqueous phase is sometimes problematic. In most of the extraction methods, deionized, degassed, or nitrogen-washed (to remove oxygen) water is preferred. Sometimes pH control is also used to increase selectivity to target compounds. In some extraction methods, some modifications are necessary to separate analytes from the aqueous phase or to solve the limited extraction power problem of the superheated water [187 190]. For example, small volumes of organic solvent need to be added. Superheated water-based extraction methods are also called hot water extraction [190], superheated water extraction [191], subcritical hot water extraction (SWE) [192], or pressurized hot water extraction [189]. The first applicability experiments of SWE were started in 1994. In this study, the extraction of polar and nonpolar compounds from soils was accomplished. Since that time, SWE has been mainly applied for the extraction of compounds including PCBs, PAHs, pesticides, and polychlorinated benzofurans from environmental solid samples [182 192]. Also, it has been used as an effective method to extract bioactive compounds and natural essential oils from plants and foodstuffs and for environmental remediation [65]. Further, it was proven that SWE method was more effective for the

extraction of natural phenols from plants than Soxhlet extraction, microwave-assisted extraction, and ultrasound-assisted extraction. Compounds extracted by SWE were also more biologically active. It should be noted that when compared with similar extraction methods, water is still the cheapest and least toxic solvent [65]. 5.3.1.2 Magnetic liquids Magnetic ILs (MILs) and magnetic DESs (MDESs) incorporate iron, manganese, or nickel salts into the synthesized IL or DES. MILs and MDES are used as extraction solvents in LPME methods such as SDME and DLLME. MILs and MDES are particularly useful for collection of the solvent following DLLME extraction, either with or without the use of solvent-assisted dispersion [193,194].

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New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

6 Ionic liquids in separation and preconcentration of organic and inorganic species Tahere Khezeli1, Mehrorang Ghaedi2, Ali Daneshfar1, Sonia Bahrani2, Arash Asfaram3 and Mustafa Soylak4 1

Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, Iran Department of Chemistry, Yasouj University, Yasouj, Iran 3Medicinal Plants Research Center, Yasuj University of Medical Sciences, Yasuj, Iran 4Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey 2

6.1 Introduction Ionic liquids (ILs) are considered to be environmentally friendly substitute solvents for volatile organic solvents. ILs are defined as organic salts having a melting point equal to or lower than 100
C and consist of ions (usually large asymmetric organic cations such as imidazolium, pyrrolidinium, pyridinium, tetraalkylammonium, or tetraalkylphosphonium and small organic or inorganic anions such as tetrafluoroborate, hexafluorophosphate, bromide) [1,2]. Ethyl ammonium nitrate was the first IL with a melting point of 12
C, prepared by Paul Walden in 1914 [3,4]. Due to the variety of anions and IL anions, Seddon et al. estimate that theoretically 1018 different ILs can be produced [5]. The most commonly used cations in room

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00006-1

temperature ILs are alkylammonium, alkyl hydrazine, N, N’-dialkyl imidazolium, and Nalkylpyridinium. The names and chemical structures of various common cations and anions used to synthesize IL are shown in Fig. 6.1 [6]. The most commonly used alkyl chain (R) is methyl, ethyl, butyl, hexyl, octyl, decyl, and the like. The number of anions studied has been BF4, PF6, SbF6, CH3CO2, HSO4, NO3, NO2, CF3SO3, (CF3SO2), 2 N, CF3CO2, B (Et3Hex), OTs, AuCl4, AlCl4, and carborane anions. The most common heteroaromatic-based ILs include imidazolium, thiazolium, tetrazolium, pyridinium, and the like. However, research on ionic liquids based on thiazolium and benzothiazolium is very rare. Among the various types of IL, those containing imidazole-based IL are the most widely used. By changing the

267

© 2020 Elsevier Inc. All rights reserved.

268

6. Ionic liquids in separation and preconcentration of organic and inorganic species

Cations R1

R3

+

N R1 N

N

+

R1 N

R2

+

R2

+ N R1

R2 Imidazolium

Pyridinium

R4 R1

N

+

R3

S

P

R1

Piperidinum

O

R1

R4

+

R2

Pyrolidinium

R3

R2

+ + N

R3

R2

R1 Ammonium

Phosphonium

R2

Sulphonium

R2

Morpholinium

Anions F F

– P

F

N

C – N

SO3CO–

F3C

N

F

F

– Br

– Cl

C

F Hexafluorophosphate

Dicyanamide

Chloride

F F

F – B F

Tetrafluoroborate

FIGURE 6.1

N

F F

F

–

C

F

F C

S O

Bromide

F

O

C

F

S O

Trifluoromethylsulfonate

F

COO

–

F

O

Bis(trifluoromethylsulfonyl)imide

Trifluoromethylacetate

Name and chemical structure of various common cations and anions used in synthesis of ILs [6].

substituents on the nitrogen atom and changing the counterions, their solvent properties such as melting point, solubility, and viscosity can be easily adjusted over a wide range. An important limitation of imidazolium-based ILs is that they do not appear as harmless solvents under strong alkaline conditions, where they

deprotonate at carbon 2, resulting in N-heterocyclic carbenes [7]. IL is called a designer solvent because it can change ions, so that the physical properties of IL can be modified and optimized for specific tasks [8]. Hajipour and Refiee [9] classify IL into 11 categories (neutral ionic liquids, acidic ionic

New Generation Green Solvents for Separation and Preconcentration

269

6.1 Introduction

liquids, basic ionic liquids, ionic liquids containing amphoteric anions, functionalized ionic liquids, proton ionic liquids, chiral ionic liquids, loads ionic liquids, bio-ionic liquids, polyionic liquids, and high-energy ionic liquids) and also describe the common characteristics and properties of these ILs. However, Suresh and Sandhu [9,10] classify ionic liquids into two classes: cationic and anionic ionic liquids. They further subdivide the anionic ionic liquids into several subclasses: borate, dicyandiamide, halides, bis(trifluoromethylsulfonyl)imide (NTF), nonaflate (NON), phosphate, sulfate, sulfonate, thiocyanate (SCN), tricyanomethane- (TCC-) based anionic liquid. Some common IL classes with examples and their salient features are described in Table 6.1. Room temperature ILs (RTIL) based on 1alkyl-3-methylimidazolium salts were first reported in 1982 by Wilkes et al. [18] as tetrachloroaluminate (first generation). The tetrafluoroborate ion and other anions introduced in 1992 replaced this moisture-sensitive anion

and converted it into air- and water-stable (second-generation) ILs [12]. Polymerized ionic liquid (PIL) is a novel IL composed of IL as a monomer unit. PIL has related properties compared to conventional polymers. Ohno et al. described the first PIL in 1998 [19]. The ionic conductivity of PIL is reduced by immobilizing anions or cations in the polymer backbone compared to IL. Due to the polymerization of IL, polymers are obtained that contain only size-specific counterions due to the free space between the polymer chains [20]. Polymerization combines the advantages of a tight polymer backbone with the characteristics of ionic liquids to achieve highly charged polymers [21]. The initiated polymerization or condensation reaction is a common method for preparing PIL [22,23]. PILs can be classified by their monomeric subunits, charge, or structure. Copolymerization of different ILs, ILs with neutral monomers, or cross-linking of individual polymer chains by homopolymerization results in a more complex

TABLE 6.1 Melting point of PF6-based ILs [11]. IL cation

Melting point

Reference

1-ethyl-3-methylimidazolium

5860

[12]

1-propyl-3-methylimidazolium

49

[13]

1-butyl-3-methylimidazolium

28

[14]

1-hexyl-3-methylimidazolium

261

[15]

1-octyl-3-methylimidazolium

282

[15]

1-dodecyl-3-methylimidazolium

60

[16]

1-tetraedecyl-3-methylimidazolium

74

[16]

1-hexadecyl-3-methylimidazolium

75

[16]

1-octadecyl-3-methylimidazolium

80

[16]

1-sec-butyl-3-methylimidazolium

83.3

[17]

1-tert-butyl-3-methylimidazolium

159.7

[17]

1-isopropyl-3-methylimidazolium

102

[13]

New Generation Green Solvents for Separation and Preconcentration

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6. Ionic liquids in separation and preconcentration of organic and inorganic species

FIGURE 6.2 Some typical cationic PILs. (A) Imidazolium; (B) quaternary ammonium; (C) pyridinium; (D) pyrrolidinium [24].

PIL than anionic, cationic, or zwitterionic polymers. Among them, cationic PILs have been extensively studied due to their less troublesome synthesis and versatility. Some typical cationic PILs are shown in Fig. 6.2 [24]. The extraction selectivity of PILs is similar to that of ILs, but they generally have higher viscosity and higher mechanical strength than ILs [25]. Due to its unique properties, ILs and polymer ILs have been used as solvent and/or sorbent coatings for environmentally friendly “green” materials, such as single-drop microextraction (SDME) in various extraction techniques: dispersionliquid microextraction (DLLME), hollow fiber liquid phase microextraction (HF-LPME), solid phase microextraction (SPME), and so on [26]. Since these liquids are capable of dissolving various organic and inorganic substances, they can be used in many fields. IL as an extraction solvent has the following advantages and/or limitations: 1. ILs have negligible vapor pressure, good thermal stability, relatively high electrical conductivity, and moderate solubility, which are associated with their low environmental interference. 2. ILs are chemically customizable solvents because they can be designed by properly combining various cations with anions to achieve the desired physical and chemical properties such as melting point, viscosity, density, and miscibility with water and other solvents. 3. ILs are relatively high cost.

4. ILs cannot be considered a completely “green” solvent because the synthesis of most ionic liquids requires a large amount of energy, organic solvents, and salts. 5. Particularly imidazolium-based ILs are proven to be dangerous for aquatic environment. 6. ILs have low biodegradability. 7. The inherent high viscosity of ILs results in a slow mass transfer and hampers extraction efficiency.

6.2 Physical properties of ionic liquids ILs have unique physical and chemical properties such as low vapor pressure, good thermal stability, relatively high electrical conductivity, and moderate solubility [2729]. Some of the inherent physical properties of ILs are being liquid at low temperatures, very low vapor pressure, and nonflammability. The quality of substitution is heavily dependent on the type of cation and anion and its chemical nature, as well as the length of the alkyl group on the cation [30]. ILs are unique in that, in addition to their ionic and covalent interactions, there are relatively weak interactions, such as H-bonds and π-stacks, that are not common in typical solvents. Since the nature of any material depends on the molecular structure at different stages, it is necessary to have a deep understanding of the basic highlights of ILs [31,32].

New Generation Green Solvents for Separation and Preconcentration

6.2 Physical properties of ionic liquids

Having a low melting point is a pressing need for ILs as a medium in organic reactions and in other chemical fields, particularly analytical chemistry. As just mentioned, quite a few ILs are liquid at room temperature, while others more commonly melt below 100
C. This physical property of ILs can be altered by replacing simple inorganic cations with asymmetric organic cations [33,34]. Scott T. Handy [11] as detailed the effect of alkyl chain length on the melting point of PF6 salt. The information is recorded in Table 6.1. It can be seen that salts containing the smallest alkyl groups (methyl, ethyl, and propyl) have a higher melting point and are generally solid at room temperature. As the alkyl chain lengthens (butyl to octyl), the melting point decreases and typically reaches a certain minimum within this range. In this path, the melting point is increased again until it has a longer alkyl group (tetradecyl group and higher), and a liquid crystal compound is often obtained. A logical reason for this trend is that longer alkyl chains reduce the symmetry of the imidazolium cations, thereby interfering with effective crystal packing. As a result, most of the decline in attraction is due to the Colombian forces. Nonetheless, the Van der Waals force of the alkyl chain can be considered as an important component of the force holding the ions together, resulting in a steadily increasing melting point. This anion affects the melting point of ILs. Increasing the size of an anion with a similar charge results in a decrease in melting point [35]. Most ILs have a higher density than water, except for pyrrolidine dicyandiamide and strontium salts, with densities ranging from 0.9 to 0.97 g cm23 [36]. Ziyada et al. considered the impact of alkyl chains of cations and anions and of temperatures (in the range between 293.15K and 353.15K) on the physical properties of a series of 1-butyl-3propanenitrile imidazolium [CNC2Bim] and 1decyl-3-propanenitrile imidazolium [CNC2Dim]based RTILs incorporating different sulfonate-

271

based anions such as dioctysulfosuccinate (DOSS), dodecylsulfate (DDS), benzenesulfonate (BS), sulfobenzoic acid (SBA), and trifluoromethanesulfonate (TFMS) [37]. The experimental density values for the considered RTILs are shown in Fig. 6.3. As can be observed, [CN C2Bim] TFMS has the greatest value, and [CNC2Dim] DOSS has the least value of density among the studied RTILs. The density values for the [C2CNCnim]-based RTILs decreased in the following order: [CNC2Bim] TFMS . [CNC2Bim]BS . [CNC2Dim] SBA . [CNC2Bim]DDS . [CNC2Bim]DOSS . [CNC2Dim]DDS . [CNC2Dim]DOSS. They found that the increase of the anion molecular weight does not specifically correspond to the rise in the density values for the present ILs (Fig. 6.3). At present, few IL surface tension studies have been conducted. The surface tension of ILs is lower than the surface tension of water but higher than that of alkanes [30]. As the water content increases, the surface tension depends on the decrease and increases as the halide content increases. Deetlefs et al. have reported a simple method to predict the density and surface tension of a series of 1-alkyl-3-methylimidazolium, the surface tension of [Cnmim] 1 ILs, and vice versa, using a surface tensionweighted molar volume parachor (Table 6.2) [38]. Bittner et al. [39] measured the physical properties, such as density, viscosity, surface tension, and the thermal stability of a series of pyridinium ILs with different cations and anions over a wide temperature range (293.15K323.15K) (Table 6.3). Densities of all investigated ILs decrease linearly as the temperature increases. They also found that the density decreases as the length of the alkyl chain of the cation increases. According to the data reported in Table 6.3, the density of ionic liquids according to the type of anion increases in the following order: [BF4] , [OTf] , [NTf2] , [FAP]. The dynamic viscosity of the ionic liquid is discussed and it is observed that the dynamic viscosity increases with the length of the cationic

New Generation Green Solvents for Separation and Preconcentration

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6. Ionic liquids in separation and preconcentration of organic and inorganic species

FIGURE 6.3 The experimental density values for [CNC2Bim]TFMS, [CNC2Bim]BS, [CNC2Dim]SBA, [CNC2Bim]DDS, [CNC2Bim]DOSS, [CNC2Dim]DDS, [CNC2Dim]DOSS ILs [37]. TABLE 6.2 Densities and surface tension of a range of 1-alkyl-3-methylimidazolium, [Cnmim]1 ILs. IL [abbrevation]

Density(g cm23)

Surface tension (mJ m22)

[C4mim][OTf]

1.2968

33.97

[C4mim][NTf2]

1.4363

33.20

[C4mim][BF4]

1.2011

43.92

[C6mim]I

1.3814

40.23

[C4mim][I3]

2.1486

51.84

[C4mim][I5]

2.5731

55.26

[C4mim][I7]

2.8642

58.19

[C2mim][I7]

3.0660

63.41

[C2mim][I9]

3.2464

64.18

alkyl chain. However, in the butylmethylpyridinium bistrifluoromethanesulfonimide series, the dynamic viscosity decreases in the following order [C4-2-C1py] [NTf2], [C4-3-C1py] [NTf2], [C4py] [NTf2]. The lowest value of the dynamic

viscosity of [C4-4-C1py] [NTf2] was measured. The effect of anion on viscosity was analyzed, and it was noted that the viscosity of the ionic liquid increased as [NTf2] ,[FAP] ,[OTf] ,[BF4] increased.

New Generation Green Solvents for Separation and Preconcentration

273

6.2 Physical properties of ionic liquids

TABLE 6.3 Physical properties of a series of pyridinium ILs at 239.15K. Surface tension (mN m21)

Cation [abbreviation]

Anion [abbreviation]

1-ethylpyridinium [C2py]

bis(trifluoromethylsulfonyl) [C2py][NTf2] imide [NTf2]

1.534

47.43

35.6

1-butylpyridinium [C4py]

bis(trifluoromethylsulfonyl) [C4py][NTf2] imide [NTf2]

1.462

75.61

35.0

1-hexylpyridinium [C6py]

bis(trifluoromethylsulfonyl) [C6py][NTf2] imide [NTf2]

1.386

275.12

34.2

1-butyl-2-methylpyridinium [C4-2-C1py]

bis(trifluoromethylsulfonyl) [C4 2 2-C1py][NTf2] imide [NTf2]

1.482

143.91

36.5

1-butyl-3-methylpyridinium [C4-3-C1py]

bis(trifluoromethylsulfonyl) [C4 2 3-C1py][NTf2] imide [NTf2]

1.429

81.71

35.8

1-butyl-4-methylpyridinium [C4-4-C1py]

bis(trifluoromethylsulfonyl) [C4 2 4-C1py][NTf2] imide [NTf2]

1.419

65.26

35.4

1-butyl-3-methylpyridinium [C4-3-C1py]

trifluoromethanesulfonate [OTf]

[C4 2 3-C1py][OTf]

1.306

142.15

38.6

1-butyl-3-methylpyridinium [C4-3-C1py]

tetrafluoroborate [BF4]

[C4 2 3-C1py][BF4

1.189

226.15

47.5

1-butyl-3-methylpyridinium [C4-3-C1py]

tris(pentafluoroethyl) trifluorophosphate [FAP]

[C4 2 3-C1py][FAP]

1.595

134.91

35.3

It is assumed that surface tension is related to the attraction of ions, which increases as the diameter of the ions decreases. In the case of [C4-3-C1py] [BF4], the [BF4] anion was significantly smaller than those of [NTf2], [OTf], and [FAP], and therefore the highest surface tension value was observed. The size of the cation is related to surface tension in a similar manner. Therefore the highest surface tension value was observed for [C2py] [NTf2], and the lowest value was observed for [C6py] [NTf2]. Ionic liquids are also thermally stable. This stability is limited by the strength of its heteroatoms—carbon and heteroatoms— hydrogen bonding [35]. Thermal gravimetric analysis (TGA) studies have shown that all ILs are thermally stable up to 500K and completely decompose above 900K in an inert atmosphere. As the alkyl chain on a given cation increases,

IL

Density Viscosity (g cm23) (mPa S)

the decomposition temperature decreases [39]. Table 6.4 illustrates the temperature at which 10% weight loss of some imidazolium and pyridinium-based ILs occurs during heating or scanning using TGA, which clearly indicates that the ionic liquid is thermally stable [34]. Pinto et al. synthesized three protic ILs with the ethylammonium cation, 2-hidroxy ethylammonium butanoate (2-HEAB), 2-hidroxy ethylammonium pentanoate (2-HEAP), and 2hidroxy ethylammonium hexanoate (2-HEAH) through acid-base neutralization reactions between ethanolamine (as a base) and the organic acids (butanoic, pentanoic, and hexanoic). They experimentally determined physical properties such as density, viscosity, and degradation temperature. Data for density, viscosity, and TGA is shown in Fig. 6.4. Therefore for all ILs, density and viscosity decrease with

New Generation Green Solvents for Separation and Preconcentration

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6. Ionic liquids in separation and preconcentration of organic and inorganic species

TABLE 6.4 The temperature of 10% weight loss of some imidazolium- and pyridinium-based ILs. IL [abbreviation]

T (K)

Reference

1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4]

664

[40]

1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI]

690

[40]

1-butylpyridinium tetrafluoroborate [BuPy] [BF4]

615

[40]

1-butylpyridinium bis(trifluoromethylsulfonyl) imide [BuPy] [TFSI]

677

[40]

1-ethyl-3-methylimidazolium trifluoroacetate [EMIM][CF3COO]

475

[41]

increasing temperature. Degradation temperature measurements by TGA analysis showed that the behaviors of all three proton ionic liquids were very similar and that ILs did not exhibit any detectable mass loss after 340K [42].

Pd21, Al31, Ag1, Hg21, Cu2 1, Pb21, Cd21, and Zn21) have been successfully performed by ILs [4855].

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

Liu et al. reported on SPME’s first attempt [56]. In this work, 1-octyl-3-methylimidazolium hexafluorophosphate IL was coated on the surface of stainless steel fiber. The prepared fiber was then used to extract BTEX (benzene, toluene, ethylbenzene, and xylene) from a paint sample. Liu found that internally manufactured fibers have comparable reproducibility and lower cost (even in a single measurement) compared to commercially available fibers. At the same time, the fiber memory effect is eliminated. The physical coating, chemical bonding, and production of hybrid materials are a common strategy for the modification of SPME fibers with ILs. In physical coatings, ILs are not directly bound (physically immobilized) to SPME fibers. The most common method of physical coating is to immerse the fibers in methylene chloride in the IL medium and then to let the solvent naturally evaporate. This process can be repeated several times to achieve the desired IL thickness on the surface of the SPME fibers. The characteristics of the physical coating are as follows:

The significant impact of ILs in the chemical process is undeniable. Therefore some of the books and reviews in analytical and nonanalytical journals focus on various creative applications of IL. Recently, various IL-assisted extraction methods have been reviewed and discussed in detail [4345]. Among them, LPME, DLLME, and SPME are potential programs that utilize IL. The significant “dual properties” solvation properties of ILs result in the interaction of these solvents with nonpolar and polar analytes [46,47]. This feature is one of the reasons why ILs have significant applications in LLE technology. The wide-ranging application of ILs in the SPME method is due to the fact that IL promotes the binding of particles to the solid phase and increases the uniformity of the active adsorption sites [45]. In addition, extractions of various organic compounds in different matrices (ions Co21,

6.3.1 Application of ionic liquids in solid phase microextraction

1. These coatings do not contain any crosslinking substances.

New Generation Green Solvents for Separation and Preconcentration

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

FIGURE 6.4 Data of density, viscosity, and TGA of 2HEAB, 2-HEAP, and 2-HEAH ILs [42].

2. They are not resistant to organic solvents. 3. They also demonstrate a tendency toward swelling. 4. They also demonstrate inferior thermal stability compared to coatings that are chemically bound to the carrier. For these reasons, unfortunately, SPME fibers prepared by physically coating with IL

275

have been used for only a single analysis. After that, it is necessary to remove the adsorption layer and apply it again before the next extraction [57]. In the chemical coating, a cross-linker is used to form a covalent bond between the IL molecule and the surface of the support as compared to the physical coating. Therefore this type of coated fiber is stable in the most popular organic solvents, swelling occurs only with some nonpolar solvents, and they also have high thermal stability. In a hybrid coating, the coating is made of two or more active materials. One of them is IL, and the other is a substance that enhances adsorption capacity, thermal stability, and mechanical stability or that ensures a higher selectivity of the coating relative to a particular analyte. Wen et al. synthesized five kinds of ILs, including (1,2-ethylenediamine, N, N’-bis (2-aminoethyl)-N,N,N’,N’-tetramethyl-chloride); (N, N’- (2-aminoethyl)-N, N, N’, N’-tetramethyl-, chloro (1:1)); (N, N’-(3-aminopropyl)-N,N,N’,N’tetramethyl-, chloride (1:1)); (N,N’-butyl-N,N,N’, N’-tetramethyl-, chlorine (1:1)); (1-butylamino, N-ethyl-N,N-dimethyl-, chloride (1:1)). These ILs were coated on the surface of magnetic graphene oxide (Fe@GO@AFDCIL) and used as an adsorbent for magnetic solid phase extraction (MSPE) of BHp (Fig. 6.5). They compared the extraction efficiencies of these adsorbents with conventional IL-coated Fe@GO composites (Fe@GO@IL) and found that the extraction efficiency of Fe@GO@AFDCIL was higher than that of Fe@GO@IL [58]. Yang developed a magnetic hybrid semifiber dispersion solid phase extraction (MMHDSPE) based on C16mimBrcoated attapulgite/polyaniline-polypyrrole/Fe3O4 (ATP/PANI-PPY/ Fe3O4) nanocomposite for extraction of three acaricides including chlorothiazide, fenpyroximate, and anthrone in a juice sample. When the surfactant concentration is lower than the critical micelle concentration (CMC), a semifiber and a half fiber are formed on the surface of the metal oxide (such as alumina, ceria, titania, and

New Generation Green Solvents for Separation and Preconcentration

276

FIGURE 6.5

6. Ionic liquids in separation and preconcentration of organic and inorganic species

Magnetic solid phase extraction (MSPE) of BHp [58].

alumina), respectively, or in a single or double layer of fiber on iron oxyhydroxide [59]. Gala´n-Cano et al. reported the use of methylimidazolium-hexafluorophosphate and

methylimidazolium-chloride ILfunctionalized silica ([SiO2-MIM-PF6]; ([SiO2-MIM-Cl]) under a dispersive microsolid phase extraction (D-μSPE) for the isolation and preconcentration of

New Generation Green Solvents for Separation and Preconcentration

277

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

N

+

FIGURE 6.6

O O toluene S O 40°C 10h

+

N

– (CH2)4 SO3

H3PW12O40 aqueous solution

+ N

r.t. 20 min, 60°C

(CH2)4

SO3H PW O 3– 12 40 3

Steps of preparation of Keggin-based IL [45].

phosmet, parathion, triazophos, and phoxim pesticides from water samples. According to the results, [SiO2-MIM-PF6] IL presents a better interaction with the analytes than [SiO2-MIMCl] due to its higher hydrophobicity [60]. Ebrahimi et al. developed a heteropolyacidsupported IL- ((PY BS)3PW12O40) mediated solgel hybrid organicinorganic material for hollow fiber solid phase microextraction (HFSPME). They studied a Keggin-based IL that was evaluated, along with a solgel. Keggin is the most famous structural form of heteropoly acid. It is a structural form of an α-Keggin anion having the formula [XM12O40] n-, wherein X is most commonly Si(IV), Ge(IV), P (V). The most common M is molybdenum and tungsten. The procedure for preparing Kegginbased IL is schematically shown in Fig. 6.6 [45]. Tian et al. first used SPME fibers coated with IL-cup aromatics. In this method, the surface of the quartz fiber is coated by a solgel method. Influencing parameters such as sample volume, extraction time, extraction temperature, desorption time, and sample pH were studied and optimized, and atrazine, simazine, ametryn, and cyanazine were optimized as extractants [61]. Jia et al. prepared nanoporous array anode titanium (NAAT/PILs)supported poly [C9OHVIm] Br/(VIM)2C4]2 [Br] SPME fibers. Titanium wire has a high surface area, and the ferrotitanium group functionalizes the titanium wire to form a highly efficient coating combination. Combined with PIL, it expands the surface area ratio, is easy to prepare, is mechanically stable, and is rich in titanium alcohol on the surface. NAAT was chosen as the cause of SPME fiber. The modification step of the NAAT vector is shown in Fig. 6.7. This

method was successfully applied to the extraction of valeric acid, caproic acid, heptanoic acid, caprylic acid, and decanoic acid from a water matrix [47]. Tang et al. synthesized IL 1-vinyl-3-(4-vinylbenzyl) imidazolium chloride and polymerized it in the presence of azobisisobutyronitrile (AIBN), followed by a polyacrylonitrile gel by a bonding method. This was used for coating on stainless steel wire. In this method, valeric acid, caproic acid, lactic acid, succinic acid, fumaric acid, and malic acid are used as extracting agents. A synthetic method for preparing a porous IL polymer is shown in Fig. 6.8. The high extraction efficiency of such internally made fibers for polar organic acids is due to the inclusion of suitable polar functional groups and nitrogen elements in the coating material. In addition, the graded porous structure of the coating material has the potential to exhibit the advantages of each type of grading hole in a synergistic manner, thereby improving the extraction ability of the internally manufactured fiber [62]. Feng et al. prepared 1-methyl-3-(3-trimethoxyformamidopropyl) imidazolium chloride IL and chemically bonded it to basalt fiber (Fig. 6.9) for in-tube SPME in order to determine eight polycyclic aromatic hydrocarbons. The method showed good enrichment factors (52814), good linearity (0.1015 and 0.2015 μg L21), low detection limit (0.030.05 μg L21), and low limit of quantitation (0.100.20). A sample volume of 50 mL achieves μg L21 [63]. Sun et al. codoped GO-doped 1-(3aminopropyl) 2 3-(4-vinylbenzyl) imidazole-4styrenesulfonate monomer and 1,6-di-(3-ethylene imidazolium). Graphene oxidereinforced polymer ionic liquid (GO-PILs) monolith was

New Generation Green Solvents for Separation and Preconcentration

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6. Ionic liquids in separation and preconcentration of organic and inorganic species

FIGURE 6.7

N

FIGURE 6.8

Modification steps of NAAT support [47].

N

CH2Cl

N

+ N – Cl

AIBN

N

+ N – Cl

Synthesis procedures for the fabrication of porous IL polymer [62].

prepared as a hexane dihexafluorophosphate cross-linker. The monolith was successfully used as an adsorbent to extract several phenolic compounds in the actual sample. The GOPILs boulders were manually installed as SPME devices, and the SPME program was also described (see Fig. 6.10) [64].

Sun et al. also used as 1-methyl-3-[3-(trimethoxysilyl) propyl] imidazolium chloride as the cross-linking agent to bond graphene oxide onto a silver-coated stainless steel wire. The preparation process of the graphene oxidecoated stainless steel wire SPME fiber is illustrated in Fig. 6.11. The extraction efficiency of this novel

New Generation Green Solvents for Separation and Preconcentration

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

279

FIGURE 6.9 In-tube SPME for determination of eight polycyclic aromatic hydrocarbons [63].

FIGURE 6.10 SPME procedures based on graphene oxidereinforced polymeric ionic liquids (GO-PILs) [64].

SPME fiber was studied using five polycyclic aromatic hydrocarbons: fluorene, anthracene, fluoranthene, 1,2-benzophenanthrene, and benzo(a) pyrene) [65]. In Table 6.5, the SPME methods based on ILs are summarized.

6.3.2 Application of ionic liquids in dispersionliquid microextraction The first study to evaluate the ability to extract ILs was in classical liquidliquid

extraction because of the formation of a twophase system (aqueous/immiscible ILs phase). In this work, the distribution of alternative benzene derivatives in ILs was evaluated, and the results were compared to the octanol-water partition coefficients [93]. The first review of the use of ILs in dispersion-liquid microextraction (DLLME) was published in 2013 by Trujillo-Rodrı´gue [94]. Conventional ILDLLME, temperature-controlled IL-DLLME, ultrasound-assisted, microwave-assisted, or vortex-assisted IL-DLLME, and finally in situ

New Generation Green Solvents for Separation and Preconcentration

280

FIGURE 6.11

6. Ionic liquids in separation and preconcentration of organic and inorganic species

Preparation process of the graphene oxidecoated stainless steel wire SPME fiber [65].

IL-DLLME are the five main modes of operation of DLLME, as reported and discussed in this review. In some modes of DLLME, the dispersing solvent can be an organic solvent, a surfactant, or a hydrophilic IL. In some cases, it is not even necessary to disperse the solvent [95]. In situ IL-DLLME was first proposed by Bahdadi and Shemirani in 2009 and applied to the determination of metals [96]. Briefly, the in situ IL-DLLME method is based on the dissolution of hydrophilic IL in an aqueous solution containing the analyte of interest. Thereafter, insoluble IL is formed, and then an ion exchange reagent is added. The ion exchange reagent enhances the metathesis reaction, resulting in the conversion of hydrophilic IL to hydrophobic IL, which precipitates and

contains preconcentrated analytes [97]. In the first in situ IL-DLLME application reported by Li et al. [98], the authors investigated the effect of different six ILs (different in substituents and functional groups) on DNA extraction efficiency. Yua et al. [99] used 1-butyl-3methylimidazolium chloride ([BMIm][Cl]), 1-(6hydroxyethyl) 2 3-methylimidazolium chloride ([HeOHMIm][Cl]), and 1-benzyl-3-(2-hydroxyethyl) imidazolium bromide ([BeEOHIm][Br]) as extraction solvents in in situ DLLME for the extraction of microcystin-RR (MC-RR) and microcystin-LR (MC-LR) from aqueous sample. In temperature-controlled IL-DLLME, the aqueous solution containing the analyte and the hydrophobic IL is heated. Through the

New Generation Green Solvents for Separation and Preconcentration

TABLE 6.5

Application of ILs in SPME.

IL [abbreviation]

SPME fiber/substrate

1-allyl-3-methylimidazolium tetrafluoroborate ([AMIM][BF4]); 1-allyl-3-methylimidazolium hexafluorophosphate ([AMIM] [PF6]); 1-allyl-3methylimidazolium bis (trifluoromethanesulphonyl) imide ([AMIM][N(SO2CF3)2])

Fused-silica

Type of modification Extractant

Sample

Reference

Chemical bonding

Tri(2-chloroethyl) phosphate; tripropyl phosphate; tri(chloroispropyl) phosphate; tri-n-butyl phosphate; triphenyl phosphate; tricresyl phosphate; tri(2-ethylhexyl) phosphate

Water samples

[66]

Polymeric 1-vinyl-3Anodized Ti wire hexylimidazolium hexafluorophosphate [VHIM][Br]

Chemical bonding

Perfluoroheptanoic acid; perfluorooctane sulfonic acid potassium salt; perfluorooctanoicacid; perfluorodecanoic acid; perfluorododecanoic acid; perfluorotetradecanoic acid

Water samples

[67]

Copolymerization of 1-trimethyl(4-vinylbenzyl) ammonium chloride

Multiple monolithic fiber

Chemical bonding

Bisphenol A; estradiol; ethinylestradiol; testosterone; estrone; dienestrol; mestranol; 4-nonylphenol

Water samples

[68]

1-hextyl-3-methyl imidazolium hexafluoro-phosphate [C6MIM] [PF6]

PDMS fiber

Chemical bonding

BTEX

Water samples

[69]

Poly(1-vinyl-3hexadecylimidazolium) bis [(trifluoromethyl)sulfonyl]imide

PDMS and PA fiber

Chemical bonding

Water samples 2-chlorophenol; 2-nitrophenol; 2,4-dimethylphenol; 2,4-dichlorophenol; naphthalene; 4-chloro-3-methylphenol; 4-tbutylphenol; 2,4,6-trichlorophenol; acenaphthene; fluorene; 4-t-octylphenol; pentachlorophenol; 4-octylphenol; phenanthrene; 4-cumylphenol; 4-n-nonylphenol; fluoranthene; bisphenol-A

[70]

1-octyl-3-methylimidazolium chlorides [OMIM][NTF2]

Cyclodextrin-functionalized magnetic core dendrimer nanocomposite

Physical bonding

Permethrin; phenothrin; bifenthrin

[71]

Juice samples

(Continued)

TABLE 6.5

(Continued) Type of modification Extractant

IL [abbreviation]

SPME fiber/substrate

Sample

1-vinyl-3-hexylimidazolium chloride ([VC6Im][Cl]); 1-vinyl-3hexadecylim-idazolium bis [(trifluoromethyl)sulfonyl]imide ([VC16Im][NTf2]); 1-vinylbenzyl3-hexadecylimidazolium bis [(trifluoromethyl)sulf-onyl]imide ([VBC16Im][NTf2]); 1,12-di(3vinylimidazolium)dode-cane dibromide ([(VIm)2C12] 2[Br]); 1,12-di(3-vinylimidazolium) dodecane dibis[(trifluoromethyl) sulfonyl]imide ([(VIm)2C12]2 [NTf2]); 1,12-di(3vinylbenzylimidazolium) dodecanedibis[(trifluoromethyl) sulfonyl]imide ([(VBIm)2C12] 2 [NTf2])

Metallic alloy fiber

Chemical bonding

2,3-pentanedione; 2,5-dimethylfuran; 1- Arabica coffee methylpyrazole; pyrazine; 1methylpyrrole; 2-methyl-2-butenal; 2methyl-3-pentanone; pyrrole; 4-penten1-ol; hex-4-yn-3-one; 3-hexanone; cyclopentanone; 3,4-hexanedione; dihydro-2-methyl-3-furanone; 2(methoxymethyl)-furan; 2methylpyrazine; furfural; 2furanmethanol; 2,6-dimethylpyridine; 2,5-dimethylpyrazine; 1-(2-furanyl)ethanone; 2-ethylpyrazine; 2,3dimethylpyrazine; 2,3-dimethyl-2cyclopentenone; 3-ethylpyridine; acetate 2-furanmethanol; 2-ethyl-3methylpyrazine; trimethylpyrazine; 6-methyl-3-pyridinol; 3-methyl-1,2cyclopentanedione; 2-acetyl-5methylfuran; 2-methylphenol; 1-(1methylpyrrol-2-yl)-ethanone; 3-methyl1,2-cyclohexanedione; 2methoxyphenol; 1,5-dimethyl-2pyrrolecarbonitrile; phenylethyl alcohol; furfuryl isovalerate; 4-ethylguaiacol; 4-vinylguaiacol

[72]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM] [PF6]

Spent fibers

Physical bonding

2,4-dichlorophenol; 2,4,6trichlorophenol; 2,3,4,6tetrachlorophenol; pentachlorophenol

[73]

1-(trimethoxysily)propyl3-(60 oxo-benzo-15-crown-5 hexyl) imidazolium bis (trifluoromethanesulphonyl) imide [TMSP(Benzo15C5)HIM] [N(SO2CF3)2]; 1-allyl-3-(6’-oxobenzo-15-crown-5 hexyl) imidazolium bis (trifluoromethanesulphonyl) imide [A(Benzo15C5)HIM][N (SO2CF3)2

Fused-silica fibers

Chemical bonding

4-methylphenol; 2,4-dimethyl phenol; — 4-tert-butylphenol; 2,4,6trichlorophenol; 2,6-di-tert-butylphenol; 4-tert-octylphenol; pen-tachlorophenol; bisphenol A; aniline; o-toluidine; 2,4dimethylaniline; 3,4-dimethylaniline; N, N-diethyl-aniline; diphenylamine

Real landfill leachate samples

Reference

[74]

Polymers of 1-vinyl-3hexylimidazolium chloride; 1vinyl-3-dodecylimidazolium bromide; 1-vinyl-3hexadecylimidazolium bromide

Fused silica fiber

Physical bonding

Hexyl tiglate; isopropyl butyrate; furfuryl octanoate; ethyl valerate; hexyl butyrate; benzyl butyrate; methyl caproate; methyl enanthate; methyl caprylate; methyl octanoate; methyl decanoate; methyl undecanoate; and methyl laurate

Synthetic wine sample

[75]

1-ethoxyethyl-3methylimidazloium bis (trifluoromethane) sulfonylimide

Silica fiber

Chemical bonding

Methamphetamine and amphetamine

Human urine

[76]

Copolymerization of cation and anion of 1-vinyl-3octylimidzaolium pstyrenesulfonate (VOIm1SS2)

Functionalized stainless steel

Chemical bonding

Aniline; 4-methylaniline; 2chloroaniline; 4-chloroaniline; dimethyl phthalate; diethyl phthalate; dibutyl phthalate; dicyclohexyl phthalate; di-2ethylhexyl phthalate; 2- methylphenol; 4-methylphenol; 2-ethylphenol; 4ethylphenol

Bottled mineral [77] water sample

1-octyl-3-methylimidazolium hexafluorophosphate

Stainless steel

Physical bonding

BTEX

Paints

Silver-based PIL

Polydimethylsiloxane; carboxenpolydimethylsiloxane; divinylbenzyl polydimethylsiloxane; divinylbenzyl/ carboxenpolydimethylsiloxane

Chemical bonding

Rinse water 1,4-pentadiene; hexane;1-hexene; 1,3hexadiene, mixture of isomers (1,3-HDE isomers 1, 2, 3, 95%); 2,4-hexadiene, mixture of isomers; 2-methyl-1,5hexadiene; 2,3-dimethyl-1,3-butadiene; 1-nonene; 1,8-nonadiene; trans 2 2hexene; cis 2 2-hexene; 1,5-hexadiene; 3hexyne; 2-hexyne; oleic acid; linoleic acid; linolenic acid

[78]

Polymers of 1-vinyl-3-(10hydroxydecyl) imidazolium chloride

Metallic wire

Chemical bonding

Tap water and Phenacetin; ketoprofen; 17 αlake water ethynylestradiol; fenoprofen calcium; diclofenac sodium; ibuprofen; 2,4,6trichlorophenol; hexaflumuron; phoxim; chlorfenapyr; flufenoxuron; hexythiazox; chlorfluazuron; deltamethrin; fenvalerate; τ-fluvalinate; 2-nitrophenol; 2,4-dinitrophenol

[79]

[56]

(Continued)

TABLE 6.5

(Continued) Type of modification Extractant

IL [abbreviation]

SPME fiber/substrate

1-vinyl-3hexadecylimidazoliumbis [(trifluoromethyl)sulfonyl]imide; 2,20-Azobis(2methylpropionitrile); 1-(4vinylbenzyl) 2 3hexadecylimidazoliumbis [(trifluoromethyl)sulfonyl]imide; 1-vinyl-3-hexylimidazolium chloride

Polyacrylate; polydimethylsiloxane; divinylbenzene/ carboxenpolydimethylsiloxane; carboxenpolydimethylsiloxane

Chemical bonding

2-heptanone; octanal; 2-nonanone; pCheese tolualdehyde; caproic acid; guaiacol; samples heptanoic acid; phenol 1 o-cresol; 2ethylphenol; p-cresol; m-cresol; eugenol; 3-ethylphenol; 2,6-dimethoxyphenol; 3methoxyphenol

[80]

Polydimethylsiloxane; polyacrylate

Chemical bonding

diazinon; methyl parathion; malathion; chlorpyrifos; parathion

Food samples

[81]

Polymerization of 1-vinyl-3octylimidazolium hexafluorophosphate

Stainless steel

Chemical bonding

Naphthalene; fluorene; anthracene; Water sample fluoranthene; 2-tertbutylphenol; 2;4-ditert-butylphenol; 4-tert-octylphenol; 2,6di-tert-p-cresol

[82]

1-butyl-3-methylimidazolium chloride ([C4MIM]Cl); 1-butyl-3ethylimidazoliumchloride ([C4MMIM]Cl); 1-hexyl-3methylimidazolium chloride; 1-hexyl-3-ethylimidazolium chloride; 1-octly-3methylimidazolium chloride; 1-octyl-3-ethylimidazolium chloride

Magnetic nanoparticles

Physical bonding

clofentezine; chlorfenapyr; fenpyroximate; pyridaben spirodiclofen

Fruit juice samples

[83]

Physical bonding

Butanol; o-xylene; p-xylene; cyclohexanol; benzonitrile; 1,2dichlorobenzene; 1-octanol; octylaldehyde; 1-pentanol; ethyl phenyl ether; 1-decanol

—

[84]

poly(1-vinyl-3-hexylimidazolium Silica fiber chloride); poly(1-vinyl-3hexylimidazolium bis [(trifluoromethyl) sulfonyl] imide); poly(1-vinyl-3hexadecylimidazolium chloride); poly(1-vinyl-3hexadecylimidazolium bis [(trifluoromethyl) sulfonyl]imide)

Sample

Reference

1-allyl-3-methylimidazolium bis [(trifluoro methyl) sulfonyl] imide

Multiple monolithic fiber

—

Estriol; 17β-estradiol; testosterone; ethinylestradiol; estrone; progesterone and mestranol

Environmental water samples and human urines

[85]

1-hexadecyl-3methylimidazolium bis (trifluoromethylsulfonyl)imide

Hollow fiber

Physical bonding

2,2-bis(4-chlorophenyl) 2 1,1,1trichloroethane (p,p0 -DDT); 1,1,1trichloro-2-(2-chlorophenyl) 2 2-(4chlorophenyl)ethane (o,p0 -DDT), 1,1dichloro-2,2-bis(p-chlorophenyl)ethane (p,p0 -DDD); 1,1-dichloro-2,2-bis(4chlorophenyl)ethylene (p,p’-DDE)

River water, tap water, and sewage water samples

[86]

1-hexyl-3-methylimidazolium hexafluorophosphate

Poly(dimethylsiloxane)grafted carbon nanotube fiber

Chemical bonding

Methyl tert-butyl ether

Water samples

[87]

(1-hydroxyethyl-3-methyl imidazolium bis [(trifluoromethyl)sulfonyl]imide)

Polycarbazole film electrodeposited on stainlesssteel wire

Methyl benzoate; ethyl benzoate; dimethyl phthalate; diethyl phthalate; methyl ortho-aminobenzoate; ethyl ortho-aminobenzoate

Lake water [88] and grape juice drink

(1-butyl-3-methylimidazole hexafluorophosphate ([BMIM] PF6); 1-hexyl-3-methyl-imidazole hexafluoro-phosphate ([HMIM] PF6); 1-octyl-3-methylimidazole hexafluorophosphate ([OMIM] PF6))

Fe3O4@SiO2 nanoparticles

Chemical bonding

Rhodamine B

Chili powder, Chinese prickly ash

[89]

1-Hexadecyl-3methylmidazoliumbromide (C16mimBr)

Fe3O4/SiO2 nanoparticles

Physical bonding

Luteolin; quercetin; kaempferol

Urine samples

[90]

1-(12-bromododecyl) 2 3Gold nanoparticles alkylimidazolium bromide; 1-(12mercaptododecyl) 2 3alkylimidazolium bromide ([(CnSAMIM)Br])

Chemical bonding

Glutamic acid; aspartic acid; histidine; glycine; glutamine; serine; threonine; citrulline; alanine; tyrosine; methionine; arginine; phenylalanine; valine; tryptophan; isoleucine; lysine; leucine

Human plasma [91]

1-Hexyl-3-methylimidazolium hexafluorophosphate; Hexyl-3butylimidazolium hexafluorophosphate; 1-hexyl-3methylimidazolium bis (trifluoromethylsulfonylimide)

Chemical bonding

Pyridoxine and folic acid

Urine; plasma; saliva

Gold nanoparticles

[92]

286

6. Ionic liquids in separation and preconcentration of organic and inorganic species

heating process, the IL is completely dissolved, completely mixed with the sample solution, and homogeneous. Thereafter, IL droplets with preconcentrated analytes were precipitated by cooling with ice water and centrifuging. The recommendation for this DLLME mode is to eliminate the dispersion solvent. Cold-induced aggregation microextraction based on ILs is another DLLME model developed by Baghdadi and Shemirani in 2008 [100] and further modified in 2010 [101]. This method can be categorized as a temperature control mode for IL-DLLME, which uses a lower heating temperature. Baghdadi and Shemirani used this method to extract mercury from water samples. After capturing the mercury with a chelating agent and a surfactant as an antiadherent agent, it is extracted into a mixture of two hydrophobic ILs. Bahar et al. developed the same method for the determination of silver ions in human hair by spectrophotometry [102]. 1-methyl-3-octylimidazolium hexafluorophosphate [OMIM][PF6], 1-methyl-3butylimidazolium hexafluorophosphate ([BMIM] [PF6]), and 1-methyl-3-hexylimidazolium hexafluorophosphate ([HMIM][PF6] ILs were examined as extraction solvents in DLLME using ionic liquid (IL-DLLME), developed by Sadeghi for the extraction of Brilliant Green (BG) and Crystal Violet (CV) dyes in aqueous solutions. In this method, a UV-Vis spectrophotometer was used for recording the zero order and first derivative absorption spectra of the mentioned dyes. They reported that [OMIM][PF6] provided the high extraction efficiencies among three ILs due to higher hydrophobicity [103]. A new method, microwave-assisted IL/IL DLLME was developed for extraction and preconcentration of triazine herbicides (desmetryn, atrazine, ametryn, promethazine, tertazine, chlorpyrifos, and dimethylformamide) in juice samples. In this work, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM] [PF6]) IL was used as a hydrophobic extraction solvent,

with 1-butyl-3-methylimidazolium tetrafluoroborate ([C4MIM] [PF6]) combined as a hydrophilic dispersion solvent, and was rapidly injected into an aqueous solution of the target analyte (Fig. 6.12). This method is described step by step. After optimizing several influencing factors, the linear range of the analyte was determined to be 5.00250.00 μg L21 with a correlation coefficient greater than 0.9982 [104]. The new IL and innovative methods in the field of DLLME are shown in Table 6.6.

6.3.3 Application of ionic liquids in liquid phase microextraction LPME is a new type of sample preparation technology developed in the mid- to late 1990s [137]. As mentioned in Chapter 2, Historical backgrounds, milestones in the field of development of analytical instrumentation, LPME is broadly divided into single droplet microextraction (SDME), headspace liquid phase microextraction (HS-LPME), hollow fiber liquid phase microextraction (HF-LPME), liquidliquidliquid phase microextraction (LLLPME), and dispersion liquid microextraction (DLLME). The outstanding properties of ILs make them widely accepted as extraction solvents in different LPME modes. This section outlines the use of IL in LPME. In 2018 Yue et al. developed an IL-based headspace in-tube microextraction coupled with capillary electrophoresis for the extraction and determination of 2,6-dibromophenol (2,6-DBP), 2,4,6-tribromophenol (2,4,6-TBP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) compounds. 1-ethyl3-methylimidazolium tetrafluoroborate ([C2 mim] [BF4]), 1-propyl-3-methylimidazolium tetrafluoroborate ([C3mim][BF4]), and 1buhyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) were used as extraction solvents. Herein, a capillary filled with IL placed in the headspace above the aqueous solution

New Generation Green Solvents for Separation and Preconcentration

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

FIGURE 6.12

287

Microwave-assisted IL/IL DLLME [104].

of target analytes. Fig. 6.13 illustrates the schematic of the laboratory-made device used in this method [138]. Yang et al. developed a dynamic ultrasonic atomization extraction combined with headspace ionic liquid SDME (UNE-HS/IL /SDME). This extraction technique is used to extract essential oils from forsythia fruit. In this inventive method, solid samples and aliquots of water are placed in laboratory-made extraction vessels (Fig. 6.14). Using nitrogen as the carrier gas, the essential oil was transferred to the IL droplets suspended on the tip of the needle, and a microsyringe was added. At the same time, the nebulizer and carrier gas were turned on, and 3 μL of IL was pushed out and suspended on the tip of the microsyringe. After

13 min of extraction of the 50 mg sample, the extract in the IL was rapidly evaporated by a thermal desorption unit in a gas chromatograph syringe [139]. Table 6.7 lists the application of IL in different LPME modes.

6.3.4 Application of ionic liquids in aqueous two-phase system extraction An aqueous two-phase system (ATPS) consists of two water-rich phases containing a typical polymer/polymer, polymer/salt or salt/salt combination. In order to improve extraction efficiency and minimize environmental impact, replacing IL with common organic solvents is a promising alternative. In 2003 Rogers et al. [162]

New Generation Green Solvents for Separation and Preconcentration

TABLE 6.6

Application of ILs in DLLME. DLLME mode

Extractant

Sample

Reference

Ultrasoundassisted

Diflubenzuron; flufenoxuron; triflumuron; chlorfluazuron

River, reservoir, lake water

[105]

Acetonitrile-Triton X- Conventional Benzophenone; 4114 hydroxybenzophenone; 2,4dihydroxybenzophenone; 2hydroxy-4-methoxybenzophenone

Sunscreencosmetic products

[106]

1-octyl-3-methylimidazolium hexafluorophosphate[C8MIM][PF6]

—

Vortexassisted

Animal feed samples

[107]

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

—

Temperature- Thiram; metalaxyl; diethofencarb; controlled myclobutanil; tebuconazole

River water; wastewater

[108]

1,3-dipentylimidazolium hexafluorophosphate [PPIm][PF6]

Methanol

Conventional 2-aminobenzimidazole; carbendazim/benomyl; thiabendazole; fuberidazole; carbaryl; 1-naphthol; triazophos

Soil samples

[109]

1-N-ethtyl-3-methylimidazolium bromide functionalized with 8hydroxyquinoline

—

In-situ

Underground, tap, refined water and artificial seawater and beverage (apple, tomato, tea)

[110]

1-Hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6] and 1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

Methanol

Conventional Carbaryl; methidathion; chlorothalonil; ametryn

Ground and lake waters

[111]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM]PF6; 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM]PF6 and 1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM]PF6

—

Ultrasoundassisted temperaturecontrolled

Tap water, well water, [112] lake water

1,3-dipenthylimidazolium hexafluorophosphate ([PPIm][PF6])

Acetonitrile

Conventional Estrone (E1), estradiol (E2), and estriol (E3); zearalenone (ZEN); diethylstilbestrol (DES), dienestrol (DS) and hexestrol (HEX)

Extraction solvent (IL)

Dispersive solvent

1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

—

1-hexyl-3-methylimidazolium hexafluorophosphate[C6MIM][PF6]

Aflatoxins B1; B2, G1, G2

Fe (III)

Azinphos-methyl; chloropyriphos; parathion-methyl; diazinon and phosalone

Mineral water, wastewater

[113]

1-hexyl-3-methylimidazolium chloride [C6MIM]Cl

—

In situ halide Methoxyfenozide; exchange tetrachlorvinphos; thiamethoxam; reaction diafenthiuron

trihexyl(tetradecyl)phosphonium chloride; [(C6)3C14P][Cl], trihexyl (tetradecyl)phosphonium bromide [(C6)3C14P][Br]; trihexyl(tetradecyl) phosphonium dicyanamide [(C6)3C14P][N(CN)2]

Methanol

River water samples Conventional Naphthalene; acenaphthylene; acenaphthene; fluorene; phenanthrene; anthracene; fluoranthene; pyrene; chrysene; benz[a]anthracene; benzo[b] fluoranthene; benzo[k]fluoranthene; benzo[a]pyrene; indeno[1,2,3-cd] pyrene; dibenz[a,h]anthracene, and benzo[g,h,i]perylene

[115]

1-octyl-2,3-dimethylimidazolium bis [(trifluoromethyl)sulfonyl]imide [ODMIM][NTF2]; 1-hexyl-3methylimidazolium bis [(trifluoromethyl)sulfonyl]imide] [HMIM][NTF2]

Acetonitrile

Ultrasoundassisted

Fruit juice samples

[116]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]; 1-Hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]; 1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

1-hexyl-3methylimidazolium tetrafluoroborate [C6MIM][BF4]

Floatation 17-β-estradiol-benzoate; 17coupled with α-estradiol conventional

Lake water and well water

[117]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]; 1-Hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

Methanol

Vortex assisted

Zearalenone

Maize product

[118]

trioctylmethylammonium thiosalicylate (task-specific ionic liquids (TSIL))

Methanol

Ultrasoundassisted

Cd (II); Co (II); Pb (II)

Tea samples

[119]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM]PF6 and 1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM]PF6]

Methanol

Vortex assisted

4-hydroxybenzophenone; 2,4dihydroxybenzophenone; 2hydroxy-4-methoxybenzophenone (2-HMBP); benzophenone

Lake water and river water

[120]

Diflubenzuron; triflumuron; hexaflumuron; flufenoxuron; lufenuron; diafenthiuron; transfluthrin; fenpropathrin; γ-cyhalothrin; deltamethrin

Tap water, reservoir water, river water, bottled mineral water

[114]

(Continued)

TABLE 6.6

(Continued)

Extraction solvent (IL)

Dispersive solvent

1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

—

1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

DLLME mode

Extractant

Sample

Reference

Temperature- Chlorotoluron; diethofencarb; controlled chlorbenzuron

Melted snow water, tap water, lake water

[121]

Methanol

Conventional Irganox 1010; Irganox 1076; Irgafos 168

Tap and mineral water

[122]

1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

Triton X-100

Microwaveassisted

Milk

[123]

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM]PF6

Methanol

Conventional Methamphetamine

Human urine

[124]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM]PF6

Methanol

Conventional Saquinavir

Rat serum

[125]

Tobramycin (TOB), NEO, GEN

Methanol 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6])

Vortexassisted

Isocarbophos; phtalofos; triazophos; Apple and pear fenthion; phoxim; profenofos samples

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM]PF6

Ultrasoundassisted

2-anilinoethanol; o-chloroaniline; 4bromo-N,N-dimethylaniline

Methanol

[126]

Tap water, river water [127]

1-octyl-3-methylimidazolium Acetone hexafluorophosphate ([C8MIM][PF6])

Conventional Bisphenol-A; β-naphthol; α-naphthol; 2, 4-dichlorophenol

Aqueous cosmetics

[128]

1-octyl-3-methylimidazolium Acetone hexafluorophosphate ([C8MIM][PF6])

Conventional MeHg1; EtHg1; PhHg1; Hg21

Lake water

[129]

1-octyl-3-methylimidazolium Methanol hexafluorophosphate ([C8MIM][PF6])

Up-anddown shakerassisted

[130] Swimming pool, wastewater; treatment plants; lake water

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM]PF6

Conventional Rifaximin

Rat serum

[131]

Conventional Permethrin and biphenthrin

Snow, rain, lake, spring water

[132]

In situ

Water, juice, red wine, [133] vinegar, soy sauce

Methanol

1-octyl-3-methylimidazolium 1-butyl-3hexafluorophosphate ([C8MIM][PF6]) methylimidazolium hexafluorophosphate [C4MIM]PF6 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

—

Benzophenone; 2-hydroxy-4methoxybenzophenone; 2,2’dihydroxy-4methoxybenzophenone

Sudan dyes

1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM] [PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

Acetone and acetonitrile

1-ethyl-3-methylimidazolium Acetone hexafluorophosphate ([C2MIM] [PF6]); 1-butyl-3- methylimidazolium hexafluorophosphate ([C4MIM] [PF6]); 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

Acetone

Conventional Sudan dyes, dibutyl phthalate; di-2- Chili powder, chili ethylhexyl phthalate; diisodecyl salt, chili sauce, chili phthalate; di-n-octyl phthalate; bean sauce, sweet sauce. ketchup

[134]

Conventional Irbesartan and valsartan

Human urine

[135]

Conventional Ni (II); Co (II); Cu (II); Zn (II)

Tap, well, mineral, river water

[136]

292

6. Ionic liquids in separation and preconcentration of organic and inorganic species

FIGURE 6.13

IL-based headspace in-tube microextraction [138].

FIGURE 6.14

Schematic of UNE-HS/IL/SDME [139].

reported for the first time that some hydrophilic ILs can form ATPS in the presence of inorganic salts [163]. A hydrophilic two-phase system can be used only for hydrophilic IL near room temperature, since only these can form two water-

rich phases. When treating hydrophobic ionic liquids, two phases already exist prior to the addition of any salt, and due to the low solubility of these ionic liquids in water, one of the phases is far from being enriched in water [164].

New Generation Green Solvents for Separation and Preconcentration

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

293

TABLE 6.7 Applications of ILs in different mode of LPME. IL

LPME mode

Extractant

Sample

Reference

1-alkyl-3-methylimidazolium hexafluorophosphate ([CnMIM][PF6]

SDME/HSLPME

BTEX (benzene, toluene, ethylbenzene, and xylene); polycyclic aromatic hydrocarbons; phthalates; phenols; aromatic amines; herbicides; organotin; organomecury

—

1-butyl-3-methylimidazolium phosphate ([BMIM][PO4]); 1-butyl-3methylimidazolium methylsulfate ([BMIM][MeSO4]); 1-butyl-3methylimidazolium octylsulfate ([BMIM][OcSO4]); 1-butyl-3methylimidazolium hexafluorophosphate ([BMIM][PF6])

Three-phase LLLME

Naphthalene; tridecane; tetradecane; Storm water acenaphthene; pentadecane; samples fluorene; heptadecane; phenanthrene; nonadecane; pyrene; chrysene

[141]

1-octyl-3-methylimidazolium hexafluorophosphate [C8min][PF6]

SDME

Formaldehyde; acetaldehyde; acrolein; acetone; propionaldehyde; crotonaldehyde and butyraldehyde

River, snow, seawater

[142]

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

SDME

Sulfachloropyridazine; sulfadiazine; sulfamerazine; sulfamethoxaline; sulfamethoxypyridazine; sulfaquinoxaline

Ground water, tap water, lake water, pool water

[143]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6], 1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]; 1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

Ionic-liquidmagnetized stirring bar LPME

Shikonin and β,β0 -dimethylacrylshikonin

Zicao

[144]

1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide [C6MIM][NTf2]

SDME

2,4,6-tricholoroanisole

Water and wine

[145]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Sulfonamides

Water

[143]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Colchicine

Fresh lily

[146]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Dichlorobenzeneisomers

Soil samples

[147]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Organochlorine pesticides

Soil samples

[148]

1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

SDME

Aromatic amines

Water

[149]

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

SDME

Trihalomethanes

Water

[150]

[140]

(Continued)

New Generation Green Solvents for Separation and Preconcentration

294

6. Ionic liquids in separation and preconcentration of organic and inorganic species

TABLE 6.7 (Continued) IL

LPME mode

Extractant

Sample

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

SDME

Chlorobenzene derivatives

Dye wastewater

[151]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Chloroaniline

Water

[152]

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

HF-LPME

chlorophenols

Water

[153]

1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6]

HF-LPME

Sulfonamides

Water

[44]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

HF-LPME

Benzene; toluene; ethylbenzene; and Water xylenes

[154]

1-hexyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate [C6MIM] [FAP]

HF-LPME

Ultraviolet filters

Water

[155]

1-butyl-3-methylimidazolium chloride HF-LPME [C4MIM]Cl

Polycyclic aromatic hydrocarbons

Water

[156]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

HF-LPME

Cd21

Water

[157]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Co21; Hg21; Pb21

Human serum and water

[158]

1-hexyl-3-methylimidazolium hexafluorophosphate [C6MIM][PF6]

SDME

Hg21

water

[159]

1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM][PF6]

SDME

Pb21

Water and food samples

[160]

1-butyl-3-methylimidazolium hexafluorophosphate ([C4MIM][PF6])

HS-LPME

2-nitrophenol; 4-chlorophenol; 2,4dichlorophenol; 2-naphthol

Tap water, underground water, reservoir water, lake water

[161]

Yu et al. used a mixture of IL/anionic surfactants in aqueous two-phase systems for the preconcentration of sulfamethyldiazine, sulfamethazine, sulfamethazine, sulfamethoxazole, and sulfisoxazole in blood samples. An ionic liquid/SDS aqueous two-phase system occurs when the IL and anionic surfactant are mixed in an appropriate ratio. In this method, after the blood sample is centrifuged, other reagents (sodium lauryl sulfate,

Reference

1-hexyl-3-methylimidazolium chloride, and K2HPO4) are added. Subsequently, the resulting mixture was ultrasonically shaken and centrifuged. Finally, an aqueous two-phase system is formed, and the analyte is extracted to the upper phase [165]. Han et al. analyzed chloramphenicol using IL-salt aqueous two-phase flotation (ILATPF) and high-performance liquid chromatography (HPLC). In this work, a sufficient amount of

New Generation Green Solvents for Separation and Preconcentration

6.3 Application of ionic liquids in extraction of organic and inorganic compounds

FIGURE 6.15

295

IL-salt aqueous two-phase flotation (ILATPF)n [166].

K2HPO4 was added to the working solution of chloramphenicol into the colorimetric tube. The solution was shaken for 20 min and then transferred to a flotation cell (Fig. 6.15) (Calibration A). 3 mL of 1-butyl-3-methylimidazolium chloride [C4mim] Cl IL solution was added to the top of the sublimation cell. The target analyte was floated by bubbling nitrogen from the bottom of the cell for 50 min and extracting into the IL phase on the surface of the sample solution. ILATPF was successfully applied to the analysis of chloramphenicol in lake water, feed water, milk, and honey samples with a linear range of 0.5500 ng mL21 and a recovery of over 97.1% [166]. ATPS is combined with an in situ DLLME method using imidazolium ionic liquid ILs for the separation of curcumin, demethoxycurcumin, and bis-demethoxycurcumin. The separation step is shown in Fig. 6.16. Briefly, 1,3diethylimidazolium iodide IL, K2HPO4, and curcuminoid were added to 1 mL of deionized water and centrifuged. The mixture was then vortexed and centrifuged. The concentration of curcumin in the salt-rich phase was determined by HPLC. In the second step, the K2HPO4-rich phase is removed, and an aliquot

of the LiNTf2 aqueous solution is added to the IL rich phase. A turbid solution (IL droplets in the liquid phase) was formed, followed by centrifugation at 3000 rpm for 3 min. Waterimmiscible IL appears at the bottom of the tube, and curcumin is simultaneously extracted into the IL phase [167]. Table 6.8 lists other applications of ILs in ATPS.

6.3.5 Other extraction methods based on ionic liquids Binary low-density solvent/IL-assisted surfactant-enhanced emulsification microextraction technology was established for the separation/enrichment and determination of pyrimethanil, fludioxonil, cyprodynil, and pyraclostrobin in apple juice and apple vinegar. In this work, a low-density solvent (such as amyl acetate) with good solubility is used as an extraction solvent, and high-density IL (1hexyl-3-methylimidazolium hexafluorophosphate ([HMIM] PF6)) as a second solvent to mix. The ratio of the two solvents is changed to ensure that the density of the mixed solvent is greater than water. After studying the influencing parameters, the method showed good

New Generation Green Solvents for Separation and Preconcentration

296

FIGURE 6.16

6. Ionic liquids in separation and preconcentration of organic and inorganic species

In situ DLLME method using imidazoliumionic liquids ILs [167].

linearity in the range of 5200 μg L21 and showed a limit of quantitation in the range of 25 μg L21 [192]. Song et al. developed a microwave-assisted liquidliquid microextraction technique based on IL curing for the extraction of sulfonamides in environmental water samples. The solid ionic liquid at room temperature was named 1-ethyl-3-methylimidazolium hexafluorophosphate and was used as an extraction solvent in this study. The solid IL was melted and dispersed into the sample solution by microwave irradiation for 90 s. The analyte is then extracted into fine droplets of IL. The tube was placed in an ice bath for 5 min. Due to the relatively low melting point (62.5
C), IL droplets solidify [193]. Kang et al. applied IL based on homogeneous microextraction to extract hormones from cosmetics. After adjusting the pH of the aqueous sample solution to the desired amount, an extraction solvent (1-hexyl-3-methylimidazolium tetrafluoroborate) was added thereto. By adding NH4PF6, a turbid solution is formed due to the formation of fine droplets of IL uniformly dispersed throughout the solution. Centrifugation of this turbid solution resulted in IL precipitation at the bottom of the centrifuge tube [194]. Zare et al. developed an effective and environmentally friendly method called ionic

liquid-based emulsification microextraction, which is accelerated by ultrasonic radiation. In this work, a sufficient amount of IL (as an extraction solvent) is injected into a mixture of a surfactant (as an emulsifier) and an analyte (doxipine and perphenazine) sample solution. The emulsion state occurs by vortexing the previous mixture. After sonication and centrifugation, the IL phase settles at the bottom of the conical tube. The extraction efficiency of ILs, such as 1hexyl-3methylimidazolium hexafluorophosphate [C6MIM][PF6], 1-butyl-3-methylimidazolium hexafluorophosphate [C4MIM] [PF6], and 1hexyl-3- methylimidazolium bis(trifluoromethylsulfonimide) [C6MIM] [N(SO2CF3)2] was studied [195]. The sunset yellow removal efficiency by IL (1,3-bis(trimethoxysilylpropyl)imidazolium chloride) based periodic mesoporous organosilica (PMO-IL) was studied by Ghaedi et al. The PMO-IL nanomaterial was prepared by hydrolysis and co-condensation of tetramethoxysilane (TMOS) and 1, 3-bis(trimethoxysilylpropyl)imidazolium chloride in the presence of surfactant template under acidic conditions [196]. Ultrasound-assisted temperature-controlled IL emulsification microextraction was developed for the determination of parabens, including methylparaben, ethylparaben, propylparaben, and butylparaben. According to

New Generation Green Solvents for Separation and Preconcentration

TABLE 6.8

Applications of ILs in ATPS extraction.

IL [abbreviation]

Phase separator agent

Extractant

Reference

K3PO4 1-ethyl-3-methylimid azolium chloride [C2mim]Cl; 1-butyl-3methylimidazolium chloride [C4mim]Cl; 1-hexyl-3-methylimidazolium chloride [C6mim]Cl; 1-heptyl-3-methylimidazolium chloride [C7mim]Cl; 1-decyl-3-methylimidazolium chloride [C10mim]Cl; 1-allyl-3methylimidazolium chloride [amim]Cl; 3-methylimidazolium chloride [C7H7mim]Cl; 1-hydroxyethyl-3-methylimidazolium chloride [OHC2mim] Cl; 1-butyl-3-methylimidazolium bromide [C4mim]Br; 1-butyl-3methylimidazolium methanesulfonate [C4mim][CH3SO3]; 1-butyl-3methylimidazolium acetate [C4mim][CH3CO2]; 1-butyl-3methylimidazolium methylsulfate [C4mim][CH3SO4]; 1-butyl-3-methylimidazoliumtriflu oromethanesulfonate [C4mim][CF3SO3]; 1-butyl-3methylimidazolium dicyanamide [C4mim][N(CN)2].

Vanillin

[168]

1-hexyl-3-methylimidazolium bromide [C6mim]Br

pH and K2HPO4

Dutasteride

[169]

Ammoeng 110

K2HPO4/ KH2PO4

Myoglobin; trypsin; lysozyme; BSA

[170]

1-hexyl-3-methylimidazolium tetracyanoborate [HMIM][TCB]; 1-decyl-3methylimidazolium tetracyanoborate [DMIM][TCB]; and 1-butyl-1methylpyrrolidinium tetracyanoborate [BMPYR][TCB]

?

2-phenylethanol

[171]

1-ethyl-3-methylimidazolium trifluoromethanesulfonate (triflate) [C2mim] Al2(SO4)3; K3C6H5O7 [CF3SO3]; 1-butyl-3-methylimidazolium trifluoromethanesulfonate (triflate) [C4mim][CF3SO3]; 1-butyl-3-methylimidazolium tosylate [C4mim][Tos]; 1-butyl-3-methylimidazoliumdicyanamide [C4mim][N (CN)2]; tetrabutylphosphonium bromide [P4444]Br; tributylmethylphosphonium methylsulphate [P4441][CH3SO4]; tri(isobutyl) methylphosphonium tosylate [Pi(444)1] [Tos]; tetrabutylphosphonium chloride [P4444]Cl

Textile dyes

[172]

1-butyl-3-methylimidazolium trifluoromethansulfonate [Im4,1]1 K2HPO4; KH2PO4 [CF3SO3]2; 1-butyl-3-methylimidazolium dicyanamide[Im4,1]1 [N(CN)2]2; 1-butyl-3-methylimidazolium thiocyanate[Im4,1]1 [SCN]2; 1-butyl-3methylimidazolium methysulfate[Im4,1]1 [CH3SO4]2; 1-butyl-3methylmorpholinium trifluoromethansulfonate[Mo4,1]1 [CF3SO3]2; 1butyl-3-methylpyrrolidinium trifluoromethansulfonate[Pl4,1]1 [CF3SO3]2; 1-ethyl-3-methylimidazolium trifluoromethansulfonate[Im2,1]1 [CF3SO3]2 1-methoxyethyl-3-methylimidazolium trifluoromethansulfonate[Im2O1,1]1 [CF3SO3]2

1,3-propanediol

[173]

(Continued)

TABLE 6.8

(Continued)

IL [abbreviation]

Phase separator agent

Extractant

Reference

1-octyl-3-methylimidazolium bromide; 1-decyl-3-methylimidazolium bromide; 1-octyl-3-methylimidazolium tetrafluoroborate; 1-decyl-3methylimidazolium tetrafluoroborate

K2HPO4

Pyritinol hydrochloride

[174]

Na2SO4; K2HPO4/KH2PO4; 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, [C2mim] [CF3SO3]; 1-butyl-3-methylimidazolium bromide, [C4mim]Br; 1-butyl-3K3PO4 methylimidazolium methylsulfate [C4mim] [CH3SO4]; 1-butyl-3methylimidazolium ethylsulfate, [C4mim] [C2H5SO4]; 1-butyl-3methylimidazolium trifluoromethanesulfonate, [C4mim][CF3SO3]; 1-butyl3-methylimidazolium dicyanamide, [C4mim][N(CN)2], 1-heptyl-3methylimidazolium chloride, [C7mim]Cl, 1-methyl-3-octylimidazolium chloride, [C8mim]Cl, and 1-butyl-3-methylimidazolium octylsulfate, [C4mim] [OctylSO4]

Gallic acid

[175]

tetrabutylphosphonate nitrate ([P4444][NO3])

NaNO3

Neodymium (III)

[176]

1-butyl-3-methylimidazolium tetrafluoraborate [Bmim]BF4

Na2CO3

Roxithromycin

[177]

1-butyl-3-methylimidazolium bromide [C4mim]Br; 1-hexyl-3methylimidazolium [C6mim]Br; 1-octyl-3-methylimidazolium [C8mim]Br

K2HPO4

Bovine serum albumin, trypsin, cytochrome c and globulins

[178]

1-butyl-3-methylimidazolium chloride[C4mim]Br

K2HPO4

Testosterone and epitestosterone

[179]

1-butyl-3-methylimidazolium tetrafluoraborate [Bmim]BF4

NaH2PO4

2,4-dichlorophenol (2,4-DCP); 2,6-dichlorophenol (2,6-DCP), 4-chlorophenol (4-CP)

[180]

Iolilyte 221PG

?

Proteins and carbohydrates

[181]

1-butyl-3-methylimidazolium bromide [BmimBr]; 1-hexy-3methylimidazolium bromide [HmimBr]; 1-octyl-3-methylimidazolium bromide [OmimBr]

K2HPO4; K3PO4; K2CO3; KF; (NH4)2SO4; C6H5Na3O7; Na2CO3; NaCl; MgSO4; NH4NO3

Succinic acid

[182]

[Bmim]BF4 (1-butyl-3-methylimidazoliumtetrafluoroborate)

NaH2PO4; (NH4)2SO4

Aloe polysaccharides; proteins

[183]

1-decyl-3-methylimidazolium chloride [C10mim]Cl; 1-dodecyl-3methylimidazolium chloride [C12mim]Cl; 1-methyl-3tetradecylimidazolium chloride [C14mim]Cl; trihexyltetradecylphosphonium chloride [P6,6,6,14]Cl; trihexyltetradecylphosphonium bromide [P6,6,6,14]Br; trihexyltetradecylphosphonium decanoate [P6,6,6,14][Dec];

Na2HPO4

(Bio)molecules

[184]

trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][N(CN)2]; trihexyltetradecylphosphonium bis (2,4,4-trimethylpentyl)phosphinate [P6,6,6,14][TMPP]; tetraoctylphosphonium bromide [P8,8,8,8]Br

  

1-Butyl-3-methylimidazolium tetrafluoroborates ([C4MIM][BF4]; 1-hexyl3-methylimidazolium tetrafluoroborates([C6MIM][BF4]; 1-octyl-3methylimidazoliumtetrafluoroborates ([C8MIM][BF4]

C6H5Na3O7 2H2O; C6H5K3O7 H2O; Na2C4H4O6 2H2O C4H4KNaO6 4H2O

Sulfathiazole; sulfameter; sul- [185] fadimidine; sulfadimethoxine; sulfaphenazole and sulfanitran

1-butyl-3-methylimidazolium bromine ([Bmim]Br)

K2HPO4; Na2CO3; K3PO4; KOH

3-O-caffeoylquinic acid; 3,5-di- [186] O-caffeoylquinic acid; 3,4-diO-caffeoylquinic acid

[Emim]Br; [Bmim]Br; [Hmim]Br; [Omim]Br; [Bmim]BF4; [Bmim]Cl; [Bmim]HSO4 and [Bmim]NO3

KOH

Psoralen

[187]

[C2mim]Br (1-ethyl-3-methylimidazolium bromide); [C4mim]Br (1-butylNaH2PO4; (NH4)2SO4; 3-methylimidazoliumte bromide); [C6mim]Br (1-hexyl-3Na2SO4; MgSO4 methylimidazolium bromide); [C2-mim]BF4 (1-ethyl-3-methylimidazolium tetrafluoroborate); [C4-mim]BF4 (1-butyl-3-methylimidazoliumte trafluoroborate); [C4mim] N(CN)2 (1-butyl-3-methylimidazoliumte dicyanamide)

Anthraquinones

[188]

N-ethyl pyridine chlorine salt ([EPy]Cl); N-butyl pyridine chlorine salt ([BPy]Cl); N-hexyl pyridine chlorine salt ([HPy]Cl)

K2HPO4

Papain

[189]

1-octyl-3- methylimidazolium bromide

NaCl

Tetracycline; oxytetracycline; chloramphenicol

[190]

[C4-mim]BF4 (1-butyl-3-methylimidazoliumte trafluoroborate)

(NH4)2SO4

Sudan IIV

[191]



300

6. Ionic liquids in separation and preconcentration of organic and inorganic species

the method described in Fig. 6.17, IL 1-octyl3-methylimidazolium hexafluorophosphate was used as an extraction solvent; further, a dispersant solvent [197] was not required. Liu et al. studied the preenrichment of sulfamethazine, sulfazine, sulfamethoxazole, and sulfisoxazole in blood by the uniform extraction of salt combined with IL/IL DLLME. After removing the protein in the serum in the presence of acetonitrile, IL1butyl-3-methylimidazolium tetrafluoroborate, dipotassium hydrogen phosphate, and IL1hexyl-3-methylimidazolium hexafluorophosphate were added to the obtained solution. After the resulting mixture was ultrasonically shaken and centrifuged, the precipitate was separated. Acetonitrile was added to the precipitate, and the analyte was extracted into the acetonitrile phase. Several experimental conditions were studied and optimized. This method can be successfully applied to recover (more than 90% of) the target analyte blood samples [198].

6.4 Magnetic ionic liquids and theory application Recently, magnetic ionic liquids (MILs) have been introduced as a new class of ILs and used

FIGURE 6.17 Ultrasound-assisted temperature-controlled IL emulsification microextraction [197].

in many analytical processes. MLI exhibits a strong sensitivity to external magnetic fields because of the presence of high autorotation or lanthanide metals (such as iron, cobalt, manganese, lanthanum, cerium, and lanthanum) in cations or anions [199,200]. Similar to conventional IL, the physicochemical properties of MIL can be controlled by adjusting the structure of the cation/anion [201,202]. There are still few publications describing the magnetic retrieval of MIL in IL-based programs. Hayashi et al. the magnetic properties of some of the first iron (III)containing MILs to be evaluated included 1-butyl-3-methylimidazolium tetrachloroferrate (III) ([BMIM 1 ] [FeCl-]) [203,204]. Bagheri et al. synthesized mercapto3-methylimidazolium-bromo-ferric chloride Decyl-3-Methylimidazolium monobromothrichloroferrate [DeMeIm]-[FeCl3Br-] by mixing 1-bromodecane with 1-methylimidazole at 70
C, stirring, and refluxing for about 24 h MIL until two phases were formed. After treating the product with ethyl acetate to remove unreacted material, equimolar FeCl3 6H2O was added to DeMeIm. A solution containing 3% MIL and 18% polyamide was charged into a syringe, and then electrospray was applied by applying a high voltage of 15 kV dc to the two electrodes, and the electrospun fiber was moved from the needle (anode) toward the aluminum plate (cathode) in a random mode to prepare nonwoven nanofibers. A sufficient amount of prepared nanofibers were packed in a μ-SPE column for the extraction of imidacloprid, metribuzin, ametryn, and chlorpyrifos [205]. MIL solvents provide a promising new magnet approach for the selective analysis of nucleic acids. Kevin D. Clark et al. prepared hydrophobic trihexyl (tetradecyl) phosphonium tetrachloroferrate (III) ([P6,6,6,141] [FeCl42]) MIL and trioctylbenzyl ammonium trifluoroferrate (III) ([(C8)3BnN1] [FeCl3Br2]) MIL and used it as a polymerase chain reaction (PCR-) compatible solvent for DNA extraction from

New Generation Green Solvents for Separation and Preconcentration



301

6.4 Magnetic ionic liquids and theory application

C8H17

C8H17 Cl– + N C8H17

+

FeCl3

C8H17

C8H17 30°C, 24h stirring

CH3

FIGURE 6.18

MeOH

C8H17 FeCl4– + N C8H17 CH3

Synthesis procedure of N8,8,8,1[FeCl4] MIL [206].

C8H17 + FeCl4– N C8H17 CH3

Stirring

Magnetic isolation

Water phase removal

Water sample Stirring bar

Magnetic stirrer

Dilution with acetonitrile/H2O

HPLC analysis

FIGURE 6.19

Stirring-assisted drop-breakup microextraction based on N8,8,8,1[FeCl4] MIL [206].

biological samples [202]. Chatzimitakos et al. synthesized and extracted phenolic endocrine disruptors and acidic drugs by stirring-assisted drop-separation microextraction using methyl trioctyl ammonium tetrachloride ferric acid N8,8,8,1 [FeCl4] MIL (Fig. 6.18). In this procedure, a drop of MIL was added to the sample, and the entire system was agitated using a magnetic stirrer. The MIL cleavage and analyte extraction was dropped into N8,8,8,1 [FeCl4] by stirring. Finally, the analyte-containing MIL was separated from the solution where the common magnet was located on the side of the glass beaker. The extraction procedure is performed as shown in Fig. 6.19 [206]. Trujillo-Rodrı´guez et al. designed three hydrophobic MILs: (1) benzyltrioctylferrocene

(III) (([N8,8,8,B][FeCl3Br], expressed as MIL A; MW 5 689.9 g mol21; thermal stability 5 258
C; effective magnetic moment 5 5.26); (2) methoxybenzyl trioctyltrifluoroborate iron (III) ([N8,8,8, MOB] [FeCl3Br] is expressed as MIL B; MW 5 716.9 g mol21; thermal stability 5 203
C; effective magnetic moment 5 5.60); and (3) 1,12bis(3-benzylbenzimidazole) dodecane bis[(trifluoromethyl)sulfonyl) acyl imine iron (III) trichloroborate ([(BBnIm)2C12] [NTf2] [FeCl3Br], expressed as MIL C; MW 5 1107.1 g mol21 thermal stability 5 314
C; effective magnetic moment 5 5.45) for an extraction group of heavy polycyclic aromatic hydrocarbons. The steps of the MIL-based microextraction method under optimal conditions are summarized in Fig. 6.20 [207].

New Generation Green Solvents for Separation and Preconcentration

302

FIGURE 6.20

6. Ionic liquids in separation and preconcentration of organic and inorganic species

MIL-based microextraction method [207].

A new noncentrifugal DLLME method, based on magnetomotive room temperature double cation IL (MRTDIL), was reported for the preconcentration and measurement of trace gold and silver in water and ore samples by the Beiraghi study group. An extraction solvent was prepared of 1,3-(propyl-1,3-diyl)bis-(3-methylimidazolium)bis-(ferric chloride(II)) by mixing and synthesizing [Pbmim] crystal powder ([Pbmim] (FeCl4)2). At room temperature, Cl2 and anhydrous FeCl3 were in a molar ratio of 1:2 until a dark brown liquid was obtained. The entire extraction step is shown in Fig. 6.21. Under optimal conditions, detection limits (LOD) of 3.2 and 7.3 ng L21 were obtained, respectively, for Au and Ag of 245 and 240 [208]. Wang et al. determined six triazine herbicides in oilseeds by matrix solid-phase

dispersion, combined with MIL dispersion liquid microextraction (MSPD-MIL-DLLME). They used 1-butyl-3-methylimidazolium iron tetrachloride ([C4mim] [FeCl4]) as the extraction solvent. In this work, first a homogeneous mixture of the sample and the diatomaceous earth was thoroughly mixed using a mortar. Then a layer of absorbent cotton, diatomaceous earth, a uniform sample adsorbent mixture, and a second layer of absorbent cotton were placed in a glass column. The other steps of the method are shown in Figs. 6.22 and 6.23 [209]. Table 6.9 lists other applications for MIL. Yun Zhang et al. determined 16 polycyclic aromatic hydrocarbons (PAHs) in vegetable oils by a novel three-dimensional ionic liquid (1-(3aminopropyl) 2 3-methylimidazolium bromide ([APMIM]Br)) functionalized magnetic graphene

New Generation Green Solvents for Separation and Preconcentration

FIGURE 6.21

Centrifuge-less DLLME method based on application of magnetomotive room temperature dicationic IL

(MRTDIL) [208].

FIGURE 6.22 Matrix solid-phase dispersion combined with MIL dispersive liquidliquid microextraction (MSPD-MIL-DLLME) [209].

304

6. Ionic liquids in separation and preconcentration of organic and inorganic species

FIGURE 6.23 Schematic diagram of the magnetic ionic liquid-based dispersive liquidliquid microextraction (MIL-based DLLME) procedure [210].

oxide nanocomposite (3D-IL@mGO). The rapid and accurate GCMS method, coupled with the 3D-IL@mGO MSPE procedure, was successfully applied for the analysis of 16 PAHs in 11 vegetable oil samples from a supermarket in Zhejiang Province. The schematic procedure of 3D-IL@mGO is summarized in Fig. 6.24 [235]. The magnetic adsorbent, which was functionalized with ionic liquid, was reusable, environmentally friendly, and easily separated from the sample solution. The GC/MS method, combined with the magnetic dispersive solid phase extraction technique, achieved good linearity, LODs, and satisfactory repeatability and accuracy. As strong ππ bonds between the 3D-IL@mGO and PAHs, this novel magnetic nanocomposites

may also have applications in the extraction and analysis of other organic pollutants [235].

6.5 Conclusion This chapter summarizes the practical potential of ILs, which have expanded in use significantly over the past few years due to their unique and tunable physical and chemical properties. Among IL-based extraction methods, they are candidates for replacing volatile organic solvents and have been the subject of much research. The combination of ILs and microextraction techniques has proven to be important because, due to the synergistic

New Generation Green Solvents for Separation and Preconcentration

305

6.5 Conclusion

TABLE 6.9 Application of MILs. MIL

Extractant

Sample

Ref.

Trihexyltetradecylphosphonium tetrachloroferrate (III) ([3C6PC14][FeCl4])

Phenol; 4-nitrophenol; 2-chlorophenol; 4chlorophenol; 2,3-dichlorophenol; 2,4dichlorophenol; 3,5-dichlorophenol; 3,4dichlorophenol; pentachlorophenol; 2benzyl-4-chlorophenol

Soil samples

[211]

Benzyltrioctylammonium bromotrichloroferrate(III) ([(C8)3BnN1] [FeCl3Br2])

DNA

Bacterial cell lysate

[212]

1,3-(propyl-1,3-diyl) bis (3methylimidazolium) chloride [pbmim]Cl2

Lead

Borago officinalis (a medicinal plant)

[213]

1-hexyl-3-methylimidazolium tetrachloroferrate ([C6mim] [FeCl4])

Cyanazine; desmetryn; secbumeton; terbutryn; dimethametryn; dipropetryn

Vegetable oils samples

[210]

1-Butyl-3-methylimidazolium tetrachloroferrate ([bmim]FeCl4); NButylpyridium tetrachloroferrate ([bPy] FeCl4) and 1-butyl-1-methylpyrrolium tetrachloroferrate ([bmP]FeCl4)

Coal direct liquefaction residues

Coal

[214]

1-n-butyric acid-3-methylimidazolium chloride/xFeCl3 ([C3H6COOHmim]Cl/ xFeCl3; x 5 0.5, 1, 1.5, 2)

Benzothiophene

Model oil

[215]

[CnC(S)Im]X (1-alkyl (methyl, butyl and octyl)-3-(tri-ethoxysilylpropyl)-imidazolium salt, X refers to Cl2, BF42, PF62)

Lipase immobilization

Water

[216]

Ionic liquid (IL) [Hmim] [PF6]

Cadmium and lead

Water samples

[217]

1-butyl-3-methylimidazolium hexafluorophosphate

Cadmium

Fruit and Vegetables

[218]

1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6]

Lead(II)

Water, plant, hair samples

[219]

Fe3O4 magnetic nanoparticles [C6MIM][PF6]

Benzoylurea insecticides

Upstream and downstream water samples

[220]

Fe3O4@SiO2@MIM-PF6 MNPs

Polycyclic aromatic hydrocarbons

Tap, river, well, reservoir ones water samples

[221]

IL ([C6MIM][NTf2])

Pyrethroids

Honey samples

[222]

[C7MIM][PF6] ionic liquid-coated Fe3O4grafted graphene nanocomposite

Nitrobenzene compounds (NBs)

Environmental water samples

[223]

1-butyl-3-methylimidazolium tetrachloroferrate ([C4mim][FeCl4])

Chloramphenicol

Water environment

[224]

(Continued)

New Generation Green Solvents for Separation and Preconcentration

306

6. Ionic liquids in separation and preconcentration of organic and inorganic species

TABLE 6.9 (Continued) MIL

Extractant

Sample

Ref.

n-hexyl-3-methylimidazolium hexafluoro phosphate

Hydrazine and Phenol

Tap and river water

[225]

[C6MIM][NTf2] supported magnetic

Acaricides

Fruit juice samples

[83]

1-hexyl-3-methylimidazolium bis (trifluoromethanesulfonimide)

Fungicides

Environmental waters

[226]

Room temperature ionic liquids (C16mimBr) and CTAB-coated Fe3O4/SiO2 NPs

Quercetin, luteolin, kaempferol

Urine samples

[90]

Hydrophobic MILs trihexyltetradecylphosphonium tetrachloromanganate (II) ([P6,6,6,141]2[MnCl422]); aliquat tetrachloromanganate (II) ([Aliquat1]2[MnCl422])

Hormones estriol; 17-β-estradiol; 17α-ethynylestradiol; estrone

Human urine samples

[227]

1-hexadecyl-3-methylmidazoliumbromide (C16mimBr)

Cephalosporins

Human urine

[228]

Fe3O4@SiO2@methylimidazolium hexafluorophosphate (MIM-PF6) nanoparticles

Butylparaben; benzophenone 3; benzophenone

Water samples

[229]

1-butyl-3-methylimidazole Linuron hexafluorophosphate ([BMIM]PF6); 1-hexyl3-methyl-imidazole hexafluorophosphate ([HMIM]PF6); and 1-octyl-3-methylimidazole hexafluoro-phosphate ([OMIM]PF6) coated Fe3O4@SiO2

Food samples

[230]

[C8MIM][PF6]

Clofentezine and chlorfenapyr

Environmental water samples

[231]

Cyano-ionic liquid functionalized magnetic nanoparticles (MNP@CN/IL)

Polycyclic aromatic hydrocarbons and chlorophenols

Environmental samples [232] (leachate and sludge from a landfill site)

Ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate

aflatoxins B1, B2, G1, G2

animal feeds

[107]

1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6)

Cadmium and arsenic

food samples

[233]

Magnetic cellulose nanoparticles (MCNPs) coated with 1-butyl-3-methylimidazolium hexafluoro phosphate [C4MIM][PF6] ionic liquid (IL)

Paracetamol; ibuprofen; naproxen and diclofenac

Natural waters

[234]

New Generation Green Solvents for Separation and Preconcentration

References

FIGURE 6.24

307

The schematic procedure of 3D-IL@mGO [235].

effects of ILs’ ideal properties (negligible vapor pressure; high heat, air, and water stability; variable solvent interactions; and synthetic stability), they can improve the sensitivity and reproducibility of the assay. Interestingly, the tunable nature of ILs allows the combination of different ions and the synthesis of new ILs with improved properties to significantly contribute to their use in microextraction techniques.

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New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

7 Supramolecular solvents in separation and preconcentration of organic and inorganic species Muhammad Balal Arain1 and Mustafa Soylak2 1

Department of Chemistry, University of Karachi, Karachi, Pakistan 2Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey

Abbreviations SUPRASs RAMs SDS CPs VOC ILs SDME CAE CPE GC FIA LC CDs THF MNPs VALLME TILDLME RTILs IL-DLLME RAS

supramolecular restricted access solvents restricted access materials sodium dodecyl sulfate cloud points volatile organic compound ionic liquids single-drop microextraction coacervative extraction cloud-point extraction gas chromatography flow injection analysis liquid chromatography cyclodextrins tetrahydrofuran Magnetic nanoparticles vortex-assisted liquid liquid microextraction temperature-controlled ionic liquid dispersive liquid phase microextraction ionic liquid-based dispersive liquid liquid microextraction Restricted access solvents

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00007-3

7.1 Introduction In the beginning, molecular chemistry was recognized as the study of atomic assemblies that are held together through covalent bonds. Afterward more research was devoted to the study of molecular arrangements and of intermolecular interactions (bonding), reformulated as chemistry of supramolecular assemblies and was thus defined as a new multidisciplinary field study of chemistry “far from the covalent bond.” Certainly, supramolecular chemistry is acclaimed to be an emergent field of research. The introduction section briefly illustrates the basics of noncovalent intermolecular forces/ interactions and SUPRAS’s fundamental concept, properties, and role in analytical chemistry. Before presenting the basics of supramolecular analytical approaches, this brief introduction provides the information, concepts, and research in supramolecular chemistry. It is intended to help readers understand some

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fundamental knowledge and developments related to supramolecular restricted access solvents (SUPRASs). The field of supramolecular chemistry is recognized as the domain of chemistry covering molecular assemblies that are combined together by noncovalent intermolecular attractions, H-bonding (hydrogen bonding), π-systems, electrostatic, hydrophobic interactions, and van der Waals forces [1]. The strength of noncovalent bonds or noncovalent interactions between molecular building blocks varies from coordinative bonds to hundreds of kilojoules per mole and to weak van der Waals interactions of only a few kilojoules per mole. Noncovalent forces have very weak binding energy in solvent effects like hydrophobicity, dipole dipole interactions, cation π interactions, dispersion, or π π stacking and are quite strong in electrostatic and coordinative interactions [2]. They are classified into several different types on the basis of the attraction/ repulsion interaction forces found between their molecules [3]. The short distance between two ions with opposite charges is the factor in the geometric structure of the supramolecular aggregate, even though no specific direction is involved in the ion ion interaction. However, interferences between ions and dipoles are in some ways not strong enough (i.e., limited to the range about 50 200 kJ mol21). Here, the important factor to be considered is the positioning of the dipole with reference to the charge. The attraction of alkali metal ions with crown ethers is the famous and classic example of such an ion dipole complexation in the domain of supramolecular interaction [4]. Noncovalent forces (biomolecules, aromatic rings such as benzene) also comprise π-systems, which can noncovalently fix to cations or any other π-systems or cation π interactions [5]. At the weak end of noncovalent interactions are van der Waals forces (,5 kJ mol21), that is, the attraction between a polarized electron cloud and adjacent nuclei [6].

The hydrophobic effect is another example that explains the reduction of the undesirable active surface among polar:protic and nonpolar:aprotic molecules. This effect plays a significant role in guest binding by cyclodextrins (CDs) [7]. Weak-force interactions between multipoles [8] and dihydrogen bridges [9] have also been studied in this domain. Molecular recognition is a specific formation between two molecules whose geometric and electronic features are complementary and that encompasses host guest chemistry. Many host guest complexes (H-bonding, biochemistry, e.g., DNA and protein structures) have been illustrated in the literature as noncompetitive solvents in which the hydrogen bonds can be quite strong and involved in artificial supramolecules [10]. Supramolecular chemistry focuses on the design, operation, and properties of these molecular structures and has made major contributions in the development of organic, inorganic, physical, and biological entities. General examples of supramolecular systems are biological systems (cell membranes and concentrated solutions of biomolecules), crystals engineering, and polynuclear metal complexes [1,11 14] (see Fig. 7.1). Supramolecular chemistry essentially comprises two extended ranges depending on two factors: size and shape of the molecules describing the host guest chemistry and selfassembly. Host guest chemistry illustrates the chemistry of complexes comprised of more than one molecule or ion, united by distinct structural associations by forces other than covalent bonds, either hydrogen bonding or ionic coupling, or by a different van der Waals interaction. In other words, the chemistry behind the host guest assembly involves the study of a cluster of solvent or “host” molecules that are capable of enclosing smaller guest molecules via specific noncovalent interactions such that, in the assembly, the host portion may be

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7.1 Introduction

FIGURE 7.1 Emergence of supramolecular chemistry with different fields of research.

defined as a molecule or as an organic ion whose binding sites converge in the complex. The guest is described as any other molecule or site containing diverging binding sites in the complex. Commonly, the host has the capacity (cavity) to fit a guest, such as CDs, calixarenes, crown, and the like [15]. These host molecules have been applied mostly for solvent extraction, chromatographic separation, extractive spectrophotometry, and emission spectroscopy of metals [16]. The development of synthetic receptors for creating single-analyte sensors and differential sensing schemes has also been an area where the host guest concept is applied [17,18]. On the other hand, CDs and their derivatives have been successfully used as constituents of the mobile and stationary phases for the enantiomeric isolation or separation of a huge range of analytes using chromatographic and electrophoretic techniques [19,20]. Self-assembly, or self-organization, enables the formation of well-defined aggregates through the unplanned (i.e., spontaneous) and reversible (i.e., adjustable) association of two or more components, linked together with noncovalent bonds or noncovalent interactions. In contrast to the host guest phenomenon, in self-assembly there is no any significant difference in dimension between the components, no entity is acting as a host for another, and is controlled thermodynamically [21]. The fundamental understanding of intermolecular inferences or attractions gained by supramolecular chemists during their studies

has given birth to nanochemistry, an area where high-technology, two- and three-dimensional nanometric structures are synthesized with the help of bottom-up strategy that has permitted the synthesis of outstanding devices such as molecular electronic and photonic devices and molecular computers or machines [22]. The preparation of nanoscale designs (modules, structures, or devices) by the bottom-up strategy is based on the self-assembly of subnanometer-scale molecules that automatically self-organize nanoscale aggregates according to their natural molecular programming [23]. Supramolecular solvents (SUPRASs) can also be characterized as nanostructured liquids formed by spontaneous and sequential coacervation phenomena through colloidal solutions of amphiphilic compounds [24]. This tactic and the knowledge acquired about nanochemistry’s ability to generate nanostructured designs in the solid state have led to the synthesis of different nanostructures in liquid state form (i.e., coacervates), called SUPRAS. This formation was better appreciated for separating SUPRAS from molecular and ionic solvents. The noncovalent attractions by which molecules form nanostructures in SUPRAS are the basis for the self-assembly processes that compose these structures. The intrinsic properties of SUPRASs—that they are structured from amphiphilic character molecules and their high concentration— make them very attractive for the extraction process [24]. Thus the nanostructures in

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SUPRASs provide sections of distinct polarities, acidities, and viscosities that are attractive as substrate solubilization sites, that are meaningful in observing impacts on chemical systems, and that are the basis for proposing several types of interactions for solutes and therefore the combined/mixed mechanisms for their solubilization. As a result, solutes in a huge polarity range can be taken out, simultaneously and efficiently. On this basis, many surfactant-modified procedures and new methodological approaches have been developed in different areas like spectral analysis, electroanalytical chemistry, and kinetic analysis [25,26]. Also, SUPRASs with the maximum concentration of amphiphiles (usually 0.11 mg μL21) have the most favorable sections for the magnification of solute ties (binding). High extractions correspond to low volumes of SUPRAS, given the maximum concentration factors (typically 100 500). Another interesting point of SUPRASs is that the properties of solvents can be regulated through the selection of appropriate amphiphilic molecules and the subsequent environment for their self-assembly. This means that, since noncovalent linkages are present between the amphiphilic structures of the SUPRASs, the resultant nanostructures are alterable and environment-responsive and that, due to these solvents, they can be customized to exert predetermined functions. This feature of SUPRASs as having restricted access properties, making them capable of extracting low-molecularweight solutes excluding macromolecules, has been recently reported [27]. In the last few years, the field of supramolecular chemistry has achieved increased popularity and a high level of maturity in analytical research work as extraordinary extractants have been used for a variety of analytes in various samples [28]. Numerous works have been published in the scientific literature dealing with SUPRASs to date.

From the experimental point of view, SUPRASs also offer attractive features in that they are structured through spontaneous selfprocedures (synthesis) that are accessible by everyone. In other words, the amphiphiles are universal, both naturally and synthetically, and are therefore easily accessible. SUPRASs are nonvolatile and nonflammable, making implementation a safer process. For many years, a few designs of SUPRASs have been applied for analytical purposes, and these are mostly formed by using nonionic surfactants (micellar solutions). Although some new solvents have been defined in recent years, they are mostly acquired from trialandtested analysis. In addition, progress and developments in supramolecular chemistry and the resulting advances in understanding self-assembly have provided researchers with the enhanced basic knowledge needed to utilize the mechanisms of the coacervation process and for the design (synthesis) of new SUPRASs. In fact, noncovalent attractions can be easily broken, given the required conditions, for the characterization of SUPRAS by means of techniques such as microscopy and mass spectrometry. Subsequent progress in this area requires even more attention to relevant fields, including the formation of new SUPRAs and the characteristics of the corresponding ordered structures. On the other hand, efforts are also needed to improve routine analysis by accepting SUPRASs in analytical extraction processes. Fig. 7.2 gives brief overview about SUPRAS.

7.2 Background A discovery is always the result of a long and continuous journey of experiences, crosschecks, contradictions, integrated results, and conclusions. Similarly, the area of supramolecular chemistry is born of a series of discoveries and prolonged research. There was no doubt

New Generation Green Solvents for Separation and Preconcentration

7.2 Background

FIGURE 7.2

323

Overview of SUPRAS.

that, as for any new event, supramolecular chemistry would be an emerging field of research. However, historically, the development of supramolecular chemistry certainly depended on the advances in analytical methods capable of solving the problems of complex structures linked by noncovalent bonds and those resulting from weak molecular interactions, as well as the highly dynamic characteristics of several supramolecular species [1,3]. This section of the chapter gives a brief historical background of SUPRASs, their development from the beginning to the inauguration of supramolecular chemistry, and their analytical application as efficient extractants. The journey begins in the late 18th century, in 1774, when Benjamin Franklin introduced the concept of self-assembly into molecular chemistry by performing an experiment with spreading oil over water [29]. In 1778, Joseph Priestley determined new inclusion complexes—clathrates, that is, an “abnormal ice”— the chemical presented as (SO2) • (H2O) X, known as the “first important substance in the clathrate hydrate family” [30,31]. Later, Humphrey Davy (United Kingdom, 1778 1829) worked on the synthesis of a clathrate hydrate, that is, chlorine. He discovered that any solution of chlorine in water froze at a temperature arising from the melting point of

the ice. During the decomposition, the new distinctive entity returned unchanged to the initiating components [32]. In 1891, Villiers and Hebd discovered molecular receptors, CDs, derived from macrocyclic compounds [33]. The concepts of “lock“and “key” were postulated in 1894 by Emil Fischer and rested on the theory of molecular recognition. As acknowledgment of his work, in 1902 he received the Nobel Prize in Chemistry [34]. In 1906, Paul Ehrlich conceived the concept of biological receptor, declaring that the molecules did not respond if they did not bind, and he received the Nobel Prize in Physiology or Medicine in recognition of his work on “immunity” [35]. In 1913, Alfred Werner received the Nobel Prize in Chemistry for his efforts in the development of coordination chemistry [36]. The beginning of supramolecular chemistry took place when Charles Pedersen’s 1967 revolutionary document on crown ethers was revisited. Some 20 years later, in 1987, Pedersen (1902 89) [37], Jean-Marie Lehn (born, 1939) [38], and Donald Cram (1919 2001) [39] were presented the Nobel Prize in Chemistry for their pioneering work in supramolecular chemistry. It took around 40 years from the foundation of the term U¨bermoleku¨ and Lehn’s definition [40] for supramolecular chemistry to become

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established and recognized as “the chemistry of molecular assemblies and the intermolecular bond.” The delay was due to the different perceptions and views of the scientists involved in this area. As long as the chemistry world accepted the model that molecules possess unique properties with little interference from the environment as an initial approximation, there was no place for supramolecular chemistry as an independent field of research. However, during various molecular experiments in a given environment, chemists began to realize that significant results change depending on the specific environment. It has become evident that the surroundings almost always have a significant effect. In this light, with a growing number of experimental results and examples of the significance of the environment’s influence on the properties of a molecule, a model shift occurred later in the 1960s, when supramolecular solvent effects had already been studied for some extent.

FIGURE 7.3

Afterward, intermolecular interactions were more focused and opened new doors for research. In this respect, chemists suddenly started to think about noncovalent forces, molecular recognition, modeling, selfassembly, and many other areas where supramolecular chemistry had meanwhile expanded. Supramolecules often have weak intermolecular forces and are highly dynamic. Because of their weak intermolecular interactions, complex designs can be arranged (tailored), might often with order. However, all these characteristics require specialized experimental methods. Supramolecular chemistry, quite often observed, made progress possible in certain areas of research depending on the development of appropriate methods. As an emerging field of research, it has opened up new possibilities for experimenters and has led to further progress in certain areas of research. The periodic development of supramolecular chemistry is illustrated in Fig. 7.3.

Historical development of supramolecular chemistry.

New Generation Green Solvents for Separation and Preconcentration

7.3 Solvent extraction system

In this view, the present chapter gives information on the current state of the methods used in supramolecular chemistry in the analytical extraction domain, mainly with organic and inorganic entities, and in the modifications in the area of research.

7.3 Solvent extraction system The solvent extraction techniques are a dynamic part of analytical chemistry and have been recognized as an excellent method for purification and separation because of its ease, simplicity, speed, and scope [41]. This part of the chapter comprises the fundamentals of solvent extraction methods, briefly discusses solvent extraction types, and presents the different parameters involved in solvent extraction systems. Conventionally, the solvent extraction system offers the basis for the preconcentration of the desired analyte from complex matrix with an adequate laboratory setup, requires just several minutes to perform, and may apply to trace- and macrolevel metals extraction procedures, thus offering much to mostly the analytical chemist. It is widely used in hydrometallurgy, waste treatment, effluent purification, and material preparation. Solvent extraction methods are dominated by the widely used precipitation method due to its sample cleanup process, which the former cannot achieve [42]. With the previous method, residues from coprecipitation phenomena are a decided limitation that is overcome only with difficulty, whereas the analog of coprecipitation, that is, coextraction, is almost unknown in solvent extraction. In routine analytical applications, solvent extraction can be used in three key areas: tracelevel pretreatment of elements, elimination of matrix interference, and differentiation of chemical bodies. In any typical sample treatment, the complexing agent, also known as an

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extractant, functions as a key component that governs the phase shift or transfer of solute (metal) between the particular liquid liquid phases. Currently, different groups of metal extractants, like cation exchanging, acidic and chelating reagents, solvating and anion exchanging reagents, are commonly used in industry. In any solvent extraction procedure, the extractant is dissolved in a suitable diluent, which acts as a solvent. The diluent, which is usually water, is immiscible with other phases. Different approaches are used, such as solvation/chelation/ion pair formation and the like, in which the extractant interacts with the solute to make the extraction from the aqueous phase. The distribution equilibrium among two phases is the controlling factor and is regulated by Gibbs phase rule by P 1 V 5 C 1 2, where the number of phases (P), the variance or degree of freedom (V), and the number of components (C) are the controlling parameters [43]. In the solvent extraction, we have P 5 2 two phases (aqueous and organic phases), the component C 5 1 (solute in the solvent and water phases), and at constant temperature and pressure P 5 1. In the extraction procedure, the formation of metals chelate plays a vital role, and all kinds of chelating agents have useful applications in metal extraction procedures. Different extraction systems are divided in several ways. The classic one is based on the type of extraction species, while the present type of division is dependent on the process of extraction and can be classified as chelate extraction, extraction by solvation, extraction involving ion pair formation, and synergic extraction. All these extractions are useful on the condition that neutral or uncharged species are extracted easily in organic solvents. In chelate extraction, the extraction is followed by the process of chelate formation or ring structure closure between the chelating agent and the metal ion to be extracted [44]. In

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extraction by solvation, the extraction performs via the solvation of the species to be extracted into the organic phase. Oxygenated organic solvents, such as alcohols (C OH), ketones, ethers, and esters, show some basicity because of the lone pair of electrons on the oxygen atom, and they can therefore directly solvate protons and metal ions and bring about their extraction: for instance, the extraction of uranium with tributyl phosphate from nitric acid and the extraction of iron(III) with diethyl ether from hydrochloric acid [45]. The third class is extraction involving ion pair formation, which works with the formation of neutral uncharged species that, in turn, is extracted into the organic phase. In this class, an ion pair is formed between the complex of metal ions with high-molecular-weight amine and anionic species of mineral acids: as a good example, the extraction of scandium and uranium with trioctyl amine from mineral acids [46]. For synergic extraction, there is improvement in the extraction process on account of two extractants: the extraction/removal of uranium with the use of tributylphosphate (TBP) as well as 2thionyltrifluroacetone (TTA) [47]. In the solvent extraction system, three basic methods of liquid liquid extraction are classified on the bases of two parameters. One is the distribution ratio of the solute of interest, and the other is the separation factors of the interfering materials. These methods are classified three ways on the basis of the distribution ratio: (1) batch extraction process, (2) continuous extraction process, and (3) countercurrent extractions process. Batch extraction is the most commonly used method compared to the other two methods. The method is used in small-scale processes in chemical laboratories and can be employed simply with a separatory funnel. Batch extraction is chosen on the basis of its large distribution ratio [48]. In continuous extraction, a constant flow of immiscible solvent is passed through the

solution, or a continuous counterflow of two phases occurs. This type of extraction is exactly applicable when the distribution ratio is comparatively small and operates on the same general principle [49]. In extraction by continuous countercurrent distribution, the separation is achieved by means of the density variance between the fluids in contact [50]. Significant factors that influence extraction efficiency for the separation or removal purposes is the high distribution ratio of the solute of interest between the two liquid phases. It is useful to use different techniques to improve the distribution ratio depending on the nature of the species to be extracted and the extraction system being used. Attaining high selectivity in an extraction method is also most important. Suitable solvent, acidity of an aqueous phase, stripping, use of masking agents, salting-out agents, variation of oxidation state, backwashing, synergic extraction, and use of organic acid media are the factors influencing extraction efficiency. Of all these factors, the selection of suitable solvent for a particular extraction procedure is the most important for effective separation. During the selection, various parameters such as solubility, boiling point/ the ease of stripping by chemical reagents, the degree of miscibility of the two phases, the relative specific gravities, viscosities, and tendency to form emulsion should be considered. For environmental considerations, the toxicity and the flammability of the solvent must be known. The formation of metal chelates and different organic molecules do not impose restrictions on the solvent; however, the general rules of solubility are applied [51]. Moreover, solvent selection is greatly dependent on the proposed standard methods and on environment, health, and safety assessment checks. Millions of liters of organic solvents are used each year in analytical laboratories, posing a potential risk to human health and

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7.4 Preparation of supramolecular solvents

contributing significantly to the production of hazardous waste, constituting an important source of volatile substances and accounting for the emission of organic compounds (VOC). Around 26 commonly used pure organic solvents are reported in the literature [52]. On the whole, greater scores were calculated for formaldehyde, dioxane, formic acid, acetonitrile, and acetic acid. To minimize the consumption of organic solvents in laboratories, the use of more environmentally friendly sample processes in analytical methods is encouraged around the globe. Strategies involving the use of auxiliary energies and thus miniaturization have been widely accepted over the past few decades. In this context, many developments have also been carried out toward finding other substitutional solvents like ionic liquids (ILs), supercritical fluids, and SUPRASs. SUPRASs have been known as excellent extraction agents in the analytical process for a long time. In addition to their outstanding characteristics of solubilizing a large number of polar/nonpolar samples with less solvent by volume, they can be prepared at minimal cost. Although little effort has been made to manipulate novel solvents and to explain their structure, significant developments have been made so far in the expansion of the new formats and in detecting different systems [53]. SUPRASs are mainly based on nanostructured liquids and readily form through aqueous or hydro-organic amphiphilic solutions derived from a self-assembly procedure called coacervation. Amphiphiles are studied either as synthetic/natural, nonionic, or ionic/zwitterionic surfactants or as the source of an agent that triggers self-assembly, frequently with variation either in temperature or in pH of the solution or by the addition of a salt/nonsolvent for the amphiphile [24]. The self-assembly procedure involves the formation of oily precipitates that modify into aggregates and then form a combination of

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discrete droplets. The concentrations of these combined droplets are unlike those of the bulk solution and are partitioned into a new and separate liquid phase called SUPRAS. Amphiphiles present in SUPRAS are very high in concentration, in the range of 0.1 1 mg μL21, while the equilibrium solution with SUPRAS has amphiphiles in a monomeric state at the critical concentration within the aggregation. SUPRASs exhibit two excellent properties that have made them excellent substitution organic solvents in analytical methods for extractions. The first is the existence of regions or sections of dissimilar polarity present in supramolecular aggregates, which have superb properties for the solvation of a variable range of organic and inorganic compounds. As far as binding sites are considered, this feature makes for an ideal ground for the magnification of the solutes binding; this is the other benefit linked with SUPRAS. Additionally, SUPRASs are prepared according to synthetic procedures that everyone can perform; amphiphiles are naturally universal, and synthetic chemistry gives them boundaries, making them easily manageable. The properties of solvents are adjustable by changing either the hydrophobic end or the polar head group of the amphiphilic, and SUPRASs are safe, in that they are nonvolatile and nonflammable, and, as a result, more environment friendly.

7.4 Preparation of supramolecular solvents This part of the chapter illustrates SUPRASs’ basic structure, sequential assembly, procedures, and various applications in development and uses, as published in the literature so far. SUPRASs are composed of compounds containing both lipophilic and hydrophilic properties, called amphiphiles, arranged by selfassembly through a sequential process taking

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place on two levels (i.e., molecular and nano). In the assembly that organizes into structures, initially three-dimensional aggregates of amphiphiles form in a colloidal solution containing aqueous or vesicles or reverse micelles, above a critical aggregation concentration (cac) (Fig. 7.4). These self-assemble nanostructures gather in greater aggregates. However, in the single-layer vesicle system, water micelles invert the micellar form of these structures and separate them from the massive colloidal dispersion or solution into a new liquid phase, termed the supramolecular solvent, at the stage when the amphiphiles exceed a certain concentration, commonly through the event called coacervation. SUPRASs consist of amphiphile concentrates and the immiscible solvent (commonly water) from which they are formed, regardless of the solvent, which is considered the greater part of SUPRASs and establishes the uninterrupted level where the supramolecular formation disperses [54]. The equilibrium solution containing SUPRAS carries monomers of amphiphiles at the cac. Aggregate growth toward coacervation involves reducing the head group head group repulsions that stop aggregation in the first self-assembly process. This step totally

depends on the particular system under process. The free energy cost of bringing the polar heads together is much smaller when the head group is uncharged than when it is charged. Aggregate growth in ionic systems can be promoted by adding a cosurfactant with a small head group, an electrolyte, or an amphiphilic counterion, as well as by a pH change. In nonionic systems, one very effective way to promote aggregate growth is to lower the number of solvent molecules available for solvation, which can be achieved by modifying the temperature or by adding a poor solvent for the aggregate to be coacervated [55]. These solvents are well known to the analytical community and have been used for many years in extraction processes under different names (e.g., cloud-point technique, coacervates). The use of the term “SUPRAS” has been encouraged because it places greater emphasis on the solvent character of SUPRASs, differentiates them from molecular and ionic solvents, considers the noncovalent interactions through which molecules are held together in the solvent, and takes into account the selfassembly processes through which they are formed.

FIGURE 7.4

Schematic illustration for synthesis of SUPRASs following self-assembly process, also showing some coacervate droplets (aqueous micelles, reveres micelles, vesicles), created during formation of SUPRASs.

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7.5 Formation mechanism of SUPRAS phase

This method is considered environmentally friendly, and, because of the use of small amounts of solvent, it is cheap (e.g., tetrahydrofuran [THF]). The entire process requires approximately 15 20 min to complete, and thus fewer sample-handling steps shorten the risk of contamination. The schematic in Fig. 7.4 demonstrates the basic composition of SUPRASs through two primary components, water and amphiphiles, orderly organized in structures. Additionally, the source/agent used to originate liquid liquid phase separation (e.g., amphiphilic counterions, electrolytes, and a water-miscible solvent) are additional parts involved in SUPRAS formation. The amount of SUPRAS received through colloidal formation from aggregates of the supramolecular assembly is linearly propositional to the amount of amphiphiles in the bulky solution. This direct/linear proposition shows that the arrangement of SUPRAS remains unchanged, keeping other variables constant. Nevertheless, the composition of some SUPRASs changes with surfactant concentration. For instance, the water content of SUPRASs varies from 80%B70% as obtained by Triton X-114 nonionic micelles, compared to 1%B3% with Triton X-114 (@ 35 C). The amphiphiles concentration present in the solvent mainly depends on their structure and operating conditions, the driving force of phase separation. Concentrations levels of 0.2, 0.25B0.75, 1, and 0.09 mg μL21 have been set for SUPRASs derived from the aqueous anionic micelles of sodium dodecyl sulfate (SDS), the reverse micelles and vesicles of alkylcarboxylic acids, and the aqueous nonionic micelles of Triton X-114, respectively. Maximum amphiphile concentration and thus a huge number of available binding poles are a promising feature of SUPRASs for analytical extractions with high extraction efficiencies and concentration factors. An application has been described of the extraction of cationic surfactants (alkylbenzyldimethyl, alkyltrimethylammonium, and

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dialkyldimethyl) from sewage sludge. These compounds have a high retention in the negatively charged organic materials in sludge. The successful extraction of organic solvents takes a week, but researchers have managed to complete the extraction in 1 h, using dodecylsulfonate-based SUPRAS, with the percentages of recovery ranging from 91% to about 100% [56]. For veterinary drug extraction, octanolbased SUPRAs (oxolinix acid and flumequine acid) in fish samples are another example where the percentage of recovery was between 99% and 102% [57]. For SUPRAs extractions, other solvents were used: decanoic acid in THF and H2O (for bisphenol A extraction in preserved foodstuff) [58], cetyltrimethylammonium bromide (for the extraction of an anionic dye called Orange II) [59], and Triton X-100 as well as sodium dodecanesulfonic acid and 4.2 M hydrochloric acid (HCl) (for vitamin E extraction from water samples) [53]. SUPRASs consisting of hexanoic acid to extract PFAS (per- and polyfluoroalkyl substances) from blood serum showed a recovery percentage between 75% and 89% for PFAS C6 to C14 [60].

7.5 Formation mechanism of SUPRAS phase This section provides information that shows how various parameters have a significant effect on SUPRAS formation. The aggregate formation constituting SUPRASs, results from the repulsion between the amphiphilic compound’s head groups. Generally, the cost of the free energy that organizes the polar heads collectively is lesser when there is no charge on the head group, unlike as in the charged head group. In the case of ionic amphiphiles, to start SUPRASs formation, cosurfactants are added with a

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lesser head group, or an amphiphilic counterion, or an electrolyte, or a pH change. However, in the other case of nonionic systems, the most useful approach is to initiate aggregate formation by reducing the amount of solvent molecules present for solvation. This can be done by changing the temperature level or by adding a poor quality solvent for the aggregate formation to be coacervated [61]. In addition, SUPRAS formation from ionic amphiphiles can also be accelerated with the addition of cosurfactants such as long-chain alcohols. However, in the case of the smaller repulsion forces of the overhead group, transition toward lamellar phase occurs in the place of supramolecular aggregates formation [62]. The effective filtering of long-chain electrostatic linkages can also be achieved by increasing the concentrations of the electrolyte. So the larger the nonpolar chain is, the smaller the amount will be of the salt needed for aggregate formation. For oppositely charged aqueous mixtures of surfactants, the formation of supramolecular aggregates starts itself when the two types of amphiphiles have a stronger attraction than that required for stable micelle formation in solution; a lesser attraction than that leads to precipitation as well [63]. An increase in salt concentration will decrease the oppositely charged surfactants’ electrostatic attraction and promote supramolecular aggregate formation. Another approach to reduce ionic head group repulsion is the accumulation of an amphiphilic counterion (such as sodium salicylate C7H5NaO3 to hexadecyl tetramethyl ammonium bromide C4H12BrN or tetrabutyl ammonium C17H36F3NO3S to dodecylsulfate C12H25O4S). One more option is to make the pH value of the solution lesser than the pKa of the amphiphilic ionic group, used to offer SUPRASs formation using anionic surfactants such as alkyl sulfates, sulfoccinates, and sulfonates, but the big problem associated is the requirement of the high hydrochloric acid HCl such as 2 3 M).

SUPRASs can also be obtained by raising the temperature of the solution higher than the cloud point, using nonionic surfactants. The temperature increase causes the removal of some water hydration from the polar groups of the amphiphilic structure; as a result, there are the reduction per head group area and an increase in aggregate interaction. This gives increase in the growth of aggregates formation and thus liquid phase separation occurs. Formation of the SUPRAS from zwitterionic amphiphiles takes place at the solution’s lower temperature [64]. As the zwitterionic head groups are highly polar in nature, so the high electrostatic interactions can play a major role in intra- and intermolecular aggregate interactions. Although these electrostatic attractions have a limited range and their effects are strongly different from those of the ionic surfactants, a less active solvent—that is, a poor solvent for the amphiphilic structure, which is solvation solvent miscible—can achieve fractional elimination of the solvent molecules present for solvation of the nonionic amphiphiles. This amphiphile polar group fractional desolvation will lead to the formation SUPRAS. The phase separation of reverse micelles of alkylcarboxylic acid in THF, favored by the addition of water [54]. According to the general rule, the environmental parameter needed to achieve phase splitting/separation is the factor of the length of the hydrocarbon chain of the amphiphile. Therefore, for any homologous chain of polyoxyethylene nonionic surfactants, the temperature required for phase splitting/separation is inversely propositional to the total carbon atoms present in the hydrocarbon chain. In general, for two nonionic surfactants aqueous phase mixtures, the cloud point values are intermediate between the two, while aqueous mixtures of nonionic and ionic surfactants have cloud point values that are greater than those of pure nonionic surfactants. In the same way, the water content needed for liquid phase

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7.7 Supramolecular solvents in separation and preconcentration methods

separation in the case of reverse micelles of alkylcarboxylic acids depends on the hydrocarbon chain length of the amphiphile. The shorter the nonpolar chain is, the larger the water amount will be to form the SUPRAS. SUPRASs, which are essentially immiscible in water, can be formed on two scales, molecular and nano, by progressive self-assembly amphiphilic molecules. The first is beyond the critical aggregation concentration; the amphiphilic molecular assembly is self-arranged in the solution, and the nanostructures formation takes place (i.e., reverse or aqueous micelles, vesicles) after that. Under the action of an inducing agent (i.e., pH, electrolyte, temperature, a nonsolvent for the surfactants), these structures assemble automatically; then a desired surfactant-rich phase, in the form of the supramolecular solvent, separates from the bulk solution [65].

7.6 Components of supramolecular solvents Supramolecular alkanol solvents have been proven to exhibit the properties of restricted access liquids [27]. The value of restricted access materials (RAMs) containing these nanostructured solvents is increasing because they have the ability to clean liquid and solid samples with combined analyte enrichment. In the self-assembly process in THF:water solution, inverted hexagonal aggregates of alkanols are composed, and a superficial hydrophobic phase is formed by the hydrocarbon chains stretched and enclosed by caries of THF. The dimension can be customized by adjusting the THF:water ratio for alkanol selfassembly. SUPRASs offer two microenvironments for solubilizing a huge polarity of analytes. THF and alkanols induce the exclusion of proteins by their precipitation, whereas polysaccharides

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and humic acids, due to size exclusion, do not integrate into the internal aqueous cavities. Because of these properties, the application of RAM is proposed for samples other than body fluids, like estrogenic disruptors in sediments and carcinogenic chlorophenols in natural water samples [66].

7.7 Supramolecular solvents in separation and preconcentration methods In the past few years, enormous research around the world has been devoted to supramolecular chemistry in analytical methods, and it is predicted that it can play a unique and powerful role in analytical procedures as an excellent extractant, so much so that this emerging cross-disciplinary field of chemistry has been acknowledged and entitled supramolecular analytical chemistry. Studies in the literature have mentioned crown ethers and calixarenes as two extensively used host molecules for solvent extraction in chromatographic separation, extractive spectrophotometry, and emission spectroscopy of metals [15]. Host guest association in supramolecular system can be easily adjusted simply by applying a variable solvent system and modifying the demanded solvation properties. Hence, the solvation properties are important characteristics for the supramolecular solutes being able to affect the thermodynamics of any complex formation. In this way, supramolecular analytical chemistry illustrates that these mostly used host molecules, crown ethers and calixarenes, play the most prominent part as solvents in supramolecular recognition. According to the supramolecular mechanism, the system with a host and a guest interacts with solvent molecules through different types of noncovalent (weak) interactions. The process effectively involves mutual interaction between host and guest molecules and between their counterparts to form

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supramolecular complexation, which is controlled thermodynamically. Normally polar solvents such as water, alcohols, amides, and the like are followed by the self-organization process, although slightly less polar solvents, such as haloalkanes, hydrocarbons, and the like, undergo nanostructuring as selforganized solvents and arrange weak supramolecular complexation. Given the patterns established by the surfactants for organic bodies extraction, researchers have paid more attention to SUPRASs, hemimicelles, and micelles over the past few years [67]. SUPRAS solvents are well acknowledged by analytical researchers and have been used in extraction processes for many years under different names. SUPRASs have become more appreciated and differentiated from regular molecular and ionic solvents in the cloud-point technique [54]. SUPRAS solvents were more encouraged due to their solvent characteristics and tailorable solvent features. Due to the exceptional behavior of SUPRAS for effective solutes solubilization in a huge range of polarity, they are well acknowledged in applications of environmental, food, and biological samples for metals and organic compounds analytical extraction. SUPRASs are particularly suitable for multiresidue analysis. The key factors and analytical features of extraction techniques based on SUPRAS and of surfactant-mediated extraction techniques have been recognized and mentioned in several reviews [16,53,68 75]. In this context, a highly promising area where the application of SUPRASs has been scarcely exploited is in industrial wastewaters treatment. A lot of interesting research has been done in this direction [75 77]. Two general procedures for SUPRAS-based analytical extractions processes are used: in situ and ex situ solvent synthesis methods. Both approaches have been broadly described in different studies [16,24,61]. However, extractions in liquid samples are always carried out

using the former approach due to the reversible nature of SUPRAS. In situ formation of the SUPRAS in an aqueous sample having both the amphiphile and operational environmental conditions required for coacervation is still the most popular format for SUPRAS-based extractions. During the procedure, the extraction of analytes generally increases with stirring, and centrifugation is used to accelerate the liquid liquid separation phase. Then the whole extract or an aliquot of SUPRAS is removed for the analysis of the crude or diluted organic solvent extract. For the recovery of the SUPRAS phase that is usually heavier than the respective aqueous phases, simply cool down the sample tube after centrifugation. In this way, the SUPRAS is left in the tube to accelerate viscosity, and finally the supernatant solution is taken out through decantation. Whole aqueous phase removal is simply done through evaporation under the effect of nitrogen stream. It is been found that most nonionic and zwitterionic surfactant-based solvents are heavier than aqueous media or samples. It has also been mentioned that alkylethoxylated surfactants with less than a 12 oxyethylene number have formed lighter surfactant-rich phases than aqueous phases in the presence of salts at elevated temperatures, such as [NaCl] 5 0.8 at 80 C. Similarly, SUPRAS consisting of cationic or anionic micelle solutions and alkanols, alkylcarboxylic acids or alkylcarboxylic acidalkylcarboxylate tetrabutylammonium also have a lower density compared to water and therefore remain at the solution top side, which facilitates extraction. Typically, for the calculation of the SUPRAS volume generated in situ in cylindrical centrifuge tubes, we use πr2h, where r represents the tube radius, and h corresponds to the solvent height in the tube. The exact value of h can be obtained with a specially designed narrow-neck centrifuge tubes and a digital caliper.

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7.7 Supramolecular solvents in separation and preconcentration methods

Cylindrical glass centrifuge tubes for intensive use with a rounded bottom are used for the manufacture of these centrifuge tubes. Weighing is another good option for accurate calculation of solvent volume. However, direct volume measurement with a graduated/calibrated syringe is typically complicated due to the viscosity of SUPRAS solvents. For the nonionic surfactants, the viscosity is studied as the surfactant concentration and the temperaturedependent factor. For instance, as the surfactant concentration increases from 300 to 630 mM, the viscosity of the Triton X-114 based SUPRAS also increases from 120 to 200 cP. On the other hand, when the temperature exceeds 30 C 50 C, a decrease in the solution viscosity (around 80%) with 630 mM Triton X114 was found. This decrease is due to the reduction in the length of the micelles forming the Triton X-114 based SUPRAS. SUPRAS application in Single-Drop Microextraction (SDME) and hollow fiber liquid phase microextraction method (HF-LPME) has also been recommended in various research works [78 82]. These solvents have a better range of applicability of SDME and HFLPME to regions where conventional waterimmiscible organic solvents are not useable/ suitable, especially with liquid chromatography (LC), for the separation of analytes or when polar or ionic organic compounds extraction is under study. In addition, SUPRAS droplets formed at the tip of the needle of formal microsyringes depend on the type of intermediate molecular forces, established between the surfactant head poles, to form supramolecular combinations or aggregates; additionally, strong H-bond interfaces form essentially spherical drops. Thus, a SUPRAS composed of alkylcarboxylic acid tetraalkylammonium alkyl carboxylate is the best choice for SDME applications, and the suitability of vesicles of decanoic acid tetrabutylammonium decanoate for this purpose has been described in the literature [16]. HF-LPME has some applications

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with vesicle-based solvents. In these procedures, the solvent is used to impregnate the pores and occupy the hollow fiber. The modern trend in extractions technique based on SUPRASs is the extraction of organic species and metals from liquid samples through automation. Fang and coauthors introduced, for the first time, the online integration of nonionic surfactant-based SUPRASs to flow injection analysis (FIA). Achieving both the control of the process of coacervation and the split-up of the surfactant-rich phase from the aqueous phase was technically done by stirring the sample mixture or the analyte solution and the surfactant with an suitable release agent, along with the recovery column packed with cotton analyte having aggregates of surfactants, respectively. Afterward, any organic solvent is used to elute these trapped analytes. The researchers have used this approach for coproporphyrin determination during the pretreatment of urine samples by applying the chemiluminescence reaction to peroxyoxalate. The automated extraction/FIA SUPRAS methodology has also been adopted by other researchers for the evaluation of hydrocarbons (such as polycyclic aromatic hydrocarbons) by LC. However, enrichment of the factors in these works was found to be lower than those of the theoretical calculations, which could be due to the dispersing action of the analytes in the solvent, which was used for their elution from the assembled column. To overcome the limitations associated with the SUPRAS online extraction/FIA methodology, some strategies have recently been introduced, although the dispersion or dilution of a preconcentrated group of analytes in the FIA variety has eluded the determination of serum bilirubin by estimating the chemiluminescence signal inside the collection column. The SUPRAS-based evaluation of liquid food contaminants is proposed in different works, such as fluorescence detection and determination of ochratoxin A in wines prior

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to quantification by LC, though an in situ scheme has been reported in a study [53]. On the other hand, SUPRAS-based extraction is suggested for solid samples, both in situ and ex situ synthesis. In situ synthesis involves the extraction of solutes with the solution at equilibrium, so that the following three phases are always obtained after extraction and separation by centrifugation: (1) the solid residue, (2) the equilibrium solution, (3) the SUPRAS containing the solutes. The two main roles that the equilibrium solution can play are studied as the main advantage of this approach: humidification of the sample and trapping polar interference. However, it is not suggested for use in the removal of polar solutes as they can become part of or distribute into the SUPRAS and the intermediate phase. From the operational point of view, the ex situ synthesis has proved more practical since it can simultaneously handle the synthesis of a high volume of SUPRAS (typically 2030 samples), and the polar analytes are also well extracted. Special care is recommended for wet samples to avoid wasting SUPRASs for sample humidification. A typical pattern of contaminant extraction in agrifood samples, such as cereals containing fusarium toxins, and prior to detection by LC-MS/MS, and some representative uses of SUPRAS that synthesized different strategies have been illustrated [24]. SUPRAS are mainly used in combination with LC, associated with visible UV detection, fluorescence, and mass spectrometry. This means that the extracts of the analytes are generally introduced straight into the LC system where the nanostructures have been taken apart in the mobile phase (hydro-organic mobile phase) and where the surfactant monomers are received without interfering with the chromatographic role of solutes. For mobile phases with higher water content, supramolecular aggregates may take longer (slowly disassemble) through the chromatographic configuration, thus providing a solute

pseudophase where they can be distributed. The separation of analytes can sometimes be favored by introducing an additional retention mechanism; however, this generally impairs the resolution, and the extract must be diluted with an organic solvent before being injected into the chromatograph. With regard to detection systems, SUPRAS consisting of nonaromatic amphiphiles are preferred for the detection of UVV and fluorescence, and, as a rule, the amphiphiles constituting SUPRAS are sent directly to the waste after the chromatographic separation (i.e., only the ion source impurities or the loss of ionization efficiency and detector sensitivity are avoided). The temperature-induced SUPRAS, consisting of polyethoxylated nonionic surfactants, has been widely used in extraction processes because it has long been the only type of SUPRAS known to the analytical community. Triton X-114 continues to be the preferred nonionic surfactant, given its lower cloud point (CP) relative to other polyethoxylated surfactants. More applications use surfactant concentrations ranging from 0.12%, although the quantitative extraction of bioactive compounds in biological samples often requires a much higher concentration (310%). The use of mixtures of nonionic and ionic surfactants promotes the extraction of opposite-charge compounds. Water-induced SUPRAS, composed of carboxylic acids or alkanols, marked a turning point in this field. The great attraction of these SUPRAS lies in the amphiphiles present in the solvent, at high concentrations (up to 0.75 mg μL21), which gives high concentration factors (e.g., 569 for the bisphenols and their equivalents, diglycidyl ethers, in the waters of the environment). SUPRAS ratios (1:1 solid sample) 79. Moreover, in mixed mechanisms, they provide the solubilization of solutes, that is, hydrogen bond, polar and diffusion, which offers advantages in terms of recovery rates

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7.7 Supramolecular solvents in separation and preconcentration methods

greater than 85% in multiresidue processes and in reductions of extraction times) and their potential as RAMs (i.e., they individually subtract the carbohydrates and proteins from the physical and chemical extraction, performing the extraction and cleaning of the samples in one step). With regard to acid-based SUPRAS, a handicap for their current application results from the robust (experimental) environmental conditions required for the coacervation process. However, such undesirable conditions have been declared vital for the success of the process with regard to highly critical environmental solid samples such as sludge, soils, and sediments. The acid environment has therefore shown that the desorption of cationic surfactants in sludge was probably due to an ion exchange mechanism. SUPRAS coacervation induced by a counterion generally requires the addition of a high concentration of inorganic salts (e.g., 400 g L21 NaCl for cetrimide) and the existence of any cosurfactant limiting their applicability. On the other hand, the conditions are different (coacervation is mild) for SUPRAS induced by amphiphilic counterions. For example, coacervation took place with vesicular mixtures of carboxylic acid carboxylates under tetrabutylammonium salts. These SUPRAS have several advantages for extraction processes, such as the possibility of establishing different types of interactions with analytes (i.e., hydrophobic and ionic interactions, hydrogen bonds, and formation mixed aggregates); the possibility of reaching high preconcentration factors (e.g., between 18 and 1334 for decanoic concentrations of 4% to 0.025%, respectively); and compatibility with LC, UV, and MS detection and high extraction efficiency. So far, the application of SUPRAS to the purification of water has been exclusively based on SUPRAS induced by temperature [75]. Interesting applications have been reported on the removal of dyes, phenols, oils, and so on [74,76,77,83 86]. In addition,

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SUPRASs exhibit exceptional physicochemical properties that make them more attractive and useful for replacing organic solvents in analytical extraction processes. The essential intrinsic properties of SUPRAS are as follows: (1) the use of synthetic procedures that depend on self-assembly within everyone’s approach; (2) easy accessibility to the natural ubiquity of amphiphiles and applicability of the synthetic chemistry that makes them; (3) solvent properties that are adjustable by means of the hydrophobic/polar group of amphiphiles; (4) the presence of different polarity sections in supramolecular aggregates with excellent solvation properties for a variety of organic and inorganic compounds; (5) the presence of several ligands among the multiple polar groups in a supramolecular aggregate, providing an ideal platform for amplification of solute binding; (6) safe processes due to the nonvolatile and inflammable nature of supramolecular aggregates, which allow the implementation of a safe and sound lab environment. SUPRASs (Fig. 7.5), water-immiscible liquids have been widely used in extraction and preconcentration procedures due to their great ability to extract various types of substances, including organic and inorganic species of amphiphile providing, (1) a supramolecular assembly, micelles or vesicles, in homogeneous solution and (2) a coacervation producing water-immiscible liquids (or SUPRAS phase) separated from the bulk solution. Aggregation of the amphiphilic molecules is the first self-assembly process in supramolecular solvent formation; it occurs autonomously and spontaneously when the amphiphilic concentration is greater than the critical aggregation concentration (cac). The second step, liquid liquid separation, requires the action of external factors or coacervation agents such as amphiphilic counterions, electrolytes, temperature, and pH. The most well-known SUPRAS extraction using surfactants is called CPE

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FIGURE

7.5 Sample treat-

ment process.

(cloud-point extraction) when coacervation is obtained from neutrally charged surfactants (nonionic or zwitterionic) or coacervative extraction (CAE). Although these techniques are simple, cost-effective, and fast and reduce the consumption of organic solvent, chromatography has certain limits. Due to the viscosity and low volatility of the SUPRAS phase, the use of these methods in gas chromatography (GC) is limited. In CPE, phase separation is obtained from a nonionic surfactant by increasing the temperature of the solution, which can be problematic for thermolabile analytes, while pH-induced ionic surfactant requires dilution and adjustment. The pH is to be set higher in order to be compatible with measurement solutions for chromatographic systems. The major advantage of SUPRAS is their high solubility capacity for a variety of solutes. These solvents always provide a hydrophobic microenvironment in the hydrocarbon region of the ordered aggregates; they therefore provide excellent nonpolar extraction compounds, regardless of the type of amphiphile composing them. Extraction of nonpolar compounds is governed by octanol-water constants, and SUPRAS behave in the same manner as organic solvents in these applications. Forces leading to the extraction of apolar compounds mainly include dispersive, dipole dipole, and induced dipole interactions.

The nature of polar groups in ordered structures determines the type of polar compounds that can be extracted by SUPRAS. So far, the polar groups most frequently used in analytical applications include polyethylene oxides, carboxylic acids, sulfates, sulfonates, carboxylates, and ammonium and pyridinium ions. The binding interactions involved in the extraction of polar compounds include primarily ionic, hydrogen bond, π-cation, and π π bonds. Hydrogen bonding is an extremely efficient retention mechanism for polar compounds. On the other hand, when the surfactant contains a benzene ring, electrophilic interactions occur via delocalized electrons in π-orbitals. These delocalized electrons interact with conjugated groups such as aromatic rings or double/triple bonds. Differences in the molecular structures of surfactants within a structural group may also result in different solubilization capabilities of SUPRASs. One of the major properties of SUPRAS is their ability to extract amphiphilic compounds (e.g., surfactants, drugs, and certain pesticides) by the formation of aggregates mixed with the amphiphiles constituting the ordered aggregates. Both non-polar and polar interactions govern the formation of mixed aggregates, with the interactions strengthened with mixtures of amphiphiles with the same polar (e.g., nonionic to nonionic) or opposite charge (e.g., anionic cationic) and with mixtures of nonionic

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7.9 Thermodynamics

polar groups (cationic and nonionic anionic) with intermediate binding energies. Exceptional applications based on the formation of mixed aggregates have been developed. The solute extraction efficiencies depend on the number of binding sites and the binding energies (ionic bonds . hydrogen . dipole dipole . dipolar dipole-induced . dispersion) in SUPRAs. On the other hand, as for the actual concentration, these factors depend on the recovery rate and sample/SUPRAs volume ratios. The concentration of amphiphiles in the solvent therefore becomes a key factor.

7.8 Efficiency The two wonderful properties of SUPRAS that make them attractive and suitable for replacing organic solvents in analytical extractions are (1) their extraordinary structure and (2)—their second most important characteristic—the resistance of supramolecular solvent amphiphiles. The marvelous structure of the ordered aggregates that create them consists of sections of different polarities that provide different types of interactions for the analytes and that offer excellent solvation properties for a variety of organic and inorganic compounds. Because the type of interaction can be modified by changing the polar group or hydrophobicity of the surfactant, we can model most extractants for particular applications because the amphiphiles are of a universal nature. Morover the existence of a large number of binding sites constitutes an ideal platform for amplification of the solute bond, considering that, due to the high concentration of supramolecular solvent amphiphiles, the binding sites may comprise typically 0.1 1 mg L21 [16]. As stated earlier, the attractive features that boost SUPRAS efficiency are that they form through synthetic procedures within the reach of all, amphiphiles are ubiquitous in nature,

and synthetic chemistry makes them easily accessible. Self-assembly is ubiquitous in nature and often occurs in many hierarchies simultaneously to generate functional systems. For example, the proteins constituting the shells of the tobacco mosaic virus must fall back into the correct tertiary protein structure before they can be organized around a strand of template RNA. All these processes are mediated by noncovalent forces that guide the formation of secondary structural elements on the lowest hierarchy level. These form the tertiary structure at the next level, which displays the binding sites required for virus assembly from 2131 building blocks as programmed at the highest level. Other examples of hierarchical selfassembly are multienzyme complexes, the formation of cell membranes within all receivers, ion channels or other functional entities incorporated therein, or molecular motors such as ATP synthase. Self-assembly is therefore an effective strategy to create complexity. The properties of accessible solvents can be adjusted by varying the hydrophobic or polar group of the amphiphile, and, since SUPRAS are nonvolatile and nonflammable, this allows the implementation of safer processes. This property makes it possible to obtain extraordinarily efficient yields by means of only the small volume of extraction agent essential for microextractions [87].

7.9 Thermodynamics Supramolecular interactions govern the process with high precision. Indeed noncovalent bonds generally carry less energy and so do not require galvanizing power for training. According to the Arrhenius equation, it is clear that, irrespective of the chemistry behind covalent bonding, the degree of bond formation is not proportional to the temperature increase. However, the chemical equilibrium equations

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indicate that the small binding energy will cause the supramolecular complexes to rupture at higher temperatures. On the other hand, low temperature is also not favorable for supramolecular processes. Supramolecular chemistry requires molecular deformations into thermodynamically unfavorable conformations (such as rotaxanes’ sliding synthesis) and may include some covalent chemistry extending from supramolecularity. Moreover, serial systems (e.g., molecular mechanics) actively use the nature of supramolecular chemistry, and lowering the system temperature would diminish these processes. Thus, for effective design and control in supramolecular chemistry, thermodynamics is an important study and plays a viable role. The warm-blooded biological system, which can terminate functioning completely outside very narrow temperature limits, is considered an outstanding example.

For stable operation, the molecular environment involving and surrounding the supramolecular system is also of paramount importance. Various solvents possess stronger characteristics, like strong hydrogen bonding, electrostatic properties, and charge-transfer capabilities, and quickly form complex equilibria within the system or even completely break up the complexes. That is why the choice of solvent can be critical.

applications, for the separation and preconcentration of organic and inorganic species from various samples, such as in a green solvent system. As mentioned earlier, the CPE with surfactants is a commonly used SUPRAS extraction method, in which the coacervation phenomenon takes place from neutral surfactants like zwitterionic or nonionic or ionic amphiphiles that can initiate CAE. Although these practices are cheap, fast, and simple and use a small amount of organic solvent, they do have limitations for chromatographic processes. While these procedures are restricted to use with the GCs due to the low volatility and low visibility of the SUPRAS phase, in CPE, by increasing the temperature of the solution, a phase separation of the nonionic surfactant is obtained, which can be troublesome for the thermally unstable analytes. The pH-induced ionic surfactant requires pH adjustment and significant dilution [88]. The discovery of SUPRASs based on alkylcarboxylic acid has shown that the properties of restricted access liquids enhance the number of available solvent-based RAMs. These solvents exhibit restricted access properties and work for both the cleanup of complex solid samples and analyte extraction. Recently, it has been shown that alkanol-based SUPRASs also act as restricted access liquids. These solvents, having nanostructures, multiply the range of application of RAMs because they have the ability to combine the analyte enrichment and cleanup of both liquid and solid samples [66].

7.11 Types of SUPRAS molecular extraction

7.12 Supramolecular solvents in liquid liquid microextraction

This segment gives detailed knowledge about distinct types of a SUPRAS’s molecular extraction compatibility with different analytical techniques and combinational use with nanomaterials (automation), in numerous

Supramolecular solvent microextraction, combined with high-performance liquid chromatography (HPLC), has been proven to be an easy and environmentally friendly sample preconcentration method. SUPRAS justifies the

7.10 Environment

New Generation Green Solvents for Separation and Preconcentration

7.14 Ultrasonic-assisted supramolecular solvent extraction

conditions of green and feasible analytical methods. Under mild conditions, the surfactant works for extraction combining without organic solvent, acid addition, and heating [88]. The HF-LPME based on SUPRASs, is efficient, recent, and environmentally friendly for the extraction of benzodiazepine drugs. According to the literature, a coacervation of aqueous vesicles of decanoic acid is formed in the presence of supramolecular solvent of tetrabutylammonium (Bu4N 1 ). A supramolecular solvent is impregnated in the pores of the wall and is also wrapped in the polypropylene hollow fiber porous membrane for the extraction of benzodiazepine from aqueous samples. Hydrogen, hydrophobic, and n-cation interactions were recognized as the driving forces, responsible for extraction between analytes and vesicular aggregates. For the separation and drug evaluation process, high-performance liquid chromatography, combined with photodiode array detection (HPLC-DAD), was used [78].

7.13 Integrated use of supramolecular solvents with nanomaterials The SUPRAS-based microextraction phase separation process requires a time-consuming centrifugation step. Further, when separating the vesicles from the aqueous solution, another difficulty in using centrifugation is its reducing productivity. For this, it was concluded from experiments that, when low quantities of decanoic acid is used, the amount of final collected phase will be ˂20 μL. For the removal of the extraction solvent, magnetic nanoparticles (MNPs) also eliminate the centrifugation step with increases in efficiency of the phase separation, which gives very high preconcentration factors, efficiency, and the reproducibility of the compounds. Automation of the method can be achieved simply when MNPs replace centrifugation for phase separation (a simple, fast, and inexpensive technique). Centrifugation and the

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addition of the tetrabutylammonium cation are replaced with the MNPs [89].

7.14 Ultrasonic-assisted supramolecular solvent extraction A new technique developed for the extraction of compounds from different matrices is ultrasonic (Fig. 7.6) emulsification microextraction, presented by Requeiro et al. [90]. A water-immiscible liquid SUPRAS, obtained from the explicit structure of their supramolecular assemblies, contains inverted micelle aggregates of nanometric dimensions circulated in a continuous phase with THF and water and bears extraordinarily beneficial properties. Any chemical or physical change is affected by ultrasonic irradiation due to the phenomenon of cavitation, in which microbubbles are produced in a liquid when a significant negative pressure is involved. It is broadly documented that in partitioning, that is, the separation and extraction processes, ultrasound plays a significant role in accelerating certain steps, for example, emulsification, homogenization, and mass transfer between immiscible phases.

FIGURE 7.6 Ultrasonic bath.

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FIGURE 7.7

7. Supramolecular solvents in separation and preconcentration of organic and inorganic species

Microwave.

7.15 Microwave-assisted supramolecular solvent extraction Control structures for use with supramolecular interactions have brought great innovations in the field of crystal engineering, chemistry, and biochemistry. Supramolecular structures are usually formulated from aminotriazines by hydrogen bonds. The importance of these secondary attractions has also been thoroughly studied. In this way, the complex formed as a result of the interaction between cyanuric acid and melamine has a stability and has been used to obtain solid-state polymers. Microwave-assisted organic synthesis (Fig. 7.7) is a method with great advantages—a major improvement in rotational speed, high productivity, and high speed. In a few cases, traditional heating reactions are different from those of stereo or regiochemical microwave-assisted heating. Advantages that are not achievable by conventional heating methods can be gained by microwave heating in a combinatorial chemistry approach, providing great efficiency and the maximum rate of synthesis of organic compounds [91].

7.16 Vortex assisted supramolecular solvent extraction A recent technique of LPME, developed by Assadi and collaborators in 2006, is called

microextraction of liquid-dispersed liquid (DLLME) [92]. The DLLME is centered on a ternary-component solvent scheme in which a dispersing solvent (a miscible organic solvent, such as methanol, acetone, acetonitrile, and the like) and an extraction agent (generally a nonorganic solvent, liquid, or ionic liquid) are injected rapidly into an aqueous sample. As a result, microdroplet turbids are formed. The fine microdroplets extract the analyte, which is then separated by centrifugation. However, the consumption of an additional organic solvent (disperser) is one of the main drawbacks of the DLLME because the partition coefficient of the hydrophobic analytes in the extraction solvent is generally reduced. Otherwise, to create or accelerate the process of emulsification, ultrasonic energy works in LPME techniques. During this process, the extraction solvent forms submicron droplets due to the large surface contact between the two immiscible phases, which results in a fast and efficient transfer of the analyte. However, due to analyte degradation and lack of uniformity in the transmission of ultrasonic energy into the sample, this process can create problems. The Psillakis research group discovered that vortex-assisted (Fig. 7.8) liquid liquid microextraction (VALLME) [93] eliminated these disadvantages. In this process, by dispersing a low-density organic extraction solvent directly into the aqueous phase (without the need for a dispersion solvent), enriched by vortexing, a mild emulsification process can be realized. Due to the smaller diffusion distance and larger surface area, the analytes are extracted more rapidly via the fine droplets. Centrifugation is normally performed for phase separation after a given extraction period. Yang et al. worked on the Psillakis methodology to increase the mass transfer of analytes from the aqueous phase to the organic phase by explaining vortex-enhanced surfactant-

New Generation Green Solvents for Separation and Preconcentration

7.17 Temperature-assisted supramolecular solvent extraction

FIGURE 7.8

Vortex mixer.

enhanced liquid liquid microextraction in which a surfactant is used as a “disperser.” However, this approach is more difficult than the old VALLME version because the surfactant monomers generally have low volatility and can therefore contaminate the inlet or stationary phases of the CG systems. The VALLME-based process offers significant advantages, including easy handling, simplicity, speed, cost-effectiveness, high enrichment capabilities, and limited consumption of organic solvent [94].

7.17 Temperature-assisted supramolecular solvent extraction Liquid liquid extraction (LLE) is the most widely used for sample preparation due to its ease and mobility. This procedure effectively

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decreases the detection limit because matrix interference is removed. Due to the fact that LLE is performed in batches to achieve low detection limits, certain weaknesses, such as the use of harmful organic solvents and the huge volumes of specimen sampling, may be time-consuming, costly, and toxic for the environment and surroundings (i.e., laboratories). Contamination flow (FI) systems offer some benefits because they use inert materials and are usually closed systems. Additional advantages are reduced discharge, a useful means of matrix adjustment, greater sampling rate, and the use of less sample material and reagent. RTILs (ionic liquids at room temperature), in combination with suitable complexing agents, have recently been discovered for the extraction of metal ions, in particular hydrophobic RTILs, which are used to extract weakly polar compounds from an aqueous solution. These solvents have been used in place of conventional organic solvents because of the remarkable properties of RTILs, that is, reduced or undetected volatility [95]. Thus, the direct (SDME) and headspace (HSME) modes in the SDME technique use RTILs based on hexafluorophosphates of 1-alkyl-3-methylimidazolium ([Cnmim] [PF6], n 5 4, 6, 8). However, when the stirring speed is increased, the drop is broken and air bubbles are formed, and its reproducibility is thus limited, and its use takes a long time. Therefore these methods are not widely used. Temperature-controlled ionic liquid dispersive liquid phase microextraction (TILDLME) and IL-DLLME based on ordinary molecular organic solvents as dispersive agents have been established as novel L L homogeneous microextraction techniques for ILs. Nevertheless, these methods have the same disadvantages as conventional LLE due to its operation in batch mode. As a result, RTILbased microextraction techniques operating in fully online mode have become a necessity. Recently, a new FI system for online TILDLME

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has been developed. The process was adjusted with initial vanadium chelation with a 2-(5bromo-2-pyridylazo) 2 5-diethylaminophenol (5-Br-PADAP) reagent quenched by TILDLME. In an ETAAS-coupled online system, formation, RTIL phase separation, and analyte extraction were performed for the determination of vanadium in environmental and biological samples [96].

7.18 Trends Sample pretreatment to extract analytes of interest in various kind of matrices is still of great importance and a big task, despite all the major developments in analytical instrumentation. Different problems emerge during sample preparation, including the complex nature of sample matrices and the analysis of trace levels, that do not match the analytical instrumentation used for direct analysis. To obtain a better separation and good enrichment, the cleaning and preparation of the analyte samples are carried out in order to make the analytes compatible with the analytical instruments. For sample preparation, conventional extraction and microextraction techniques have been widely implemented and carry their own advantages and weaknesses. For good extraction with cleaning efficiency, conventional extractions are useful but naturally sometimes exhaustive. Recently, the integration of conventional techniques and microextraction has come forward as a new trend. The techniques deal with sample preparation in groups, making it possible to introduce a new extraction procedure developed from the advantages of individual approaches, thus improving the enrichment and quality of the extraction analysis and performance by the separation of the analyte as well. These concepts were used by the author’s research group to develop a technique based

on RASs, namely supramolecular solventbased microextraction for the determination of lead and nickel in biological and environmental samples prior to analysis by flame atomic absorption spectrophotometer. They found the preconcentration approach to be simple, novel, and fast. Another research group, supervised by the author, used SUPRAs-assisted silver nanoparticles for the microextraction of zinc and iron from drugs using FAAS, showing a great ability to extract metals and sample cleanup.

7.19 Conclusion Supramolecular chemistry is today known to be a mature and highly dynamic field of chemistry. Researchers have successfully explored the extraordinary benefits of supramolecular design and its applications in various field of chemistry. Further, chemists in laboratories have achieved an amazing degree of control over the noncovalent bond and have acquired a growing knowledge about the training and characteristics of supramolecular entities, especially in analytical chemistry. Host guest chemistry and self-assembly are the two phenomena of supramolecular chemistry that have attracted great attraction for analytical separation. Amphiphiles for the synthesis of new SUPRASs have been studied for a variety of interactions and supramolecular sorbents. Further, self-assembly, being a discrete field of study, proposes a very general approach for high-capacity solvents and sorbents, as well as the ability to solubilize various kinds of solutes, making them the best option for multiresidue analysis. This option has proven suitable for the establishment of generic sample treatments and shows, with minor changes, flexibility in the different types of samples’ multiple analytes extraction.

New Generation Green Solvents for Separation and Preconcentration

References

Important progress related to SUPRAS, hemimicelles/admicelles, both theoretical and practical, has been frequently reported during the last decade. This extended the scope of SUPRAS systems in analytic extraction. Automation using a variety of schemes for extractions based on the supramolecular system is now possible but needs some improvements in this area. The flexibility of these systems in different extraction formats justify their cost. Important works have also contributed to the study of the compatibility of the supramolecular system with various separation and detection techniques. Surfactant elimination and back-extraction of analytes in aqueous/ organic solutions have been the most commonly reported studies so far. Extensive work has been devoted to applying supramolecular aggregates-based solvents and sorbents in analytical laboratories. The scientific world has to pay more attention to new structure designs and formations of supramolecular-based solvents/sorbents with explicit purposes and applications, so as to broaden their scope in analytical extractions techniques, methods validation supporting supramolecular extractions by interlaboratory research, and the establishment of automation and patterns that are more compatible with separation and detection techniques.

Acknowledgment I would like to express my deepest thanks to Prof. Dr. Mustafa Soylak, who provided me the opportunity, guidance, contribution, and encouragement. A special gratitude I give to my research scholars (Ammara Laila and Seema Nawaz), for their contribution in method development for supramolecular solvent-based microextractions. Further, special thanks go to my family, especially my wife Engg. Sana Balal, who provided stimulating suggestions and encouragement, helped me to coordinate this project, especially in writing this chapter.

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salt-free and salt-containing aqueous solutions, Langmuir 21 (7) (2005) 2713 2720. D. Lombardo, et al., Amphiphiles self-assembly: basic concepts and future perspectives of supramolecular approaches, Adv. Condens. Matter Phys. 2015 (2015). V. Carden˜osa, M.L. Lunar, S. Rubio, Generalized and rapid supramolecular solvent-based sample treatment for the determination of annatto in food, J. Chromatogr. A 1218 (50) (2011) 8996 9002. N. Caballero-Casero, et al., Nanostructured alkyl carboxylic acid-based restricted access solvents: application to the combined microextraction and cleanup of polycyclic aromatic hydrocarbons in mosses, Analytica Chim. acta 890 (2015) 124 133. S. Rubio, D. Pe´rez-Bendito, Supramolecular assemblies for extracting organic compounds, TrAC. Trends Anal. Chem. 22 (7) (2003) 470 485. A. Melnyk, J. Namie´snik, L. Wolska, Theory and recent applications of coacervate-based extraction techniques, TrAC. Trends Anal. Chem. 71 (2015) 282 292. I. Hagarova´, M. Urı´k, New approaches to the cloud point extraction: utilizable for separation and preconcentration of trace metals, Curr. Anal. Chem. 12 (2) (2016) 87 93. C.B. Ojeda, F.S. Rojas, Separation and preconcentration by a cloud point extraction procedure for determination of metals: an overview, Anal. Bioanal. Chem. 394 (3) (2009) 759 782. Md.A. Bezerra, M.A.Z. Arruda, S.L.C. Ferreira, Cloud point extraction as a procedure of separation and preconcentration for metal determination using spectroanalytical techniques: a review, Appl. Spectrosc. Rev. 40 (4) (2005) 269 299. M.F. Silva, E.S. Cerutti, L.D. Martinez, Coupling cloud point extraction to instrumental detection systems for metal analysis, Microchim. Acta 155 (3-4) (2006) 349. E.K. Paleologos, D.L. Giokas, M.I. Karayannis, Micelle-mediated separation and cloud-point extraction, TrAC. Trends Anal. Chem. 24 (5) (2005) 426 436. W.R. Melchert, F.R. Rocha, Cloud point extraction in flow-based systems, Rev. Anal. Chem. 35 (2) (2016) 41 52. C.D. Stalikas, Micelle-mediated extraction as a tool for separation and preconcentration in metal analysis, TrAC. Trends Anal. Chem. 21 (5) (2002) 343 355. E. Tatara, et al., Cloud point extraction of direct yellow, Environ. Sci. & Technol. 39 (9) (2005) 3110 3115. R. Melo, et al., Removal of reactive blue 19 using nonionic surfactant in cloud point extraction, Sep. Purif. Technol. 138 (2014) 71 76.

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[78] F. Rezaei, et al., Supramolecular solvent-based hollow fiber liquid phase microextraction of benzodiazepines, Analytica Chim. acta 804 (2013) 135 142. [79] J. An, et al., Non-conventional solvents in liquid phase microextraction and aqueous biphasic systems, J. Chromatogr. A 1500 (2017) 1 23. [80] F. Aydin, E. Yilmaz, M. Soylak, Supramolecular solvent-based dispersive liquid liquid microextraction of copper from water and hair samples, RSC Adv. 5 (50) (2015) 40422 40428. [81] P. Zohrabi, et al., Liquid-phase microextraction of organophosphorus pesticides using supramolecular solvent as a carrier for ferrofluid, Talanta 160 (2016) 340 346. [82] F. Rezaei, et al., Determination of diphenylamine residue in fruit samples by supercritical fluid extraction followed by vesicular based-supramolecular solvent microextraction, J. Supercrit. Fluids 100 (2015) 79 85. [83] B. Haddou, J.-P. Canselier, C. Gourdon, Use of cloud point extraction with ethoxylated surfactants for organic pollution removal, The Role of Colloidal Systems in Environmental Protection., Elsevier, 2014, pp. 97 142. [84] M. Purkait, et al., Cloud point extraction of toxic eosin dye using Triton X-100 as nonionic surfactant, Water Res. 39 (16) (2005) 3885 3890. [85] N. Pourreza, S. Elhami, Removal of malachite green from water samples by cloud point extraction using Triton X-100 as non-ionic surfactant, Environ. Chem. Lett. 8 (1) (2010) 53 57. [86] J. Chen, et al., Study of adsorption behavior of malachite green on polyethylene glycol micelles in cloud point extraction procedure, Coll. Surf. A. Physicochem. Eng. Asp. 345 (1-3) (2009) 231 236. [87] E. Mayans, et al., Effect of solvent choice on the selfassembly properties of a diphenylalanine amphiphile stabilized by an ion pair, Chem. Phys. Chem. 18 (14) (2017) 1888 1896.

[88] K. Seebunrueng, et al., Development of supramolecular solvent based microextraction prior to high performance liquid chromatography for simultaneous determination of phenols in environmental water, RSC Adv. 7 (79) (2017) 50143 50149. [89] M. Safari, et al., Magnetic nanoparticle assisted supramolecular solvent extraction of triazine herbicides prior to their determination by HPLC with UV detection, Microchim. Acta 183 (1) (2016) 203 210. [90] J. Regueiro, et al., Ultrasound-assisted emulsification microextraction of phenolic preservatives in water, Talanta 79 (5) (2009) 1387 1397. ´ . Dı´az-Ortiz, et al., Microwave-Assisted Synthesis [91] A and Dynamic Behaviour of N2, N4, N6-Tris (1H-pyrazolyl)-1, 3, 5-triazine-2, 4, 6-triamines, QSAR & Combinatorial Sci. 24 (5) (2005) 649 659. [92] M. Rezaee, et al., Determination of organic compounds in water using dispersive liquid liquid microextraction, J. Chromatogr. A 1116 (1-2) (2006) 1 9. [93] E. Yiantzi, et al., Vortex-assisted liquid liquid microextraction of octylphenol, nonylphenol and bisphenolA, Talanta 80 (5) (2010) 2057 2062. [94] C.K. Zacharis, C. Christophoridis, K. Fytianos, Vortexassisted liquid liquid microextraction combined with gas chromatography-mass spectrometry for the determination of organophosphate pesticides in environmental water samples and wines, J. Sep. Sci. 35 (18) (2012) 2422 2429. [95] J.D. Holbrey, et al., Ionic liquids as green solvents: progress and prospects, ACS Symposium Series., American Chemical Society, Washington, DC, 2003. [96] P. Berton, E.M. Martinis, R.G. Wuilloud, Development of an on-line temperature-assisted ionic liquid dispersive microextraction system for sensitive determination of vanadium in environmental and biological samples, J. Hazard. Mater. 176 (1-3) (2010) 721 728.

New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

8 Switchable solvents in separation and preconcentration of organic and inorganic species Usama Alshana1, Erkan Yilmaz2,3 and Mustafa Soylak4 1

Department of Analytical Chemistry, Faculty of Pharmacy, Near East University, Nicosia, TRNC, Mersin, Turkey 2Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, Turkey 3ERNAM—Erciyes University Nanotechnology Application and Research Center, Kayseri, Turkey 4Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey

Abbreviations %RSD 5-BrPADAP ANOVA APDC CCD CyNMe2 DAD DBU DETA DLLME DMCHA ETD FAAS FLD GC-FID GC-MS GFAAS HG-AAS

percentage relative standard deviation 2-(5-bromo-2-pyridylazo) 2 5diethylaminophenol analysis of variance pyrrolidinedithiocarbamate central composite design cyclohexyldimethylamine diode-array detector 1,8-diazabicyclo-[5.4.0]-undec-7-ene diethylenetriamine dispersive liquid
liquid microextraction dimethylcyclohexylamine evaporation-to-dryness flame-atomic absorption spectrometry fluorescence detection gas chromatography
flame ionization detector gas chromatography
mass spectrometry graphite furnace
atomic absorption spectrometry hydride generation
atomic absorption spectrometry

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00008-5

LLME LOD LOQ MWCNT PAHs PAN PPDOT RSM SHDS SHS SHSLLME SPS SQT SS-LPME TEA UV

liquid
liquid microextraction limit of detection limit of quantification multiwalled carbon nanotube polycyclic aromatic hydrocarbons 1-(2-pyridylazo) 2 2-naphthol 1-phenyl-1,2-propanedione-2oximethiosemicarbazone response surface methodology switchable-hydrophilicity dispersive solvent switchable-hydrophilicity solvent switchable-hydrophilicity solvent
liquid
liquid microextraction switchable-polarity solvents slotted quartz tube switchable solvent-based liquid phase microextraction triethylamine ultraviolet

8.1 Introduction Several indoor devices and machines are designed to be switched on and off upon

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© 2020 Elsevier Inc. All rights reserved.

348

8. Switchable solvents in separation and preconcentration of organic and inorganic species

demand to serve multiple purposes, lightbulbs and air conditioners being two examples from our daily life. However, some things have never been expected to be switchable; solvents are an example. Polar solvents are expected to remain as polar and nonpolar ones to remain so. Properties of solvents have never been expected to change upon command. Luckily, such solvents are now a reality. Switchable, or “smart,” solvents can be switched reversibly, upon command, from a liquid with one set of properties to another. Such solvents would facilitate separation processes and eliminate several tedious and time-consuming steps during the course of extraction. Furthermore, this would enable the recycling and use of the same solvent to be used for several separations [1].

8.2 Switchable-hydrophilicity solvents Carbon dioxide(CO2-) triggered switchable-hydrophilicity solvents (SHS), also referred to as switchable-polarity solvents (SPS), were first introduced in 2005 by Dr. Philip G. Jessop and coworkers at the Department of Chemistry, Queen’s University, Canada, in collaboration with Dr. Charles A. Eckert and Dr. Charles L. Liotta at the Schools of Chemistry and Chemical Engineering, Georgia Institute of Technology, United States [2]. They found that exposure of a 1:1 mixture of two solvents, of 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) and 1-hexanol, to gaseous CO2 at ambient pressure and temperature converted the mixture into an ionic liquid, which could be converted back into its original form through bubbling of an inert gas, such as nitrogen or argon, into the liquid at ambient temperature or at 50 C for a more rapid conversion. The switched-off nonionic liquid was nonpolar, while the switched-on ionic liquid was polar in nature. The change of polarity of this

switchable solvent system was verified by testing the miscibility of decane, a nonpolar liquid, with each liquid. Decane was miscible with the liquid under nitrogen but not under CO2, showing that CO2 and nitrogen at 1 atm could be used to “trigger” miscibility and immiscibility, respectively. Polarity of a solvent such as DBU can be switched reversibly under mild conditions. Converting a liquid into its ionic form induces a change in its polarity, ionic liquids being usually more viscous and much more polar than their neutral form. Advantages of using CO2 as the trigger of this change include its benign nature and easy removal from the medium. The reversal is also feasible not only because CO2 is a gas but also because the thermodynamics of the reaction are roughly balanced (ΔH 5 2 136kj mol21 , ΔG 5 2 8:6kj mol21 , 21 21 ΔS 5 2 425j mol K ). The forward reaction is favored enthalpically, while the reverse is favored entropically [3]. Limitations of this two-solvent alkylcarbonate-based SHS included the following: First, they are somewhat water sensitive because the base/CO2/water reaction to give solid [BH1] [HCO32] is thermodynamically preferred over the base/CO2/ROH reaction to give liquid [BH1][RCO32], where BH1 is the protonated base. Second, the need for a two-solvent system increases the price of the process, amidine and guanidine bases being themselves expensive. Third, while the polarity change induced by CO2 was large enough, a wider range of polarity was desired. Finally, amidines and guanidines are not inert solvents toward alkyl halides and strong acids, where their extraction is sometimes necessary [1]. The water-sensitivity problem was overcome by the use of amidine/primary amine SHS instead of amidine/alcohol mixture because primary amines form carbamate salts that are thermodynamically more stable than bicarbonate and alkylcarbonate salts [4]. The price of the process was reduced by

New Generation Green Solvents for Separation and Preconcentration

8.3 Synthesis and chemistry of switchable-hydrophilicity solvents

introducing one-solvent SHS systems and replacing amidine and guanidine bases with secondary amines. The amine acts as the nucleophile and the proton donor. Thus, carbamates derived from the reaction of CO2 and the secondary amine served as a single-component SHS [5]. The polarity difference between the switched-on and the switched-off SHS dictates its selection for the separation of polar substances from nonpolar ones in an extraction process or a product produced in a chemical synthesis. The most desired SHS systems would be the ones with large polarity difference in such processes. When exposed to CO2, the switched-on SHS would be very hydrophilic and completely miscible with water. The removal of CO2 from the system would switch off the SHS back to its hydrophobic form, which would be completely immiscible with water. Thus, allowing the latter form to be easily recovered without applying an extra step such as distillation, whose disadvantages involve flammability of volatile solvents, vapor emissions, smog formation, and adverse health impacts through inhalation. SHS can be applied for the extraction of low-polarity organic compounds from vegetable oils, after which the solvent can be recovered by the use of carbonated water. Such recovery is possible as CO2 converts the SHS into its hydrophilic form. Removal of CO2 can then induce the separation of the hydrophobic form of the SHS from the carbonated water. The most important feature of this process is that distillation is not required for removal of the solvent from the product. N,N,N0 -tributylpentanamidine was the first SHS proposed by Jessop et al. to be used as an alternative to volatile organic solvents. This solvent could be removed from organic products (such as soybean oil) without the need for a tedious and energy-consuming distillation step [6]. More applications of SHS will be discussed in some detail in later sections.

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Despite its demonstrated applicability, N,N, N0 -tributylpentanamidine was impractical as a solvent in further studies because it is commercially unavailable, difficult in its synthesis, unstable, and bioaccumulative due to its hydrophobic nature. Alternatively, several simple tertiary amines that can serve as SHS, which were commercially available and could be easily prepared, were described in another study by Jessop et al. [7]. A series of amines were tested for their phase behavior: in other words, their miscibility with water in the presence of CO2 at 1 bar and immiscibility with water when CO2 was absent. Many of the investigated amines were found to be unsuitable as SHS because they were originally miscible with water. These amines included triethanolamine (predicted logP of 21.5), N-ethylmorpholine (0.3), N-methylpiperidine (1.2), and N,N,N0 ,N0 tetramethylethylenediamine (2.5). On the other hand, other amines were not suitable because they were immiscible with water in the presence of CO2, which included tripropylamine (2.9), trioctylamine (9.5), N,Ndimethyldodecylamine (5.1), N,N-diisopropylethylamine (2.2), and N,N-dimethylaniline (2.2). It was found that amines having logP values between 1.2 and 2.5 were suitable as SHS, in contrast to the results found with amidines and guanidines, where the appropriate solvents had logP values between 3 and 7. Other considerations such as toxicity and flammability hindered the applicability of some other tested amines as SHS [7].

8.3 Synthesis and chemistry of switchable-hydrophilicity solvents Protonation of the amines via the use of CO2 is the cause of change in their miscibility behavior with water. In the presence of CO2, the amines can be converted in water into their

New Generation Green Solvents for Separation and Preconcentration

350

FIGURE 8.1

8. Switchable solvents in separation and preconcentration of organic and inorganic species

Synthesis of SHS by purging CO2.

water-soluble bicarbonate salts according to Eq. (8.1)   NR3 1 CO2 1 H2 O" NR3 H1 ½O2 COH2  (8.1) Synthesis of the SHS is generally performed via bubbling of CO2 or through the addition of dry ice into a 1:1 (v/v) solution of water and the amine, causing the two phases to merge after a time that is dependent on the type of the amine (e.g., in the range of 15
45 min per 10 mL of the mixture). This phase merger occurred most rapidly with cyclohexyldimethylamine (i.e., 15 min) but the slowest with N-butylpyrrolidine (i.e., 45 min). The time required to obtain complete miscibility of the amine with water depends also on the sample size, size and shape of the container, and the method of addition of CO2, presumably because the rate of the reaction is controlled by the rate of mass transfer of CO2 into the aqueous solution. SHSs can be considered a form of ionic liquids but are much cheaper. The simplicity of preparing these solvents and their low cost gained them particular interest among researchers in different fields. The switching

mechanism between the two forms can take place at ambient temperature and pressure by the direct addition or removal of CO2 (Fig. 8.1). CO2 can lead to protonation of the SHS, for example, a tertiary amine, through to an acid
base reaction of hydrated CO2 or carbonic acid in the carbonated water and SHS, resulting in the hydrophilic bicarbonate salt of the SHS according to Eq. (8.1) [8]. Synthesis of SHS by purging CO2 into a mixture of triethylamine (TEA) and water is shown in Fig. 8.1. Lists of solvents investigated for their use as SHSs by Jessop et al. and some of their physical properties [8] are shown in Tables 8.1 and 8.2. Monophasic SHS systems are solvents that are completely miscible with water in their “switched-off,” or unprotonated, form (i.e., before introducing CO2 into the system). On the contrary, biphasic systems are the ones that remain immiscible even after introducing CO2 into the system. SHSs are immiscible with water in their switched-off or unprotonated form but can be switched-on, or converted to their protonated form, upon purging CO2 into the mixture to achieve a monophasic system.

New Generation Green Solvents for Separation and Preconcentration

351

8.3 Synthesis and chemistry of switchable-hydrophilicity solvents

TABLE 8.1 Tertiary amines solvents tested for their applicability as SHS [8]. Behavior

Solvent

Monophasic

Triethanolamine

Ratio of solvent to water ðv=vÞ

LogP

pK a

1:1

2 1.51

7.85

Monophasic

0

N,N,N ,N -Tetramethylethylenediamine

1:1

0.21

9.20

Monophasic

N-Ethylmorpholine

1:1

0.30

7.70

Monophasic

N,N-Dimethylaminoethanol

1:1

2 0.44

9.31

Monophasic

N,N-Dimethylaminopropanol

1:1

2 0.08

9.76

Monophasic

N,N-Diethylaminoethanol

1:1

0.41

9.87

Monophasic

N,N-Diethylglycine methyl ester

1:1

0.76

7.75

Monophasic

N,N-Diethylaminopropanol

1:1

0.77

10.39

Monophasic

5-(Diethylamino)pentan-2-one

1:1

1.21

10.10

Monophasic

Ethyl 3-(diethylamino)propanoate

1:1

1.40

9.35

Switchable

Triethylamine

1:1

1.47

10.70

Switchable

N,N-Dimethylbutylamine

1:1

1.60

10.00

Switchable

N-Ethylpiperidine

1:1

1.75

10.50

Switchable

N-Methyldipropylamine

1:1

1.96

10.40

Switchable

N,N-Dimethylcyclohexylamine

1:1

2.04

10.50

Switchable

N-Butylpyrrolidine

1:1

2.15

10.40

Switchable

N,N-Diethylbutylamine

1:1

2.37

10.50

Switchable

N,N-Dimethylhexylamine

1:1

2.51

10.20

0

Switchable

N,N-Dimethylbenzylamine

5:1

1.86

9.03

Switchable

5-(Dipropylamino)pentan-2-one

2:1

2.15

10.15

Switchable

Diisopropylaminoethanol

1:1

1.16

10.14

Switchable

4,4-Diethoxy-N,N-dimethylbutanamine

1:1

1.48

9.83

Switchable

Ethyl 4-(diethylamino)butanoate

1:1

1.82

10.15

Switchable

N,N-Dimethylphenethylamine

1:1

2.18

9.51

Switchable

Dibutylaminoethanol

1:1

2.20

9.67

Biphasic

N,N-Dimethylaniline

1:1

2.11

5.10

Biphasic

N,N-Diisopropylethylamine

1:1

2.28

11.00

Biphasic

Tripropylamine

1:1

2.83

10.70

Biphasic

Nv-Hexyl-N,N,N0 ,N0 -tetrabutylguanidine

2:1

7.91

13.60

Biphasic

Trioctylamine

1:1

9.45

10.90 (Continued)

New Generation Green Solvents for Separation and Preconcentration

352

8. Switchable solvents in separation and preconcentration of organic and inorganic species

TABLE 8.1 (Continued) Behavior

Solvent

Ratio of solvent to water ðv=vÞ

Biphasic

Propyl 3-(diethylamino)propanoate

1:1

1.85

9.45

Biphasic

N,N-Dibutylaminopropanol

1:1

2.56

10.50

Biphasic

Ethyl 3(dipropylamino)propanoate

1:1

2.72

9.29

Biphasic

N,N-Dibutylaminobutanol

1:1

2.93

10.70

LogP

pK a

TABLE 8.2 Secondary amines, amidines, and guanidines solvents tested for their applicability as SHS [8]. Behavior

Solvent

Ratio of solvent to water ðv=vÞ

LogP

pK a

Monophasic

Diethylamine

1:1

0.71

10.92

Monophasic

Ethyl 3-(tert-butylamino)propanoate

1:1

1.38

10.09

Monophasic

tert-Butylethylamine

1:1

1.42

11.35

Monophasic

Diisopropylamine

1:1

1.46

11.07

Monophasic

N,N,N0 ,N0 -Tetramethylguanidine

2:1

0.30

13.60

Monophasic

1,8-Diazabicycloundec-7-ene

2:1

1.73

12.00

Monophasic

N-Hexyl-N0 ,N0 -dimethylacetamidine

2:1

2.94

12.00

Switchable

N,N,N0 -Tripropylbutanamidine

2:1

4.20

12.00

Switchable

N,N,N0 -Tributylpentanamidine

2:1

5.99

12.00

Switchable

Butyl 3-(isopropylamino)propanoate

1:1

1.90

9.77

Switchable

Propyl 3-(sec-butylamino)propanoate

2:1

1.95

9.80

Switchable

Ethyl 3-(sec-butylamino)propanoate

1:1

1.53

9.73

Switchable

Dipropylamine

1:1

1.64

11.05

Switchable

N-Propyl-sec-butylamine

1:1

2.03

11.05

Switchable

Di-sec-butylamine

Irreversible Irreversible

1:1

2.43

11.02

0

2:1

2.82

13.60

Nv-Butyl-N,N,N ,N -tetraethylguanidine

2:1

3.52

13.60

0

Nv-Hexyl-N,N,N ,N -tetramethylguanidine 0

0

0

0

Irreversible

Nv-Hexyl-N,N,N ,N -tetraethylguanidine

2:1

4.43

13.60

Precipitates

tert-Butylisopropylamine

1:1

1.84

11.39

Precipitates

Ethyl 3-(isobutylamino)propanoate

1:1

1.46

9.45

Precipitates

Ethyl 4-(tert-butylamino)butanoate

1:1

1.75

10.77

Precipitates

Dibutylamine

1:1

2.61

11.28

Precipitates

Dihexylamine

1:1

4.46

11.02

New Generation Green Solvents for Separation and Preconcentration

8.4 Applications of switchable-hydrophilicity solvents

Some guanidines are immiscible with water and can be switched on successfully, but the process is irreversible (i.e., they cannot be switched off to their unprotonated form), mainly due to their high basicity compared to others. It was observed that switchable amines have logP values ranging between 1.2 and 2.5; otherwise, the amines will be too hydrophilic or hydrophobic and will be monophasic or biphasic, respectively. In addition, they have pKa higher than 9.5; amines with less pKa will not react with carbonated water sufficiently due to insufficient basicity, preventing the switching process. It is worth mentioning that, although some amines fulfill these two criteria, they are not switchable, meaning that these criteria are necessary but not sufficient requirements for the switchable behavior. Exceptionally, N;Ndimethylbenzylamine has pKa of 9.03 but could form a SHS. Secondary amines have a different reactivity pathway, faster than the bicarbonate salt formation, which allows them to react with CO2 directly and form ammonium carbamate salts (Eq. 8.2), resulting in faster CO2 uptake. Accordingly, less time is needed, that is, less than 10 min, for switching secondary amines compared to tertiary amines and amidines, which ranges between 20 and 120 min. However, it requires higher energy to remove the CO2 from ammonium carbamate than from ammonium bicarbonate [8,9]. 1

2

2R2 NH 1 CO2 "R2 NH2 1 R2 NCOO

(8.2)

It was observed that some secondary amines were precipitated during the switching on, as confirmed by X-ray crystallography [8], which was due to the low solubility of their salts in water, limiting their use as SHS. Despite the sparse data in the literature about biodegradation of amines, it is thought that secondary amines are more biodegradable than tertiary ones, with some exceptions [10].

353

For example, although biodegradation of N,N-dimethylcyclohexylamine (DMCHA) is not rapid, it is considered to be biodegradable in an aqueous environment [8]. Among their fascinating advantages, the complete miscibility of SHS with water provides infinite surface area with aqueous solutions, which allows for the rapid extraction of analytes. In addition, the synthesis procedure itself is neither expensive nor complicated compared to that of ionic liquids, for instance. Phase separation can also be achieved instantaneously when an appropriate method is used, eliminating the need for centrifugation. Several physical and chemical methods can be applied for removing CO2 or for triggering phase separation. For example, physical methods such as the use of ultrasound, heating, bubbling of nitrogen, or ion-exchange resins can be applied. Chemical methods involve the use of salts, acids, bases, or TEA, as shown in Fig. 8.2. Among these methods, the addition of a strong base, such as sodium hydroxide at high concentration (e.g., 10
20 M), has been reported to be the most efficient for phase separation. Other methods are tedious and timeconsuming and/or may cause analyte loss [11].

8.4 Applications of switchablehydrophilicity solvents In a webinar given by Dr. Philip Jessop on March 23, 2018 (https://www.youtube.com/ watch?v 5 8xYntTazEqo&t 5 6s, accessed on May 27, 2019), he classified the applications of SHS into seven main categories: (1) large-scale and small-scale extractions, (2) catalysis, (3) settling of clays, (4) collapsing emulsions and suspensions, (5) controlling conventional surfactants, (6) switching viscosity, and (7) forward osmosis. Despite the valuable applications and advantageous use of SHS in many fields, this

New Generation Green Solvents for Separation and Preconcentration

354

8. Switchable solvents in separation and preconcentration of organic and inorganic species

FIGURE 8.2 Methods for phase separation [11].

chapter will be mainly focused on their uses for extractions of organic and inorganic analytes from different matrices prior to their determination by analytical instruments. Nevertheless, some applications of SHS in large-scale extractions for isolation purposes are discussed next.

8.5 Switchable-hydrophilicity solvents in large-scale extractions Despite their wide-ranging applications, in this section, only a few of those applications of SHS for large-scale extractions are presented. The extraction of soy oil from soybean flakes at industrial scale requires the use of large amounts of n-hexane. This process results in a significant loss of the extraction solvent and requires a high amount of energy for the distillation of the solvent. Due to their toxicity, the use of n-hexane and similar hydrophobic hydrocarbons in extraction has led to environmental and health concerns. Supercritical CO2 can also be used, but it requires 500 bar for the most energy-efficient extraction of soy oil from

soybeans, which is the least amount of energy necessary per kilogram of the extracted oil. The use of SHS for this purpose would eliminate the necessity for n-hexane and distillation. The most promising methods are (1) extraction by an amidine SHS that can be removed from the soy oil by the use of carbonated water and (2) extraction using a moderately hydrophilic solvent that can then be removed easily from the oil by the use of water. Jessop et al. [12]. used SHS for the extraction and separation of soybean oil from soybean flakes. This was done through the use of SHS in hydrophobic form to extract the soybean oil from the flakes, and then the solvent was switched to its hydrophilic form and extracted from the oil with water. This was followed by removing the solvent from the water by switching off the solvent back to its hydrophobic form. Preferably, the high-polarity form would be so immiscible with the oil that the level of contamination of the oil with the solvent would be extremely low. In such a case, further purification of the oil might be necessary to remove traces of the solvent. In this study, two kinds of switchable solvents were evaluated: mixtures of DBU and

New Generation Green Solvents for Separation and Preconcentration

8.5 Switchable-hydrophilicity solvents in large-scale extractions

alcohol as well as N-butyl-N-ethylamine and N-benzyl-N-methylamine as secondary amines. The separation of the ionic liquid layer of DBU from the oil layer was quite poor with methanol. Better results were obtained with ethanol. Because the oil still contained small amounts of both solvent components (ethanol and DBU), bubbling of extra CO2 was necessary to precipitate more of the ionic liquid and to reduce the level of contamination. A process for separating soy oil from the extraction solvent using secondary amine SHS would be similar to the one using amidine/alcohol SHS. However, the use of a single-liquid component solvent simplifies the process even more. Another disadvantage of using a DBU/ethanol system is that transesterification was observed unlike the case with secondary amines. Analysis of the oil layer showed that it contains 12% (by weight) of the amine. Although removal of residual amine seemed to be possible through washing the oil with acidic water, the high impurity after the CO2 treatment made this method undesirable. Lipid extraction is necessary for the development of biofuels from microalgae. SHS were applied for the extraction of hydrocarbons from microalga Botryococcus braunii by Samorı` et al. [13]. In this work, the lipid extraction efficiency of two SHS systems based on DBU/ethanol and DBU/octanol was compared with that obtained with traditional solvents, such as n-hexane, and chloroform/methanol from freeze-dried and liquid samples of B. braunii. The high affinity of the nonionic form of DBU/ alcohol SHS toward nonpolar compounds made it possible to extract hydrocarbons from the algae, whereas the high polarity of the DBU-alkyl carbonate form, obtained by the addition of CO2, was used to recover the hydrocarbons from the SHS. DBU/octanol and DBU/ethanol SHS were tested for this purpose and compared with n-hexane and chloroform/ methanol. The DBU-alkyl carbonate salts are usually obtained from a 1:1 mixture of two

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neutral liquid components, DBU and an alcohol, whose chain length can be chosen to finely tune the polarity of the nonionic form and the melting point of the ionic form. The DBU/octanol system was further evaluated for the direct extraction of hydrocarbons from algal culture samples. DBU/octanol exhibited the highest yields of extracted hydrocarbons from both freeze-dried and liquid algal samples (16% and 8.2%, respectively, versus 7.8% and 5.6% with n-hexane). Jessop et al. proposed an SHS-based method for the separation of bitumen from oil sands [14]. Conventional methods developed for this purpose are followed in a distillation step to remove the solvent, which is problematic because they require significant energy input and the use of a volatile solvent. Volatile solvents are flammable, contribute to smog, and cause inhalation risks to workers; they can be toxic, carcinogenic, neurotoxic, mutagenic, or narcotic, all by inhalation. Thus, the use of SHS is a nondistillative method that employs nonvolatile or low-volatility solvents, posing fewer problems. Cyclohexyldimethylamine (CyNMe2) was investigated as the SHS in this study. This is a solvent that can readily interconvert between two forms: One form is hydrophobic and forms a biphasic mixture when mixed with water (this is the normal behavior for CyNMe2). The other form is hydrophilic and is completely miscible with water. The trigger for the change to hydrophilic is the addition of CO2 at 1 bar, which converted CyNMe2 into water-soluble [CyNHMe2][HCO3], whereas the trigger for the return to hydrophobic was the removal of the CO2. The proposed oil sands separation process started with the conventional extraction of the bitumen from the sand and clay using CyNMe2 as the SHS in its hydrophobic form. After filtration or decantation, the solids were separated from the bitumen/solvent mixture. The solids were washed with fresh solvent and then with carbonated water.

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The bitumen/solvent mixture was treated with carbonated water to extract the CyNMe2 by converting it to the water-soluble bicarbonate salt [CyNMe2H][HCO3]. The washed bitumen was removed by decantation, and the bicarbonate salt solution was heated and treated with either N2 or air to remove the CO2. The CyNMe2 solvent was separated from the water. Both the amine and the water could be reused. The recovered sand/clay mixture was dry and free flowing (90% of the original mass). On average, the solids contained 0.096 g of residual bitumen (0.4 wt.% of the mass of solids). Thus, the removal of bitumen from the oil sand was at least 94% complete. Keeping in mind that some bitumen was lost to the sides of the glassware, the extraction of bitumen was likely somewhat more than 94% complete. A second extraction would presumably greatly increase this value. Simply rinsing the solids with CyNMe2 multiple times while still on the filter, rather than doing a second extraction, increased the bitumen removal to over 97% complete. The proposed method recovered more oil than the Clark process, a conventional method used for this purpose, produced cleaner solids, worked with low-grade high-fines oil sands, and required neither distillation nor the use of a volatile solvent.

8.6 Switchable-hydrophilicity solvents in microextractions Despite their large-scale applications, it was not until 2015 when the first application of SHS in the microextraction context was proposed by Lasarte-Aragones et al. [11]. In this study, DMCHA was used as the extraction solvent after being switched on in water in a 1:1 ratio using CO2. After the completion of extraction, phase separation was achieved by the addition of sodium hydroxide, without the need for a centrifugation step. The proposed method was used for the determination of benz[a]anthracene

in water samples by fluorimetry. It was noticed, however, that the native fluorescence of the compound was quenched in DMCHA, a problem that was overcome by diluting the final extract with acetic acid in a ratio of 1:1. Parameters affecting extraction recovery, such as the volume of DMCHA as well as different chemical and physical methods for triggering phase separation, were evaluated. Physical methods, such as bubbling of nitrogen, heating up to 40 C, ultrasound irradiation, and the use of ion-exchange resins, were investigated. Chemical methods included the addition of calcium chloride, 5% TEA, acidification and basification with calcium hydroxide, barium hydroxide, and sodium hydroxide (10 and 20 M). It was concluded that the addition of 20 M sodium hydroxide was the most efficient tool for phase separation. The proposed method allowed the extraction and determination of the target analyte with a limit of detection (LOD) of 0.08 μg L21 and percentage relative standard deviation (%RSD) of 6.7% at the limit of quantification (LOQ) level. The recoveries obtained were in the range of 72%
100%. Finally, the potential use of this microextraction technique in combination with gas chromatography
mass spectrometry (GC-MS) was shown with several polycyclic aromatic hydrocarbons (PAHs) because fluorescence spectroscopy presents a limited selectivity in discriminating the analyte among different PAHs. It was stated that for GC-MS analysis, it was not necessary to dilute the DMCHA with acetic acid. According to the results obtained, the proposed method presented high extraction efficiency, was simple and fast, and did not require complex or special labware for phase separation.

8.6.1 Switchable-hydrophilicity solvents for extraction of organic analytes Another homogeneous liquid
liquid microextraction (LLME) method that was based on

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8.6 Switchable-hydrophilicity solvents in microextractions

the use of SHS was proposed by LasarteAragones et al. [15] for the extraction of six triazine herbicides (i.e., prometon, terbumeton, secbumeton, simetryn, prometryn, and terbutryn) from environmental water samples. The extraction method made use of 125 μL of DMCHA that was solubilized in water at a ratio of 1:1 (v/v) using CO2. After extraction, phase separation was induced by using sodium hydroxide with no centrifugation step. The method was optimized for the determination of the triazine herbicides by GC-MS. The presence of interfering metallic ions in environmental waters was avoided by the addition of ethylenediaminetetraacetic at a concentration of 0.1 M, which also increased the recovery of the analytes. LODs ranged between 0.1 and 0.37 μg L21, with precision of between 3.1% and 12.5%. Extraction time was reported as 5 min per sample. The proposed method allowed the determination of the target analytes in tap, river, and bottled waters. Vakh et al. [16] developed a fully automated effervescence-assisted switchable-hydrophilicity solvent
liquid
liquid microextraction (SHS-LLME) method for the determination of ofloxacin in human urine samples. Mediumchain-saturated fatty acids were tested as SHS. The conversion of the fatty acids into their hydrophilic form was carried out by the use of sodium carbonate. The addition of sulfuric acid to the solution decreased its pH and produced microdroplets of the fatty acids. Bubbling of CO2 was done in situ, promoting the extraction process and phase separation. The performance of the proposed method was demonstrated through the determination of ofloxacin in human urine samples using HPLC with fluorescence detection (HPLC-FLD). Parameters influencing the extraction efficiency were investigated and were found as follows: type of extraction solvent, hexanoic acid; its volume, 50 μL; sample volume, 1 mL; type of mineral acid, sulfuric acid; pH, 6.0; and concentrations of sodium carbonate and sulfuric

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acid, 2.0 and 2.5 M, respectively. The effect of interfering substances was also studied. To eliminate their effect, urine samples were diluted 1000 times before analysis. Under optimum conditions, linearity for ofloxacin fell within the concentration range of 3 3 1028 to 3 3 1026 M. LOD was found to be 1 3 1028 M. The results showed that the proposed method was highly cost-effective, simple, rapid, and environmentally benign. Gao et al. [17]. proposed a centrifuge-less dispersive liquid
liquid microextraction (DLLME) based on solidification of the SHS for rapid on-site extraction of four pyrethroid insecticides from water samples and their determination using HPLC with ultraviolet detector (HPLC-UV). In this extraction method, medium-chain-saturated fatty acids (i.e., decanoic, undecanoic, and dodecanoic acids), which rapidly solidify at low temperatures below 20 C, were studied as the SHS. The fatty acids were converted into their hydrophilic form by adding sodium hydroxide. Microdroplets of the fatty acids were generated when injected into an acidic solution that had been pretreated with sulfuric acid. Upon cooling the cloudy solution, the fatty acids solidified, which were then separated by filtration, thus avoiding the time-consuming step of centrifugation. Following filtration, a 40-μL aliquot of acetonitrile was added to dissolve the solid phase collected from the surface of a filter paper, and 10 μL of the mixture was directly injected into the HPLC for analysis. The microextraction process was performed in a 10-mL syringe, and the whole process could be finalized within 5 min. No external energy was required, which made this method ideal for on-site extraction. Optimum experimental parameters were as follows: extraction solvent, 1 M decanoic acid; its volume, 350 μL; 150 μL of sulfuric acid (2 M) to decrease the pH of the samples; no salt was added; and extraction temperatures were in the range of 20 C
40 C. Cooling in an ice bath took 3 min. Under these

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8. Switchable solvents in separation and preconcentration of organic and inorganic species

optimum conditions, good linearity for the four pyrethroid insecticides was observed in the concentration ranges of 1
500 μg L21, with coefficients of determination (R2) greater than 0.9993. Recoveries of the studied insecticides ranged from 84.7% to 95.3%, with %RSD ranging from 1.6% to 4.6%. LODs were found in the range of 0.24
0.68 μg L21, and the enrichment factors in the range of 121
136. The results demonstrated that this method could be applied for the determination of these pyrethroid insecticides in real water samples. Elimination of the centrifugation step made it a promising method for rapid field analysis of the analytes. The proposed method was recommended as a simple, effective, rapid, and environmentally benign. SHS were used for dispersive solvents in DLLME. An automated DLLME method using a switchable-hydrophilicity dispersive solvent (SHDS) with HPLC-FLD was developed by Timofeeva et al. [18] for the determination of ofloxacin in chicken meat. This extraction method made use of a mixture of dichloromethane as the extraction solvent and acrylic acid as the SHDS. This binary mixture was injected into an aqueous sample solution containing NaOH. Upon addition of the SHDS into the aqueous phase, a cloudy solution consisting of fine droplets of the extraction solvent was observed. As a consequence of the fast neutralization reaction, the SHDS was converted into a water-soluble salt, and phase separation was achieved due to the switching of its polarity. Conversion of the SHDS overcame the disadvantage of the conventional dispersive solvents used in DLLME on the increased solubility of target analytes in the aqueous phase, which enhanced the efficiency of DLLME. The proposed extraction method was automated using a flow system before it was applied for the determination of ofloxacin in the chicken meat samples. The automated method also included online ultrasoundassisted solid
liquid extraction of the analyte

from the samples prior to DLLME using SHDS and its determination by HPLC-FLD. Under optimum conditions, a good linearity was recorded within the concentration range of 6 3 1029 to 5 3 1027 M, and LOD was calculated as 2 3 1029 M. An SHS membrane-based microextraction method was developed prior to HPLC-FLD for the determination of fluoroquinolones in shrimp by Pochivalov et al. [19]. The procedure was based on the extraction of the target analytes from an aqueous sample into a porous hydrophobic membrane impregnated with nonanoic acid as an SHS, a step that was followed by ionization of SHS and backextraction of the analytes into a basic acceptor solution. Medium-chain fatty acids were tested as SHS for the extraction of four fluoroquinolones (i.e., fleroxacin, lomefloxacin, norfloxacin, and ofloxacin). The method was used prior to HPLC-FLD for the determination of these fluoroquinolones in shrimp samples with no extra sample pretreatment steps. The effect of extraction parameters, such as the type of membrane and the medium-chain fatty acid, size of the membrane, volume of the aqueous sample phase, time of extraction and backextraction, as well as concentration and volume of the potassium hydroxide solution used for ionization of nonanoic acid and back-extraction of the analytes, were studied. The membrane was cut into squares of equal size (10mm 3 10mm), before it was impregnated with 4 μL of nonanoic acid. The shrimp sample (250 mg) was mixed with 2.5 mL of deionized water and 0.5 mL of citrate phosphate buffer solution (pH 4.9). The impregnated membrane was placed into a vial and stirred for 30 min. The membrane was placed into 0.5 mL of 0.1 M potassium hydroxide solution, where the SHS ionization assisted back-extraction of the analytes took place. The solution was neutralized partially by 2 μL of 10% acetic acid aqueous solution and analyzed by HPLC-FLD. With this optimized procedure, the response was

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8.6 Switchable-hydrophilicity solvents in microextractions

linear over the concentration ranges of 3
1500 μg L21 for ofloxacin, 10
1000 μg L21 for norfloxacin, and 15
1500 μg L21 for lomefloxacin and fleroxacin. LODs were found as 1 μg L21 for ofloxacin, 3 μg L21 for norfloxacin and 5 μg L21 for lomefloxacin and fleroxacin. It was concluded that SHS ionization could have a potential application in membrane-based liquid phase microextraction. Rameshgar et al. [20] used SHS-LLME with gas chromatography
flame ionization detector (GC-FID) for the determination of nitroaromatic compounds in water samples. Dipropylamine was used as the SHS with miscibility being switched on and off upon the addition or removal of CO2, respectively. Experimental parameters affecting the extraction efficiency were investigated and were found as follows: volume of the extraction solvent (acceptor phase), 800 μL switched on dipropylamine; volume of sample solution (donor phase), 15 mL; concentration and volume of sodium hydroxide solution, 10 M, 2 mL; pH of sample solution, no effect; and extraction time, 2 min. Under optimum conditions, LODs and preconcentration factors were obtained in the ranges of 0.9
1.8 μg L21 and 132
138, respectively. Extraction recoveries from the water samples were higher than 88%. Good precision, wide linear dynamic range, and high extraction recoveries were demonstrated, suggesting that this method can be used for the extraction and determination of nitroaromatic compounds in various water samples. Kakavandi et al. [21] proposed an ion pair SHS-LLME for the extraction of paraquat from environmental and biological samples before determination using HPLC-UV. The analyte was monitored at 258 nm. TEA was used as the SHS for extraction, while sodium dodecyl sulfate was used as the ion-pairing agent. The complex formed between the cationic paraquat and sodium dodecyl sulfate was extracted into TEA. The separation of the two phases was

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carried out through the addition of sodium hydroxide. The effect of influential parameters on the extraction recovery was investigated, and optimum values were found as follows: pH of sample solution, 4.0; volume of extractant, 500 μL; concentration and volume of sodium hydroxide solution, 10 M, 2 mL; amount of sodium dodecyl sulfate, 1 mg; and extraction time, 3 min. Under optimum conditions, LOD and LOQ were found as 0.2 and 0.5 μg L21, respectively, with a preconcentration factor of 74, and %RSD was found to be , 5%. The percentage recoveries of paraquat from river water, apple juice, human urine and plasma were in the range of 90.0%
92.3%. Shishov et al. [22] developed an effervescence tablet-assisted SHS-LLME for on-site preconcentration of some steroid hormones in water samples, followed by their determination with HPLC-UV. The studied steroid hormones included testosterone, progesterone, estradiol, and hydrocortisone. The procedure involved dissolution of two effervescent tablets in the water sample. The tablets contained oxalic acid as a proton donor agent, sodium hydrogen carbonate as an effervescence agent, and sodium nonate as a source of the organic phase. The proton donor agent reacted with the effervescence agent and with the water-soluble source of organic phase in the aqueous sample phase. Changing the pH promoted conversion of sodium nonate into a water-insoluble nonanoic acid dispersed by CO2 bubbles, which were generated in situ. After phase separation, an organic phase containing steroid hormones was collected, and HPLC-UV analysis were performed. Experimental parameters affecting the recovery of steroid hormones from water were investigated and were found as follows: type and amount of fatty acid, sodium nonate, 150 mg; type and amount of the proton donor agent, oxalic acid, 1400 mg; type and amount of effervescence agent, NaHCO3, 800 mg. As for the amount of effervescent tablets, two tablets were found to be enough to achieve a

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8. Switchable solvents in separation and preconcentration of organic and inorganic species

high recovery value (90 6 5)% for hormones studied from a 1 L water sample, each tablet containing 1400 mg of oxalic acid, 150 mg of sodium nonate, and 800 mg of NaHCO3. Under these optimum conditions, linear dynamic ranges were found to be within 5
500 ng L21 for testosterone, 25
750 ng L21 for progesterone, 10
1000 ng L21 for estradiol, and 50
500 ng L21 for hydrocortisone. LODs were calculated as 2, 8, 3, and 17 ng L21, respectively. The proposed method was applied for the determination of the previously mentioned analytes in river water samples. It was concluded that this approach could be considered as a green, rapid, simple, costeffective, and convenient method for on-site preconcentration of a variety of analytes from water samples. Lamei et al. [23] proposed an ultrasoundassisted SHS-LLME coupled with GC-MS for the extraction and determination of the quaternary ammonium herbicide paraquat in biological, environmental water, and apple juice samples using chemical reduction. The chemical reduction of the analyte was performed to produce a volatile derivative of paraquat through the addition of sodium borohydride to the sample solution. The derivative was extracted into TEA. The ionic and nonionic forms of TEA were reversed by adding or removing CO2, respectively. Phase separation was achieved by the addition of sodium hydroxide. Ultrasound was used to form fine droplets of the extractant in the sample solution. The effect of experimental parameters on the recovery of the analyte’s derivative were found as follows: pH of sample solution, 8.0; volume of SHS, 750 μL; concentration and volume of sodium hydroxide solution, 10 M, 2 mL; ionic strength adjusted with 1.5 g of sodium chloride (NaCl); volume of sample solution, 10 mL; and time of ultrasound agitation, 2 min. Under optimum conditions, LOD and LOQ were found in the range of 0.06
0.13 and 0.20
0.30 μg L21, and preconcentration

factors were calculated between 150 and 230 in the biological and environmental samples, respectively. Intraday and interday precisions were less than 8% and 9%, respectively. Accuracy of the method was tested by spiking real samples. The developed method was applied for the analysis of biological (human urine and plasma) samples, as well as environmental samples (distilled, mineral, and river water) and apple juice. Zare et al. [24] presented a method based on SHS-LLME for the simultaneous determination of 19 amino acids in human plasma samples using HPLC-FLD. The SHS was based on the application of DBU, methanol, and CO2. Phase separation was brought about by the addition of sodium hydroxide, which led to a reverse of the ionization state of the solvent. The use of ortho-phthalaldehyde/ 3-mercaptopropionic acid as a derivatizing agent provided several advantages, including the formation of low-polarity substituted isoindole products, the generation of highly fluorescent derivatives, and the occurrence of the reaction in an aqueous medium that is reproducible, quantitative, and rapid at room temperature. A central composite design (CCD) of response surface methodology (RSM) was used to optimize the parameters affecting the extraction efficiency. Optimum parameters were found as follows: type and volume of SHS, DBU/methanol, 300 μL; sample volume, 6 mL; concentration and volume of sodium hydroxide solution, 10 M, 0.5 mL; and ultrasonic time, 6 min. Under optimum conditions, the response was linear within the concentration range of 0.5
300 μmol L21, with correlation coefficients higher than 0.996. LODs and LOQs were in the ranges of 0.01
0.6 μ mol L21 and 0.3
2.2 μmol L21, respectively. The proposed method was successfully applied for the determination of the target analytes in human plasma samples with relative recoveries ranging from 81.3% to 102.1%.

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8.6 Switchable-hydrophilicity solvents in microextractions

Shahvandi et al. [25] developed a pHassisted SHS-LLME coupled with GC-MS for the determination of methamphetamine in human urine samples. An acid rather than CO2 was used to switch the polarity of SHS during the extraction. Dipropylamine was used as the SHS. The effect of extraction parameters was studied and was found as follows: volume of SHS, 100 μL; extraction temperature, 40 C; type, concentration, and volume of acid used for switching the polarity of the SHS, HCl, 6.0 M, 100 μL; concentration and volume of sodium hydroxide solution, 10 M, 200 μL; no salt was added for salting out. Under optimum conditions, the preconcentration factor was found as 98.9. LOD and linearity of the method were achieved in the ranges of 1.5 and 5
1500 μg L21, respectively. Within-run and between-run precisions were found in the ranges of 6.2
7.3 and 6.9
7.8, respectively. Extraction time was approximately 5 min. The proposed method was successfully applied for the determination of methamphetamine in urine samples with percentage recoveries higher than 97.4%. Ahmar et al. [26] proposed an SHS-LLME method for the determination of methadone and tramadol in human urine by GC-FID. Dipropylamine was used as the extraction solvent with CO2 as the switching trigger. Influential parameters on extraction recovery were found as follows: volume of SHS, 800 μL; sample volume, 15 mL; pH of sample solution, no effect; concentration and volume of sodium hydroxide solution, 10 M, 2 mL; the addition of NaCl had no significant effect (no salt was added); extraction time, no effect, and extraction temperature had no significant effect (the extraction was performed at room temperature). Under these optimum conditions, the preconcentration factors, LOD, and the linearity of the method were achieved within the ranges of 122
118, 2.4, and 8
1000 μg L21, respectively. The proposed method was successfully applied for the

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determination of methadone and tramadol in urine samples. Chormey et al. [27] suggested a method based on SHS-LLME for the extraction of some hormones, endocrine disruptors, and pesticides prior to their determination by GC-MS. The selected analytes were 4-n-octylphenol, bisphenol A, 4-n-nonylphenol, diazinon, heptachlor, aldrin, α-endosulfan, chlordane, dieldrin, β-endosulfan, estrone, and 17-β-estradiol. N,Ndimethylbenzylamine was used as the SHS. A Box
Behnken experimental design was used to evaluate the main variables and their interaction effects, and optimum parameters were determined as follows: volume of the SHS, 1.5 mL; volume of sample solution, 8.0 mL; vortex time, 10 s; concentration and volume of sodium hydroxide solution, 1.0 M, 1.0 mL; and centrifugation time and rate, 2.0 min, 3461 rpm. Under these conditions, the proposed method yielded LODs and LOQs between 0.20
13 and 0.90
46 ng mL21, respectively. Accuracy and applicability of the developed method were checked in tap water and in two different wastewater samples by additionrecovery tests. Percentage recoveries were found to range between 91% and 110%, and % RSD were all below 10%. The results indicated that the method could effectively be used for the accurate and sensitive determination of these analytes in the studied matrixes. Hamid and Fat’hi [28] developed a cationic surfactant-assisted SHS-based DLLME for the determination for Orange II dye in food samples using UV
Vis spectrophotometry. This extraction method was based on SHS and the ion pair effect of a cationic surfactant. Parameters affecting the extraction efficiency of Orange II were optimized and were found as follows: sample pH, 7.0
10.0; type, concentration, and volume of surfactant, Aliquat 336 (3% w/v), 200 μL; type and volume of SHS, TEA, 500 μL; ionic strength through the addition of sodium nitrate, no effect; and concentration and volume of sodium hydroxide solution,

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10 M, 1.5 mL. Extraction time was approximately 3 min. Under optimum conditions, the calibration graph was linear within the range of 2
450 μg L21, LOD was 0.9 μg L21, and % RSD was 1.68% at a concentration of Orange II at 80 μg L21. Potential interfering ions investigated in this research did not pose any serious interference on the preconcentration and determination of Orange II. The developed method was used for the determination of Orange II dye in food samples (i.e., sweet and cotton candy), and satisfactory results were obtained. It was concluded that simplicity, highperformance extraction, rapidity, stability, and reduction of volatility of the extractive phase were among the advantages of the proposed method. Wang et al. [29] developed a CO2-mediated SHS-LLME and combined it with HPLC-UV for the determination of bisphenols in foods and drinks. DMCHA was used as the SHS. Several important parameters affecting extraction efficiency, examined and optimized by a one-parameter-at-a-time approach and CCD, were found as follows: volume of SHS, 782 μL; pH of sample solution, no effect; centrifugation rate, no effect; concentration and volume of sodium hydroxide solution, 10 M, 375 μL; and SHS: water ratio, 1.1:1 (v/v). The proposed method was applied to whole-fat (3.0% fat), low-fat (1.5% fat), and skimmed (,0.5% fat) milk, as well as to orange juice and energy drink samples. LODs were in the range of 0.17
0.67 μg L21, and extraction recoveries were in the range of 79.5%
103.4% in milk, 84.5%
97.5% in orange juice, and 91.9%
101.2% in energy drinks. Intraday and interday precision of the method, based on %RSD, ranged from 1.7% to 4.8% and from 2.1% to 5.7%, respectively. It was concluded that the method possessed several advantages, such as high extraction recovery and sensitivity, did not require dispersive solvents, required a simple operational procedure, and reduced the pretreatment time and workload. Therefore

it could have potential application value for the detection of trace bisphenols in routine food quality control tests. Hamid and Fat’hi [30] proposed a method based on a surfactant ion pair-SHS-DLLME for the determination of phenazopyridine in pharmaceutical and biological samples using UV
Vis spectrophotometry. TEA was used as the SHS, and Aliquat 336 was used as the ionair agent, the use of which resulted in an enhancement of extraction efficiency of phenazopyridine into the SHS. Variables affecting the extraction performance were optimized, and optimum conditions were found as follows: pH of sample solution, 9.0; concentration and volume of the surfactant, (3% w/v), 400 μL; volume of SHS, 750 μL; and concentration and volume of sodium hydroxide solution, 10 M, 2 mL. Under optimum conditions, %RSD was found as 3.1% for five repeated determinations of phenazopyridine in solutions containing 20 μg L21 of the analyte. The linear dynamic range was found as 5
180 and LOD as 0.88 μg L21. The proposed method was successfully applied for the determination of phenazopyridine in pharmaceutical and biological samples (i.e., human urine and plasma). Hu et al. [31]. presented a sodium dodecyl sulfate
sensitized SHS-LLME for the extraction and preconcentration of protoberberine alkaloids in Rhizoma coptidis, followed by determination using HPLC with diode-array detector (HPLC-DAD). TEA was used as the SHS and sodium hydroxide as the phase separation trigger. Several parameters affecting the extraction efficiency were studied, and optimum conditions were found as follows: concentration of sodium dodecyl sulfate, 1.2 mM; pH of sample solution, 5.0; volume of the SHS, 700 μL; concentration and volume of sodium hydroxide solution, 10 M, 2 mL; extraction (ultrasound) time, 8 min; and centrifugation time and rate, 2 min, 4000 rpm. Under optimum conditions, the enrichment factors of four protoberberine alkaloids (epiberberine, coptisine, palmatine,

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8.6 Switchable-hydrophilicity solvents in microextractions

and berberine) ranged between 101.8 and 152.0. The linear dynamic ranges (with r2 $ 0.990) were found as 0.032
4.23, 0.031
4.33, 0.0026
10.04, and 0.0013
4.13 μg mL21 for the analytes, respectively. LODs were in the range of 0.16
0.32 ng mL21. Satisfactory recoveries of 98.8%
104.6%, and precisions (%RSD 1.9%
10.9%) were obtained. The proposed method was used for the determination of the four active alkaloids in R. coptidis. Shahraki et al. [32] developed a pHassisted SHS-LLME for the extraction and determination of nitrazepam by differential pulse voltammetry. N,N-dipropylamine was used as the SHS with the assistance of HCl and NaOH for pH adjustment. Initially, the SHS was added to the aqueous sample containing the analyte, where a two-phase mixture formed. Then, HCl was added drop-wise until a clear monophasic mixture was obtained due to switching of N,N-dipropylamine to its hydrophilic form. Afterward, the separation of the two phases was achieved by the addition of NaOH, which triggered the switching-off of the SHS back into its hydrophobic form. Finally, following evaporation of the solvent, the extracted nitrazepam was determined by voltammetric method. The effect of experimental parameters on extraction efficiency was investigated and was found as follows: pH of sample solution, 7.0; volume of SHS, 100 μL; extraction time, 2 min; and salt addition, no effect. Under optimum conditions, two linear ranges of 0.03
20 and 20
450 ng mL21 with correlation coefficients of 0.996 and 0.998 were obtained from voltammetry measurements. LOD and LOQ were found as 9 ng L21 and 0.03 ng mL21, respectively. %RSD was found as 7.4%. The proposed method was applied for the determination of nitrazepam in human urine samples. Pochivalov et al. [33] proposed a surfactantmediated microextraction approach using SHS prior to HPLC-UV for the determination of

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Sudan dyes in solid food samples. The phenomenon of micellar solution formation and the switchable behavior of medium-chain fatty acids were shown to be effective for the extraction of hydrophobic analytes from solid samples. In this method, mixing of the solid food sample with the aqueous solution of sodium hexanoate resulted into the formation a micellar solution, into which Sudan dyes, as hydrophobic analytes, were extracted from the sample. The injection of sulfuric acid solution into the mixture promoted phase separation of a hexanoic acid layer. Parameters affecting extraction recovery were optimized, and optimum values were found as follows: concentration of sodium hexanoate, 2.5 M; type, volume, and concertation of mineral acid, sulfuric, 200 μL of 6 M; mass of sample, 200 mg; extraction temperature, 60 С for salted salmon samples and at 70 C for spices powder; and extraction time, 20 min for salted salmon samples and 10 min for spices powder. Under optimized extraction conditions, LODs were calculated as 0.19, 0.028, and 0.18 mg kg21 for Sudan I, Sudan II, and Sudan III, respectively. The extraction time was 25 min. The performance of the proposed method was demonstrated through the use of HPLC-UV for the determination of Sudan dyes (Sudan I, Sudan II, and Sudan III) in spiked salted salmon and spices powder samples. It was concluded that, in comparison with other existing methods, the proposed method offered some advantages including the low consumption of extraction solvent and simplicity and that it could be applied for microextraction of hydrophobic analytes from other solid samples such as pharmaceuticals, food, soil samples, and the like. Erarpat et al. [34] developed an SHS-LLME method prior to gas chromatography
quadrupole isotope dilution-mass spectrometry for the determination of 4-n-nonylphenol in municipal wastewaters. N,N-Dimethylbenzylamine was applied as the SHS. The Box
Behnken design

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based on three-level incomplete factorial designs was used to examine the significant variables and set optimum extraction conditions. Also, analysis of variance (ANOVA) was used to evaluate the main influential parameters and their interactions. Optimum conditions were found as follows: volume of protonated SHS, 2.0 mL; concentration and volume of sodium hydroxide solution, 1.0 M, 1.5 mL; extraction (vortex) time, 20 s. Three calibration blends and one wastewater sample blend were prepared with 4-n-nonylphenol and 4-n-nonylphenol-D8. Under optimum conditions, the response was linear within the range of 1.0
50 ng mL21, while LOD and LOQ were calculated as 0.32 and 1.05 ng mL21, respectively. The enrichment factor was found as 115 based on comparisons of LOD values obtained with and without preconcentration. Recovery of the method for wastewater spiked at 40 ng g21 was calculated as 101.5%. Li et al. [35] proposed a switchablehydrophilicity dispersive solvent-based LLME method coupled to HPLC-UV for the determination of amphenicols in food samples. A mixture of an extraction solvent (i.e., n-butanol) and a dispersive solvent (i.e., tetraethylenepentamine) was injected into acidified aqueous sample solution. After a fast neutralization reaction, the dispersive solvent was converted into a water-soluble salt, and phase separation occurred. Experimental conditions were optimized, and optimum values were found as follows: ratio of extraction solvent and sample solution. 1:7 (v/v); ratio of extraction and SHDS, 1:1 (v/v, 1 mL mixture); concentration of sulfuric acid, 1.8 M; sonication time, 15 min; and ratio of raw matter and solvents, 3:5 (v/v). Under optimum conditions, linearity was observed in the range of 0.27
50.0 μg kg21. LODs for chloramphenicol and thiamphenicol were found as 0.03 and 0.08 μg kg21, respectively. Recoveries for the spiked samples obtained were between 81.5% and 113.5%, and %RSD was less than 8.6%. The proposed

method was successfully applied for the analysis of amphenicols in four food samples (chicken, pork, shrimp, Basha fish). Di et al. [36] hyphenated solid phase extraction with SHS-LLME for the extraction of chloramphenicol from environmental waters prior to its determination by HPLC-UV. Oasis HLB sorbent was chosen for solid phase extraction. DMCHA was used as a CO2-triggered SHS. The parameters influencing both extraction techniques were investigated and optimized. Optimum values were found as follows: pH of sample solution, no effect; type and volume of elution solvent, acetonitrile, 2.0 mL; type and volume of SHS, DMCHA/ water mixture at the ratio of 1:2 (v/v), 500 μL; and concentration and volume of sodium hydroxide solution, 2.0 M, 1.0 mL. Under optimal conditions, the method exhibited low LOD (0.1 ng mL21), good linearity (0.5
50 ng mL21), acceptable precision (%RSD ,5.0%), and an enrichment factor of 340. Erarpat et al. [37] proposed an SHS-LLME method for the extraction of fluoxetine, estrone, pesticides, and endocrine disruptors from wastewater prior to their determination by GC-MS. The SHS employed was N,N-dimethylbenzylamine. Influential parameters on the extraction efficiency were studied and optimized. Optimum values were found as follows: volume of switched-on SHS, 1.0 mL; mixing type and time, vortex, 45 s; and concentration and volume of sodium hydroxide solution, 1.0 M, 1.0 mL. Under optimal conditions, LODs and LOQs were calculated in the ranges of 0.16
8.6 and 0.54
29 ng mL21, respectively. Enrichment factors ranged between 22 and 307. Accuracy of the method was verified through spiked recovery tests. The proposed method was applied for the determination of 2,4,6-trichlorophenol, 4-tert-octylphenol, atrazine, fluoxetine, penconazole, estrone, and di-noctylphthalate in synthetic wastewater and in two municipal wastewater samples. None of the studied analytes could be detected in the

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samples. Recovery values higher than 94.8% were obtained, demonstrating that the proposed method was applicable to complex matrices such as wastewater. Xu et al. [38] developed an SHS-LLME for the simultaneous extraction and determination of 11 pharmaceuticals (chlordiazepoxide, clozapine, cocaine, codeine, diazepam, ketamine, meperidine, methaqualone, papaverine, tramadol, and zolpidem) in human urine by GC-MS. DMCHA and sodium hydroxide were used as the SHS and the trigger for phase separation, respectively. The extraction procedure was optimized, and optimum values were found as follows: volume of protonated SHS, 400 μL; extraction time, 3 min; and concentration and volume of sodium hydroxide solution, 6.0 M, 400 μL. Under optimum conditions, %RSD were found in the range of 2.2%
13.5%. The linear dynamic range was from 5.0 to 2000.0 μg L21, R2 was greater than 0.99, and LODs were in the range of 0.36 to 12.50 μg L21. The proposed method was used to determine these pharmaceuticals in urine with percentage recoveries ranging from 73.8% to 103.0%.

8.6.2 Switchable-hydrophilicity solvents for extraction of inorganic analytes Yılmaz and Soylak [39] applied SHS in the microextraction of copper (II) ions from environmental, food, and biological samples as its metal chelate with 1-(2-pyridylazo) 2 2naphthol (PAN) prior to its determination by microsampling flame-atomic absorption spectrometry (FAAS). The method was termed switchable solvent-based liquid phase microextraction (SS-LPME). The authors used TEA as the extraction solvent for copper as its metal chelate, that is, Cu(II)-PAN. The experimental conditions were comprehensively studied and optimized, which included pH of the donor solution (8.0), the amount of PAN (0.3 mg), the volume of the switched-on TEA solution

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(1 mL), concentration and volume of sodium hydroxide as a phase separation trigger after extraction of the metal complex (10 M, 2.0 mL), and the volume of sample solution (15 mL). The effect of coexisting ions was also studied. LOD and repeatability (expressed as %RSD) of the method were found as 1.80 mg L21 and 3.8%, respectively. Accuracy was assessed against certified reference materials (i.e., TMDA-64.2-fortified water, TMDA-53.3-fortified water, TMDA-51.3-fortified water, 1573a tomato leaves, INCT-OBTL-5 Oriental Basma tobacco leaves, and NCS ZC 8100 2b human hair) and by addition-recovery tests. The proposed SS-LPME-FAAS method was applied for the determination of trace amounts of copper in water, food, and hair samples. A comparison of this method with other reported preconcentration methods coupled with FAAS was made, and it was concluded that SS-LPME had a comparatively low LOD (1.80 mg L21) and a high enhancement factor (17.6) for copper, with high sample throughput (at least 16 samples per hour). The authors also concluded that the main advantage of using SHS for microextraction studies was that they allowed the extraction of analyte in a homogeneous phase without the use of a dispersive solvent and/or the requirement for additional apparatus and experimental steps. Synthesis of the switchedon TEA solution was simple when dry ice was used. This solution was stable for at least 10 months. The need for vortex and ultrasonic bath, which are generally necessary for other liquid phase microextraction methods, was eliminated. There was no need for timeconsuming steps such as heating, cooling, pressure assistance, air assistance, or addition of salt. Yılmaz and Soylak [40] applied SHS-LLME for the extraction of cadmium(II) as pyrrolidinedithiocarbamate (APDC) chelate into switched-on TEA prior to its determination using microsampling FAAS. Analytical parameters affecting the complex formation and

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microextraction efficiency were studied and optimized. Optimum parameters were found as follows: sample pH, 4.0; amount of ligand, 1.25 mL, 0.1%, w/v; volume of SHS, 750 μL; concentration and volume of sodium hydroxide, 10 M, 2.0 mL; and sample volume, 15 mL. Under these conditions, LOD was found as 0.16 μg L21 and %RSD as 5.4%. The proposed method was validated by the analysis of certified reference materials [TMDA-51.3-fortified water, TMDA-53.3-fortified water, and SPSWW2 wastewater, 1573a Tomato Leaves, and Oriental Basma Tobacco Leaves (INCT-OBTL-5), and addition-recovery tests]. The method was applied to determination of cadmium in water, vegetables, fruits, and cigarette samples. Soylak et al. [41] described an SHS-LLME method for the extraction and preconcentration of uranium(VI) from environmental samples. The authors used UV
Vis spectrophotometry for the determination of uranium in its complex form with PAN. A quartz microcell with a path length of 10 mm and a volume of 700 μL was used for absorbance measurements. TEA in its protonated bicarbonate form was applied as the SHS in this work. Optimum parameters were found as follows: sample pH, 9.0; amount of ligand, 20 μg; volume of SHS, 1000 μL; concentration and volume of sodium hydroxide, 10 M, 1.5 mL; and sample volume, 20 mL. Under these optimum conditions, %RSD was found as 2.5% for five replicate measurements of model solutions spiked at 6 μg L21 of the analyte. LOD and LOQ were found as 0.3 and 1.0 μg L21, respectively, while the enhancement factor was calculated as 40. The accuracy of the method was verified with certified reference materials (i.e., GBW07424 [GSS-10] soil, HR-1 Harbour River sediment, and TMDA-64.2 environmental water) and addition-recovery tests. The proposed SHS-LLME
UV
Vis method was applied for the determination of uranium in water, sediment, soil, and rock samples. Khan and Soylak [42] proposed an SHS-LLME as an environmentally friendly approach prior

to the determination of mercury using UV
Vis spectrophotometry. Dithizone was used as a complexing reagent that formed a hydrophobic complex with Hg(II) and could be determined at 574.7 nm after being extracted into DMCHA. Optimum parameters were found as follows: sample pH, 7.0; amount of ligand, 12 μg; volume of SHS, 1000 μL; concentration and volume of sodium hydroxide, 10 M, 1.5 mL; and sample volume, 40 mL. Under these optimum conditions, %RSD was found as 0.8% for five replicate measurements of Hg(II) solution spiked at 1.06 μg L21. LOD, LOQ, and enhancement factors were calculated as 0.19 μg L21, 0.62 μg L21, and 40, respectively. Accuracy check was done using human hair certified reference material (i.e., NCS ZC81002B). The suggested method was applied for the determination of mercury in water and hair samples, and satisfactory results were obtained. Ezoddin et al. [43] developed an air-assisted SHS-LLME for the preconcentration and determination of palladium(II) ions in environmental samples using graphite furnace
atomic absorption spectrometry (GFAAS). PAN was used as the chelating agent, and TEA was used as SHS. Phase separation was achieved through the addition of sodium hydroxide. Air assistance led to the rapid formation of fine droplets of the SHS in the aqueous solution. Influential parameters on extraction efficiency were studied and optimized, which included the following: pH, 4.0; concentration of the ligand, 2 3 1025 M; extractant volume, 750 μL; volume of sodium hydroxide (20 M), 1 mL; and number of extraction cycles, 5. It was also demonstrated that the common coexisting ions did not have significant effect on the determination of palladium(II) ions in the studied matrices. Under these optimum conditions, the LOD, preconcentration factor, and %RSD were calculated as 0.07 μg L21, 64, and 3.5%, respectively. The recovery of palladium(II) ions from water, road dust, and catalytic converter

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samples was in the range of 98.3%
103.2%. The results obtained showed that the proposed method can be efficient for the determination of palladium(II) ions in environmental samples in routine work. It was concluded that the use of air to assist the extraction accelerated the formation of fine droplets and mass transfer of the target analyte into the sample solution, increasing the turbidity of the solution. This method could be applied for the determination of other metal ions with the help of various chelating agents. Reclo et al. [44] suggested an SHS-LLME method for the preconcentration and separation of ultratraces of palladium from environmental samples prior to its determination by FAAS when equipped with a microsampling injection unit. Switching of DMCHA, as the extraction solvent, was achieved through a reaction with carbonated water. The hydrophilic bicarbonate salt of the protonated DMCHA was used as the extractant for palladium complexed with 2-(5-bromo-2pyridylazo) 2 5-diethylaminophenol (5-BrPADAP). Formation of the hydrophobic form of the SHS into its hydrophilic form was achieved by the addition of sodium hydroxide into the extractant-sample mixture solution. The influence of key parameters affecting extraction recovery were studied and optimized using Plackett
Burman design, CCD, and three-dimensional (3D) surface response. These parameters were as follows: sample pH, 4.0, adjusted by addition of 2 mL of acetate buffer to the sample solution; concentration and volume of the chelating agent, 0.1% (w/v), 400 μL; volume of sample solution, 15 mL; volume of SHS, 600 μL; concentration and volume of sodium hydroxide 10 M, 1.5 mL; and vortex time, 1 min. Approximately 250 μL of the switched-off SHS were completed to 400 μL with 33% (v/v) nitric acid before being introduced into FAAS. Under these conditions, the calibration plot was linear over the range 0.015
1.6 mg L21 of palladium with a

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correlation coefficient of 0.999. The LODs for liquid and solid samples were found as 4.28 μg L21 and 0.54 μg g21, respectively. The preconcentration factor was calculated as 37.5. Accuracy of the method was confirmed by determination of palladium in certified reference material (HP-CRM-SA-C-Sandy Soil C). The procedure was applied for the determination of palladium content of real samples as automotive catalytic converter, roadside dust, seawater, and river water with percentage recoveries above 95.3% and %RSD less than 8.0%. It was concluded that the proposed method could be considered green since it consumed small amounts of nonflammable and low-volatility solvent and that it could play a useful role in monitoring the level of palladium in environmental samples. Memon et al. [45] proposed an SHS-LLME method for the extraction, preconcentration, and determination of cobalt in tobacco and food samples prior to FAAS with a microinjecting system. N,N-Dimethyl-n-octylamine bicarbonate was synthesized in the presence of CO2 and was used for the extraction of Co(II) as its metal chelate with 1-nitroso-2-naphthol at pH 4.0. Experimental parameters influencing the extraction recovery were found as follows: volume of sample solution, 5 mL, buffered through the addition of 2 mL to the desired pH; concentration and volume of the chelating agent, 0.01%, 200 μL; time of complex formation, 2 min; volume of the SHS, 600 μL; concentration and volume of sodium hydroxide, 10 M, 600 μL; vortex time, 30 s; and centrifugation rate and time, 4000 rpm, 10 min. The analyte-rich SHS, N,N dimethyl-n-octylamine, 250 μL, was diluted to 500 μL with concentrated HNO3 (65%) before being injected into the instrument. Under these optimum conditions, LOD and LOQ were found as 3.2 and 10.6 μg L21, respectively. Accuracy and validity of the method were verified through the use of certified reference material (IC-INCT-OBTL-5) and by addition-recovery check. Consequently,

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the method was effectively carried out for the determination of the cobalt level in tobacco and food samples. The use of ligandless SHS-LLME was demonstrated by Reclo et al. [46] for the extraction of nickel from food and cigarette samples prior to its determination by microsampling FAAS. The use of 1-ethylpiperidine after exposure to CO2, as the extraction solvent, allowed the simple and effective extraction of nickel from the samples without the need for an organic chelating agent, which presented the main advantage of this method. Important factors affecting extraction efficiencies were as follows: 5 mL of the digest containing nickel(II) was buffered to pH 4.0 through the addition of 2 mL of 0.2 M phosphate buffer. The solution was made up to 10 mL with DI water; volume of the switchedon SHS, 800 μL; concentration and volume of sodium hydroxide, 10 M, 1000 μL; vortex time, 30 s; and centrifugation rate and time, 4000 rpm, 10 min. An aliquot of concentrated HNO3 (65%) (250 μL) was added to the analyte-rich SHS, and the solution was diluted with DI water to 1 mL before being injected into the instrument. Under optimum conditions, LOD was calculated as 5.2 μg L21. Accuracy of the developed method was evaluated by the analysis of certified reference materials (NCS ZC73032 Celery and INCT-OBTL-5 Oriental Basma tobacco leaves) and additionrecovery tests before it was applied for the determination of nickel in food (i.e., tea, cauliflower, balsam, eggplant, pomegranate, and rosemary) and in cigarette samples. Habibiyan et al. [47] developed an ultrasonic-assisted SHS-LLME combined with microsample injection in FAAS for the determination of some heavy metals (i.e., Cd, Ni, Pb, and Co) in water, urine, and tea infusion samples. TEA was applied as the SHS to extract the complexes of metal ions. Ultrasonic energy accelerated the formation of fine droplets of the extractant into the aqueous solution. Several factors influencing the recovery of the

analytes were studied: amount of chelating agent (dithizone), 0.1 mL 0.1% (w/v); pH of donor solution, 6.0; concentration and volume of sodium hydroxide, 10 M, 2 mL; volume of SHS, 900 μL; ultrasonic time, 2 min; and the amount of NaCl, as an ionic strength modifier, 1.5 g. It was also shown that the presence of common coexisting ions had no significant effect on the extraction recovery of the analytes. Therefore, the analytes could be successfully determined in various matrices. Under optimum conditions, LODs were in the range of 0.24 and 0.76 μg L21, and %RSD in the range of 1.3%
3.8% at 50 μg L21 of the analytes. Preconcentration factors of approximately 100 were obtained for the studied analytes. The accuracy of the proposed method was verified using a certified reference material (CRM TMDW-500) and addition-recovery tests. The method was utilized to determine Cd, Ni, Pb, and Co in tap and bottled water, as well as in human urine and tea infusion samples. Bazel et al. [48] used SHS-LLME for the extraction of nickel prior to its determination with UV
Vis spectrophotometry. The procedure was developed for the extraction and preconcentration of nickel as its dimethylglyoxime complex using TEA as the extraction SHS. Phase separation of the extractant was achieved by adding a concentrated alkaline solution to the extraction mixture. The nickelenriched TEA extract was separated and evaporated, the residue was dissolved in chloroform (50 μL), and absorbance was measured at 380 nm. Conditions affecting the extraction efficiency of nickel were examined: pH of the medium, 3.0; concentration and volume of dimethylglyoxime, 0.5% (w/v), 1.4 mL; type and volume of the disperser solvent, ethanol, 1 mL; concentration and volume of sodium hydroxide, 15 M, 1.5 mL; and vortex time, 30 s. Under these optimum conditions, LOD of 0.020 μg mL21 was obtained. Linear dynamic range was found to be between 0.050 and 0.60 μg mL21. It was shown that coexisting

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ions, such as Fe31, Fe21, Co21, Cu21, Zn21, Cd21, Pb21, Hg21, did not interfere with the determination of nickel. Accuracy of the developed method was verified by the analysis of certified reference materials (certified sample of the SPS-WW2 wastewater and water from the Horna´d river) before it was applied for the determination of nickel in water samples with recoveries higher than 93% and %RSD lower than 12% obtained. Ali et al. [49] suggested an SHS-based liquid
solid dispersive microextraction method for the determination of arsenic in water samples using hydride-generation
atomic absorption spectrometry (HG-AAS). In this method, multiwalled carbon nanotube (MWCNT) was immobilized with diethylenetriamine (DETA) and then used as the solid phase adsorbent for the determination of trace concentrations of arsenic ion. Reversible hydrophobic-hydrophilic
switchable, functionalized MWCNT can occur upon exposure to CO2 as the antisolvent trigger. Optimum conditions were found as follows: sample pH, 6.0; amount of MWCNT-DETA, 13 mg; CO2 pressure and purging time, 1.0 MPa, 23 min; type and volume of acid and its concentration for backextraction, HNO3, 300 μL, 0.5 M; and sample volume, 25 mL. Under optimized conditions, enrichment factor and LOD were found as 83 and 3.05 ng L21, respectively. Accuracy of the developed method was confirmed by the analysis of certified water reference materials (Lake Ontario water [TM-28.3] and river water [NRCC-SLRS-5]). The proposed method was successfully applied for the determination of arsenic ions in real water samples. Vessally et al. [50] applied SHS-LLME for the preconcentration and detection of cadmium ions in baby food samples using FAAS after its chelation with 2,9-dimethyl-1,10-phenanthroline (neocuproine). Optimum values for the factors influencing the extraction efficiency were found as follows: pH of sample solution, 7.0; concentration ratio of [ligand]/[cadmium],

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5; volume of switched-on SHS, 500 μL; concentration and volume of sodium hydroxide, 10 M, 1.5 mL; and volume of sample solution, below 20 mL. The results revealed that the presence of potential interfering ions in various real samples had no significant effect on the separation and determination of cadmium ions. Under the optimized conditions, LOD, LOQ, and the enrichment factor were found as 0.02, 0.1 μg L21, and 54.2, respectively. The calibration graph was linear within the range of 0.1
60 μg L21 with a correlation of determination (r2) of 0.99. %RSD for the determination of 40 μg L21 of Cd(II) was found as 3.1%. The intraday and interday precisions for real samples analysis were in the range of 4.4%
5.6% and 4.9%
5.7%, respectively. Accuracy of the proposed method was evaluated by the analysis of certified reference materials (NIST-1549 nonfat milk powder) and by addition-recovery tests before it was applied for the determination of cadmium in baby food samples and satisfactory analytical results were achieved. Arain et al. [51] developed an SHS-LLME method for the extraction and determination of aluminum from acid-digested blood samples of patients with neurological disorders using FAAS. SHS was made of 1,8-Diazabicyclo [5.4.0]undec-7-ene and decanol, which reversibly changed from its hydrophobic to hydrophilic form by switching the system on and off in aqueous medium upon exposure to CO2. The SHS polar microemulsion was switched on by bubbling CO2 and off by heating to 55 C upon exposure to nitrogen gas. The switchedoff SHS effectively extracted the hydrophobic aluminum chelate with 3,5,7,2,4-pentahydroxyflavone (morin). The enriched hydrophobic Almorin-SHS was treated with 1.0 M HNO3 and CO2 purging at various time intervals in order to switch it to a miscible polar hydrophilic monophase state. The SHS was easily recycled up to six times for further enrichment. Several experimental parameters were optimized as follows: pH of sample solution, 6.0;

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concentration and volume of chelating agent, 0.125% (w/v); 0.3 mL; pressure and exposure time to CO2, 4 MPa, 5 min; and concentration and volume of back-extraction acid solution, 1.5 M, 0.5 mL of HNO3. Interference studies indicated that Cd21, Cu21, Zn21, and Fe31 were tolerable up to 25 mg L21, whereas the tolerance levels of Co21 and Ni21 were greater than 30 mg L21. Under optimum conditions, the enhancement factor and LOD were calculated as 25 and 0.47 μg L21, respectively, for 10 mL of samples or standards solution. The accuracy of the developed method was verified using certified blood reference material (SRM 3101a), with a standard addition procedure. The method was used for the preconcentration of aluminum in blood samples, and satisfactory results were obtained. It was also concluded that concentration of aluminum in the blood samples of patients with neurological disorders (Alzheimer’s disease, stroke, and dementia) was about twofold higher than that found for control subjects (p , 0.001). Zhang et al. [52] proposed a method based on SHS-LLME for the extraction of trace amounts of lead and cadmium from environmental and biological samples prior to their determination by GFAAS. Pb(II) and Cd(II) were complexed with APDC before being extracted into the TEA phase. Vortex assistance led to the rapid formation of fine droplets of the extractant in the aqueous solution and increased the contact surface between both immiscible liquids. The factors affecting the microextraction procedure were investigated and found as follows: pH of sample solution, 4.0; concentration of APDC, 0.4 g L21; volume of SHS, 2 mL; concentration and volume of sodium hydroxide, 10 M, 1.0 mL, vortex time, 30 s; and sample volume, up to 10 mL. The collected organic phase was made up to 0.2 mL with 1 M HNO3 in ethanol before being injected into GFAAS. Interference studies showed a high tolerance to coexisting ions. Under optimum conditions, the enrichment

factor of 50 was achieved with consumption of 10 mL aqueous samples, and LODs of 16 and 3.9 ng L21 were obtained for Pb(II) and Cd(II), respectively. An accuracy check was done through the analysis of certified reference materials (i.e., GSBZ50009-88 environmental water, GBW07605 tea, and GBW07601[GSH-1] human hair). The method was also successfully applied for the determination of Pb(II) and Cd (II) ions in water, tea, and human hair samples with satisfactory analytical results. Shishov et al. [53] developed an automated continuous homogeneous microextraction method for the determination of selenium and arsenic in environmental water and liver samples by hydride generation
atomic fluorescence spectrometry (HG-AFS). Nonanoic acid was used as the SHS for the homogeneous microextraction of As(III) and Se(IV) complexes with APDC. The procedure involved online mixing of APDC, sodium nonanoate and the acidified sample solution, which resulted in the formation of nonanoic acid as the SHS. By this continuous process, analyte complexes with PDC were formed and extracted into the fine SHS droplets, followed by retention into a monolithic column packed with a block of porous PTFE. Finally, the retained complexes were eluted with NaOH solution and delivered to the HG-AFS system. Parameters affecting the efficiency of the microextraction procedure were investigated, and optimum values were found as follows: concentration of sodium nonanoate, 6.0 mM; concentration of HCl in the sample, 10 mM; concentration of APDC, 6.0 mM; sample volume, 25 mL; sample flow rate, 5 mL min21; elution rate was 1 mL min21, with a concentration of NaOH, and its flow rate, 0.25 M, 2 mL min21. Under these optimum conditions, the enrichment factor was found as about 48, and LOD was 0.01 μg L21 for both analytes. Potential interfering ions such as Mg, K, Na, and Ca were tolerable at 900
1000-fold excess. Zn, Mn, Cu, and Fe interfered even at 100
300-fold excess. To verify the accuracy of

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the developed method, certified reference materials of water (EnviroMAT Waste Water [EU-H-3], EnviroMAT Ground Water [ES-H-2]), and liver (CRM185R Bovine liver) were used. The proposed method was applied successfully for the determination of selenium and arsenic in environmental water and liver samples. presented a vortex-assisted SHS-LLME for the preconcentration of cadmium in environmental samples prior to its determination using FAAS. CO2-protonated N,N-dimethylbenzylamine was applied as the SHS. A slotted quartz tube (SQT) was used to increase the residence time of Cd atoms in the light path. Optimum extraction conditions were found as follows: type and amount of ligand, diphenylcarbazone, 1.0 mL of (0.05% w/v) ligand solution; volume of SHS, 1.0 mL; pH and volume of sample solution, 10, 8.0 mL; mixing type and time, vortex, 15 s; volume of HNO3, 150 μL; and concentration and volume of sodium hydroxide solution, 1.0 M, 2.0 mL. Under these optimum conditions, LOD and LOQ were calculated as 0.7 and 2.6 μg L21, respectively. % RSD of 5.9 indicated high precision of the developed method. Accuracy was checked by using a standard reference material (coal fly ash SRM 1633c). Spiked recovery tests were also performed on lake water and wastewater samples at different concentrations with recoveries in the range of 90%
103%. The proposed method was successfully applied for the determination of cadmium in lake and wastewater. Tekin et al. [54] also suggested a vortexassisted SHS-LLME method prior to slotted quartz tube
FAAS for the determination of cobalt in egg yolk and vitamin B12. N,NDimethylbenzylamide was used as the SHS, which was converted to its protonated form by the addition of dry ice. Cobalt was complexed with 1,5-diphenylcarbazone and extracted into the SHS phase. After the extraction, HNO3 was added to the extract to increase the nebulization efficiency of the SHS phase into the instrument. SQT was combined with FAAS to

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enhance the detection power of the system as compared to conventional FAAS. Optimized conditions were found as follows: volume of switched-on SHS, 1.0 mL; mixing type and time, vortex, 30 s; volume of HNO3, 250 μL; and concentration and volume of sodium hydroxide solution, 1.0 M, 2.0 mL. Under these optimum conditions, LODs were calculated as 75 μg L21 for FAAS, 33 μg L21 for SQT-FAAS, 7.6 μg L21 for SHS-LLME-FAAS, and 2.3 μg L21 for SHSLLME-SQT-FAAS. The developed method was applied for the determination of cobalt in egg yolk and vitamin B12, and the recovery results were found in the range of 105%
114%. Moghadam et al. [55] developed an effervescence-assisted LLME method based on the use of a medium-chain fatty acid for the determination of silver and cobalt ions using microsampling in FAAS. 1-phenyl-1,2-propanedione-2-oximethiosemicarbazone (PPDOT) was used as the chelating agent to form hydrophobic complexes, causing an easy and effective extraction of the two metal ions into the organic extraction phase. In addition, with proper pH and the addition of an effervescent agent, the extraction medium could acquire a dual hydrophilicity/hydrophobicity nature, leading to a simple and efficient microextraction, followed by collection of the organic solvent (upper phase). Influential parameters found using a CCD were as follows: type and volume of the SHS, hexanoic acid, 340 μL; concentration of the chelating agent, 1 3 1026 M; and type and concentration of effervescent agent, sodium carbonate and sulfuric acid, 2 and 3 M, respectively. Under optimum conditions, linear dynamic ranges of 5.0
150 and 8.0
200 ng mL21 for Ag1 and Co21 ions, respectively, with coefficients of determination (R2) higher than 0.98, were obtained. LODs and %RSD were found to be within the span of 2.0
3.0 ng mL21 and 3.4%
4.2%, respectively. The proposed method was efficiently applied for the determination of the two metal ions in cow’s milk, vitamin B12, orange juice, and tap water.

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8. Switchable solvents in separation and preconcentration of organic and inorganic species

Fırat and Bakırdere [56] presented an SHSLLME method for the determination of palladium in water samples using SQT-FAAS after preconcentration using a Schiff base ligand. Efficient extraction of palladium was facilitated by complexation with a Schiff base ligand (referred to as S12), synthesized for this study. Optimum parameters were found as follows: sample pH, 8.0; concentration of the ligand, 5.0 mM; volume of SHS, 0.5 mL; mixing type and time, vortex, 15 s; volume of HNO3, 100 μL, as well as concentration and volume of sodium hydroxide solution, 1.0 M, 1.5 mL. Under these optimum conditions, enrichment factor was 34. The method showed a linear dynamic range between 50 and 750 μg L21 with R2 values larger than 0.9991. LOD and LOQ were 15 and 50 μg L21, respectively. % RSD was below 9.0% for all measurements. Spiked recovery tests performed for a palladium electroplating bath solution gave poor results when quantified against aqueous calibration standards. Therefore, matrix-matched calibration was used to improve recovery, which ranged between 97% and 105% for four different spiked concentrations.

8.6.3 Maximizing extraction efficiency with switchable-hydrophilicity solvents To maximize the extraction efficiency of SHS-LLME in addition to optimization of instrumental parameters, experimental parameters affecting the extraction efficiency of atomic and molecular analytes should be studied in detail and optimized. These parameters can be optimized using a one-parameter-at-atime approach or though using statistical experimental designs such as Plackett
Burman, central composite, three-dimensional (3D) surface response, or the like. Parameters that have been found to affect extraction efficiency included the following: type and volume of SHS, ratio of SHS to water in preparing

the switched-on SHS, volume of sample solution, sample pH, extraction temperature, type, concentration and amount of ligand (for atomic analytes), mixing type (e.g., mechanical shaking, ultrasonication, vortex) and time, ionic strength (type and concentration of salt added to the sample solution), concentration and volume of sodium hydroxide solution to trigger phase separation (or any method that can serve this purpose), type of sample introduction into the analytical instrument (e.g., direct injection, dilution of the final extract, evaporation-todryness, and reconstitution into a more compatible solvent, and back-extraction, and so on). Interference studies to examine the effect and tolerance level of coexisting ions and/or compounds should also be investigated.

8.6.4 Trends in switchable-hydrophilicity solvents
based microextractions Although SHS were introduced by Jessop et al. in 2005 [2], their first use in the microextraction context was not suggested before 2014 [11]. In this study, benz[a]anthracene was extracted from water samples before its determination using fluorescence spectrophotometry. Since then, these solvents started to attract the attention of researchers working in this field. The rapid increase of publications where SHSLLME was used is shown in Fig. 8.3, reaching about 37 publications in the last six years.

FIGURE 8.3 Number of publications using SHS-LLME (Web of Science, May 2019).

New Generation Green Solvents for Separation and Preconcentration

373

8.6 Switchable-hydrophilicity solvents in microextractions

Although the first publication used SHSLLME for studying molecular analytes, the method was adapted soon to elemental analysis. The number of publications for both molecular (Table 8.3) and atomic (Table 8.4) analytes is almost equal nowadays (Fig. 8.4), demonstrating the applicability of this method to a variety of molecular and atomic analytes.

Another point related to SHS-LLME that drew the attention of researchers was the possibility to automate this method. The first attempt to automate SHS-LLME was shown in 2015. This was done using a syringe and peristaltic pumps prior to HPLC for the determination of ofloxacin in human urine samples [16]. Researchers have used SHS-LLME for the analysis of environmental, biological, and food

TABLE 8.3 Summary of SHS-LLME methods applied for molecular analytes. Analyte

Sample

SHS/volume (µL)

Instrument

Refs.

Eleven pharmaceuticals

Human urine

DMCHA, 166

GC-MS

[38]

4-n-Nonylphenol

Municipal wastewater

N,N-Dimethylbenzylamine, GC-MS 1000

[34]

Benz[a]anthracene

Water

DMCHA, 375

Fluorescence spectrophotometer

[11]

Bisphenols

Beverages

DMCHA, 391

HPLC-UV

[29]

Chloramphenicol

Water

DMCHA, 333

HPLC-DAD

[36]

Endocrine disruptors, pesticides, Water hormones.

N,N-Dimethylbenzylamine, GC-MS 750

[27]

Fluoroquinolones

Shrimp

Nonanoic acid, 4

[19]

Fluoxetine, estrone, pesticides, endocrine disruptors

Wastewater

N,N-Dimethylbenzylamine, GC-MS 500

[37]

Methadone, tramadol

Human urine

Dipropylamine, 400

GC-FID

[26]

Methamphetamine

Human urine

Dipropylamine, 100

GC-MS

[25]

Nitrazepam

Aqueous

N,N-Dipropylamine, 100

Differential pulse voltammetry

[32]

Ofloxacin

Human urine

Hexanoic acid, 50

HPLC-FLD

[16]

Ofloxacin

Chicken meat

Dichloromethane and acrylic acid, 600

HPLC-FLD

[18]

Paraquat

Biological, river water

TEA, 250

HPLC-UV

[21]

Protoberberine alkaloids

Rhizoma coptidis

TEA, 350

HPLC-DAD

[31]

Quaternary ammonium herbicide, paraquat

Human urine, plasma, river water, apple juice

TEA, 375

GC-MS

[23]

Steroid hormones

Water

Nonanoic acid, 100

HPLC-UV

[22]

Sudan dyes

Solid food

Hexanoic acid, 300

HPLC-UV

[33]

Sudan dyes

Spices

Hexanoic acid,130

HPLC-UV

[57]

HPLC-FLD

New Generation Green Solvents for Separation and Preconcentration

TABLE 8.4 Summary of SHS-LLME methods applied for atomic analytes. Analyte

Sample

SHS/ Volume (µL)

Instrument Refs.

Arsenic

Water

Diethylenetriamine, 1400

HG-AAS

[49]

Arsenic, selenium

Environmental water, liver

Sodium nonanoate, 5.4 (mg)

HG-AFS

[53]

Cadmium

Water, vegetable, fruit, cigarette

TEA, 375

FAAS

[40]

Cadmium

Baby food

TEA, 250

FAAS

[50]

Cadmium

Environmental

N,N-Dimethylbenzylamine, 500

SQT-FAAS

[58]

Cadmium, nickel, lead, Water, urine and tea infusion cobalt

TEA, 450

FAAS

[47]

Cobalt

Tobacco, food

N,N-Dimethyl-n-octylamine, 200

FAAS

[45]

Cobalt

Egg yolk and vitamin B12

N,N-Dimethylbenzylamide, 500

SQT-FAAS

[54]

Copper

Environmental

TEA,

FAAS

[39]

Lead and cadmium

Water, tea, human hair

TEA, 1000

GFAAS

[52]

Mercury

Environmental

DMCHA, 1000

UV
Vis

[42]

Nickel

Tobacco, food

1-Ethylpiperidine, 400

FAAS

[45]

Palladium

Automotive catalytic converters, roadside dust, river water

DMCHA, 300

FAAS

[44]

Palladium

Water

TEA, 376

GFAAS

[43]

Palladium

Water samples

N,N-Dimethylbenzylamine, 250

SQT-FAAS

[56]

Silver and cobalt

Bovine milk, orange juice, vitamin B12, tap water

Hexanoic acid, 300

FAAS

[55]

Uranium

Environmental

TEA, 1000

UV
Vis

[41]

FIGURE 8.4 Type of analytes preconcentrated with SHS-LLME (Web of Science, May 2019).

8.6 Switchable-hydrophilicity solvents in microextractions

375

FIGURE 8.5 Type of samples studied using SHS-LLME (Web of Science, May 2019).

samples (Fig. 8.5). Some studies used SHSLLME for studying pharmaceuticals [54,55], in addition to only one publication studying the applicability of this method to plant samples. In this study, SHS-LLME was used to determine protoberberine alkaloids in R. coptidis samples [31]. As mentioned earlier, the first application of SHS-LLME was done using fluorescence spectrometry [11], the only one using this technique. Two other studies used SHS-LLME prior to UV
Vis to determine uranium [41] and mercury [42] in environmental samples. Most of the studies used AAS (Table 8.4), which were as follows: copper in environmental sample using FAAS [39]; lead and cadmium in water, tea, and human hair samples using GFAAS [52]; cadmium in water, vegetable, fruit, and cigarette samples using FAAS [40]; palladium in water samples using GFAAS [43]; cobalt in tobacco and food samples using FAAS [45]; nickel in tobacco and food samples using FAAS [46]; silver and cobalt in bovine milk, orange juice, Vitamin B12 (methylcobalamin) pill, and tap water using FAAS [55]; cadmium, nickel, lead, and cobalt in water, urine, and tea infusion samples using FAAS [47];

cobalt in egg yolk and Vitamin B12 pill using slotted quartz tube (SQT-FAAS) [54]; arsenic in water samples using HG-AAS [49]; cadmium in environmental samples using SQT-FAAS [58]; palladium in water samples using SQTFAAS [56]; palladium in automotive catalytic converters, roadside dust, and river water using FAAS [44]; and cadmium in baby food samples using FAAS [50]. In addition, one study applied hydride generation
atomic fluorescence spectrometry (HG-AFS) to determine arsenic and selenium in environmental water and liver samples [53]. Chromatography is another technique that was combined with SHS-LLME in the literature, particularly GC and HPLC. In general, SHS-LLME-GC does not require any further pretreatment after the extraction step, such as solvent reconstitution throughout evaporationto-dryness (ETD), which is due to the volatility of SHS [26,27,34,37]. However, in some studies, ETD was applied for other reasons such as derivatization of the analyte [25] or when the solvent was incompatible with the detector used in GC [23,38]. On the other hand, SHS-LLME-HPLC needed an extra step before injecting the

New Generation Green Solvents for Separation and Preconcentration

376

8. Switchable solvents in separation and preconcentration of organic and inorganic species

extract into the instrument, which was due to the low solubility of the SHS in the switchedoff form in the mobile phase [18,29,31]. Nevertheless, in cases where the mobile phase contained more than 90% of the organic solvent, the extract could be injected directly into the system in its switched-off form without any further treatment [21,33,57]. Another solution to this problem with HPLC was to dissolve or dilute the extract with an acid and/or organic solvent before injecting the extract into

the instrument [16,22,36] or via back-extraction of the analytes into an aqueous solution [19] (see Fig. 8.6). The majority of studies used tertiary amines as SHS, as shown in Tables 8.3 and 8.4, and Fig. 8.7, besides secondary amines, fatty acids, and amides. The main reason behind the use of these solvents was the proper physical properties, low cost, applicability, and stability of these solvents after being switched on.

FIGURE 8.6 Type of instruments used with SHS-LLME (Web of Science, May 2019).

FIGURE 8.7

Types of SHS used in microextraction (Web of Science, May 2019).

New Generation Green Solvents for Separation and Preconcentration

References

8.7 Future aspects Several future aspects regarding SHS and their uses might be summarized: 1. More types of SHS and systems need to be discovered, and their physicochemical properties need to be studied with a wide range of polarities for the extraction of polar, intermediate-polarity, and nonpolar molecules. 2. Application of SHS-LLME for speciation analysis should be considered. 3. Automation of SHS-LLME is highly desired for high-throughput analysis. 4. More applications of SHS-LLME to cover pharmaceutical, biological, and environmental samples are worth exploration. 5. Hyphenation of SHS-LLME to a wider range of analytical instruments is needed. 6. Simultaneous extraction of acidic and basic analytes is highly required. 7. Displacement of the use of highly concentrated sodium hydroxide to switch off the SHS is required because some analytes may undergo hydrolysis during this step. 8. Large-scale applications of SHS are worth exploring for isolation of important compounds from natural products. 9. In situ derivatization of molecular analytes in SHS-LLME can be interesting. 10. Hyphenation of SHS-LLME with other contemporary extraction techniques, such as solid phase microextractions, can have potential applicability.

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based liquid phase microextraction prior to slotted quartz tube flame atomic absorption spectrometry, Food Chem. 286 (2019) 500
505. [55] A.G. Moghadam, M. Rajabi, M. Hemmati, A. Asghari, Development of effervescence-assisted liquid phase microextraction based on fatty acid for determination of silver and cobalt ions using micro-sampling flame atomic absorption spectrometry, J. Mol. Liq. 242 (2017) 1176
1183. [56] M. Firat, E.G. Bakirdere, An accurate and sensitive analytical strategy for the determination of palladium in aqueous samples: slotted quartz tube flame atomic absorption spectrometry with switchable liquid-liquid

microextraction after preconcentration using a Schiff base ligand, Environ. Monit. Assess. 191 (3) (2019) 9. [57] M. Hemmati, M. Rajabi, Switchable fatty acid based CO2-effervescence ameliorated emulsification microextraction prior to high performance liquid chromatography for efficient analyses of toxic azo dyes in foodstuffs, Food Chem. 286 (2019) 185
190. [58] M. Firat, S. Bodur, B. Tisli, C. Ozlu, D.S. Chormey, F. Turak, et al., Vortex-assisted switchable liquid-liquid microextraction for the preconcentration of cadmium in environmental samples prior to its determination with flame atomic absorption spectrometry, Environ. Monit. Assess. 190 (7) (2018) 8.

New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

9 Deep eutectic solvent in separation and preconcentration of organic and inorganic species Tahere Khezeli1, Mehrorang Ghaedi2, Sonia Bahrani2, Ali Daneshfar1 and Mustafa Soylak3 1

Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, Iran 2Department of Chemistry, Yasouj University, Yasouj, Iran 3Department of Chemistry, Faculty of Sciences, Erciyes University, Kayseri, Turkey

Abbreviations ATPS ChCl DES EA-EMESSDES ELME HBA HBD IL LPME LTTM MDES OA PAC PPAs RSD RSM TMAC1 TPMBr TTL UALPME

aqueous two-phase systems choline chloride deep eutectic solvents effervescent-assisted emulsification microextraction emulsion
liquid microextraction hydrogen bond acceptor hydrogen bond donor ionic liquids liquid phase microextraction low transition temperature mix magnetic eutectic solvent oleic acid proanthocyanidins polyisoprene acetate relative standard deviation response surface methodology tetra methyl ammonium chloride tetra propyl ammonium bromide terpene lactone ultrasonic-assisted liquid phase microextraction

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00009-7

9.1 Introduction There is no doubt that most of the functional programs used in many industries require particular solvents. Therefore it is important to replace conventional hazardous organic solvents with economical environmental solvents. Therefore progress in the field of green solvents is important to minimize the environmental problems related to the using old solvents in the chemical systems, as well as to decrease costs and improve the safety and healthness. How do we describe green solvents? If the solvent is safe for both humans and nature, some people will develop it, which can be considered a green solvent [1]. Anastas and Warner mention 12 criteria that green solvents must meet (Table 9.1).

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© 2020 Elsevier Inc. All rights reserved.

382

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.1 Twelve criteria for a green solvent. Criteria

Concept

Availability

A green solvent should be accessible on a large-scale, and the generation limit should not vary much with the ultimate goal of ensuring the consistent accessibility of available solvent.

Price

Green solvents should not only be price competitive, but their prices should not be unstable over time to certify the chemical process sustainability.

Recyclability

Green solubility must be completely reused in the chemical process, clearly using green production strategies.

Grade

A technical-type solvent is preferred to avoid the purification process that consumes the energy necessary to obtain a solvent of high purity.

Synthesis

Green solvents should be acquired by energy-saving procedures, and the synthesis reaction should be very atomic.

Toxicity

Green solvents must exhibit insignificant toxicity, with the ultimate goal of reducing all hazards associated with human-made major pollution or expelling them in the nature when used for personal and household, paint, and the like.

Biodegradability Green solvents should be biodegradable and should not generate toxic metabolites. Performance

To be acceptable, the green solvent should have similar or even better properties (viscosity, density, polarity, etc.) in comparison to the conventional solvents used.

Stability

For using in chemical processes, the green solvent must be stable chemically and thermally.

Flammability

In the process of manipulation, for the sake of safety, green solubility should not be flammable.

Storage

Green solvents should be easy to store and should meet all regulations for safe transportation by road, train, boat, or aircraft.

Renewability

In terms of carbon footprint, green solvents should be produced preferentially, using renewable raw materials.

Solvents that meet all these 12 criteria are not available. In any case, in the last decade, some creative solvents have been provided in writing, some of which meet a large number of these standards [2]. Similarly, we have recently encountered many applications of water, supercritical fluids, perfluorinated solvents, glycerol and derived solvents, biobased solvents, and ionic liquids (IL) as green solvents. In many cases, a number of problems such as poor solubility or stability of certain materials and reagents in the water, the need for complex equipment in supercritical fluids, complexity and high production costs, the toxicity of nature, and the

costly process of synthesis of IL lead to the use of another solvents in extraction process. Limit [3]. To resolve these shortcomings, in 2003 Abbot et al. suggested for the first time new solvents called deep eutectic solvents (DES) [4]. This section focuses on the physical and chemical characteristics of DES and describes some of recent applications of these new solvents in extraction and preconcentration technologies. Francisco et al. proposed a new set of solvents based on natural compounds and called low transition temperature mix (LTTM). Unlike DES, LTTM shows no eutectic points but has a glass transition at low temperatures. Similar to DES, the liquid state of LTTM is the

New Generation Green Solvents for Separation and Preconcentration

9.2 Deep eutectic solvent (definition and preparation)

result of hydrogen bonding interactions. Many liquid mixtures classified as DES cannot be designated as any of the previous DES groups because they do not show a fusion peak in differential scanning calorimetry; therefore the term “low transition temperature mixture” is more suitable for this solvent [5,6]. In 2011 the natural deep eutectic solvents (NADES) concept was exhibited for the first time as a new DES group [7]. NADES is characterized by a mixture of conventional compounds in certain molar ratios, for example, biologically rich sugars, organic acids, amino acids, and organic bases. As of now, more than 150 NADES combinations have been proposed by several researchers [8
12].

9.2 Deep eutectic solvent (definition and preparation) A new type of ionic solvent called DES has emerged to overcome the cost and toxicity of conventional solvents. They are analogs of IL because the physical properties and phase behavior of DES are similar to the physical properties and phase behavior of IL. The main DES is manufactured by Abbott, mixing choline chloride (ChCl is a quaternary ammonium salt) and urea (Fig. 9.1) [13,14]. Both solids have a high melting point; ChCl has a 302 C melting temperature, and urea has a 133 C melting point. The mixture of the two solid starting materials produces an eutectic mixture that is liquid at ambient temperature. In general, the melting point of DES is lower than the melting point of its starting component.

A eutectic mixture is formed by hydrogen bonding interaction between the halide anion of choline and urea hydrogen. The subsequent DES has a melting point lower than the melting point of each component because charge delocalization occurs through hydrogen bonding [15]. The primary driving force for producing a eutectic mixture is a hydrogen bonding interaction. In this way, the strength of the hydrogen bond can be correlated with the phase transition temperature, stability, and solvent type for the corresponding mixture [16]. In general, DES refers to substances involved in two or three reasonable and safe components capable of self-association, usually through hydrogen bonding interactions [14]. DES is typically achieved by complexation of a hydrogen bond acceptor (HBA, e.g., a quaternary ammonium salt) with a hydrogen bond donor (HBD, a metal salt). These mixtures form cocrystals with a wide liquid range and significant properties that can be used for solvent purposes. One of the most commonly used components of DES is choline chloride (ChCl), an inexpensive, nontoxic, fully biodegradable, and biocompatible quaternary ammonium salt. The basic HBD used to plan DES is an amine, an amide, an organic acid (such as oxalic, citric, succinic, or levulinic), or a renewable polyol (e.g., glycerol or ethylene glycol) [17]. Gilli et al. reported that the pKa value of HBD/HBA affects the efficiency of hydrogen bonding within eutectic mixtures, which should be considered when selecting components [18]. Most DESs are produced using ChCl as an ionic species, but DES cannot be considered IL O HN

80 °C

N+ HO

–

Cl

Choline chloride

+ 2 H2N

NH2 Urea

N+

NH H H

Cl

HO

NH

H Deep eutectic solvent

FIGURE 9.1 Interaction of HBD (urea) with the quaternary ammonium salt ChCl.

H

O

383

N H

O

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384

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

because (1) DES is not completely composed of ionic species, and (2) it is also available from nonionic species [19]. Preparing DESs is very easy and can be done in one step. However, it is necessary to synthesize DES by moderate heating to 80 C
100 C and mechanically mixing HBD with HBA in an appropriate molar ratio. The mixing and heating process is carried out until a clear, colorless, and homogeneous liquid phase is obtained. This reality makes DES production much cheaper than IL production, which requires expensive starting materials and different cleaning steps. Since the purity of DES is affected only by the purity of the raw materials, their reaction mass efficiency is 100%. Furthermore, since DES’s initial materials are readily available and affordable, DES is expected to be used in large-scale

FIGURE 9.2

industrial production [1,14,17]. Other phenomena with DES, particularly ease of use, biodegradability, low toxicity, flammability, chemical inertia with water, ease of storage, and ease of synthesis, highlight their benefits as promising economic green solvents [20
23]. Fig. 9.2 shows the common quaternary ammonium salts that are usually mixed with different HBDs to form DES. As shown in the figure, different DESs can be produced by altering the R group, the halogen anion of the quaternary ammonium salt, and the HBD type [19]. DES is generally described by the formula Cat 1 X-zY, where Cat 1 is the cation of any ammonium, phosphonium, or phosphonium salt; X- is a Lewis base, typically a halide anion of the salt; Y is a Lewis or Bronsted base; and z is the number of Y molecules [24].

Common HBAs and HBDs used in the formation of DESs.

New Generation Green Solvents for Separation and Preconcentration

9.3 Physicochemical properties of deep eutectic solvents

385

TABLE 9.2 Different type of DES. Type Components I

Metal salt 1 organic salt: R1R2R3R4N1 X2. MClx with M 5 Zn, Sn, Fe, Al, Ga (e.g., ZnCl2 1 ChCl)

II

Metal salt hydrate 1 organic salt: R1R2R3R4N1 X2. MClx.yH2O with M 5 Cr, Co, Cu, Ni, Fe (e.g., CoCl2.6 H2O ChCl)

III

HBD 1 organic salt: R1R2R3R4N1 X2.R5Z with Z 5 -CONH2, -COOH, -OH (e.g., ChCl and urea)

IV

Metal salt 1 HBD: (ZnCl21urea, ethylene glycol, acetamide, or hexanediol)

Abbott Group focuses on the use of metal halide salts, including hydrated and nonhydrated quaternary ammonium salts and hydrogen bond donors. They describe four types of DES (Table 9.2). Most of the DES presented is Type III. Briefly, Tome et al. listed the significant DES used in literatures, by a year of first using from 2003 to 2017 (Table 9.3). Fig. 9.3 shows the synthesis of ChCl/resorcinol DES reported by Malaeke et al. and used for lignin solubilization and wood delignification [48]. Jorda˜o et al. prepared lithium trifluoromethanesulfonate (LiTfO)/ethylene glycol DES, mixed with a molar ratio of 1:6 with vigorous stirring for 6 h at 60 C
70 C, concentrating its electrochemical behavior as electricity to a discoloring electrolyte [49]. Ren et al. synthesized DES based on glycerol and L-arginine. The two components were added to a 250 mL flask at various molar ratios (L-arginine: glycerol, 1:4, 1:5, 1:6, 4:7, 1:8). The mixture was heated with stirring until a homogeneous liquid phase appeared (Fig. 9.4). The product was placed under vacuum to dry at 100 C during 4 h to give the desired product [50]. The predominant early DES was hydrophilic, limiting its use in aqueous samples, and the expansion of hydrophobic DES has fully considered the ultimate goal of expanding its use. The progress of hydrophobic DES has also been studied. So far, only a few articles have been devoted to hydrophobic DES. The preparation of hydrophobic DES is achieved by

combining citric acid with various quaternary ammonium salts [39]. Zhu et al. prepared four different hydrophobic DESs by mixing citric acid and octanoic acid as HBD with trioctyl methylammonium chloride and tetrabutylammonium chloride as HBA agents [51]. Recently, Mako has talked about a new hydrophobic DES based on a combination of thymol with 6 camphor, 10-undecanoic acid, or decanoic acid to get a mixture with a molar ratio of 7:3, 1:1, 3:2, 1:2, 1:4, and 1:3. The mixture was then magnetically stirred at 60 C until a homogeneous liquid was obtained. The resultant liquid was then naturally cooled to reach to room temperature [52]. Interestingly, Palomba prepared a new group of eutectic solvents based on the combination of two enantiomers of camphorsulfonic acid: (1 R)
(2)
10-camphorsulfonic acid and (1 S)
(1)
10-camphorsulfonic acid sexual DES with two N enantiomers, N,N-trimethyl (1-phenethyl) ammonium methanesulfonate [52].

9.3 Physicochemical properties of deep eutectic solvents Generally, the physico-chemical features of liquid solvents, including density, viscosity, liquid range, vapor pressure, conductivity, and polarity, make them to suit for reaction and separation. DES is a new environmentally friendly solvent with a high range of physical and chemical properties. The physical and chemical properties of DES and conventional IL have

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.3 Main DES found in the literature, with a year of first use. Year

DES

Method

Reference

2003

ChCl/urea

Direct mixing and stirring of the components at 80 C

[14]

2004

ChCl/carboxylic acid

Direct mixing and stirring of the components at 100 C

[17]

2007

Metal salts/alcohol or amides

Direct mixing and stirring of the components at 100 C

[25]

2009

ChCl/urea

Freezing
drying method

[26]

2012

ChCl/fructose

Direct mixing and stirring of the components at 400 rpm and 80 C

[27]

2013

ChCl/D-glucose

Direct mixing and stirring of the components at 400 rpm and 80 C

[28]

2013

ChCl/phenol;

Direct mixing and stirring of the components at 40 rpm and 80 C

[29]

Direct mixing and stirring of the components at 400 rpm and 80 C

[30]

Heating mixtures at 100 C

[31]

Direct mixing and stirring of the components at 70 C and 60 C, respectively

[32]

ChCl/o-cresol; ChCl/2,3-xylenol 2014

tetrapropylammonium Br/EG; tetrapropylammonium Br/triethyleneglycol; tetrapropylammonium Br/glycerol

2014

1-butyl-3-methylimidazoliumCl/ZnCl2/ acetamide;

2014

Guanidine HCl/urea;

1-butyl-3-methylimidazolium Cl/ZnCl2/urea

Guanidine SCN/urea 2015

ZnCl2/urea

Direct mixing and stirring of the components at 80 C

2015

ChCl/ZnCl2;

Mixing the components mechanically in jacketed vessel at 90 C

[33]

N,N-diethylethanolammonium Cl/ZnCl2; ethyltriphenylphosphonium Br/ZnCl2; tetrabutylphosphonium Br/ZnCl2 2015

tetra-n-butylphosphonium Br/FeCl3

Direct mixing and stirring of the components at 270 rpm and 80 C

[34]

2015

MnCl2/acetamide;

Direct mixing of the components at 80 C

[35]

MnCl2/glycerol; MnCl2/d-glucose; MnCl2/d-fructose; (Continued)

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387

9.3 Physicochemical properties of deep eutectic solvents

TABLE 9.3 (Continued) Year

DES

Method

Reference

2015

methyltriphenylphosphonium Br/ tetraethyleneglycol;

Direct mixing and stirring of the components at 350 rpm and 80 C

[36,37]

Stirring ChCl in crude glycerol at 80 C

[38]



Direct mixing of the components at 35 C

[39]

[40]

benzyltriphenylphosphonium Cl/ tetraethyleneglycol; allyltriphenylphosphonium Br/ tetraethyleneglycol; ChCl/tetraethyleneglycol; N,N-diethylethanolammonium Cl/ tetraethyleneglycol 2015 2015

Biodiesel waste-glycerol/ChCl tetrabutylammonium chloride/decanoic acid; methyltrioctylammonium chloride/decanoic acid; tetraheptylammonium chloride/decanoic acid; tetraoctylammonium;chloride/decanoic acid; methyltrioctylammonium bromide/decanoic acid; tetraoctylammonium bromide/decanoic acid

2016

ChCl/CaCl2.6H2O

Direct mixing and stirring of the components at 400 rpm and 90 C

2016

1-methylimidazole/propanoic acid;

Direct mixing and stirring of the components with [41] a magnetic stirrer at 50 C

1-methylimidazole/nitric acid; diethanolamine/propanoic acid 2016

ChCl/levulinic acid;

Direct mixing of the components at 80 C

[42]

Ch acetylchloride/levulinic acid; tetraethylammonium Cl/levulinic acid; tetraethylammonium Br/levulinic acid; tetrabutylammonium Cl/levulinic acid; tetrabutylammonium Br/levulinic acid 2016

Betaine/urea

Direct mixing of the components

[43]

2016

ChCl/phenol/FeCl4;

Direct mixing of the components at room temperature and at 802 C, respectively

[44]

ChCl/EG/FeCl4

(Continued)

New Generation Green Solvents for Separation and Preconcentration

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.3 (Continued) Year

DES

Method

Reference

2017

ChCl/phenylacetic acid

Direct mixing and stirring of the components at 35
50 C

[45]

2017

ChCl/urea/glycerol;

Direct mixing of the components at 80 C

[46]

Direct mixing and stirring of the components at 80 C

[47]

ChCl/urea/malic acid 2017

ChCl/p-toluenesulfonic acid; ChCl/trichloroacetic acid; ChCl/monochloroacetic acid; ChCl/propionic acid

FIGURE 9.3

Synthesis procedure of ChCl/resorcinol DES.

been systematically assessed. The results show that DES has different chemical properties from IL, while the physical properties (density, refractive index, viscosity, surface tension, etc.) and the phase behavior of DES are close to ordinary IL. In this part, the most important physico-chemical characteristics of DES will be discussed.

9.3.1 Freezing point As previously described, DES is prepared by mixing HBD and HBA components, and the HBD and HBA components can form a eutectic mixture and self-associate by hydrogen bonding to produce a new liquid phase. When the hydrogen bonds of HBD and HBA isoforms

New Generation Green Solvents for Separation and Preconcentration

389

9.3 Physicochemical properties of deep eutectic solvents

Temperature

mp(A) mp(B) ΔTf

Liquid A + Liquid

B + Liquid Eutectic point Solid A + Solid B

A

B

Mole fraction of B

FIGURE 9.5 Phase diagram of a binary mixture and eutectic point of the compounds. 350 300 250

FIGURE 9.4 Synthesis procedure and photographs of L-Arg/Gly DESs at different mole ratios. Solutions labeled A, B, C, D, and E correspond to 1:4, 1:5, 1:6, 1:7, 1:8 of glycerol/L-arginine DES.

are strong, it can be seen that the freezing point of the eutectic mixture is greatly reduced. The combination of HBD and HBA destroys the crystal structure of quaternary ammonium salt, causing a drop in the melting point and therefore, forming a liquid at ambient temperature. The phase behavior of the binary mixture of A 1 B is schematically illustrated in Fig. 9.5 [24]. Here ΔTf is the difference between freezing point of the eutectic mixture and theoretical ideally mixture. It can be related to the degree of A and B interactions. The greater interaction is associated with the greater the ΔTf. The eutectic point of the mixture is the molar ratios of the two compounds that administer the lowest possible melting point. Fig. 9.6 displays the phase diagram of mixtures of ChCl and urea. A eutectic happens at a urea to choline-chloride ratio of 2. The Tf of the

Tf /°C

200 150 100 50 0 0

20

40

60

80

100

Mol % urea

FIGURE 9.6 Freezing point of ChCl/urea mixtures versus of composition.

eutectic mixture (12 C) is significantly lower than both of the components (mp choline chloride 5 303 C, urea 5 133 C), and enables the mixture to be applied as room temperature solvent [14]. Fig. 9.7 exhibits the phase behavior of ZnCl2/Urea mixtures as function of compound. It is seen that the compound with minimum freezing temperature, Tf (the eutectic composition), occures at urea/ZnCl2/Urea ratio of 1:3.5. The freezing points of urea and ZnCl2 are 134 C and 293 C, respectively.

New Generation Green Solvents for Separation and Preconcentration

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

300 250

Tf /°C

200 150 100 50 0 0

20

40

60

80

100

Mol % urea

FIGURE 9.7 Phase diagram of urea:ZnCl2 system as a function of composition.

Accordingly, the depression of the freezing point (concerning an ideal mixture of the two components at the eutectic ratio) is 150 C [53]. In type I DES, the interaction between different metal halides and halide anions from quaternary ammonium salts will result in halogenated metal salts species with a similar formation enthalpy. The metal halides, SnCl2, ZnCl2, and FeCl3, when mixed with ChCl in a 1:2 ratio, form a composite anion such as Al2Cl7 or Zn2Cl5 with a freezing point below 100 C. Complex anions lead to a decrease in freezing point and lattice energy [3,15,54,55]. This is very much in line with the idea of DES because they show very large depressions at the freezing point. Type II cocrystals were created when trying to incorporate other metals into the DES formulation. The metal halide hydrate was found to have a lower melting point than the associated anhydrous salt. Hydrated water will lower the melting point of metal salts because they will lower the lattice energy [24]. One of the major fields of DES is using of quaternary ammonium salts and their complexation with HBD (type III). The type of eutectic mixture depends on the formation of hydrogen bonds between HBD and the halide anion of the salt; in cases of multifunctional these HBDs, the eutectic point tended to

be 1:1 in a molar ratio of HBD and salt. In a similar report, the decrease in freezing point appears to be related to the amount of HBD in the mixture [17]. If chloride ions and urea are contained [13], we may speculate that the term “DES” was originally written to define type III cocrystals but is thereafter used to define all eutectic mixtures defined herein. The freezing point of any mixture possessing a quaternary ammonium salt and a hydrogen bond donor generally depends on several factors; however, the two most important factors are first and foremost the lattice energy of the the quaternary ammonium salt and HBD. This is followed by the degree of anion
hydrogen bond donor interaction. If the anion
hydrogen bond donor interaction is strong, the system entropy enhances, causing the system to become more disturbed, thus providing a lower freezing point [17]. In type IV DES, metal halide is essentially a substitute for the quaternary ammonium salt. HBD is combined with one or more halides of the metal and removed from the metal center. Much work in this field has been with the use of ZnCl2 as metal halide and acetamide, 1,6-hexanediol, urea, and 1,2-ethanediol as HBDs [book]. For ZnCl2 containing acetamide and 1,2-ethanediol (1:4) but containing 1,6-hexanediol, the eutectic is formed at 1:3 metal halide types. Table 9.4 shows the freezing points of the mixture formed between the different HBDs having different HBAs. All reported DESs have melting points below 150 C, and most are liquid even at 50 C or lower, undoubtedly making them attractive to many people. From the information described in Table 9.5, it can be deduced that, in the case of ChCl as an HBA, the selection of HBD is an important point in developing DES with a low freezing point. In addition, the nature of the ammonium or phosphonium salt affects the freezing point of the matched DES. The anion of the derived salt also affects the freezing point of DES. Table 9.5 shows the freezing point of the

New Generation Green Solvents for Separation and Preconcentration

391

9.3 Physicochemical properties of deep eutectic solvents

TABLE 9.4 Freezing points of mixtures formed between varieties of HBDs with different HBAs. HBA

mp  C21 HBD

HBA:HBD mp  C21 (molar ratio)

DES Tf  C21

References

ChCl

303

Urea

134

1:2

12

[17]

ChCl

303

Thiourea

175

1:2

69

[14]

ChCl

303

1-Methyl urea

93

1:2

29

[14]

ChCl

303

1,3-Dimethyl urea

102

1:2

70

[14]

ChCl

303

1,1-Dimethyl urea

180

1:2

149

[14]

ChCl

303

Acetamide

80

1:2

51

[14]

ChCl

303

Benzamide

129

1:2

92

[14]

ChCl

303

Ethylene glycol

212.9

1:2

266

[56]

ChCl

303

Glycerol

17.8

1:2

240

[57]

ChCl

303

Mannitol

1:1

108

[58]

ChCl

303

D-Fructose

1:2

5

[58]

ChCl

303

D-Glucose

1:2

14

[58]

ChCl

303

Vanillin

1:2

17

[58]

ChCl

303

Xylitol

1:1

Liquid at RT

[21]

ChCl

303

D-Sorbitol

1:1

Liquid at RT

[59]

ChCl

303

D-Isosorbide

1:2

Liquid at RT

[59]

ChCl

303

2,2,2Trifluoroacetamide

1: 2.5

245

[56]

ChCl

303

Imidazole

3: 7

56

[60]

ChCl

303

Adipic acid

153

1:1

85

[17]

ChCl

303

Benzoic acid

122

1:1

95

[17]

ChCl

303

Citric acid

149

1:1

69

[17]

ChCl

303

Malonic acid

134

1:1

10

[17]

ChCl

303

Oxalic acid

190

1:1

34

[17]

ChCl

303

Phenylacetic acid

77

1:1

25

[17]

ChCl

303

Phenylpropionic acid 48

1:1

20

[17]

ChCl

303

Succinic acid

185

1:1

71

[17]

ChCl

303

Tricarballylic acid

159

1:1

90

[17] (Continued)

New Generation Green Solvents for Separation and Preconcentration

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.4 (Continued) HBA:HBD mp  C21 (molar ratio)

DES Tf  C21

HBA

mp  C21 HBD

ChCl

303

Levulinic acid

1:2

Liquid at RT

[59]

ChCl

303

Itaconic acid

1:1

57

[59]

ChCl

303

L-(1)-Tartaric acid

1:0.5

47

[59]

ChCl

303

D-Isosorbide

1:2

Liquid at RT

[59]

ChCl

303

4-Hydroxybenzoic acid

1:0.5

87

[59]

ChCl

303

Caffeic acid

1:0.5

67

[59]

ChCl

303

p-Coumaric acid

1:0.5

67

[59]

ChCl

303

trans-Cinnamic acid

1:1

93

[59]

ChCl

303

Suberic acid

1:1

93

[59]

ChCl

303

Gallic acid

1:0.5

77

[59]

ChCl

303

Resorcinol

1:4

87

[59]

ChCl

303

MgCl2 6H2O



116

1:1

16

[61]

methyltriphenylphosphonium bromide

231
233 Glycerol

17.8

24.03

[62]

methyltriphenylphosphonium bromide

231
233 Ethylene glycol

212.9

249.34

[62]

methyltriphenylphosphonium bromide

231
233 2,2,2Trifluoroacetamide

73
75

269.29

[62]

benzyltriphenylphosphonium chloride

345
347 Glycerol

17.8

50.36

[62]

benzyltriphenylphosphonium chloride

345
347 Ethylene glycol

212.9

47.91

[62]

Benzyltriphenyl phosphonium chloride

345
347 2,2,2Trifluoroacetamide

73
75

99.72

[62]

ZnCl2

293

Urea

134

9

[62]

ZnCl2

293

Acetamide

81

216

[53]

ZnCl2

293

Ethylene glycol

212.9

230

[53]

ZnCl2

293

Hexanediol

42

223

[53]

New Generation Green Solvents for Separation and Preconcentration

References

393

9.3 Physicochemical properties of deep eutectic solvents

TABLE 9.5 Effect of anion in freezing point (Tf) of DESs. Organic salts Cation N+

HBD

HBA:HBD (mol ratio)

Tf  C21

Reference

F

Urea

1:2

1

[14]

BF4

Urea

1:2

67

[14]

NO3

Urea

1:2

4

[14]

Cl

Urea

1:2

238

[14]

Br

Urea

1:2

113

[14]

Cl

Urea

1:2

214

[14]

Cl

Urea

1:2

233

Cl

Urea

1:2

14

[14]

Br

Urea

1:2

55

[14]

Br

Glycerol

1:2

3
4

[63]

Br

Glycerol

1:3

25.5

[63]

Br

Glycerol

1:4

15.6

[63]

OH

N+

OH

N+

OH

N+

OH

Et Et

Anion (X2)

+

N

Et

Et O N+

O

N+

Cl

N+

F

P+

P+

P+

(Continued)

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.5 (Continued) Organic salts Cation

Anion (X2)

HBD

HBA:HBD (mol ratio)

Tf  C21

Reference

Cl

Glycerol

1:5

59

[63]

Br

Ethylene glycol

1:3

246

[63]

Br

Ethylene glycol

1:4

250

[63]

Br

Ethylene glycol

1:5

248

[63]

Cl

Ethylene glycol

1:3

47.9

[62]

Br

Triethylene glycol

1:3

28

[63]

Br

Triethylene glycol

1:4

219

[63]

Br

Triethylene glycol

1:5

221

[63]

Cl

2,2,2- Trifluoracetamide

1:2

91

[62]

P+

P+

P+

P+

P+

P+

P+

P+

P+

(Continued)

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9.3 Physicochemical properties of deep eutectic solvents

TABLE 9.5 (Continued) Organic salts Cation

Anion (X2)

HBD

HBA:HBD (mol ratio)

Tf  C21

Reference

Br

2,2,2- Trifluoracetamide

1:8

269

[62]

Cl

Glycerol

1:2

21

[64]

Cl

Glycerol

1:3

1.7

[64]

Cl

Glycerol

1:4

2

[64]

Cl

Ethylene glycol

1:2

231

[64]

Cl

Ethylene glycol

1:3

222

[64]

Cl

Ethylene glycol

1:4

221

[64]

P+

N+

N+

N+

N+

N+

N+

OH

OH

OH

OH

OH

OH

mixtures and it indicates that the freezing point of the combination of choline salt with urea, reduced in order of F- . NO3- . Cl- . BF4-, and suggesting the correlation with hydrogen bonding strength [14].

9.3.2 Viscosity Viscosity depicts the internal friction of a flowing fluid, in other words the resistance of flowing substance. Typically, the dynamic viscosity η is calculated in centipoise (cP), which is coupled in SI units to millipascal

seconds (mPa s). Viscosity is critical for practical applications: High viscosity reduces the rate of chemical reactions due to diffusioncontrolled process. In design, low viscosity is preferable to limit operating costs such as stirring, mixing, and pumping [65]. The viscosity of the mixture is exponentially exposed to the temperature following the Arrhenius equation: ln ɳ 5 lnɳ 0 1

Eɳ RT

where ɳ is a constant, and Eɳ is the energy that activates viscous flow [66]. Hole theory has

New Generation Green Solvents for Separation and Preconcentration

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

been used to define the viscosity of ionic liquids. It was first established by Furth [67] to clarify the properties of the liquid, later extended by Bockris et al. for using molten salt [68]. It has been reported that this model has severe limitations in molten salts because the ionic compound significantly affects ionic activity. Various positions have been taken account on different models of pure molten salt [69]. It has recently been shown that E is related to the size of the ions and the size of the voids present in the ionic liquid, which has discrete anions and DES. The results show that the viscosity of the molten salt at ambient temperature is several orders of magnitude higher than that of the molten salt at high temperature. This is partly due to the different sizes of ions and partly due to the increased void volume in the liquid [70,71]. Abbott later revealed that pore theory can be used for ionic and molecular fluids to account for viscosity. It has been shown that the viscosity of a liquid can be modeled by assuming that it behaves as an ideal gas. However, its motion is limited by the availability of ion/ molecular sites [70,71]. Hence, it was revealed that: ɳ5

mc=2:12ơ Pðr . RÞ

where m is the molecular weight (considered the geometric mean of the ionic liquid), c is the average velocity of the molecule (8 kT. πm21)1/2), and ơ is the collision diameter of the molecule (4πR2). The probability of finding a radius r in a given liquid greater than the radius of the solvent molecule R (P (r . R)) is given by the integral of the following expression [72]: Pdr 5

16 7=2 6 2ar2 pffiffiffi a r e dr 15 π

where a 5 4πγ kT21 and γ is the surface tension. A good correlation was obtained between the calculated viscosity and the measured

viscosity, indicating that the viscosity of the liquid is limited by the availability of the pores large enough to allow the mobile species to enter. Note that inspection of these equations indicates that a reduction in viscosity can be achieved by reducing the surface tension of the liquid, that is, increasing the free volume or by reducing the ionic radius. The viscosity of DESs shows Arrhenius-like behavior as the temperature increases. In addition, to the eutectic mixture of ChCl/ethylene glycol, most DESs have relatively high viscosities at room temperature ( . 100 cP) compared to molecular solvents and molten salts [6,19]. The main reason for high-viscosity DES is due to the network of intramolecular hydrogen bonds. The size of the assembly also primarily produces small free volumes and small voids, contributing to reduced free species mobility [6,71]. Van der Waals interactions and electrostatic interactions also have a necessary effect on viscosity. Temperature, composition, and water content also have an effect [73]. A less viscous liquid can be obtained by using a small quaternary ammonium cation such as ethyl ammonium and a fluorinated HBD such as trifluoroacetamide. Surprisingly, in the case of ChCl/glycerol DES, the viscosity decreases as the amount of ChCl increases, while the mixture with ethylene glycol has the opposite effect [74]. This example shows that the viscosity depends on the composition and interaction produced. Glycerol has strong cohesive energy due to the existence of an important network of intermolecular hydrogen bonds. Fig. 9.8 shows the viscosity of the eutectic mixture of urea/ZnCl2 as a function of temperature [53]. Interestingly, the water content of DESs reduces their viscosity and melting point. The introduction of water into DES can also affect their solubility (hydrogen bonds between DES components), as well as reaction/conversion or processing efficiencies [75].

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9.3 Physicochemical properties of deep eutectic solvents

Including urea in ZnCl2 reduces pore size, which increases density [53]. Density varies with the nature and molar ratio of HBD/HBA in DES.

25000 20000

η/cP

15000

9.3.4 Conductivity

10000 5000 0 280

300

320 T/K

FIGURE 9.8 Viscosity of the eutectic mixture of urea/

ZnCl2 as a function of temperature: ’: 1,6-hexanediol/ ZnCl2; x: ethylene glycol/ZnCl2; ▲: acetamide/ZnCl2; X: urea/ZnCl2.

9.3.3 Density In general, the density of the solvent is specified by a hydrometer. This physical property of most DESs is higher than the water’s density. Recently, tissue donation methods and artificial neural networks have produced DES density measurements. In this technique, Spencer and Danner-adjusted Rackett equations are used to determine the density of DES. The advantage of this approach is that the calculation uses the critical point for the improved Lydersen-JobackRied technique. Therefore it is considered that the density of DES with lower molecular weight is less than the experimental value [76]. Table 9.6 records the density data for regular DES. Density is directly dependent on temperature, and viscosity and conductivity depend on the presence of vacancies in the DES network [53]. In addition, most of the densities were found to be higher than the density of the hydrogen bond donor material. This can be clarified because of the hole theory. For example, a deep eutectic made of ZnCl2 and urea in a ratio of 1:3.5 or a ratio of ZnCl2 to acetamide of 1:4 shows densities of 1.63 and 1.36 g cm23, respectively. The density of pure urea is 1.16 g cm23, and the density of acetamide is 1.32 g cm23.

Conductivity is the material’s ability to conduct electricity. It depends on the available charge carriers (ionic) and their mobility, the valence, and the temperature of the ions [65]. Conductivity is also strongly dependent on the viscosity of the system and increases with rising temperature, following Arrhenius-like behavior, as shown in the following equation [19,74,79]: lnðκÞ 5 lnðκ0 Þ 2

Eʌ RT

where κ0 is a constant, and Eʌ is the activation energy of the conductivity. For example, the conductivity can be increased by raising the organic salt content [book]. In general, DES exhibits poor electrical conductivity (less than 2 mS cm21 at room temperature) due to their high viscosity. However, the conductivity of DES increases significantly with rising temperature because the respective viscosities decrease [19,74,80]. Cardellini et al. reported the properties of new DES formed from zwitterionic trimethylglycine (TMG) and high-melting aromatic and aliphatic carboxylic acids. Some of them are liquids and the others are solid. They quantified the conductivity of DES for liquids at room temperature and found that the conductivity of these systems is very low, as expected, due to the nonionic nature of the molecules. Among them, oxalic acid/TMG DES showed the highest conductivity value (5.1 mS cm21, 30 C). This is because the size of the acid molecule is small. This fact leads to higher fluidity and hydration water, which improves the ionicity of DES [81]. The 1/T curve of the natural conductivity logarithm and the most representative mixture are shown in Fig. 9.9 [81].

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.6 Densities of common DESs at 25 C. HBA

HBD

HBA:HBD (mol:mol)

Density (ρ, g cm23)

Reference

EtNH3Cl

CF3CONH2

1:1.5

1.273

[70]

EtNH3Cl

Acetamide

1:1.5

1.041

[70]

EtNH3Cl

Urea

1:1.5

1.140

[70]

ChCl

CF3CONH2

1:2

1.342

[70]

AcChCl

Urea

1:2

1.206

[70]

ChCl

Urea

1:2

1.25

[70]

ZnCl2

Urea

1:3.5

1.63

[53]

ZnCl2

Acetamide

1:4

1.36

[53]

ZnCl2

Ethylene glycol

1:4

1.45

[53]

ZnCl2

Hexanediol

1:3

1.38

[53]

ChCl

Glycerol

1:2

1.18

[77]

ChCl

Glycerol

1:3

1.20

[77]

ChCl

Glycerol

1:1

1.16

[64]

ChCl

Glycerol

1:3

1.20

[64]

ChCl

Ethylene glycol

1:2

1.12

[77]

ChCl

Ethylene glycol

1:3

1.12

[77]

ChCl

Malonic acid

1:2

1.25

[78]

ALCl3

Acetamide

1:1

1.40

[79]

Et2(EtOH)NC

Glycerol

1:2

1.17

[78]

Et2(EtOH)NC

Glycerol

1:3

1.21

[64]

Et2(EtOH)NC

Glycerol

1:4

1.22

[64]

Et2(EtOH)NC

Ethylene glycol

1:2

1.10

[64]

Et2(EtOH)NC

Ethylene glycol

1:3

1.10

[64]

Et2(EtOH)NC

Ethylene glycol

1:4

1.10

[64]

Me(Ph)3PBr

Glycerol

1:2

1.31

[64]

Me(Ph)3PBr

Glycerol

1:3

1.30

[64]

Me(Ph)3PBr

Glycerol

1:4

1.30

[64]

Me(Ph)3PBr

Ethylene glycol

1:3

1.24

[64]

Me(Ph)3PBr

Ethylene glycol

1:4

1.23

[64]

Me(Ph)3PBr

Ethylene glycol

1:6

1.22

[64]

New Generation Green Solvents for Separation and Preconcentration

9.3 Physicochemical properties of deep eutectic solvents

FIGURE 9.9

399

Plots of conductivity vs. 1/T of (A) aromatic acids and (B) aliphatic acid.

9.3.5 Polarity Polarity is one of the most important, unique features of DES, for its recovery capacity and miscibility with other solvents. Typically, the ET (30) is the electron transition energy of a probe color (e.g., Reinhardts Dye 30) in a solvent to estimate the polarity of DES. Using UV-Vis technology and Reinhardt’s Dye 30, ET (30) can be determined based on the following equation [82
84]:   ETð30Þ Kcal mol21 5 hcNA =λmax 5 5 2859=λmax where h 5 Planck constant, c 5 speed of light, NA 5 Avogadro number, and λmax 5 the wavelength of the maximum absorption. Moreover, a normalized scale (EN T ) was introduced to obtain dimensionless values, using water (EN T 5 1:00) and tetramethylsilane (EN 5 0:00) as reference solvents and using the T following equation [84
86]: EN T 5

½ET ðsolventÞ 2 ET ðTMSÞ ½ET ðwaterÞ 2 ET ðTMSÞ

Rub et al. summarized ET (30), EN T values of some common molecular solvents, ILs, sugar melts, and DES (Table 9.7). The polarities of DES (EN T 5 0:80
0:86) are similar to those of

short-chain alcohols (e.g., ethylene glycol, 2propanol) and other polar, aprotic solvents (e.g., DMSO, DMF) (EN T 5 0:39
0:81), and follow a comparable tendency to that of common ionic liquids [1]. Table 9.8 summarizes the polarity data for the different ChCl-glycerol eutectic mixtures by applying the Reinhardt’s Dye method. These results indicate that ChCl/glycerol DESs exhibit similar polarities to RNH3 1 X- and R2NH2 1 X-ILs with discrete anions [91]. An increase in the ChCl/glycerol molar ratio increases the ET of DES (30). Moreover, an approximately linear increase in ET (30) with ChCl concentration was observed [3].

9.3.6 Acid-base behavior of deep eutectic solvents The Hammett function has been widely used to evaluate the acidity and alkalinity of anhydrous solvents. For the basic solution, the Hammett function determines the tendency of the solution to capture protons [92]. When the indicator is slightly acidic, the Hammett function H_ is determined by the following equation: H2 5 pKðHI Þ 1 logð½I 2 =½HI

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.7 Overview of determined ET (30) and ETN (for the dye Nile Red) values of some common molecular solvents, ILs, sugar melts, and DES. Solvent

ET(30) kcal21 per mol

ETN

Reference

Water

63.1

1.000

[87]

Glycerol

57.0

0.812

[82]

Ethylene glycol

56.1

0.784

[87]

56.3

0.790

[82]

Ethanol

51.9

0.654

[82]

2-Propanol

48.5

0.549

[87]

48.4

0.546

[82]

45.0

0.441

[87]

45.1

0.444

[82]

43.6

0.398

[87]

43.2

0.386

[82]

[Bmim][acetate]

50.5

0.611

[88]

[Bmim][propionate]

49.1

0.568

[88]

[Bmim][H-maleate]

47.6

0.522

[88]

Citric acid-DMU

70.8

1.238

[87]

Sorbitol-DMU-NH4Cl

68.1

1.154

[87]

Maltose-DMU-NH4Cl

67.8

1.145

[87]

Fructose-urea-NaCl

66.5

1.105

[87]

Mannitol-DMU-NH4Cl

65.8

1.083

[87]

Glucose-urea-NaCl

64.4

1.040

[87]

Lactose-DMU-NH4Cl

53.9

0.716

[87]

Mannose-DMU

53.9

0.716

[87]

Carnitine-urea

—

—

[89]

Glycerol-ChCl

58.58

0.86

[74]




0.84

[90]

Ethylene glycol-ChCl




0.84

[90]

Urea-ChCl




0.84

[90]

Dimethylsulfoxide

Dimethylformamide

[Emim]: 1-ethyl-3-methylimidazolium, [Bmim]: 1-butyl-3-methylimidazolium.

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9.3 Physicochemical properties of deep eutectic solvents

TABLE 9.8 Solvent polarity of various ChCl-glycerol mixtures. Solvent

Molar ratio of ChCl:glycerol

ET(30)/kcal mol21

Glycerol

—

57.17

ChCl:Glycerol

1:3

57.96

ChCl:Glycerol

1:2

58.28

ChCl:Glycerol

1:1.5

58.21

ChCl:Glycerol

1:1

58.49

FIGURE 9.10 pH values for selected phosphonium-based DESs as a function of temperature t in the range of 5 C
95 C.

8

7

pH

6

Me(Ph)3PBr/glycerol (1:1.75) Me(Ph)3PBr/EG (1:4) Me(Ph)3PBr/CF3CONH2 (1:8) Bz(Ph)3PBr/glycerol (1:5) Bz(Ph)3PBr/EG (1:3)

5

4

3

2 0

20

40

60

80

100

t/°C

where pK(HI) is the thermodynamic ionization constant of the indicator in water, [I2], and [HI] are the concentrations of the anionic and neutral forms of the indicator, respectively. For example, when 4-nitrobenzyl cyanide is used as an indicator, DES ChCl:urea (1:2 molar ratio) shows a value of 10.86 at 25 C, which means that DES is weakly basic [93]. The presence of water slightly affected this value (1%
3% by weight water, and the H_ value decreased from 10.77 to 10.65). Due to its weak basality, this DES can absorb a small amount of carbon

dioxide, resulting in an H₂ value of 6.25. Only bubble N2 through DES restores the initial value, which means that the acidity or alkalinity can be reversibly changed. The chemical nature of HBD significantly affects the acidity or alkalinity of the corresponding DES. The measured pH values for several DESs (Fig. 9.10) clearly show this strict correlation. When glycerol was used as HBD, the observed pH was neutral, while the presence of trifluoroacetamide resulted in a low pH (2.5 at 20 C) [62].

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9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

9.3.7 Miscibility of the novel deep eutectic solvents with protic and aprotic solvents

(some formulations can even be produced from food grade ingredients) [24].

DES exhibits various dissolution properties strongly influenced by hydrogen bonding, and these properties result in high affinity with all compounds capable of providing electrons or protons. According to Abbott et al. [14], a solvent that forms a hydrogen bond with a halide salt tends to be miscible with DES, and a solvent without a hydrogen bonding group does not remain miscible to form a second phase. Protic solvents such as methanol, ethanol, or water tend to be miscible with DES, while nonprotic solvents (such as toluene, hexane, ethyl acetate, acetonitrile, diethyl ether, etc.) are immiscible.

9.3.9 Thermal stability study

9.3.8 Toxicity The toxicity of eutectic mixtures is a central theme in the structure of green and safe materials. DES may present as green, unlike many traditional ILs, but they are not green. Although the components of DES can be nontoxic and have a low environmental impact, it is not a given that the mixture of these components is nontoxic and inherently green. This is supported by reality. DES has unique characteristics. Hayyan et al. did not study the toxicity and cytotoxicity of choline chloride and HBDs glycerol, ethylene glycol, triethylene glycol, and urea [94,95]. They found that the cytotoxicity of DES is much higher than its unique components, and the toxicity and cytotoxicity vary depending on the structure of the components. There is no doubt that more toxicity testing for DES is needed before it can be declared truly nontoxic and biodegradable. All cocrystals containing metal salts of type I, II, and IV are inherently toxic; however, type III crystals can include various amides and polyols, such as urea, glycerol, ethylene glycol, fructose, erythritol, and the like. It has low peculiar toxicity

The physical properties of 100 DES, such as water activity, density, viscosity, polarity, and thermal properties, were studied for water and methanol. Thermogravimetric analysis was used to study the thermal behavior of DES. DES made from sugar has a low decomposition temperature of approximately 135 C, but other decomposition temperatures are even higher than 200 C (Table 9.9). They report that these DESs can be used as solvents with a temperature range of at least 0 C
100 C [8]. Cardellini et al. prepared a new DES formed from zwitterionic trimethylglycine (TMG) and high-melting carboxylic acids (aromatic and aliphatic). These DESs are characterized by their thermal stability and other physicochemical properties. Thermogravimetric analysis was performed to obtain information on the thermal stability of DES. As shown in Fig. 9.11, all analyzed DESs showed good stability at 200 C. They found that the decomposition temperature of DES was independent of the acid structure, as all the systems studied recorded this temperature so that they can be evaluated. Oxalic acid DES began to mutate from 100 C due to loss of hydration water [81].

9.4 Application of deep eutectic solvents in extraction techniques The main steps in the extraction method are to select suitable, economical, and green solvents, to avoid the use of old toxicological solvents, and to provide low costs and improve health and safety [96]. Currently, hydrophilic or hydrophobic DESs aim to improve the extraction efficiency of different components from

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9.4 Application of deep eutectic solvents in extraction techniques

TABLE 9.9 Decomposition temperature of DESs compared to water and methanol as references. Composition (mole ratio) of DES

Decomposition temperature ( C)

Malic acid:choline chloride:water (1:1:2)

201

Glycerol:choline chloride:water (2:1:1)

187

Malic acid:β-alanine:water (1:1:3)

164

Proline:malic acid:water (1:1:3)

156

Fructose:choline chloride:water (2:5:5)

160

Xylose:choline chloride:water (1:2:2)

178

Sucrose:choline chloride:water (1:4:4)

.200

Fructose:glucose:sucrose:water (1:1:1:11)

138

Glucose:choline chloride:water (2:5:5)

170

1,2-Propanediol:choline chloride:water (1:1:1)

162

Lactic acid:glucose:water (5:1:3)

135

Sorbitol:choline chloride:water (2:5:6)

.200

Xylitol:choline chloride:water (1:2:3)

.200

Water

—

Methanol

—

(A) 100

(B) 100

90

90

80

80 70

2-Furanoic

60

Benzoic Weight (%)

Weight (%)

70

4-chloro benzoic

50

Glycolic

40

60 Oxalic 50 Salicylic 40

30

30

20

20

10

10

Phenylacetic

0

0 0

50

100

150

200

Temperature (°C)

250

300

0

50

100

150

200

250

300

Temperature (°C)

FIGURE 9.11 TGA analyses of DESs. Panel A: (&) 4-chloro-benzoic acid/TMG; (¢) glycolic acid/TMG; (◆) 2furanoic acid/TMG. Panel B: (&) oxalic acid/TMG; (¢) salicylic acid/TMG; (e) benzoic acid/TMG; (K) phenylacetic acid/TMG.

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various matrices. Most DES applications are dedicated to extracting biological compounds from natural sources. Among the analytes evaluated, organic compounds continue to be widespread, and the extraction of inorganic compounds is still rarely explored. We will not discuss each item in detail here, but we believe that some items are interesting to us.

9.4.1 Application of deep eutectic solvents in aqueous two-phase extraction method When a water-soluble polymer is mixed with another polymer or some inorganic salts are above a critical concentration, an aqueous two-phase system (ATPS) is typically formed. It is a reliable, fast, and sophisticated method to enrich compounds. There are many types of ATPS, such as two or more polymers, inorganic polymers and salts, cationic and anionic surfactants [97], cationic and anionic surfactants [98,99], ionic liquids (IL), and inorganic salt [100]. Based on the advantages of DES, the combination of these solvents with ATPS can be a good choice to enrich various chemical compounds. Van Osch initially developed a hydrophobic two-phase DES-water system and evaluated the recovery of volatile fatty acids in dilute aqueous solutions [39]. It has also been shown that the two-phase system of the DES saline extracts proteins and hydrazine [101
104]. Cao et al. established a two-phase system with hydrophilic and hydrophobic DES. The proposed extraction method can effectively extract bioactive compounds (terpene lactone and proanthocyanidins as hydrophobic compounds), polyisoprene acetate (PPA) as hydrophilic compounds, and flavonoids from Ginkgo biloba leaves. In this study, three hydrophilic DESs, Ch-LA1, BE-EG, and Ch-M, were chosen to construct a two-phase DES system [105].

Zhang et al. developed a two-stage aqueous system consisting of DES and a new highperformance pigment extraction salt (Amaranth, Sunset Yellow FCF, Sudan III). The DES used, consisting of polypropylene glycol 400 (PPG 400) and tetrabutylammonium bromide (TBAB), is mixed with a series of new salts such as quaternary ammonium salts, amino acids, and polyols to form a two-phase aqueous system. To synthesize the DES, TBAB and PPG 400 were mixed in a round-bottomed flask with a molar ratio of 1:2 and heated by continuous magnetic stirring (about 40 min). According to their results, among the 12 salts, including Na2CO3, Na2SO4, glycine, β, ChCl, glucose, sorbitol, sucrose, tetramethylammonium chloride (TMAC), tetramethylammonium bromide (TMAB), tetraethylammonium chloride (TEAC), and tetraethylammonium chloride, the polyols produce a relatively weak phase power in the range studied. Moreover, the shorter the length of the salt carbon chain is, the easier it is to obtain a phase separation. As the phase formation capacity of the salt decreases, the extraction efficiency of the entire system begins to gradually decrease [106]. Zeng et al. studied DES based on two-phase aqueous systems (ATPS). In this study, four types of green DESs were synthesized, including choline chloride (ChCl)/urea, tetramethylammonium chloride/urea, tetrapropylammonium bromide/urea and ChCl/methylurea. Singlefactor experiments showed that the BSA extraction effect was influenced by the quality of DES, the concentration of the K2HPO4 solution, separation time, and extraction temperature. The results show that, under optimal conditions, the average extraction effect can reach 99.94%, 99.72%, 100.05%, and 100.05% [107]. Li et al. synthesized four types of eutectic solvents (DES) consisting of choline chloride (ChCl) and various alcohols, characterized by 1 H NMR and FT-IR spectroscopy. Based on the DES (ChCl and 1,4-butanediol) and inorganic saline solution (K2HPO4), ATPS was

New Generation Green Solvents for Separation and Preconcentration

9.4 Application of deep eutectic solvents in extraction techniques

established and applied in combination with high-performance liquid chromatography. The method is applied to the effective extraction and determination of eight common ginsenosides in the injection of traditional Chinese medicine, Kangai. The experimental results show that the recovery of the analyte is 92.7%
110.8% and that the relative standard deviation (RSD) is 1.2%
3.9%. DES-ATPS has been shown to have great potential to determine the active ingredients in injections of traditional Chinese medicine and other fields of analytical science [108]. Xu et al. studied the protein extraction process in DES-ATPS based on ChCl/alcohol. Four ChCl/alcohol-based DESs were synthesized for the extraction of bovine serum albumin (BSA), and ChCl/glycerol was selected as the appropriate extraction solvent. Unfortunately, chlorine/alcohol
based DESATPS does not have good selectivity for BSA. Because they discovered that in the presence of bovine hemoglobin (BHb), despite the presence of BHb, the extraction efficiency of DES-ATPS for BSA was still 92%. However, 60% of BHb was extracted at the most advanced stage of DES enrichment, indicating that DES-based ATPS did not have good selectivity for specific proteins [102].

9.4.2 Application of deep eutectic solvents in liquid/solid extraction/ microextraction Currently, DES is used to extract biologically active compounds from various natural sources, such as flavonoids, phenolic acids, polyphenols, tanshinones, rosiglitazones, saponins, and anthraquinones [11,109
120]. The bioactive compounds were extracted from various samples using the different extraction methods described in Tables 9.10. 9.11 summarizes the various techniques for using DES from 2006 to 2016.

405

The new UAME application based on DES, defined by the author as an emulsion-liquid microextraction (ELLME-DES) was introduced by the Khezeli Group for the simultaneous extraction of BTE (benzene, toluene, and ethylbenzene) and seven samples of polycyclic aromatic hydrocarbons from water. Here, ultrasonic waves contributed to the mass transfer between the phases and to the development of tiny emulsified droplets, increasing the contact area. Another novelty is the use of watermiscible aprotic solvents, such as THF, which can reduce the tendency of water molecules to interact with DES, thus promoting the selfaggregation of DES droplets. In short, 100 μLSES (ChCl: phenol molar ratios of 1:2, 1:3, and 1:4 mixture) were added to a 1.5 mL sample, and a homogeneous solution was directly formed. A further injection of 100 μL of THF, followed by sonication in an ultrasonic bath for 20 min, provided a turbid state in which the DES droplets were completely dispersed in all the aqueous phases, thus increasing the transfer rate of the compound from the water at DES. After the centrifugation phase (10 min at 3000 rpm), the upper DES layer was taken through a microsyringe and analyzed by HPLC/UV. A schematic diagram of the ELLME-DES program is shown in Fig. 9.12 [157]. Although UALLME-DES has excellent extraction efficiency, it is difficult to disperse the droplets of DES generated by the ultrasound treatment of a sample solution, and a centrifuge is required. Subsequently, the research team prepared a magnetic eutectic solvent (MDES) to remedy the shortcomings of the UALLME-DES process. They prepared two new hydrophilic MDES by mixing ChCl/phenol and ChCl/ethylene glycol with anhydrous FeCl3. MDES is used to extract the thiophene from the heptane solution. The MDES was dispersed in the solution by ultrasonic waves in 5 min to favor the mass transfer of the thiophene from the n-heptane to the MDES phase.

New Generation Green Solvents for Separation and Preconcentration

TABLE 9.10

Extraction of bioactive compounds from different sample using DESs.

Extraction method

Type of DES (molar ratio)

Extractant

Sample

Microwave-assisted extraction

1,6-hexanediol:ChCl (7:1) (30% water [v/v])

Genistin (polyphenolic); apigenin

Pigeon pea roots [121]

ChCl:1,3-butanediol (1:6) (10% water [v/w])

Chlorogenic acid; caffeic acid;

Lonicerae japonicae

[117]

3,4-dicaffeoylquinic acid;

Reference

4,5-dicaffeoylquinic acid

Heating and agitating

ChCl:maltose (1:2) (20% water [v/v])

Phenolic acids

Cajanus cajan leaves

[119]

ChCl:1,4-butanediol (1:4) (30% water [v/v])

Chimaphilin; hyperin; 2-O-galloylhyperin; quercetin; quercetin-orhamnoside

Pyrola incarnate Fisch

[122]

ChCl:lactic acid (1:2) (20% water [v/v])

Wogonoside; baicalein; wogononin

Radix scutellariae

[115]

L-proline:glycerol (2:5) (10% water [v/v])

quercetin; kaempferol

Flos sophorae

[120]

ChCl:1,2-propanediol (1:1);

Oleacein (Hy-EDA); oleocanthal (Ty-EDA)

Virgin olive oil

[116]

Lactic acid:glucose (25% water [v/v]); Proline: malic acid (25% water [v/v]); Sucrose:ChCl (5:5) (25% water [v/v])

Hydroxysafflor yellow A; cartormin; carthamin

Carthamus tinctorius

[118]

Lactic acid:ammonium acetate (3:1) (20% water [v/v]);

Total polyphenols

Dittany, fennel, marjoram, mint, sage

[11]

Methyl trioctyl ammonium chloride:1-butanol (1:4)

Artemisinin

Artemisia annua

[123]

Methyl triphenyl phosphonium bromide:1,2butanediol (1:4) (0.25 mg mL21)

Astaxanthin

Portunus trituberculatus waste

[124]

ChCl:ethylene glycol (1:4) (36% water [v/v])

Rosmarinic acid

Prunella vulgaris

[125]

ChCl:1,2-butanediol (1:5) (30% water [v/v])

Tanshinone; tanshinone II A; Crytotanshinone

Salvia miltiorrhiza Bunge

[109]

ChCl:lactic acid (1:2); ChCl:malonic acid (1:1); ChCl:xylitol (2:1)

Ultrasonic

lactic acid:glycine:water (3:1:3) (20% water [v/v]); lactic acid:ChCl (3:1) (20% water [v/v]); lactic acid:sodium acetate (3:1) (20% water [v/v])

Ball mill-assisted extraction

Aqueous two-phase systems

Betaine:urea:water (1:2:1)

Protein

N/A

Incubated in water bath with continuous stirring

ChCl:1,4-butanediol (1:4) (20% water [v/v]);

Rutin

Sophora japonica

[126]

ChCl:citric acid (1:1) (20% water [v/v]); ChCl:D-sorbitol (1:1) (20% water [v/v]); ChCl:ethylene glycol (1:2) (20% water [v/v]); ChCl:fructose:water (5:2:5) (20% water [v/v]); ChCl:glucose:water (5:2:5) (20% water [v/v]); ChCl:glycerol (1:2) (20% water [v/v]); ChCl: levunilic acid (1:2) (20% water [v/v]); ChCl:malic acid (1:1) (20% water [v/v]); ChCl:malonic acid (1:1) (20% water [v/v]); ChCl:maltose:water (5:2:5) (20% water [v/v]); ChCl:oxalic acid (1:1) (20% water [v/v]); ChCl:p-toluenesulfonic acid (1:1) (20% water [v/ v]); ChCl:sucrose:water (5:2:5) (20% water [v/v]); ChCl:tartaric acid (2:1) (20% water [v/v]); ChCl: triethylene glycol (1:4) (20% water [v/v]); ChCl:urea (1:2) (20% water [v/v]); ChCl:xylitol (1:1) (20% water [v/v]); ChCl:xylose:water (1:1:1) (20% water [v/v])

Stirring, heating, and ultrasonic irradiation

ChCl:1,4-butanediol (1:5) (35% water [v/v])

Myricetin; amentoflavone

Chamaecyparis obtusa

[112]

Negative pressure cavitation-assisted extraction with macroporous resin enrichment

ChCl:betaine hydrochloride:ethylene glycol (1:1:2) (20% water [v/v])

Kaempferol-3-O-β-d-rutinoside-7-O-β-d glucopyranoside; luteolin-7-O-β-d glucopyranoside; apigenin-5-O-β-d glucopyranoside; genkwanin-5-O-β-d glucopyranoside; luteolin; kaempferol-3-Oβ-d glucopyranoside-7-O-βd-glucopyranoside; quercetin-3-O-β-d glucopyranoside; apigenin; genkwanin

Equisetum palustre

[114]

408

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.11 Summary of the application of DES in several extraction techniques from 2006
17. Method

DES

Sample

Analytes extracted

Reference

LPME

ChCl/1,4-butanediol

Leaves (Chamaecyparis obtusa)

Flavonoids (myricetin, amentoflavone)

[112]

LPME

ChCl/xylitol

Olive oil

Phenolic compounds (hydroxytyrosol, tyrosol, oleacein, oleocanthal, oleuropein agylcon, ligstroside aglycon)

[116]

DLLME

ChCl/urea

Water samples (farm water, rural water, lake water, and river water)

Pesticides (alpha-HCH, betaHCH, gamma-HCH, deltaHCH, heptachlor, aldrin, heptachlor-endo-epoxide, alphaendosulfan, dieldrin, 4,40
DDE, endrin, betaendosulfan, 4,40
DDD, endrinaldehyde, endosulfan-sulfate, 4,40
DDT, endrin-ketone and methoxychlor)

[127]

AGDLLME

ChCl/4-chlorophenol

Fruit and vegetable juice

Pesticides (penconazole, hexaconazole, diniconazole, tebuconazole, diazinon, fenazaquin, clodinafoppropargyl, and haloxyfop-R-methyl)

[128]

AAELLME ChCl/5,6,7,8-tetrahydro-5,5,8,8- Water, urine, and plasma tetramethylnaphthalen-2-ol

Methadone

[129]

HPLME

ChCl/ethylene glycol

Gasoline, diesel fuel, kerosene

Phenolic (phenol, ρ-cresol, β-naphthol)

[4]

HPLME

ChCl/ethylene glycol

Leaves of Chamaecyparis obtusa Bioactive terpenoids (linalool, α-terpineol, terpinyl-acetate)

[130]

LPME

Lactic acid/glucose-water

Orange petals of Catharanthus roseus

Anthocyanins

[110]

LPME

Sucrose/ChCl:water

Safflower (Carthamus tinctorius L.)

Phenolic compounds (Hydroxysafflor Yellow A, cartormin, and carthamin)

[131]

LPME

Sucrose/ChCl/water

Safflower (Carthamus tinctorius L.)

Colorants (carthamin)

[132]

UALME

ChCl/phenol

Tea

Cobalt (II)

[133]

UALME

ChCl/phenol

Waters (tap, lake, waste)

Chromium (III/VI)

[134]

UALME

ChCl/phenol

Waters (farmed and ornamental aquarium fish)

Malachite Green

[135] (Continued)

New Generation Green Solvents for Separation and Preconcentration

409

9.4 Application of deep eutectic solvents in extraction techniques

TABLE 9.11 (Continued) Method

DES

Sample

Analytes extracted

Reference

UALME

ChCl/Ox

Grape skin

Phenolics ([ 1 ]-catechin, delphinindin-3-O- glucoside, cyanidin-3-O-glucoside, petunidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, quercetin-3-O-glucoside)

[136]

UALME

Tetramethylammonium chloride/ethylene glycol

Safflower, olive, camellia, colza, and soybean oils

Plant growth regulators (IAA, IBA, 4-IPOAA)

[137]

UALME

ChCl/laevulinic acid

Platycladi cacumen

Flavonoid glycosides and aglycones (myricitrin, quercitrin, amentoflavone, hinokiflavone)

[138]

UAME

ChCl/malic acid

Wine lees

Anthocyanins

[139]

UAME

ChCl/glycerol

Tartary buckwheat hulls

Flavonoid (rutin)

[12]

UAME

Fructose/citric acid

Raw and processed food (spaghetti, biscuits, and ham)

Gluten

[140]

UAME

ChCl/citric acid

Soy products (soybeans, flour, Isoflavones (GT, DA, GTGL, pasta, breakfast cereals, daidzin DAGL) cutlets, tripe, soy drink, soy nuts, soy cubes, and three different dietary supplements)

[141]

UAE

ChCl/1,4-butanediol

Dioscorea opposita Thunb.

Polysaccharides

[142]

Water samples

Ultraviolet filters

[143]

UADLLME ChCl/ trioctylmethylammonium chloride, decanoic acid UAE

Lactic acid/ChCl, lactic acid/ Native Greek medicinal plants Antioxidant polyphenols sodium acetate, lactic acid/ ammonium acetate, lactic acid/ glycine/water, lactic acid/ glycine

[11]

LLE

Betaine monohydrate/glycerol

Palm oil

Palmitic acid

[144]

LLE

DL-menthol/octanoic acid

Aqueous solutions

Pesticides

[145]

LLE

ChCl/malonic acid

Crude palm oil

Tocopherols, tocotrienols

[146]

SPE

Lactic acid/glucose/water

Agrofood industrial byproducts

Phenolic compounds

[147]

SPE

Malic acid/ChCl, 20% water (w/w); glycerol/proline/ sucrose, 20% water (w/w); malic acid/ChCl, 20% water (w/w); malic acid/glucose, 20% water (w/w)

Ginkgo biloba, Panax ginseng

Ginkgolides, phenolics acid, ginkgolic acids, ginsenosides

[148]

(Continued) New Generation Green Solvents for Separation and Preconcentration

410

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

TABLE 9.11 (Continued) Method

DES

Sample

Analytes extracted

Reference

SPE

Citric acid/D-(1)-maltose, 24% water (w/w)

Grape skin

Anthocyanins

[149]

SPE

ChCl/fructose, 30% water

Grape skin

Total phenolic compounds, total anthocyanins content

[150]

SPE

Citric acid/glucose/ water

Onion

Quercetin

[151]

SPE

L-proline/glycerol, 10%water

Sophora japonica L.

Quercetin, kaempferolisorhamnetin, glycosides

[120]

SPE

ChCl/ascorbic acid,10% water

Oil sample

tert-Butylhydroquinone

[152]

SPE

Choline chloride/D-(1)-glucose Mentha piperita L.

Volatile monoterpenes compounds, phenolic compounds

[153]

SPE

Lactic acid/fructose, 25% water Vanilla pods (v/v)

Vanillin

[154]

SPE

Glycerol/xylitol/D(-)

Ficus carica

Phenolic compound

[155]

Lippia citriodora

Phenolic compounds

[156]

Fructose, 20% water SPE

ChCl/lactic acid, 32.19% water

FIGURE 9.12

Schematic diagram of ELLME-DES (DES phase colored by Congo Red dye).

New Generation Green Solvents for Separation and Preconcentration

9.4 Application of deep eutectic solvents in extraction techniques

Subsequently, the droplets of MDES were collected by a magnet, and the remaining concentration of thiophene in heptane was analyzed by GC-FID. This method provides excellent results in removing the thiophene (close to 100%) from the initial solution, with the great advantage of removing the centrifugation steps normally required in any liquid phase microextraction (LPME) extraction. The authors believe that the developed MDES can be reused after four cycles without loss of extraction efficiency [44]. Babaee et al. used a similar approach [49]. Hexanal and heptaldehyde were extracted from a sample of edible oil and then subjected to a gas chromatography flame ionization detector. In this work, [choline/p-cresol solvent] [FeCl4] was used as an extraction solvent [158]. Khezeli et al. [159] reported a simple and highly reproducible UAME technique for the determination of ferulic acid, caffeic acid, and cinnamic acid in olive oil, almond oil, sesame oil, and cinnamon oil using ChCl and ethylene glycol (1:2, molar ratio) as the DES extraction solvent. The solvent was added to the sample dissolved in n-hexane, then the mixture was placed in an ultrasonic bath for 5 min to form an emulsion of the droplets, and then the contact surface between the DES and the sample was increased. Once the extraction was complete, the DES phase containing the analyte was separated by centrifugation and subjected to HPLC-UV analysis. According to the results, this new method shows good sensitivity (detection limit between 0.39 and 0.63 μg L21), reproducibility (RSD ,5.1%), practicality (extraction time less than 15 min), and high precision (recovery speed) 95%
105%). Recently, it has not been necessary to disperse the solvents, and the ultrasound-assisted dispersion or microextraction techniques have become increasingly popular to reduce environmental side effects (i.e., reagents and energy consumption). The generation of CO2

411

bubbles in this technique facilitates the extraction of solvent in an equivalent manner to form fine droplets in an aqueous sample, which improves the effective mass transfer of the analyte of interest. Ghorbani Ravandi et al. applied a simple, fast, and sensitive technique called DESassisted effervescent liquid dispersion
liquid microextraction technique based on DES to extract synthetic dyes (fruit pastels, chocolates, ice creams, etc.) from food samples. The research was done by mixing a quaternary ammonium halide salt (Aliquat 336) with carboxylic acid (tannic acid, oleic acid, and ibuprofen) in molar ratios of 1:2, 1:2 and 7:3, respectively. These extraction solvents were injected into an aqueous sample containing NaHCO3 and led to an effervescence reaction. After phase separation, the DES-rich phase (upper phase) was diluted with a suitable solvent to measure the absorbance of the target food dye. Fig. 9.13 schematically shows this extraction procedure [160]. Jouyban et al. reported a new microextraction technique called dispersion-based microextraction in the liquid phase based on glass filters to extract and preconcentrate various classes of pesticides, including dichlorvos, diazinon, and west, applying lighter-thanwater DES. The main purpose of this work was to develop a new LPME method for the extraction and preconcentration of the aforementioned pesticides by applying DES in a self-made device. Here, lighter-than-water DES is made by combining ChCl: n-butyric acid, ChCl: pivalic acid, and ChCl: 3,3dimethylbutyric acid in a molar ratio of 1:2. This technique use an autonomous device (see Fig. 9.14) containing a filter glass tube as an extraction device. The aqueous solution of the sample containing the analyte was transferred to the apparatus in the upper part of the glass filter, and the DES lighter was placed under the glass filter. The extraction solvent is passed through a glass filter and

New Generation Green Solvents for Separation and Preconcentration

412

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

FIGURE 9.13 Schematic diagram of effervescence-assisted dispersive liquid
liquid microextraction for determination of mentioned dyes in the food sample.

FIGURE 9.14 Schematic procedure of glass-filter-based dispersive liquid phase microextraction using lighter-thanwater DES.

buried in the aqueous solution by applying an air flow. Thus the extraction solvent is dispersed in an aqueous solution, and the analyte is extracted into fine droplets of the

extraction solvent. The resulting droplets of extraction solvent increase through the solution and can be obtained without centrifugation [161].

New Generation Green Solvents for Separation and Preconcentration

9.4 Application of deep eutectic solvents in extraction techniques

A new emulsified microextraction technique based on immobilized organic droplets was developed by combining a new tailored superhydrophobic DES with effervescentassisted emulsification microextraction (EA-EME-SSDES). The target analytes are 2-nitrotoluene, 3-nitrotoluene, nitrobenzene, 1,2-dinitrobenzene, 1,3,5-trinitrobenzene, 2,6dinitrotoluene, 2,4-nitritroluene, and TNT. The extraction solvent was synthesized by mixing DL-menthol with octanoic acid, citric acid, oleic acid, and salol as an HBD agent. Briefly, an effervescent precursor and DES aliquots were added to the sample solution of the analyte (Fig. 9.15A and B). Subsequently, DES was uniformly dispersed in the aqueous sample due to effervescence (Fig. 9.15C). After centrifugation in a cooled centrifuge, the stabilized, solidified DES was separated from the aqueous solution simply by a decantation tube (Fig. 9.15D and E). Finally, DES was melted at room temperature and injected into the HPLC-UV for analysis. Despite other methods of microextraction of emulsion based on the hydrophilic DES, no emulsifying solvent (e.g., tetrahydrofuran) is used in the solvent-free organic process [162].

413

Zhu et al. developed liquid
liquid microextraction and then used high-performance liquid chromatography to determine eight synthetic pigments in beverage samples, using hydrophobic DES as a microextraction solvent. After optimizing the important conditions such as the type and volume of hydrophobic DES, the pH value, the vortex time, and the salt content, the detection limit was in the range of 0.016
1.12 ng mL21, and the recovery rate was in the range of 74.5%
102.5% with standard deviation ,5.4% [51]. The Mako´s group has introduced the synthesis of new nonionic and hydrophobic eutectic solvents for natural compounds (thymol, camphor, citric acid, and 10-undecenoic acid) and their use as extractants in microextraction with liquid
liquid ultrasonic dispersion for use as reagents in the separation and enrichment of hydrocarbons in water samples of polycyclic aromatic hydrocarbons. The final assay was performed by gas chromatography
mass spectrometry. After optimization, the process established by the lower limit of detection and quantification is 0.0039
0.0098 μg L21 and 0.012
0.029 μg L21, respectively, in good order, with good precision

FIGURE 9.15 Steps in EA-EME-SSDES. (A) Sample solution containing analytes; (B) after adding the effervescence tablet containing the extraction solvent; (C) after dissolving the tablet and shaking the sample solution; (D) after centrifuging; (E) after decanting the aqueous phase; and (F) the extractant at room temperature.

New Generation Green Solvents for Separation and Preconcentration

414

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

(RSD ,6.09%), an analyte recovery interval from 73.5% to 126.2%, and a large linear range [52]. Yilmaz and Soylak proposed a new green DES based liquid phase microextraction procedure (DES-LPME) for the evaluation of Rhodamine B in cosmetics and water samples using tetrabutylammonium chloride/capric acid (1:2) as the extraction solvent. Composition with tetrahydrofuran as an emulsifier for the microextraction of Rhodamine B was followed by spectrophotometer UV-Vis analysis of a microcuvette at 550 nm. The experimental steps for the consolidated technique are shown in Fig. 9.16 [96]. Bi et al. used a series of alcohol-based DES and different alcohols compared to ChCl, mixing the ratios to extract flavonoids (myricetin and amentoflavone) using different

extraction methods, which are well-known and widely used antioxidants. Other factors such as temperature, time, water addition, and solid:liquid ratio have been systematically tested by applying the response surface methodology [112]. Panhwar et al. proposed a microextraction in liquid ultrasonic phase ultrasonic-assisted liquid phase microextraction based on the ecological DES extractor for the analysis of selenium speciation. In the present study, five different compositions of DES solvent (ChCl/tetrabutylammonium chloride, trioctyl ammonium chloride, and phenol) were prepared and used with Se (IV) and 3,3-diaminobenzidine (an effective extraction medium for hydrophobic DAB chelates). They observed an Se (IV) recovery of over 97% from ChCl/phenol DES [163].

2-Addition of 300 mL of DES and THF 5- DES phase

0.4 0.3 0.2 0.1 0 0

3- Ultrasonication for 2 min

1

2

3

6- Spectrophotometric analyze

4- Centrifugation for 10 min Water phase

Rhodamine B 1- Aqueous sample solution (Rhodamine B+ pH 3 Buffer) Nano-sized and microsized cloudy DES droplets

FIGURE 9.16

Microextraction procedure for Rhodamine B.

New Generation Green Solvents for Separation and Preconcentration

4

415

9.4 Application of deep eutectic solvents in extraction techniques

An

al ys

e

Ul tra

so

ho

ni ca

tio

n

Sa mp mo an ling ge d niz ati on

Ultrasonic bath 20 kHz, 200W 45 min

FAAS

Liver sample DES addition Liver samples

Deep eutectic solvent (DES)

Separation of solid and DES phase

Anelyte solution

FIGURE 9.17

Schematic procedure developed by Soylak et al.

In 2016 Soylak et al. reported the effect of ultrasound-assisted DES on the morphology of total chromium, chromium (III), and chromium (VI) on the basis of emulsion microextraction in liquid phase and of atomic absorption spectrometry with microinjection flame. The proposed liquid microextraction method has been successfully applied to tap water, two different samples of chromed factory wastewater (Kayseri), and samples of lake water (Van, Turkey). They showed that the recovery of Cr (VI) and Cr (III) in water samples was between 97% and 109% with a standard deviation of less than 6.0 [134]. The team used the same method to extract iron from sheep liver, cattle, and chicken samples. DES is prepared by combining ChCl with ethylene glycol, glycerin, oxalic acid, and lactic acid as HBD agents. The results reported show that the best recovery was obtained with DES chloride/ lactic acid in a molar ratio of 1:1. The extraction technique is described in Fig. 9.17 [164]. In 2016 for the first time, proteins were extracted by magnetic solid phase extraction based on Fe3O4-NH2@GO@ DES. In this study,

Wang et al. synthesized four ChCl-based DESs, which then prepared core
shell magnetic graphene oxide (Fe3O4-NH2@GO) nanoparticles and coated them with ChCl-based DESs. The preparation of Fe3O4-NH2@GO@ DES and its application in protein magnetic solid phase extraction are shown in Fig. 9.18. In this study, different types of extractants (Fe3O4-NH2, Fe3O4-NH2@GO, studied Fe3O4-NH2@GO@ DES). They found that when the solid phase extractant was coated with four DES (ChCl-EG, ChCl-G, D-ChCl-Glu, D-ChCl-S), the interaction with the protein was enhanced by the hydroxyl group of DES [165]. Mohebbi et al. established dispersive solid phase extraction and solvent-based eutectic airassisted liquid
liquid microextraction for some tricyclic antidepressants (amitriptyline and nortriptyline) in human urine and plasma. After extraction and preconcentration, the samples were determined by gas chromatography
mass spectrometry. In this technique, ChCl/4-chlorophenol based on C18 and DES was used as an adsorbent solvent and desorbent, respectively [166].

New Generation Green Solvents for Separation and Preconcentration

416

FIGURE 9.18

9. Deep eutectic solvent in separation and preconcentration of organic and inorganic species

Procedure of DES-based ultrasound-assisted extraction procedure.

Alipanahpour Dil et al. applied a hydrophobic DES as a ferrofluid vector for the determination of mefenamic acid in human urine [167]. Ferrofluid has currently been introduced as an extraction step for the pre-preparation method and as a new colloidal magnetic phase. The popularity of this method is due to its simple operation and speed, as well as its minimum requirements for organic solvents. Ferrofluids are generally the suspensions of magnetic nanoparticles and have the ability to be suspended in a carrier liquid [168]. Using the mix of fluid behavior and magnetic properties, as well as their stability, it is possible to use van der Waals forces, magnetostatic interactions, attractive dipolar interactions, or the like [169]. The objectives of the Alipanahpour Dil and associates study were the preparation of a ferrofluid of magnetic nanoparticles, oleic acid (OA), combined with DES hydrophobic (Fe3O4 [iron oxide]-OA-DES) and its application

for residual acid determination mefenamic based on a vortex-assisted microextraction method.

9.5 Conclusion Safety, non/low toxicity, availability, adjustable physical-chemical characteristics, low price, and biodegradability of DESs are consistent with the term “green chemistry.” DES has been used as a new alternative and ecological solvent for various microextraction techniques such as ATPS, LPME, UAME, and SPME, as well as more conventional extraction procedures such as LLE. DES’s high purity, thermal stability, ease of use, low cost, and environmental safety led them to be used in a variety of documents. Recently, new specific DES tasks have been favored by the available natural materials. Moreover, from the

New Generation Green Solvents for Separation and Preconcentration

References

application point of view, selective DESs should be explored as an extension of the extraction medium.

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2982. [2] Y. Gu, F. Jerome, Bio-based solvents: an emerging generation of fluids for the design of eco-efficient processes in catalysis and organic chemistry, Chem. Soc. Rev. 42 (2013) 9550
9570. [3] A.P. Abbott, G. Capper, D.L. Davies, R. Rasheed, Ionic liquids based upon metal halide/substituted quaternary ammonium salt mixtures, Inorg. Chem. 43 (11) (2004) 3447
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335. L. Zhang, M. Wang, Optimization of deep eutectic solvent-based ultrasound-assistedextraction of polysaccharides from Dioscorea opposita Thunb, Int. J. Biol. Macromol. 95 (2017) 675
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161.

New Generation Green Solvents for Separation and Preconcentration

C H A P T E R

10 Supercritical fluid extraction in separation and preconcentration of organic and inorganic species Tahere Khezeli1, Mehrorang Ghaedi2, Sonia Bahrani2 and Ali Daneshfar1 1

Department of Chemistry, Faculty of Sciences, Ilam University, Ilam, Iran 2Department of Chemistry, Yasouj University, Yasouj, Iran

Abbreviations

HS-SPMEGC-MS SFE SFC

essential oils flame ionization detector gas chromatography high-performance liquid chromatography
ultraviolet headspace solid phase microextraction
gas chromatography
mass spectrometry supercritical fluid extraction supercritical fluid chromatography

Pc Pressure

EO FID GC HPLC-UV

of the gaseous phases in supercritical conditions is shown in Fig. 10.1 [1]. Hannay and Hogarth reported on early research on the dissolution of solutes in supercritical fluids since 1879. However, the use of commercial processes for the extraction of

10.1 Introduction A supercritical fluid is defined as a liquid that is above its critical value at a certain temperature and pressure. In the supercritical area, it is in only a liquid state that has properties similar to gases and liquids. In this case, the gas does not condense as the pressure increases. The diagram

New Generation Green Solvents for Separation and Preconcentration DOI: https://doi.org/10.1016/B978-0-12-818569-8.00010-3

Solid

Supercritical fluid region Liquid

Gas

Tc

Temperature

FIGURE 10.1 Phase diagram of gases [1].

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© 2020 Elsevier Inc. All rights reserved.

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10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

supercritical fluids around 1960 has been extensively studied [2,3]. Therefore, the supercritical fluid extraction (SFE) analytical method emerged in the late 1980s and was developed as an excellent candidate for adhering to some or most of the ideal sample preparation techniques, such as fast, easy, and economical, unless they are used with a very pure, expensive, and often toxic solvent [4]. SFE not only reduces the use of organic solvents, but it is also possible to incorporate it into automated analysis systems. It is suitable for the production of heat-sensitive substances to serve as pure and organic extracts [5,6]. SFE has many benefits over common extraction methods because it uses supercritical solvents with different physicochemical properties such as density, diffusion coefficient, viscosity, and dielectric constant. Thanks to their low viscosity and relatively high diffusivity, supercritical fluids improve transmission properties compared to liquids and be able to easily spread in solid materials, thus providing more rapid extraction. One of the key features of supercritical fluids is the ability to change the fluid density by varying its pressure and/or temperature. Since density is related to solubility, the intensity of the solvent liquid can be adjusted by varying the extraction pressure. Other advantages of SFE, compared to other extraction techniques, are the use of solvents that are generally considered safe, the efficiency of the extraction process to increase the yield and reduce the extraction time, and the possibility of direct coupling to chromatographic analysis methods such as gas chromatography (GC) or supercritical fluid chromatography [7,8]. Carbon dioxide, which is typically applied as an extraction solvent in SFE, is not toxic; it is not combustible, it is not corrosive, it is easy to obtain in large quantities, it has high purity and low cost, and it can change the characteristics of solvency by changing the pressure or

the temperature of the liquid. Organic carbon dioxide is generally considered safe by the EFSA (European Food Safety Authority) and FDA (Food and Drug Administration). Compared to traditional methods, the main advantages of SFE are moderate temperature, low energy prices, and the production of highpurity extracts [9]. However, these aspects are compromised by many factors, such as (1) higher investment costs compared to traditional technologies and (2) high pressure associated with them, which requires adequate insulation equipment, including their safety systems [10,11]. Another disadvantage of SFE-based carbon dioxide is the low polarity of the extraction solvent, which can be overcome using polar modifiers (cosolvents) to change the polarity of the supercritical fluid and increase the solvation power of the target analyte.

10.2 Properties of supercritical fluid Several solvents are available for SFE technology, including carbon dioxide, ethane, nitrous oxide, propane, ammonia, n-pentane, sulfur hexafluoride, fluoroform and water. Table 10.1 lists these and their key parameters [12,13]. The latest supercritical solvent used is carbon dioxide, and over 90% of all SFE analytical processes are carried out with CO2. It has a relatively low critical pressure (74 bar) and temperature (32 C). Supercritical carbon dioxide is also preferred because of its high diffusivity and easily adjustable solvent resistance. Another benefit is that at ambient pressure and temperature CO2 is in its gaseous state, which makes recovery analysis very easy and provides solvent-free analysis. Moreover, the ability of SFE to utilize CO2 at low temperatures using nonoxidizing media, capable of extracting thermally unstable or easily oxidizable compounds [14,15], is important for the

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10.3 Instrumentation

TABLE 10.1 Properties of some supercritical fluids at Cp. Tc ( C)

Supercritical fluid

Pc (atm)

CO2

31.0

72.0

N2O

36.5

70.5

Ethane

32.3

47.6

Propane

96.7

42.4

n-Pentane

196.6

32.9

Ammonia

132.5

109.8

Fluoroform

26.0

46.9

SF6

45.5

38.0

Water

374.2

214.8

Methanol

240.0

78.0

Ethylene

10.0

51.0

TABLE 10.2 Comparison of the physical properties of gases, organic liquids, and supercritical fluids. Phase

Density (g cm23)

Viscosity (P) 3 104

Diffusivity (cm2 s21) 3 104

Gases

B1023

0.4
3.4

100
10,000

Organic liquids

0.6
1.1

32
251

0.05
0.2

Supercritical fluid

0.2
0.9

2.1
10.8

0.11
3.3.45

preparation of food samples and natural products. Table 10.2 shows the comparison between density, viscosity, and diffusion coefficient of gases, supercritical liquids, and organic liquids to provide a clearer picture [1]. In the 1990s, some reports on N2O selection were published as an extract for the analysis of SFE. Due to its permanent dipole moment, this liquid is considered more suitable for polar compounds. One of the applications in which N2O shows a significant improvement compared to CO2 is, for example, in the extraction

of polychlorinated dibenzodioxine from fly ash. It has been discovered that this liquid causes serious explosions when used in samples of high organic matter and thus should be applied only when required. Other exotic supercritical fluids have been applied in environmental SFE, SF6, and freon. SF6 is a nonpolar molecule (although sensitive to polarization) and, as a supercritical fluid, has been shown to selectively extract aliphatic hydrocarbons around C-24 from a mixture containing aliphatic and aromatic hydrocarbons. Freon, in particular CHClF2 (freon-22), has repeatedly been shown to improve extraction efficiency compared to CO2 extraction. The fact that supercritical H2O is often used to destroy dangerous organic compounds, high temperatures and pressures (T . 374 C and P . 221 bar) in these conditions and the corrosive nature of H2O limit possible practical applications. In the analysis of vegetable oils in subcritical conditions, H2O is shown to be an effective liquid for the extraction of different types of essential oils [16
20].

10.3 Instrumentation The basic SFE tool is very simple and consists mainly of common components in liquid chromatography. A pump (syringe or reciprocator) that cools the head to ensure that liquid pumping is applied to deliver the extract into a high-pressure extraction chamber containing the sample of interest. The battery is kept at a temperature above the critical temperature of the liquid by placing the battery in an oven. Extraction units of different sizes and geometries are applied, generally built-in stainless steel able to withstand the high applied pressure. The cell geometry can affect the extraction, but it is less important if the cells are completely packed. SFE can be executed in static or dynamic mode. The pressure in the system is maintained by a fixed or variable

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10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

flow limiter. The fixed limiter is a tube with a diameter small enough to reduce the flow of the fluid. Use a piece of fused silica or a corrugated stainless steel tube. Problems exist with fixed flow limiters, including blocked analyte or blockage of the matrix and irregular flow. The restriction block is reduced by applying heat outside the flow limiter. The variable limiter is a mechanical or electronic control that quickly opens and closes the hole to control fluid flow. The main advantage of their relationship with the much cheaper fixed rate is that they allow for independent control of supercritical fluid flow and extraction pressure by continuously changing the pore size. When the fluid passes through the limiter, it can simply be pressurized, and the analyte is trapped in a collection device, which generally includes a vial containing the solvent or a cartridge containing the chromatographic package. Another method of collection is to connect SFE directly to the chromatographic system and deposit the analyte directly without the need for an intermediate collection phase. An overview of a typical SFE tool is shown in Fig. 10.2 [21,22]. The modifiers have been proposed in different ways in SFCs and SFEs. The first technique to add modifiers is to use premixed cylinders available from commercial suppliers. These cylinders, for example, have specific modifiers to separate CO2 levels. The cylinder is connected Pump

Oven

Modifier pump (optional)

Restrictor

Collection

FIGURE 10.2

Schematic diagram of a typical SFE

system [21]. Extraction cell

Fixed or variable Supercritical fluid cylinder

directly to the feed pump, directing the improved fluid to SFE. A disadvantage of this method is that the pump and the entire system can be contaminated with modifiers. Another way to add modifiers to the SFE system is to use two separate feed pumps. In this way, a feed pump is mainly used for the delivery of CO2, and a second feed pump is used for dispensing the modifier. Downstream of these two pumps, there is a thermostatic mixing jacket. The T-tube mixes the modifier with CO2 to balance the liquid in the constant temperature area and then supplies mixed liquid to the extraction vessel. Modifiers can also be added to the feed pump using a high-pressure auxiliary valve. The valve generally has a known volume on the circuit (i.e., 1
5 mL), which can be filled with a liquid modifier and then fed directly to the feed pump after the activation of the valve. Then the liquid is mixed in a feed pump tank and delivered as a liquid mixed with the SFE oven. In most cases, this mixing method should be considered an approach in rapid detection modifiers at different concentration levels. The last and probably the most effective way to provide an SFE modifier is to add the modifier directly as a liquid to the sample matrix before filling the extraction vessel or before the sample matrix has been in the container but before the extraction. Therefore the modifier is isolated from the actual main feed pump so that the pump (as well as the

Co2 pump (reciprocating or syringe)

Chromatographic packing Solvent or solventless Online

Pump head cooling systems

New Generation Green Solvents for Separation and Preconcentration

10.4 Mechanism and kinetic of supercritical fluid

entire system) is not contaminated by the modifier [23]. In general, SFE can be run online or offline. In online mode, the output of the SFE tool is directly linked to the analytical tool. In offline mode, however, the extracted analyte is determined by capture and elution and analyzed by an analytical tool. About 10 years ago, supercritical carbon dioxide was considered a very selective extractor, and the extract was relatively free of coextraction. Therefore many researchers are advocating methods to analyze target analytes using tools directly linked to a supercritical liquid chromatography system. However, when using the online mode for a matrix containing significant amounts of lipids, the coextracted substances cause problems. Due to the limited size of the sample, the electronic extraction method has disadvantages. For offline SFE, the acquisition of extracted analytes is an important aspect. The capture of the analyte after extraction can be carried out with a small collection of traps for solvents or absorbents. In solvent capture, the supercritical CO2 containing the analyte is pressurized, and the analyte is collected directly in the liquid solvent, while in the uptake of the adsorbent, the supercritical CO2 containing the analyte adsorbed on the solid material, for example glass microspheres, C18 bonded with oxide of cerium or Florisil and then analyte eluted with a suitable solvent.

10.4 Mechanism and kinetic of supercritical fluid The SFE experiment is commonly categorized into three sequential steps: 1. Primary partitioning of tile analytes from active sites of matrix into the supercritical fluid; 2. Elution the analytes from extraction cell; and

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3. Gathering of analytes in SFE trapping system [13]. In the extraction of supercritical liquids (SFE), the extractor is in a supercritical state, which means that both the pressure and the temperature are above their critical values. Supercritical fluids have unique properties, between gas and liquid, depending on the pressure, temperature, and composition of the liquid. In particular, its viscosity is lower than the viscosity of the liquid and the diffusion coefficient is greater, thus improving the extraction efficiency. Furthermore, the density (and therefore the power of the liquid solvent) can be adjusted by varying the pressure and the temperature to allow theoretically high selectivity extraction [22]. The task of SFE is to specify the best extraction parameters for the target analyses in a particular matrix. Parameters such as pressure, temperature, extraction cell geometry, fluid flow rate, and selection of the appropriate collection media have their cumulative effects on analyte recovery and have been studied to determine mutual dependence. The solvent power of the extract, controlled by density, temperature, and composition, is the main parameter that must be controlled for optimal recovery. The definition of solvent power used here is as defined by Snyder and Kirkland [24]. The low density will extract nonpolar volatile compounds, and the high density will extract relatively polar and less volatile compounds. A quick way to evaluate the effect of density is to perform different extractions with different densities (low, medium, and high) to see when the analyte starts to be extracted [25]. The increase in supercritical fluid pressure at a constant temperature causes an increase in density, and thus the solvent resistance of the supercritical fluid is greater. One way to describe this association is to use a modified version of the Hildebrand equation (δ 5 1.25 P ^ (1/2) (ρ_SF/ρ1)), which provides a solvent resistance

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10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

(Hildebrand parameter, δ) as a function. The density of the typical liquid density (ρ1) and the critical fluid pressure (P) of the liquid are lowered, and the density of the supercritical liquid (ρSF) is lowered. Theoretically, the maximum solubility of analyte in supercritical fluid [12,26] is obtained when the density of the supercritical fluid is equal to the density of the target analyte. Another parameter to check is the extraction temperature. When the pressure of the supercritical fluid is constant and the temperature increases, the effect of the solvent force depends on pressure. If the pressure is lower than the intersection, the high temperature causes a decrease in the strength of the liquid solvent due to a decrease in the density of the liquid. Although the density of the liquid is reduced above the “junction,” the increase in temperature can increase the extraction efficiency due to increasing in vapor pressure of analyte. The “cross” depends on the analyte
supercritical fluid interaction [27]. In addition, to affecting the density, the increase in temperature can also add heat to the system. This can increase the partial pressure of the solution or reach the melting point of the matrix, thus releasing the dissolved substance and allowing its transport from the matrix through the extract. An increase in temperature also causes enhancing in the rate of diffusion of the liquid above the critical temperature. Another factor that can influence the recovery process is the addition of modifiers. The effects of the modifiers are still unknown, but they will alter the capacity of the solvent in the liquid and/or alter the solid
solid interaction (usually both). After specifying the fluid properties, it is necessary to determine the fluid/sample interaction time and the fluid volume. This interaction is specified by flow rate, extraction time, and whether the extraction is performed in static or dynamic mode [28]. Once the favorable analytes have been extracted, they must be collected/captured for

analysis and quantification. Once they are assembled/acquired, it may be necessary to reconstruct, filter, or derivatize them before the final analysis. Similarly, the chemical/physical properties of the analyte will specify the collection and reconstruction of the rinsing parameters. During the extraction phase, the volatility of the analyte will determine the collection temperature or the type of adsorbent material used for collection. If the analyte is volatile, it is necessary to apply a cold trap or a cooled collection solvent and a reduced flow rate. This is because the analyte is volatile and the evolution of CO2 can produce an aerosol or mechanically move the analyte through the collection device. Lower-volatility analytes resist higher extraction rates, and higher harvest temperatures can be used. If an absorbent trap is used for collection, the chemist can specify an appropriate absorbent and rinse the solvent for optimal recovery of the beneficial analyte. Flow and volume are also parameters that must be specified. The flow rate and amount of rinse are determined by the solubility of the analyte in the rinsing agent and the amount of material removed from the trap.

10.5 Applications of supercritical fluid 10.5.1 Supercritical fluid in the environment SFE combined with statistical analysis and response surface methodology was applied to explore the removal of petroleum hydrocarbons from contaminated soil by Meskar et al. In this work, the effects of fluid temperature, pressure and time duration and also the effect of mode of extraction (static and dynamic) on the extraction of the target analyte were evaluated. The effects of two independent factors (pressure
temperature) in SFE have been studied in detail through experimental design. The SFE method has been widely used to extract

New Generation Green Solvents for Separation and Preconcentration

10.5 Applications of supercritical fluid

many metal ions from different substrates. The extraction of metal ions with CO2-based SFE can be achieved by converting a species of charged metal into a neutral metal solvate using a suitable complexing agent. The general experimental procedures and the procedures followed in this study are shown in Fig. 10.3 [29]. Pitchaiah has developed a process based on SFE for the complete recovery of uranium and plutonium from substrates of thermochemical salts (UCl3-LiCl-KCl, PuCl3-LiCl-KCl, and UO2Cl2-NaCl-CsCl). The team first determined the solubility of the specific ligands of the

431

actuator and their ligands: n-propanol, methanol, acetylacetone, tributyl phosphate, 8 N tributyl phosphate, balanced with acid (di-2ethylhexyl), isobutyramide (di-2-ethylhexyl), isobutyamide, CO2. They then used SC-CO2 with the appropriate ligand to recover the actuator elements and improve the experimental parameters (temperature, pressure, the concentration of solvents and acids, etc.) and finally strengthen the typical SFE process to extract uranium from the matrix saline. Current research indicates that SFE-based technology can provide an important alternative for

FIGURE 10.3 (A) Flowchart of the experimental procedure; (B) removal rate of PHC F2 for various SFE modes and duration of times (S: static mode, C: cycle), D: dynamic mode [29].

New Generation Green Solvents for Separation and Preconcentration

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10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

FIGURE 10.4 Schematic of an online SFE-SFC system [31].

Vent 6

2 1

7

8

5

4

9

11

12

10

3

recovering actinides from a chloride salt matrix with generating least secondary waste [30]. Online supercritical SFE liquid mass spectrometry has been applied by Wicker et al. to specify 16 polycyclic aromatic hydrocarbons (PAHs) in the soil. The connection of SFE to SFC provides minimal sample preparation, minimal sample loss or contamination, and reduced total analysis time. Fig. 10.4 shows a diagram of a mass spectrometer for online supercritical SFE liquid chromatography. This method evaluates the concentration of 10
1500 ng of PAH per soil gram in the deposits of standard reference material (CRM), clay, and sand [31]. Han et al. developed an SFE technique with an online solids trap (multiwall carbon nanotubes [MCNT]) to specify 16 polycyclic aromatic hydrocarbons (IPAs): naphthalene, acenaphthylene, acenaphthene, fluorine, phenanthrene, anthracene, fluorene, pyrene, benzene[a] anthracene, cryogen, benzo[b]fluorant, benzo[k] fluorant, benzo[a]pyrene, indeno [1,2,3-cd] pyrene, dibenz[a,h]anthracene and benzo[g,h,i]perylene (and 15 typical derivatives of nitro, oxy, and PAH alkyl in solid matrix). The dynamic CO2 based on SFE carried out at 300 bar pressure, 40oC temperature, an extraction time of 15 min, % and 10% dichloromethane. Subsequently, the target compounds were collected on the CNTs and captured via adsorbent and eluent dichloromethane.

The content of the eluent was analyzed with GC-MS [32]. Jowkarderis et al. developed an innovative SFE mixed dispersion liquid microextraction, followed by gas chromatography and flame ionization detector (GC-FID) to determine 4nitrotoluene and 3-nitrotoluene in soil samples. This combination prevents evaporation of the solvent after extraction and increases the enrichment factor for organic compounds in solid samples [10]. In a typical experiment, the standard 4-nitrotoluene and 3-nitrotoluene are added to the soil samples in an SFE extraction vessel. The CO2 based on SFE has an oven temperature of 35 C at a pressure of 350 atm, 30 min dynamic extraction time, and 10 min static extraction time. The extracted analyte is collected in a collector containing methanol as a dispersant solvent. Carbon tetrachloride as an extraction solvent is added to the collector solvent. Finally, the resulting mixture is rapidly injected into aqueous sample in presence of an ionic strength of 3.0% NaCl (w/v). A cloudy mixture forms immediately in the conical tube. After centrifugation of the turbid solution, the extraction solvent is placed on the bottom of the centrifuge tube and injected into a GC instrument at a pressure of 350 atm, temperature 35 C temperature, a dynamic 30 min extraction time, and 10 minstatic extraction time. The extracted analyte is collected in a collector containing methanol as a dispersant

New Generation Green Solvents for Separation and Preconcentration

10.5 Applications of supercritical fluid

solvent. Carbon tetrachloride as an extraction solvent is added to collector solvent. Ultimately, the resulting mixture is rapidly injected into a water sample with an ionic strength of 3.0% NaCl (w/v). A cloudy mixture forma immediately in the conical tube. After centrifugation of the turbid solution, the extraction solvent is placed on the bottom of the centrifuge tube and injected into the GC instrument [33]. Hasan Bagheri et al. introduced an SFE to extract three pyrethroid residues, phenpropatrin, cialotrine, and fenvalerate, from fruit and vegetable samples (see Fig. 10.5). They synthesized a new magnetic adsorbent adapted with ionic liquid (IL), Fe 3. The extracted pyrethroid residues were introduced in high-performance liquid chromatography
ultraviolet for ultratrace analysis. In optimal conditions, reasonable linearity 2.5
250 μg L21 (0.9941 # R2 #

FIGURE 10.5

433

0.9999) and 0.3
5 mg kg21 (0.9999 # R2 # 0.9999), good precision at 3.2% 2 6.5% and 5.1% 2 8.4%, and appropriate detection limits of 1 μgL21 and 0.1 mg kg21 were obtained for the extraction of SFE and magnetic solid phase, respectively. The results revealed that the present method is a simple, accurate, and very effective method for determining pyrethroids in fruit and vegetable samples [34] .

10.5.2 Supercritical fluid in foods and herbs Essential oils represent a small fraction of plants and herbs, composed of lipophilic substances, which contain volatile aromatic components, in particular oxygenated derivatives such as alcohols, aldehydes, ketones, acids, phenols, ethers, and esters. Essential oils are

SFE extraction of three pyrethroid residues [34].

New Generation Green Solvents for Separation and Preconcentration

434

10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

extracted from roots and rhizomes, leaves, bark and branches, flowers, fruits and plants, and herbaceous seeds. The most important research and exploration of herbal extracts and essential oils are characterized by antioxidant activity. Because of usingessential oils in production of food, cosmetics, cleaning products, spices, herbicides, pesticides, and traditional medicines, it is necessary to develop accurate, fast, and inexpensive extraction procedures. Steam and water distillation and liquid
liquid extraction are traditional extraction methods used to extract essential oils from various plant substrates. One of the disadvantages of steam distillation and water distillation processes is related to the thermal stability of the essential oil component, which undergoes a chemical change because of applying high temperature (close to the normal boiling temperature of water). Therefore the quality of the extracted essential oil is extremely compromised [35]. Among the innovative extraction technologies, SFE is mainly used to extract essential oils. Bayrak et al. studied the extraction of colchicine from Colchicum speciosum L. using conventional extraction methods and SFE. In both methods, the seeds were first degreased, and from the extraction with 150 mL of petroleum ether almost 7.92% of oil was obtained. The seeds were then used for routine extraction and SFE. In the conventional extraction method, the effect of the extraction solvent (95:5 methanol/water mixture) and the stirring time were evaluated. Following the SFE method, 10 g of seeds were extracted with an SFE-CO2 system (temperature: 35 C; CO2 flow rate: 1.50 mL min21; CO2 density: 0.90 g ml21; 247 bar; container volume: 0.50 L and in period of 1, 3, 5 h). Under the CO2-SFE study conditions, the highest yield was obtained using a methanol modifier 0.5 mL min21 [36]. SFE assisted by pressing (SFEAP) is a new integration of SFE technology and cold pressing recently developed by Johner et al. In the first minute of recovery, the extraction rate for

the SFEAP combination method was 8 times higher than for conventional SFE. Hatami et al. developed SFEAP technology to extract and fractionate fennel. A representation diagram of SFEAP system is illustrated in Fig. 10.6. The temperature of the cooling bath of 25 C and of the heating bath of 43 C was adjusted 1 h before extraction. Then 40 g of ground fennel was added to the extract. After the SFEAP extraction process, the CO2 mixture and extract come out of the extractor through a micrometric valve and then enter the first separator at 80 bar and 35 C. In this phase, the first fraction is collected in a separator. Then the mixture of CO2 and the remaining extract leave the first separator and flow into the second separator at 20 bar and 8 C to collect the product rich in essential oil. Finally, the content of each mark is collected for analysis. They compared the recovery rate of SFEAP with conventional SEF and reported that SFEAP used 40 Nm of torque, which was efficient compared to SFE and increased overall production by 24.5% [37]. Hatami et al. used a similar approach, which is used to determine the volatile oil from the cloves of the carnation at 150 bar, 40 C and which uses two pairs (40 and 80 Nm). The purpose of this research was to invistigate the effects of cold pressing on the SFE of cloves, including the production of volatile oil, the concentrations of eugenol, alpha-carotene, beta-caryophyllene, and butyric acid of acetic acid in volatile oils, as well as production prices [38]. Pavli´c et al. used conventional steam distillation, Soxhlet extraction, and SFE extraction to qualitatively and quantitatively characterize essential oils (EO) and lipid extracts obtained from sage powder. According to GC-MS and GC-FID analysis, the oxygenated monoterpenes (camphor, alpha-thiophene, and eucalyptol), viridiflorol, and epizosmanol are the most important compounds in all samples. Therefore there is no significant difference in

New Generation Green Solvents for Separation and Preconcentration

10.5 Applications of supercritical fluid

FIGURE 10.6

435

Schematic diagram of SFEAP unit [37].

the relative quantity of the main subgroups of EO obtained using the traditional steam distillation and the extracts obtained from the extraction of Soxhlet and SFE (Fig. 10.7). The highest yield of dominant monoterpene was observed in some SFE samples, while the lowest was obtained by the extraction of sodium methyl chloride (SOX-MeCl). It can be said that SFE offers the advantage of a single yield of oxime and an improvement in the selectivity concerning the distillation of water concerning the extraction of Soxhlet [39]. Søgmen et al. reported the continuous extraction of caffeine and (2)-epigallocatechin, (2)-epicatechin, (-) epicatechin gallate and (2)-epigallocatechin gallate from the green tea biomass using the optimized SFE method. For a 10 g sample, SFE caffeine was performed at various temperature (30, 40, 50, 60 C),

pressures (10, 20, 25, 30 MPa), and extraction time (1, 2, 3, 5 h). The extraction conditions were obtained were a 25 MPa pressure, a 60 C temperature, and 3 min extraction time [40]. The Johner group has studied the technical and economic effects of the grinding time and the flow rate of CO2 on the dynamic recovery rate and economic response of the pequi oil. the following responses are oil production, cost of manufacturing (COM), contribution to the specified cost (price of raw materials, labor price, utilities price, and investment in fixed capital), project index (investment returning), amortization period, gross profit margin, internal return value, and present value. According to experimental tests, GT of 30 s, FR of 1.08 3 1024 kg CO2 s21 (scale 5 mL) give the maximum yield of 53.65 g oil per 100 g of mass pequi. In the economic evaluation, the

New Generation Green Solvents for Separation and Preconcentration

436

10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

EO

(A) Monoterpene hydrocarbons 1%

Oxygenated monoterpenes 38%

Diterpenes 33%

Oxygenated sesquiterpenes 22%

Sesquiterpenes 6%

SOX-MeCI

(B)

Monoterpene hydrocarbons 1% Oxygenated monoterpenes 43%

Diterpenes 30%

Oxygenated sesquiterpenes 21%

(C)

Sesquiterpenes 5%

SFE-14 Monoterpene hydrocarbons 1% Diterpenes 24%

Oxygenated sesquiterpenes 19%

Oxygenated monoterpenes 50%

Sesquiterpenes 6%

FIGURE 10.7 Distribution of main terpene subgroups in (A) EO, (B) SOX-MeCl, (C) SFE-14 samples [39].

investment committee is interested in potential testing in industrial plants (,USD60.69 kg21 of oil) [41]. The enzyme-assisted SFE method was combined with the Box-Behnken construct to improve the extraction factors and the plant enzymatically degradation, thus improving bioactive compounds release from alfalfa. The parameters studied were extraction temperature, pressure, total phenol content, and cosolvent percentage of the antioxidant. The optimal extraction parameters for the total phenol and antioxidant activity were 68 C temperature, 205 bar pressure, and 15.5% solvent addition [42]. SFEAP was presented by Johner et al. to extract the target analyte in pequid, a Brazilian native fruit containing high lipid values. The extraction performance of SFEAP was comparible with SFE. Before executing SFEAP, the extraction of pequi with SFE was carried out at 313K and 333K temperatures and 20, 25, 30, 35, 40 MPa 15.5% to specify the optimal pressure and temperature. It was reported that 333K and 40 MPa yielded the maximum yield in SFE, 48 g of extract. The comparison between the yield of SFEAP in this optimal performing condition and SFE showed that the yield of SFEAP was eight times higher than that of the SFE inthe first minute of recovery. Fig. 10.8 shows the compositions of pequi fruit [43]. Liu et al. established offline SFE-SFC-MS/ MS technology for the analysis, extraction, and detection of 15 phenolic compounds in garlic. The enrichment of the phenolic compound was initially investigated by an automated SFE, and extracted components were then analyzed by supercritical liquid chromatography
mass spectrometry. Under optimal conditions, the linear range of the target compound is 0.02
8 μg g21, and the correlation coefficient is greater than 0.93333 [44]. The main disadvantages of the extraction of supercritical fluids compared to conventional processes are the slow extraction kinetics and low extraction yields. Another alternative to

New Generation Green Solvents for Separation and Preconcentration

10.5 Applications of supercritical fluid

437

FIGURE 10.8 Compositions of pequi fruit: (A) mass distribution graph of each part of pequi fruit (B) centesimal compositions of dried pulp [43].

the improvement process is using ultrasonic power [45
47]. The use of ultrasound in extraction offers important benefits that can improve the mass transfer process. Ultrasounds have been used in laboratory equipment since the 1950s. The extraction with traditional ultrasonic solvent has been extremely applied in the pre-concentration of food components such as lipids, essential oils, proteins, flavonoids, polysaccharides and carotenoids, [35]. Santos-Zea et al. investigated the effect of ultrasound on antioxidants and SFE of bagasse saponins of fiber-rich materials. The effects of temperature, pressure, solvent ratios, and ultrasound of the different configurations of the transducer on the antioxidant capacity, on the antioxidant compounds, and on the saponin concentrations were evaluated. The optimization of pressure, temperature, and volume of cosolvent was based on the Box-Behnken design. They reported that using 0.086 g cm23 mass loading, no ultrasound effects were recorded due to sample expansion and cell compression. For 0.043 g cm23, the strengthening ultrasound effect is significant (p , 0.05), and the amplitude depends on the geometry of the transducers. For the multiplatform sensor geometry, the antioxidant capacity is enhanced from 12.18 6 1.01 to 20.91 6 1.66 μmol TE g21; using ultrasound, the saponin content was between 19.05 6 1.67 and 61.59 6 1.99 μg g21 [45].

The same group studied the effect of ultrasonic transducer design on ultrasound-assisted supercritical fluid extraction of oregano antioxidants. The energy supplied to the vehicle by the transducer is different [48]. Varaee et al. used SFE to enrich free amino acids from cane molasses and sugar beet, called aspartic acid, glutamic acid, and alanine. According to the response surface method, influences of important parameters such as temperature, pressure, and extraction time were studied in the range of 150
350 bar, 40 C
60 C, and 10
90 min, respectively. Under optimal conditions, the recovery of amino acids derived from sugar beet and sugar cane molasses is between 20% and 63%. Compared to sugar beet molasses, sugarcane molasses requires higher pressures and temperatures. It can be seen that the higher viscous sugarcane molasses contains higher tannins, fibers, starches, minerals, making the extraction of free amino acids more difficult [49]. Filip et al. used SFE of volatile thermolabile Ocimum basil compounds. The SFE was performed based on the following methode: Mark basil was located in an extraction vessel, and the first extract (E1) was achieved using CO2at 100 bar pressure and 60 C temperature. The material was again extracted with carbon dioxide (after the extraction of E1), but the extract E2 was prepared at a pressure of 150 bar at a temperature of 60 C. Further, the

New Generation Green Solvents for Separation and Preconcentration

438

10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

depleted material (after the extraction of E1 and E2) was separated using CO2 at 60 C and 200 bar to separate the E3 extract, and the E4 extract was prepared using CO2 at 60 C and 300 bar using the same procedure (Fig. 10.9). In all cases of extraction, the flow rate and extraction time were the same, 3.225 g CO2 min 21and 4 h. The extract obtained was analyzed by gas chromatography
mass spectrometry [50].

FIGURE 10.9

SFE based on CO2 was done by Radojkovi´c et al. and used for the extraction of Morus species (Morus nigra and Morus alba) and compared with maceration as the conventional extraction technique (Fig. 10.10). The composition and biological activity of extracts were assessed. The 13 fatty acids (pentadecanoic acid [C15:0], myristic acid [C14:0], palmitic acid [C16:0], heptadecanoic acid [C17:0], palmitoleic acid [C16:1], stearic acid [C18:0], cis 2 9-oleic acid [C18:1 n9],

SFE of thermolabile volatile compounds from Ocimum basilicum [50].

FIGURE 10.10 SFE extraction of Morus species (Morus alba and Morus nigra). AA, Antioxidant activity; TCC, total carotenoid contents; TFC, total phenolic contents; TPC, total phenolic contents [51].

New Generation Green Solvents for Separation and Preconcentration

10.5 Applications of supercritical fluid

cis 2 9,12-linoleic acid [C18:2 n6], arachidic acid [C20:0], cis 2 11-eicosenoic acid [C20:1], α-linolenic acid [C18:3 n3], behenic acid [C22:0], and lignoceric acid [C24:0]) were quantified in obtained extracts by GC-FID analysis. Their percentages varying from 0.33% for palmitoleic acid (C16:1) to 37.57% for α-linolenic acid (C18:3 n3). The main fatty acids were α-linolenic acid (C18:3 n3) (34.97 and 37.57%), palmitic acid (C16:0) (26.38 and 25.99%), and linoleic acid (C18:2 n6c) (14.76 and 16.05%). The total phenolic and flavonoid content was determined spectrophotometrically, and the phenolic distribution was determined using HPLC-DAD analysis. Antioxidant and cytotoxic activities were also determined. The main phenolic compound is caffeic acid. Derivatives of rutin, caffeic acid, and quercetin have also appeared in large numbers [51].

10.5.3 Supercritical fluid in drug and biological sample Methods based on SFE have already been introduced to extract drugs from biological fluids. El-Aty et al. [52] used the SFE program to separate olbyzacin from plasma and milk collected from breast-feeding and as administered intravenously and intramuscularly at a dose of 2.5 mg kg21 weight. The optimal conditions for maximum extraction of the analyte in the plasma were T 5 150 C, time 5 40 min, 30% methanol; for milk, the parameters were T 5 60 C, time 5 20 min, and 35% methanol. In the evaluation of the linearity of the calibration curve and the LOD/LOQ tool, a good linearity was obtained (measured with a coefficient greater than 0.999) in the range of 0.2
0.01 μg mL21. This method showed a good recovery of 74.2% and accuracy (RSD: 1.64%
20%). Yang et al. developed a new combination of supercritical liquid extraction in the in situ derivatization and solid phase microextraction of the online headspace coupled with gas

439

chromatographic mass spectrometry (in situ derivatization SFE online HS-SPME-GC-MS). Methylparaben, butylated hydroxytoluene, hydroxyanisole butylate, hydroxybenzoate, isopropyl p-hydroxybenzoate, propyl p-hydroxybenzoate, isobutyl hydroxybenzoate, and butyl p-hydroxybenzoate SFE were extracted statically at 55 C for 10 min and extracted dynamically for 15 min. The extraction agent was then derivatized in situ into N, O-bis (trimethylsilyl) trifluoroacetamide, and 0.1% trimethyl chlorodecane. The product was then adsorbed on the head of solid phase microextraction polyacrylate fibers. The experimental configuration of the SFE derivatization in situ with the HS system
SPME is shown in Fig. 10.11 [53]. Rezaei et al. introduced first SFE and then microextraction with supramolecular solvent (SUPRAS) to extract and measure levonorgestrel and megestrol acetate in blood samples. SUPRAS is a nanostructured fluid produced by a continuous process of amphiphilic selfassembly, which occurs on two scales: molecules and nanometers. The formation of SUPRAS requires two steps. First, amphiphilic molecules spontaneously form threedimensional aggregates above the concentration of critical aggregation. The resulting nanostructures are then grouped into larger aggregates by external stimuli and separated from the mass solution as an immiscible liquid via a phenomenon known as agglomeration [54]. In the SFE-SUPRAS procedure, a blood sample is mixed with anhydrous sodium sulfate and placed in an SFE extraction vessel and extracted for a predetermined time. The extraction was performed under the following conditions: static extraction for 15 min, dynamic extraction for 240 bar, 40 min, 55 C, 0.5 mL min 2 1 CO2 flow rate, limitation of body temperature and temperature equal to 90 and 95 C [55]. Three drugs, methimazole, phenazopyridine, and propranolol, were extracted from the spiked glass matrix and SFE tablets. In this

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440

10. Supercritical fluid extraction in separation and preconcentration of organic and inorganic species

FIGURE 10.11 Experimental configuration of SFE in situ derivatization online by HS-SPME system [53].

work, the orthogonal array design was used to study and improve the effect of pressure, temperature, modification volume and the dynamic extraction time on the recovery of drug’s SFE. The ANOVA results obtained identified stress as an important factor. Specially, it was discovered that the extraction of pressure from 100 to 300 atm, in a dynamic time of 15 to 25 min and at a temperature from 308K to 318K, improves the extractability of the substance. For several drugs, the effect of polarity modifiers on percentage recovery varies widely [56]. Deniz et al. studied the effect of pressure, temperature, solvent ratio, and process duration on the SCF of phycocyanin (PC) of Spirulina platensis. After the examination, the experimental conditions were chosen as 250 bar, 60 C, and 10% ethanol as a cosolvent. The dynamic duration was 45 min, the amount of PC was 90.74%, and the purity of the PC was 75.12%. The extracts obtained with

SCF were examined against lung cancer cell lines (A549) to quantify cytotoxicity and comparing with the obtained cytotoxicity from solvent extraction. The SCF extract had an IC 50 value of 26.82 μg mL21, while the solvent extract had a value of 36.94 μg mL21, indicating a lower cytotoxic effect. Table 10.3 shows other applications of SFE in different areas [57].

10.6 Conclusion The purpose of this chapter was to summarize and discuss representative information and advances related to SFE technology used to extract organic and inorganic species from environmental, biological, food, and agricultural samples. The effect of SFE extraction conditions on the extraction yield was evaluated.

New Generation Green Solvents for Separation and Preconcentration

TABLE 10.3 Other application of SFE. Sample

Target analyte

Solvent Pressure

Temperature ( C)

Time (h)

Modifier

Reference

Drug and biological samples Urine

Ketamine, norketamine, dehydronorketamine, hydroxynorketamine CO2

163 bar

25

1

2-Propanol

[58]

Human blood

Carotenoids and apocarotenoids

CO2

150 bar

40

20 min

Methanol

[59]

Sunscreen agents

Nanoparticle

CO2

131

40

30




[60]

Blood and plasma Phospholipids

CO2

10 MPa

35

5 min

Methanol with 0.1% (w/v) ammonium formate

[61]

Poppy capsules

Papaverine and noscapine

CO2

150 bar

338K

30 min

Methanol

[62]

Vitis vinifera L. seeds

Lipids and fatty acids

CO2

40.0 MPa

313 2 333







[63]

Apple pomace

Phenolic compounds and antioxidants

CO2

30 MPa

40

2

Ethanol

[64]

Fish caviar

Fatty acids

CO2

300
350 bar 40 and 60

150 min




[65]

Tobacco

Solanesol

CO2

300 MPa

40

5 min




[66]

Argemone mexicana L. seeds

Seed oil

CO2

275 bar

80




Ethanol

[67]

Cacao pod husk

Gallic acid, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)

CO2

299 bar

60

2.5 h

Ethanol

[68]

Curcuma longa herb (turmeric root)

Turmeric oil

CO2

20
40 MPa

40
60




Ethanol

[69]

Eucalyptus globulus leaves

Triterpenic acids

CO2

200
300 bar 40

6h

Ethanol

[70]

Broccoli leaves

Proline, alanine, valine, glutamine, glutamic acid, phenylalanine, leucine, isoleucine, aspartic acid, glycine, amino butyric acid, threonine, serine, asparagine, methionine, ornitine, lysine, tyrosine, tryptophan

CO2

250 bar

30 min

Methanol

[71]

Foods and herbs

70

(Continued)

TABLE 10.3 (Continued) Sample

Target analyte

Solvent Pressure

Temperature ( C)

Time (h)

Modifier

Reference

Scenedesmus almeriensis

Lutein and β-carotene

CO2

400 bar

60

5h




[72]

Linseed

Lipids

CO2

30 MPa

80

90 min

Ethanol

[73]

Spent coffee grounds and coffee husks

Theobromine, caffeine

CO2

100, 200 bar

323.15,333.14K 2.3, 4.3 h

Ethanol

[74]

Brown onion skin

Protocatechuic acid, 2-(3,4-dihydroxybenzoyl) 2 2,4,6-trihydroxy-3 (2 H)-benzofuranone, quercetin-7,40 -diglycoside, quercetin 3,40 diglycoside, isorhamnetin-3,40 diglycoside, quercetin-3-glycoside, quercetin-40 -glycoside, isorhamnetin-40 -glycoside, quercetin, protocatecoyl quercetin, kaempferol, isorhamnetin, quercetin dimer 40 -glycoside, quercetin dimer hexoside, quercetin dimer, quercetin trimer

CO2

100 bar

40

120 min

Ethanol

[75]

Lavandula viridis

α-Pinene, camphene, β-pinene, α-terpinene, p-cymene, 1,8-cineole, trans-β-ocimene, cis-linalool oxide, trans-linalool oxide, linalool, α-campholenal, norinone, camphor, pinocarvone, epoxy linalool, borneol, terpinen-4-ol, myrtenal, myrtenol, verbenone, cis-carveol, trans-pinocarvyl acetate, carvone, isobornyl formate, carvacrol, myrtenyl acetate, eugenol, neryl acetate, geranyl acetate, β-bourbonene, trans-α-bergamotene, spathulenol, caryophyllene oxide, globulol, viridiflorol, Juniper camphor

CO2

12,18 MPa

40







[76]

Thymus munbyanus

About 166 analytes (antioxidant)

CO2

45 MPa

70

210 min




[77]

Hylocereus polyrhizus flesh and peel

Betanidin 5-O-bsophoroside, betanin (betanidin 5-o-β-glucoside), isobetanin, apiosyl-betanin, phyllocactin(60 -omalonylbetanin), butyrylbetanin, hylocerenin(3-hydroxy-3-methylglutaryl-betanin), isophyllocactin, iso-butyrylbetanin, 20 -apiosylphyllocactin, isohylocerenin, 20 -apiosylisophyllocactin

CO2

25 MPa

50




Ethanol/water

[78]

Myrtus communis L. leaves

Isobutyl isobutyrate, α-thujene, α-pinene, sabinene, β-pinene, myrcene, δ 2 3-carene, p-cymene, limonene, 1,8-cineole, o-cymene, γ-terpinene, α-terpinolene, linalool, fenchol, trans-pinocarveole, γ-terpineole, terpinen-4-ol, α-terpineol, myrtenol, geraniol, linalyl acetate, methyl geranate, α-terpenyl acetate, neryl acetate, methyl eugenol, β-caryophyllene, α-humulene, geranyl isobutyrate, caryophylleneb epoxide, humulene oxide

CO2

350 atm

25 min




Methanol

[79]

Dracocephalum kotschyi Boiss

Alpha-pinene, limonene, gamma- terpinene, 1-[alpha-(1-adamantyl) CO2 benzylidene] thiosemicarbazide, 2-ethyl-1,4-dimethylbenzene, alpha-campholenal, 1-(3,5-dimethyl-1-adamantanol) semicarbazide, cis-pinen-3-ol, mentha-1,4,8-triene, di-t-butylacetylene, cis-pmentha-2,8-dien-1-ol, tricyclo[4.3.1.1(3,8)]undecan-1-ol,oallytoluene, 2-bromoethanol, camphene, 2-methyl-1-octen-3-yne, 2pinen-4-one, cosmene, 10-methylidenespiro[4.5]decane, 70 ,70 dimethylspiro[1,3-dioxane-4,20 -bicyclo[3.1.1] hept-3-ene], 7-(2,6dimethyl-hepta-1,5-dienyl) 2 3,8,8-trimethylbicyclo [4.2.0] oct-2-ene, p-mentha-1,3,8-triene, 2-oxo-3-methyl-cis-perhydro-1,3-benzoxazine, s-3-carene, 2-bromoethanol, citral, 2-methyl-6-methylene-1,7octadien-3-one, hedycaryol, epoxy-linalooloxide, 3-methyl-1hpyrazole-5-carboxylic acid, santolina triene, methyl geranate, 1-(2,4dimethylphenyl) 2 2-propanamine, 2,6,6-trimethyl-5-(3-methyl-2buten-1-yl) 2 2-cyclohexene-1-carbaldehyde, 4-isopropyl-1-methyl7-oxabicyclo[4.1.0]hept-3-ene, p-menth-1-en-3-one, 1,1-dimethyl-2[(1e) 2 3-methyl-1,3-butadien-1-yl] cyclopropane, neric acid, geranic acid, (z)-undec-3-en-5-yne, 8a-methyl-1,3,4,4a,5,6,7,8octahydronaphthalen-2-one, 5,7-dimethylenebicyclo[2.2.2]oct-2-ene, (4-fluorophenyl)hydrazine, 4-amino-2(1 h)-pyrimidinethione, 4,8dimethylbicyclo[3.3.1]nonane-2,6-dione, aromadendrene, germacrene d, artemiseole, 3,5-dimethylamphetamine, 1,2dodecanediol, 3-ethoxy-5-methyl-1h-pyrazole, 2-methyl-1-penten-3one, 2-methyl-2-pentenoic acid, benzyl benzoate, (s)-cis-verbenol, n(3,4-dichlorobenzyl)ethanamine, decahydroisoquinoline, benzaldehyde, 2-nitro-, diaminomet hylidenhydrazone, (z,e)farnesol, 2-((2-ethylhexyloxy)carbonyl) benzoic acid

240

60

100 min




[80]

Cydonia oblonga Miller seed

Dodecane, tetradecane, hexadecane, palmitic acid methyl ester, linoleic acid methyl ester, stearic acid methyl ester, oleic acid, stearic acid, 11-eicosenoic acid methyl ester, eicosanoic acid methyl ester, gamma-sitosterol

CO2

353

35

10,60 min

Methanol

[81]

Sunflower oil

Fatty acids

CO2

400 bar

80




Ethanol

[82]

Diospyros kaki L. fruits

β-Carotene, lutein, β-cryptoxanthin, zeaxanthin

CO2

300 bar

60

30 min

Ethanol

[83]

Hops flowers

α- and β-acids

CO2

350

35

10 min




[84]

Rosemary leaves, basil leaves, vetiver roots

Essential oil

CO2

100 bar

40




[85]

(Continued)

TABLE 10.3 (Continued) Sample

Target analyte

Solvent Pressure

Temperature ( C)

Time (h)

Modifier

Reference

Pyrethrum flowers

Pyrethrins

CO2

40 MPa

40

3.5 h




[86]

Roots of Saposhnikovia divaricata Turez.

Prim-O-glucosylcimifugin, cimifugin, 5-O-methylvisammioside, and sec-O-glucosylhamaudol

CO2

5,10 MPa

25,45

60 min

Ethanol

[87]

Olive tree derivative

Triterpens and aliphatic hydrocarbons

CO2

90, 300 bar

40,60







[88]

Litsea japonica fruit

Antiinflammators

CO2

300 bar

60

180




[89]

Leaves of Eichhornia crassipes

Cholesterol, methylcholesterol, stigmasterol, β-sitosterol

CO2

25
300 bar

50




Ethanol

[90]

Dracocephalum kotschyi seed oil

Omega-3

CO2

100
220 bar 35
55

10130 min




[91]

Satureja montana L., Coriandrum sativum L., Ocimum basilicum L.

Essential oil

CO2

100 bar

40

4.5 h




[92]

Argania spinosa L.

Palmitic acid, stearic acid, oleic acid, linoleic acid, squalene

CO2

297.71 bar

317.78







[93]

Citrus unshiu peels

Narirutin, hesperidin, neoponcirin, quercetin, poncirin, apigenin, sinensetin, nobiletin, acacetin, tangeretin

CO2

30 MPa

333K

180 min

Ethanol

[94]

Tomato peels

Lycopene and β-carotene

CO2

300
500 bar 50
80

105 min




[95]

Pterocaulon balansae (Asteraceae)

Coumarins

CO2

120 bar

40

40 min




[96]

Anethum graveolens L.

α-Pinene, myrcene, p-cymene, limonene, γ-terpinene, metacymene, trans-p-mentha-2,8-dien-1-ol, cis-limonene oxide, trans-limonene oxide, dill ether, cis-dihydro carvone, trans-dihydro carvone, isodihydro carveol, trans-carveol, carvone, trans-Carvone oxide, Eanethole, piperitenone, eugenol, myristicin, elemicin, dodecanoic acid, dillapiole, apiole, n-eicosane, ethyl hexadecanoate

CO2

100 bar

35

1.5 h




[97]

Juc¸ara (Euterpe edulis Mart.)

Phenolic compounds and anthocyanins

CO2

Black poplar (Populus nigra L.)

Saturated fatty acids, monounsaturated fatty acids, polyunsaturated CO2 fatty acids, unsaturated fatty acids

20 MPa

60

39 min

Ethanol/water (pH 5 2)

[98]

15,25 MPa

40
60

150 min




[99]

Capsicum baccatum Bioactive compounds L. var. pendulum

CO2

15
25 MPa

40
60

40
60 min


[9]

Myrtle leaves and Bioactive compounds berries

CO2

23 MPa

45




Ethanol

[100]

Rocket salad

Phenolic and glucosinolate extracts

CO2

25 MPa

75




Water

[101]

Grape seeds

C14:0 (myristic acid), C16:0 (palmitic acid), C16:1 (palmitoleic acid), CO2 C17:0 (heptadecanoic acid), C18:0 (stearic acid), C18:1 (oleic acid), C18:2 (linoleic acid), C18:3 (linolenic acid), C20:0 (arachidic acid), C20:1 (eicosenoic acid), SFAs (saturated fatty acids), MUFAs (monounsaturated fatty acids), PUFAs (polyunsaturated fatty acids)

300 bar

40







[102]

Finnish wild mushrooms (Craterellus tubaeformis)

Volatile compounds

CO2

85 bar

45







[103]

Red habanero Carotenoids peppers (Capsicum chinense Jacq.)

CO2

150 bar

40
80

, 17 min

Methanol

[104]

Vanilla

Vanillin, p-hydroxybenzaldehy de, vanillic acid, p-hydroxybenzoic acid

CO2

15 MPa

45

12 min

Methanol

[105]

Soybean meal

Isoflavone

CO2

59.45 MPa

323.15

283 min

Methanol

[106]

Leaves of Murraya exotica L.

Hainanmurpanin, meranzin, phebalosin

CO2

27 MPa

52

60 min

Ethanol

[107]

Medicago sativa

Saponin hydrolysis products

CO2

150 bar

50

40 min

Ethanol

[108]

Environmental samples Soil

Alkali(M1), alkaline-earth(M21) cations

CO2

200 kg cm22 40

30 min

Methanol/ 4MHNO3

[109]

Sediments

Tridecafluoroheptanoic acid, pentadecafluorooctanoic acid, perfluorononanoic acid, nonadecafluorodecanoic acid

CO2

30 MPa

30 min




[110]

70

(Continued)

TABLE 10.3 (Continued) Temperature ( C)

Time (h)

Modifier

Reference

300 bar

75

40 min

Pyridine/ diethylamine

[111]

CO2

30 MPa

75

15, 30 min

Chloroform, tetrahydrofuran, methylene chloride

[112]

Palladium and silver

CO2

30 MPa

50

10 min

Water/ethanol/ acetone

[113]

Spent lithium-ion batteries

Cobalt

CO2

75 bar

75

5 min

2 M H2SO4 and H2O2

[114]

Nickel metal hydride battery

Rare earth elements

CO2

20.7 MPa

35

1h




[115]

Soil

Hexabromocyclododecane

CO2

25 MPa

50

18 min

Ethanol
2% Triton X-114

[116]

Sample

Target analyte

Solvent Pressure

Diesel engine

Naphthalene, biphenyl, acenaphtene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[k]fluoranthene, benzo[e] pyrene, benzo[a]pyrene, perylene, dibenz[a,h]anthracene, 1nitronaphthalene, 1,5-dinitronaphthalene, 2-nitrofluorene, 9nitroanthracene, 3-nitrofluoranthene, heneicosane, tetracosane, acenaphtylene, chrysene and indeno[1,2,3-c,d]pyrene, Benz[a] anthracene, benzo[b]fluoranthene, benzo[g,h,i]perylene

CO2

Diesel oils

Naphthalene, biphenyle, acenaphtene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[k]fluoranthene, benzo[e] pyrene, benzo[a]pyrene, perylene, dibenz[a,h]anthracene, acenaphtylene, chrysene, indeno[1,2,3-c,d]pyrene, Benz[a] anthracene, benzo[b]fluoranthene, benzo[g,h,i]perylene, 1nitronaphthalene, 1,5-dinitronaphthalene, 2-nitrofluorene, 9nitroanthracene, 3-nitrofluoranthene, 2,7-dinitrofluorene, heneicosane, tetracosane, triacontane

Waste printed circuit boards powder

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322. A. Issaoui, H. Ksibi, M. Ksibi, Supercritical fluid extraction of triterpens and aliphatic hydrocarbons from olive tree derivatives, Arab. J. Chem. 10 (2017) 3967
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51. P.F. Martins, M.M.R. de Melo, P. Sarmento, C.M. Silva, Supercritical fluid extraction of sterols from Eichhornia crassipes biomass using pure and modified carbon dioxide. Enhancement of stigmasterol yield and extract concentration, J. Supercrit. Fluids 107 (2016) 441
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1189.

New Generation Green Solvents for Separation and Preconcentration

Index

Note: Page numbers followed by “f” and “t” refer to figures and tables, respectively.

A AAB. See 4-Aminoazobenzene (AAB) Absorption methods, 49 ABSs. See Aqueous biphasic systems (ABSs) Accelerated solvent extraction (ASE), 19, 132
133 Accelerated solvent extraction technology (ASET), 156
157 Acenaphthylene, 29 N-Acetylprocainamide (NAPA), 30
31 Acid-base behavior of deep eutectic solvents, 399
401 Acid-based solvents, 15 Acidic drugs, 175
176 Activated carbon, 25
26 ADS. See Alkyl-diol-silica (ADS) Adsorptive microextraction (AμE), 35, 118, 128
129 Adsorptive-extraction (AE), 129 AES. See Atomic emission spectroscopy (AES) Affinity chromatography, 47 AFS. See Atomic fluorescence spectrometry (AFS) Agglomeration, 439 AIBN. See Azobisisobutyronitrile (AIBN) Alcohol-based solvents, 15 Alkaline earth salts, 8 Alkanol-based SUPRASs, 338 Alkyl chain (R), 267 Alkyl-diol-silica (ADS), 132, 194
195 Almond oil, 411 Alpha spectrometry, 9 α-19-nortestosterone (α-19-NT), 32
33 Aluminum chloride, 8 Amberlite LA 2, 16 Amberlite XAD-1, 27

Amberlite XAD-4 adsorbents, 28 AMI. See Amitriptyline (AMT) Amine-based solvents, 15 4-Aminoazobenzene (AAB), 152 Amitriptyline (AMT), 125
126, 190 Ammonium pyrrolidinedithiocarbamate (APDC), 9 Ammonium salts, 390 Amperometry, 66
67 Amphiphiles, 327
328 Amphiphilic molecules, 439 Amphiphilic solvents, 245
251, 246f AMT. See Amitriptyline (AMT) AMTPS. See Aqueous micellar twophase systems (AMTPS) Analysis of variance (ANOVA), 363
364 Analyte
antibody interaction, 32
33 Analytical Eco-Scale, 215
216, 219
221 PPs, 218t, 219 Analytical methods, 45, 213 advancement in sampling systems for analytical instruments, 70
71 development in field of chromatography, 46
49 in field of spectroscopy, 49
62 electroanalytical techniques, 62
67 hyphenated techniques, 67
70 Analytical protocols, 214
215 Analytical voltammetry, 66 Analyzers, 56 Anionic surfactants, 330 Anodic deposition, 62
63 ANOVA. See Analysis of variance (ANOVA) Anthracene, 16

453

Antibodies, 32
33, 136 Antimony, 7 Antioxidant, 438
439 Antipyrine salts, 17
18 APDC. See Ammonium pyrrolidinedithiocarbamate (APDC) Apium graveolens, 188 Aqueous biphasic systems (ABSs), 180
182 Aqueous micellar two-phase systems (AMTPS), 180 Aqueous two-phase system (ATPE), 176
185 DES-based ABSs for RNA extraction, 182f phase formation mechanism, 182f selective removal of soy antinutritional factors, 181f Aqueous two-phase system (ATPS), 150, 176
178, 181f, 404 application, 183t extraction, 294
296 applications of ILs, 297t recyclable, 180 L-Arginine, 385 Argon, 58
59 gases, 61 ionization detector, 47
48 Arnetryn, 30
31 Arrhenius equation, 337
338 Arsenic (As), 7 Arsenic(III), 11, 83 Arsenic(V), 11 AS. See Atomic spectroscopy (AS) ASE. See Accelerated solvent extraction (ASE) ASET. See Accelerated solvent extraction technology (ASET) At211 radiochemical analysis, 7
8

454 Atomic absorption spectroscopy, 57
59, 58f Atomic emission spectroscopy (AES), 59
61 Atomic fluorescence spectrometry (AFS), 61
62 Atomic spectroscopy (AS), 70
71, 82 Atomization, 59 ATPE. See Aqueous two-phase system (ATPE) ATPS. See Aqueous two-phase system (ATPS) Attapulgite/polyaniline-polypyrrole/ Fe3O4 (ATP/PANI-PPY/ Fe3O4), 276
277 Automated in-syringe single-drop headspace microextraction method, 88
90 Automated magnetic D-μ-SPE procedure, 190 Azinphos-ethyl, 105 Azobisisobutyronitrile (AIBN), 277
278 AμE. See Adsorptive microextraction (AμE)

B Babington nebulizers, 59 BAM. See Benzamidine (BAM) BaPy. See Benzo (a)pyrene (BaPy) Bar AμE (BAμE), 128
129 Barium sulfate, 6
7 Batch extraction process, 326 BAμE. See Bar AμE (BAμE) Beam splitters, 54 Bendiocarb, 105 Benzamidine (BAM), 33 Benzene, toluene, ethylbenzene, xylene (BTEX), 85, 274
275 Benzenesulfonate (BS), 271 Benzo (a)pyrene (BaPy), 249
250 Benzoate method, 6
7 Benzophenone-3 (BZ3), 87 1-Benzyl-3-(2-hydroxyethyl) imidazolium bromide ((BeEOHIm) (Br)), 286 β-19-nortestosterone (β-19-NT), 32
33 β-diketones, 13
14 BG. See Brilliant Green (BG) BHb. See Bovine hemoglobin (BHb) BID SDME. See Bubble-in-drop SDME (BID SDME) Binary solvent
based DLLME, 161

Index

Binodal curve, 178
179, 179f Bio-DLLME method, 161 Biobased solvents, 382 Biological receptor, 323 N,O-Bis(trimethylsilyl) trifluoroacetamide (BSTFA), 108 Bisphenol-A (BPA), 97, 249
250 Bisphenol-AF (BPAF), 97 Botryococcus braunii, 252, 355 Bottom-up strategy, 321 Bovine hemoglobin (BHb), 405 Bovine serum albumin (BSA), 405 Box-Behnken design, 437 BPA. See Bisphenol-A (BPA) BPAF. See Bisphenol-AF (BPAF) 5-Br-PADAP. See 2-(5-Bromo-2pyridylazo)25diethylaminophenol (5-BrPADAP) Brassica oleracea, 188 Brij (polyoxyethylene-10-akyl ether), 23 Brilliant Green (BG), 286 2-(5-Bromo-2-pyridylazo)25diethylaminophenol (5-BrPADAP), 341
342, 367 BS. See Benzenesulfonate (BS) BSA. See Bovine serum albumin (BSA) BSTFA. See N,O-Bis(trimethylsilyl) trifluoroacetamide (BSTFA) BTEX. See Benzene, toluene, ethylbenzene, xylene (BTEX) Bubble-in-drop SDME (BID SDME), 78, 83 n-Butene, 159
160 1-Butyl-3-methylimidazolium chloride ((BMIm) (Cl)), 286 N-Butyl-N-ethylamine, 354
355 BZ3. See Benzophenone-3 (BZ3)

C C16mimBr. See 1-Hexadecyl-3methylimidazolium bromide (C16mimBr) C18 bonded polymers, 31 C18 silica
based solid phase extraction system, 29 cac. See Critical aggregation concentration (cac) Cadmium (Cd), 9, 368
369 CAE. See Coacervative extraction (CAE)

CaF2-made beam splitter, 54 Caffeic acid, 438
439 Caffeine, 32 Capillary analysis, 46 Capillary electrophoresis (CE), 21, 82, 95
96, 150 Capillary electrophoresis-inductively coupled plasma-mass spectrometry (CE-ICP-MS), 70 Capillary electrophoresis-mass spectrometry (CE-MS), 69
70 Capillary electrophoresis-nuclear magnetic resonance (CE-NMR), 68 Capillary gas chromatography
mass spectroscopy (CGC
MS), 132 Capillary zone electrophoresis. See Capillary electrophoresis (CE) CAR. See Carboxen (CAR) Carbon carbon-based nanomaterials, 138 carbon-based solvents, 15, 26 filter method, 25 Carbon dioxide (CO2), 159
160, 348, 426 Carbon disulfide (CS2), 15 Carbon nanofibers (CNF), 175
176 Carbon nanotube-poly (dimethylsiloxane) (CNTPDMS), 194
195 Carbon nanotubes (CNTs), 26, 34, 120, 186
187, 195, 197f application in separation, 195
198 Carbon tetrachloride (CCl4), 15, 432
433 Carbonyl components, 15 Carbopack B, 120 Carbowax (CW), 118 Carboxen (CAR), 118 Carboxyl multiwall carbon nanotubes (MWCNTs-COOH), 236 Carboxylated nanoporous graphene, 187
188 Carboxylic acid (COOH), 244
245, 248
249 Carthamus tinctorius, 241 Cary 11 (combined spectrophotometer), 51 Cationic surfactants, 329 CCD. See Central composite design (CCD)

Index

Cd(II)
1-(2-thiazolylazo)-2-naphthol, 13 CDs. See Cyclodextrins (CDs) CE. See Capillary electrophoresis (CE) CE-ICP-MS. See Capillary electrophoresis-inductively coupled plasma-mass spectrometry (CE-ICP-MS) CE-MS. See Capillary electrophoresismass spectrometry (CE-MS) CE-NMR. See Capillary electrophoresis-nuclear magnetic resonance (CE-NMR) Central composite, 372 Central composite design (CCD), 153, 360 Centrifugal extruders, 14 Cerium(IV) hydroxide coprecipitation method, 12 Certified reference material TMDW500 (CRM TMDW-500), 368 Certified reference materials (CRMs), 9
10 Cesium, 51 Cetyltrimethylammonium bromide, 329 CF. See Continuous-flow (CF) CF-SD-LPME. See Continuous-flow microextraction/single-drop microextraction (CF-SD-LPME) CFME. See Continuous-flow microextraction (CFME) CGC
MS. See Capillary gas chromatography
mass spectroscopy (CGC
MS) Chamaecyparis obtusa (CO), 242 Charcoal, 24
25 Chelate coprecipitation
graphite furnace AAS procedure, 11 Chelate extraction, 325
326 Chitosan, 188 Chlorine, 323 4-Chloro-o-toluidine (CT), 152 Chloroform (CHCl3), 15 Chlorophenols (CP), 136, 232
233 Chlorophenoxy acid herbicides (CPAHs), 188
190 CP. See Chlorophenols (CP) Choline chloride (ChCl), 240, 242, 383 Choline chloride/urea (ChCl/urea), 404 Cholinephenol-based DES, 174
175 Chromatography, 375

analysis methods, 426 chromatography-based techniques, 150 development in field of, 46
49 Chromium (Cr), 6
7 Chromosorb 102, 28 Chronopotentiometric stripping analysis, 65 Cialotrine, 433 CIAME. See Cold-induced aggregation micro extraction (CIAME) Cinnamon oil, 411 Citrate salts, 176
178 Classical methods of chemical analysis, 45 Clathrates, 323 “Clean waste”, 209
210 Cloud point (CP), 334 Cloud-point extraction (CPE), 5, 22, 102, 153
154, 224
225 historical development, 22
24 Cloud-point temperature (CPT), 22, 152 CMC. See Critical micelle concentration (CMC) CNF. See Carbon nanofibers (CNF) CNT-PDMS. See Carbon nanotubepoly(dimethylsiloxane) (CNTPDMS) CNTs. See Carbon nanotubes (CNTs) CO. See Chamaecyparis obtusa (CO) Coacervation, 327
328 Coacervative extraction (CAE), 335
336 Coagulated colloidal particles, 7 Cobalt (Co21), 368
369 Colchicine, 434 Colchicum speciosum, 434 Cold vapor atomic absorption spectrometer (CV AAS), 104
105 Cold vapor atomizers, 59 Cold-induced aggregation micro extraction (CIAME), 231, 231f Colorimetric coulometer, 61
62, 64 Commercial syringes, 90 Commonwealth Scientific and Industrial Research Organization (CSIRO), 57
58 Concentration efficiency, 11
12 Conductivity, 397
398, 398t, 399f Conductometry, 64
65 conductometric analysis, 64
65

455 Contamination flow systems, 341 Continuous extraction process, 326 Continuous wave NMR (CW-NMR), 54
55 Continuous-flow (CF), 79
80 LLE, 17 Continuous-flow microextraction (CFME), 21, 77
78, 82
83 Continuous-flow microextraction/ single-drop microextraction (CF-SD-LPME), 21 Continuous-wave mode (CWM), 151 Controlled current coulometry, 64 Conventional solid phase extraction procedures, 35 Cooled mercury cadmium telluride detectors, 54 Cooled photoelectric detectors, 54 Cooled silicon or germanium bolometers, 54 Copper (Cu), 6
7, 368
369 Copper-diethyldithiocarbamate, 12 Coprecipitation (CP), 5 CP
X-ray fluorescence analysis, 8
9 historical development, 6
13 time, 11
12 Cortisol, 161 Cortisone, 161 Coulometer, 61
62, 64 Coulometry, 61
64 Countercurrent chromatography, 49 distribution, 326 extraction process, 14 mass spectrometer system, 49 CP. See Chlorophenols (CP); Cloud point (CP); Coprecipitation (CP) CPAHs. See Chlorophenoxy acid herbicides (CPAHs) CPE. See Cloud-point extraction (CPE) CPT. See Cloud-point temperature (CPT) Critical aggregation concentration (cac), 327
328, 335
336 Critical micelle concentration (CMC), 276
277 CRM TMDW-500. See Certified reference material TMDW-500 (CRM TMDW-500) CRMs. See Certified reference materials (CRMs)

456 Cross-flow nebulizer, 10
11 CSIRO. See Commonwealth Scientific and Industrial Research Organization (CSIRO) CT. See 4-Chloro-o-toluidine (CT) CTC CombiPal autosampler, 84 Cuproine in isoamylalcohol, 15 Curcumin, 163
164 Current
voltage curve, 65 CV AAS. See Cold vapor atomic absorption spectrometer (CV AAS) CW. See Carbowax (CW) CW-NMR. See Continuous wave NMR (CW-NMR) CWM. See Continuous-wave mode (CWM) Cyanide, 95
96 Cyclic structure solvents, 15 Cyclodextrins (CDs), 320 Cyclohexanone, 16 Cyclohexyldimethylamine (CyNMe2), 355
356 Cytotoxic activities, 438
439 Cytotoxicity of choline chloride, 402

D D-μ-SPE. See Dispersive microsolid phase extraction (DMSPE) Dansyl chloride, 114 2,6-DBP. See 2,6-Dibromophenol (2,6DBP) DBU. See 8-Diazabicyclo-(5.4.0)-undec7-ene (DBU) DCB. See 3,30 -Dichlorobenzidine (DCB) DCP. See Dicyclohexyl-phthalate (DCP); Direct current plasma (DCP) 2,4-DCP. See 2,4-Dichlorophenol (2,4DCP) DD. See Drop-to-drop (DD) DDC. See Diethyldithiocarbamate (DDTC) DDS. See Dodecylsulfate (DDS) DDT. See Dichlorodi phenyltrichloroethane (DDT) DDTC. See Diethyldithiocarbamate (DDTC) Deep eutectic solvents (DESs), 19, 85, 97
98, 109, 113, 152, 161, 180
182, 209, 214, 228,

Index

239
245, 240f, 242f, 243f, 382
385, 382t application in aqueous two-phase extraction method, 404
405 application in extraction techniques, 402
416 decomposition temperature, 403t TGA analyses, 403f application in liquid/solid extraction/microextraction, 405
416, 408t DES-based ultrasound-assisted extraction procedure, 416f EA-EME-SSDES, 413f effervescence-assisted dispersive liquid
liquid microextraction, 412f ELLME-DES, 410f extraction of bioactive compounds, 406t glass-filter-based dispersive LPME, 412f microextraction procedure, 414f chemical properties, 385
388 DES-based magnetic Bucky gel, 87
88 HBAs and HBDs, 384f physical properties, 385
388 physicochemical properties, 385
402, 386t acid-base behavior of DESs, 399
401 conductivity, 397
398 density, 397 freezing point, 388
395 polarity, 399 synthesis procedure of ChCl/ resorcinol DES, 388f toxicity, 402 viscosity, 395
396 with protic and aprotic solvents, 402 quaternary ammonium salt ChCl, 383f thermal stability study, 402 DEHP. See 2-Ethylhexyl-phthalate (DEHP) DEHPA. See Di2-ethylhexyl, phosphoric acid (DEHPA) Dendrimer-modified halloysite nanotubes, 187 Dendrimers, 187 Density of eutectic solvent, 397, 402 DEP. See Di-ethyl-phthalate (DEP)

DES-AAELLME. See DES-based airassisted emulsification liquid
liquid micro extraction method (DES-AAELLME) DES-assisted effervescent liquid dispersion
liquid micro extraction technique, 411 DES-based air-assisted emulsification liquid
liquid micro extraction method (DES-AAELLME), 243 DES-UA-ELPME. See DES-ultrasoundassisted emulsification liquid phase micro extraction method (DES-UA-ELPME) DES-ultrasound-assisted emulsification liquid phase micro extraction method (DESUA-ELPME), 244 Desirability function (DF), 163 Desirability function approach (DFA), 153 DESs. See Deep eutectic solvents (DESs) DETA. See Diethylenetriamine (DETA) Detection limit, 11
12 Detectors, 56, 61 DF. See Desirability function (DF) DFA. See Desirability function approach (DFA) DI. See Direct immersion (DI) Di-(2-ethylhexyl)phosphoric acid (HDEHP), 119 Di-ethyl-phthalate (DEP), 24 DI-SDME. See Direct immersion single-drop microextraction (DI-SDME) Di2-ethylhexyl, phosphoric acid (DEHPA), 15 3,3-Diamino-benzidine, 414 Diantipyrylmethane salts, 17
18 Diatomaceous earth, 24
25 8-Diazabicyclo-(5.4.0)-undec-7-ene (DBU), 252, 348 2,6-Dibromophenol (2,6-DBP), 287 Dibutyltin, 10 3,30 -Dichlorobenzidine (DCB), 152 Dichlorodiphenyltrichloroethane (DDT), 18, 121
122 2,4-Dichlorophenol (2,4-DCP), 136, 232
233, 287 Dichlromethane (CH2Cl2), 15 Diclofenac, 175
176 Dicyclohexyl-phthalate (DCP), 24

457

Index

Diethyldithiocarbamate (DDTC), 9, 11, 31 Diethylenetriamine (DETA), 369 Dihexylether, 97
98 Diisobutyl carbinol, 16 N,N-Diisopropylethylamine, 349 3,30 -Dimethoxybenzidine (DMOB), 152 Dimethyl dithiocarbamate (DMDC), 250
251 3,30 -Dimethyl-4,40 diaminobiphenylmethane (DMDAB), 152 N,N-Dimethylaniline, 349 3,30 -Dimethylbenzidine (DMB), 152 N,N-Dimethylbenzylamide (DMBA), 174
175 N,N-Dimethylbenzylamine, 353, 361, 371 N,N-Dimethylcyclohexylamine (DMCA/CyNMe2), 253
254, 255f N,N-Dimethyldodecylamine, 349 Dimethylglyoxime, 13
14 Dioctysulfosuccinate (DOSS), 271 Direct current amperometry, 66
67 Direct current plasma (DCP), 61 Direct immersion (DI), 35, 79
80, 118, 170 mode, 78, 83 Direct immersion single-drop microextraction (DI-SDME), 20, 80
81, 84
85, 172, 224
225, 230 Directly suspended droplet (DSD), 79
80 Disperser solvent SFODME (DLLMESFO), 116, 164 Dispersion-based microextraction, 411
412 Dispersion
liquid micro extraction, 280
286 Dispersive liquid
liquid micellar micro extraction (DLLMME), 247 Dispersive liquid
liquid microextraction (DLLME), 21, 76, 102
115, 160
164, 224
226, 229
230, 270, 280, 286
287, 340, 357
358 application of ionic liquids in, 288t applications, 165t, 171t IL-based headspace in-tube micro extraction, 292f

microwave-assisted IL/IL, 287f pressure variation in-syringe DLLME, 163f using imidazoliumionic liquids ILs, 296f Dispersive microsolid phase extraction (DMSPE), 138, 150, 186
190, 224
225, 277 application, 191t automated magnetic D-μ-SPE procedure, 191f D-μ-SPE procedure based on Fe3O4@SiO2@N3, 193f Fe3O4@SiO2@MIP
based D-μ-SPE, 189f Dispersive solid phase extraction (DSPE), 179 Dispersive solvent, 162 Dispersive spectrometers, 50 Dithizone (DTz), 13
14, 113 Divinylbenzene (DVB), 118 DLLME. See Dispersive liquid
liquid microextraction (DLLME) DLLME-SFO. See Disperser solvent SFODME (DLLME-SFO) DLLMME. See Dispersive liquid
liquid micellar micro extraction (DLLMME) DMB. See 3,30 -Dimethylbenzidine (DMB) DMBA. See N,NDimethylbenzylamide (DMBA) DMDAB. See 3,30 -Dimethyl-4,40 diaminobiphenylmethane (DMDAB) DMDC. See Dimethyl dithiocarbamate (DMDC) DME. See Drop mercury electrode (DME) DMOB. See 3,30 -Dimethoxybenzidine (DMOB) DMSPE. See Dispersive microsolid phase extraction (DMSPE) Dodecylsulfate (DDS), 271 Dodecyltrimethylammonium hydroxide (DTAOH), 247 DOSS. See Dioctysulfosuccinate (DOSS) Doxepin (DOX), 125
126 Drop mercury electrode (DME), 66
67 Drop-to-drop (DD), 79
80 liquid
liquid microextraction, 78
79

mode, 170 solvent extraction system, 76, 82
83 DSD. See Directly suspended droplet (DSD) DSPE. See Dispersive solid phase extraction (DSPE) DSSBME. See Dual-solvent stir-bar microextraction (DSSBME) DTAOH. See Dodecyl trimethylammonium hydroxide (DTAOH) DTz. See Dithizone (DTz) Dual-solvent stir-bar microextraction (DSSBME), 99 DVB. See Divinylbenzene (DVB) Dynamic LPME, 77
78, 80
81, 83 Dynamic viscosity, 272
273

E EA-EME-SSDES. See Effervescentassisted emulsification microextraction-SSDES (EAEME-SSDES) EDMA/GO. See Poly(ethylene glycol dimethacrylate/graphene oxide) (EDMA/GO) EF. See Enrichment factor (EF) Effervescence-assisted DLLME, 162 Effervescent-assisted emulsification microextraction-SSDES (EAEME-SSDES), 413 Effusion separator, 69 EFSA. See European Food Safety Authority (EFSA) EG. See Ethylene glycol (EG) Electroanalytical techniques, 62
67. See also Hyphenated techniques (HPT) amperometry, 66
67 conductometry, 64
65 coulometry, 63
64 electrogravimetry, 63 polarography and analytical voltammetry, 66 potentiometry, 65 voltammetry, 65 Electrochemical analysis, 63 Electrochemical atomizers, 59 Electrodeposition, 9 Electrogravimetry, 63 Electrolytic analysis, 63 Electrolytic cell, 63
64 Electromagnetic radiation, 61

458 Electromembrane extraction (EME), 100
101, 103f Electromembrane isolation (EMI), 100
102, 103f Electron capture detector, 47
48 Electrospray mass spectrometer (ESMS), 122
125 Electrostatic interactions, 330 Electrothermal atomic absorption spectrometry (ETAAS), 11, 214 Electrothermal vaporization and inductively coupled plasma mass spectrometry (ETV-ICPMS), 87 ELISA method, 136 ELLME-DES. See Emulsion-liquid microextraction-DES (ELLMEDES) EME. See Electromembrane extraction (EME) EMI. See Electromembrane isolation (EMI) Emission spectra, 59
60 Emulsion-liquid microextraction-DES (ELLME-DES), 405, 410f Enhancement factor, 11
12 Enrichment factor (EF), 135 Enteromorpha polysaccharides (EPs), 180 Environment, supercritical fluid in, 430
433 Environmental Protection Agency (EPA), 2
3, 157
158 Enzyme-assisted SFE method, 436 EO. See Essential oils (EO) EPA. See Environmental Protection Agency (EPA) EPs. See Enteromorpha polysaccharides (EPs) Equilibrium extraction method, 115
116 ES-MS. See Electrospray mass spectrometer (ES-MS) Escherichia coli, 179
180 Essential oils (EO), 433
435 Estrogens, 47
48 ETAAS. See Electrothermal atomic absorption spectrometry (ETAAS) ETBE. See Ethyl tert-butyl ether (ETBE) ETD. See Evaporationto-dryness (ETD) Ethane, 159
160

Index

Ethanol, 402 Ether extraction, 13
14 Ethyl tert-butyl ether (ETBE), 120 1-Ethyl-3-methylimidazolium tetraisothiocyanatocobaltate(II), 87 Ethylene, 159
160 Ethylene glycol (EG), 242, 402 Ethylene
dimethacrylate-XAD-7 resin, 27
28 2-Ethylhexyl-phthalate (DEHP), 24 N-Ethylmorpholin, 349 ETV-ICP-MS. See Electrothermal vaporization and inductively coupled plasma mass spectrometry (ETV-ICP-MS) European Food Safety Authority (EFSA), 426 Eutectic mixtures, 390, 402 Evaporationto-dryness (ETD), 375 Extractant, defined, 325

F F. Carthami, 159 FAAS. See Flame atomic absorption spectrometer (FAAS) Far IR beam splitters, 54 Faraday’s law, 63 Fast automated dual-syringe-based dispersive liquid
liquid microextraction, 108 Fatty acids, 438
439 FDA. See Food and Drug Administration (FDA) Fe3O4-functionalized metal-organic framework, 136 Fenvalerate, 433 Ferric hydroxide, 6
8 Ferrofluid-based SPME method, 135 Ferrous sulfate, 46 FI. See Flow injection (FI) FIA. See Flow injection analysis (FIA) Film-coated inert support, 47
48 FIP. See International Pharmaceutical Federation (FIP) FITC. See Fluorescence isothiocyanate (FITC) Flame atomic absorption spectrometer (FAAS), 11
12, 254, 365, 375 Flame atomizers, 59 Flame ionization detector, 47
48 Fleroxacin, 190 Flow injection (FI), 32

Flow injection analysis (FIA), 11
12, 19, 333 Fluorene, 29 Fluorescence, 56
57 emission, 150 Fluorescence isothiocyanate (FITC), 135 Fluorimeter, 61
62 Fluoroquinolones, 104
105 antimicrobial drugs, 190 Food and Drug Administration (FDA), 426 Foods, supercritical fluid in, 433
439 Fourier transform NMR (FT-NMR), 54
55 Fourier-transform infrared (FT-IR), 150 Fraunhofer lines, 51 Freezing point, 388
395, 391t effect of anion in, 393t phase diagram of urea, 390f Freon, 427 FT-IR. See Fourier-transform infrared (FT-IR) FT-NMR. See Fourier transform NMR (FT-NMR) Fullerenes, 26, 34 Fused silica capillary columns, 49 optical fibers, 118
119

G G-DES@silica, 244
245 G-IL@silica, 244
245 Gabapentin (GBP), 96 GAC. See Green analytical chemistry (GAC) Gadolinium, 13 Gallium hydroxide, 10
11 γ-mercaptopropyltrimethoxysilane (γ-MPTMS), 134
135 GAPI. See Green analytical procedure index (GAPI) Gas chromatography (GC), 17, 47, 48f, 76
77, 150, 335
336, 426 Gas chromatography with electron capture detection (GC
ECD), 121
122 Gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS), 70

Index

Gas chromatography-nuclear magnetic resonance (GC-NMR), 67 Gas chromatography
flame ionization detection (GC-FID), 118
119, 122, 359, 432
433 Gas chromatography
mass spectrometry (GC-MS), 29, 69, 118
119, 164, 356 GBP. See Gabapentin (GBP) GC. See Gas chromatography (GC) GC-FID. See Gas chromatography
flame ionization detection (GC-FID) GC-ICP-MS. See Gas chromatographyinductively coupled plasmamass spectrometry (GC-ICPMS) GC-MS. See Gas chromatography
mass spectrometry (GC-MS) GC-NMR. See Gas chromatographynuclear magnetic resonance (GC-NMR) GCB. See Graphitized carbon black (GCB) GC
ECD. See Gas chromatography with electron capture detection (GC
ECD) Gel permeation chromatographynuclear magnetic resonance (GPC-NMR), 68 Genapol X (oligoethylene glycol monoalkyl ether), 23 GFAA. See Graphite furnace atomic spectroscopy (GFAA) GFAAS. See Graphite furnace atomic absorption spectrometer (GFAAS) Gibbs phase rule, 325 Glow-discharge atomizers, 59 Glycerol, 382, 385, 402 GO. See Graphene oxide (GO) GO-PILs. See Graph eneoxide
reinforced polymer ionic liquid (GO-PILs) GPC-NMR. See Gel permeation chromatography-nuclear magnetic resonance (GPCNMR) Graph eneoxide
reinforced polymer ionic liquid (GO-PILs), 279 Graphene, 34
35, 187
188, 197f

Graphene oxide (GO), 26, 35, 125
126 Graphene-based bucky gel-coated stainless steel fiber, 122 Graphite furnace atomic absorption spectrometer (GFAAS), 10, 135, 366
367, 375 Graphite furnace atomic spectroscopy (GFAA), 70
71 Graphite tube atomizers, 59 Graphitized carbon black (GCB), 26 Gravimetric method, 3
4 Gravimetry, 45 Green analytical chemistry (GAC), 208
251, 213t analytical procedure description, 214 history, principles, and recent trends in, 209
211 milestones of, 211f principles of, 211
213, 212f new-generation solvents, 224
251 Green analytical procedure index (GAPI), 214
224, 219f, 220t application of, 217
219 assessment of, 216f evaluated analytical procedures, 219
224, 221f assessment of green profile, 222f, 224f green assessment profile proposed, 217f life cycle management in, 215f Green chemistry, 18, 156
157 Green fluorescent protein, 179
180 Green solvents green analytical chemistry, 209
251 switchable hydrophilicity solvents, 251
258 Green tea biomass, 435

H H-bonding. See Hydrogen bonding (H-bonding) Halloysite, 187 Hammett function, 399
401 HBDs. See Hydrogen bond donors (HBDs) HBPE. See Hyperbranched polyester (HBPE) HCB. See Hexachlorobenzene (HCB) HDEHP. See Di-(2-ethylhexyl) phosphoric acid (HDEHP)

459 2-HEAB. See 2-Hidroxy ethylammonium butanoate (2HEAB) Head space
single-drop microextraction (HS-SDME), 20
21, 78, 81, 83, 172 Head-space solvent extraction (HSSE), 194
195 Headspace (HS), 35, 118 Headspace liquid phase micro extraction (HS-LPME), 286
287 modes, 170 Headspace solid phase micro extraction (HS-SPME), 81
82, 118
119, 120, 122, 224
225 Headspace water-based LPME (HSWB-LPME), 84 Headspace-solvent microextraction (HSME), 20
21, 81, 242 2-HEAH. See 2-Hidroxy ethylammonium hexanoate (2HEAH) 2-HEAP. See 2-Hidroxy ethylammonium pentanoate (2HEAP) Herbs, supercritical fluid in, 433
439 Hexachlorobenzene (HCB), 99 Hexachlorocyclohexane, 29 1-Hexadecyl-3-methylimidazolium bromide (C16mimBr), 135, 238
239 Hexafluroisopropanol (HFIP), 112
113, 247, 247f Hexane, 97
98 n-Hexane, 354
355 1-Hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM] [PF6]), 87 HF. See Hollow fiber (HF) HF-HS-LPME. See Hollow-fiberprotected headspace liquid phase microextraction (HF-HSLPME) HF-LPME. See Hollow fiber liquid phase microextraction (HFLPME) HF-VMME. See Hollow fiber vesicular-mediated microextraction (HF-VMME) HFIP. See Hexafluroisopropanol (HFIP)

460 HFSLPME. See Hollow-fiber solid
liquid phase microextraction (HFSLPME) HFSPME. See Hollow fiber solid phase microextraction (HFSPME) HG-AFS. See Hydride generation
atomic fluorescence spectrometry (HGAFS) HGAAS. See Hydride generation atomic absorption spectrometry (HGAAS) 2-Hidroxy ethylammonium butanoate (2-HEAB), 274 2-Hidroxy ethylammonium hexanoate (2-HEAH), 274 2-Hidroxy ethylammonium pentanoate (2-HEAP), 274 High-diffusion liquids, 155
156 coupling of CPE, 155f liquid-coacervate extraction, 155f High-performance liquid chromatography (HPLC), 10, 30
31, 48
49, 48f, 150, 219, 230, 295, 338
339 High-performance liquid chromatography, combined with photodiode array detection (HPLC-DAD), 339, 362
363 High-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS), 70 High-pressure liquid chromatography. See High-performance liquid chromatography (HPLC) High-speed liquid chromatography. See High-performance liquid chromatography (HPLC) High-technology hyphenated instruments, 150 Hildebrand equation, 429
430 HLLE. See Homogeneous liquid
liquid extraction (HLLE) HMDTC. See Iron(II)hexamethylenedithiocarbamate (HMDTC) Hollow cathode lamp, 58
59 Hollow fiber (HF), 170

Index

Hollow fiber liquid phase microextraction (HF-LPME), 76, 92
102, 172, 174f, 224
225, 229, 232
233, 270, 286
287, 333 active transport in, 95f applications, 95
102 basic principle, 93f two-phase and three-phase, 94f Hollow fiber solid phase microextraction (HFSPME), 277 Hollow fiber vesicular-mediated microextraction (HF-VMME), 250, 251f Hollow-fiber solid
liquid phase microextraction (HFSLPME), 98 Hollow-fiber-protected headspace liquid phase microextraction (HF-HS-LPME), 95
96, 96f Homogeneous liquid phase microextraction, 76 Homogeneous liquid
liquid extraction (HLLE), 102 Host
guest chemistry, 320
321 HP-CRM-SA-C-Sandy Soil C, 367 HPLC. See High-performance liquid chromatography (HPLC) HPLC with fluorescence detection (HPLC-FLD), 357 HPLC with ultraviolet detector (HPLC-UV), 357
358, 411 HPLC-DAD. See High-performance liquid chromatography, combined with photodiode array detection (HPLC-DAD) HPLC-FLD. See HPLC with fluorescence detection (HPLCFLD) HPLC-UV. See HPLC with ultraviolet detector (HPLC-UV) HPT. See Hyphenated techniques (HPT) HS. See Headspace (HS) HS-LPME. See Headspace liquid phase micro extraction (HSLPME) HS-SDME. See Head space
singledrop microextraction (HSSDME) HS-SPME. See Headspace solid phase micro extraction (HS-SPME) HS-WB-LPME. See Headspace waterbased LPME (HS-WB-LPME)

HSME. See Headspace-solvent microextraction (HSME) HSSE. See Head-space solvent extraction (HSSE) Hydride atomizers, 59 Hydride generation atomic absorption spectrometry (HGAAS), 12, 369 Hydride generation
atomic fluorescence spectrometry (HGAFS), 370
371, 375 Hydrochloric acid (HCl), 329 Hydrogen flame detector, 47
48 Hydrogen bond donors (HBDs), 240, 383 Hydrogen bonding (H-bonding), 319
320, 388
389 Hydrophobic effect, 320 Hydrophobic organic solvents, 109 Hydrous manganese dioxide, 12 1-(6-Hydroxyethyl) 23methylimidazolium chloride ((HeOHMIm) (Cl)), 286 Hydroxyl (OH), 248
249 Hydroxyl-terminated polydimethylsiloxane (PDMS-OH), 135 8-Hydroxyquinoline, 10, 13
14 precipitation, 6
7 Hyperbranched polyester (HBPE), 188 Hyperbranched polymers, 188 Hyphenated techniques (HPT), 67
70, 150, 151f. See also Electroanalytical techniques CE-ICP-MS, 70 CE-MS, 69
70 CE-NMR, 68 GC-ICP-MS, 70 GC-MS, 69 GC-NMR, 67 GPC-NMR, 68 HPLC-ICP-MS, 70 LC-MS, 69 LC-NMR, 68 SFC-NMR, 68 SFE-NMR, 69 “Hyphenation” expression, 150

I IASPE. See Immunoaffinity solid phase extraction (IASPE) Ibuprofen, 175
176 IC. See Ion chromatography (IC)

461

Index

ICP. See Inductively coupled plasma (ICP) ICP-AES. See Inductively coupled plasma atomic emission spectrometry (ICP-AES) IL-DLLME. See Ionic liquid dispersive liquid
liquid micro extraction (IL-DLLME) IL-salt aqueous two-phase flotation (ILATPF), 295, 295f ILATPF. See IL-salt aqueous twophase flotation (ILATPF) ILs. See Ionic liquids (ILs) Imidazolium-based ILs, 190 Immunoaffinity solid phase extraction (IASPE), 136
137 Immunosorbents (ISs), 118 Impact bead nebulizers, 59 In situ stir-bar DLLME approach, 161
162 In tube solid phase micro extraction (In-tube-SPME), 224
225 In-tube-SPME. See In tube solid phase micro extraction (In-tubeSPME) In-vial temperature gradient HSSDME, 91 INCT-OBTL-5. See 1573a Tomato Leaves, and Oriental Basma Tobacco Leaves (INCT-OBTL-5) Indium hydroxide, 11 Inductively coupled plasma (ICP), 52, 61, 214 Inductively coupled plasma atomic emission spectrometry (ICPAES), 10
11 Infrared (IR) spectrometry, 46, 49
50, 53
54 Inorganic analytes switchable-hydrophilicity solvents for extraction of, 365
372 Inorganic species, 2
3 Instrumental methods, 45 Interferometer, 54 International Organization for Standardization (ISO), 18 International Pharmaceutical Federation (FIP), 2
3 Iodine coulometer, 61
62, 64 Ion chromatography (IC), 70
71 Ion exchange, 9 chromatography, 47 resins, 26

Ionic liquid dispersive liquid
liquid micro extraction (IL-DLLME), 231
232, 232f Ionic liquids (ILs), 19, 85, 97
98, 104
105, 109, 176
178, 190, 209, 228
239, 233f, 267, 268f, 269t, 271, 273, 274t, 277f, 327, 382, 404, 433 application, 274
300 ATPS, 294
296 dispersion
liquid micro extraction, 280
286 extraction methods based on ionic liquids, 296
300 liquid phase micro extraction, 286
294 solid phase micro extraction, 274
280 ultrasound-assisted temperaturecontrolled, 300f extractor droplet, 78
79 GO-and IL-coated magnetic GO/ PPy materials, 238f fabrication of porous, 278f hybrid material production methods, 235f MILs, 300
307 one-step self-assembly formation, 236f physical properties, 270
274, 273t densities and surface tension of range, 272t experimental density values, 272f Ionic liquids at room temperature (RTILs), 341 Ionization sources, 55
56 Iron (Fe), 6
7, 368
369 Iron hydroxide, 8
9 Iron(II)hexamethylenedithiocarbamate (HMDTC), 11
12 ISO. See International Organization for Standardization (ISO) Isoamylacetate, 15 Isooctane, 97
98 Isotope dilution ICP-MS, 10 ISs. See Immunosorbents (ISs)

J Jet/orifice separator, 69

K KBr-made beam splitter, 54

Keggin, 277 Ketoprofen, 175
176 Knotted reactor (KR), 11
12

L LA. See Lauric acid (LA) Lanthanum hydroxide, 10 Lauric acid (LA), 247 Layered double hydroxides (LDHs), 187 LC. See Liquid chromatography (LC) LC-ESI-MS. See Liquid chromatography and electrospray ionization mass spectrometer (LC-ESI-MS) LC-MS. See Liquid chromatographymass spectroscopy (LC-MS) LC-NMR. See Mass spectrometernuclear magnetic resonance (LC-NMR) LDHs. See Layered double hydroxides (LDHs) Lead (Pb), 7, 368
369 Lead dioxide (PbO2), 122 Lead sulfate, 6
7 Limit of detection (LOD), 131, 163
164, 356 Limit of quantification (LOQ), 163
164, 356 Liquid helium, 54 microextraction, 168 nitrogen, 54 Liquid adsorption chromatography, 47 Liquid chromatography (LC), 230, 333 Liquid chromatography and electrospray ionization mass spectrometer (LC-ESI-MS), 131 Liquid chromatography-grade styrene
divinylbenzene polymer, 28 Liquid chromatography-mass spectroscopy (LC-MS), 69 Liquid phase extraction/ microextraction methods, 13
22 Liquid phase microextraction (LPME), 5, 19, 75
76, 77f, 150, 170
176, 209, 214, 224
226, 229, 242
243, 242f, 286
294, 340, 405
411. See also Solid phase microextraction (SPME)

462 Liquid phase microextraction (LPME) (Continued) application, 177t DLLME, 102
115 fully automatic HF-assisted LPME method, 176f HF-LPME, 92
102 ILs in different mode, 293t SDME, 76
92 SFODME, 115
117 Liquid
liquid extraction (LLE), 5, 13
22, 27
28, 149, 229, 326, 341, 434 Liquid
liquid microextraction (LLME), 356
357 supramolecular solvents in, 338
339 Liquid
liquid
liquid microextraction (LLLME), 19 modes, 170 Liquid
liquid
liquid phase micro extraction (LLLPME), 286
287 Liquid
solid adsorption (LSA), 26
27 Liquid
solid extraction (LSE), 26
27 LiTfO. See Lithium trifluoromethanesulfonate (LiTfO) LiTfO/ethylene glycol DES, 385 Lithium trifluoromethanesulfonate (LiTfO), 385 LLE. See Liquid
liquid extraction (LLE) LLLME. See Liquid
liquid
liquid microextraction (LLLME) LLLPME. See Liquid
liquid
liquid phase micro extraction (LLLPME) LLME. See Liquid
liquid microextraction (LLME) “Lock” and “key” concepts, 323 LOD. See Limit of detection (LOD) LODs. See Lowest possible detection limits (LODs) LOQ. See Limit of quantification (LOQ) Low transition temperature mix (LTTM), 382
383 Lowest possible detection limits (LODs), 228 LPME. See Liquid phase microextraction (LPME) LSA. See Liquid
solid adsorption (LSA)

Index

LSE. See Liquid
solid extraction (LSE) LTTM. See Low transition temperature mix (LTTM) Luminescence spectroscopy, 56
57, 57f

M m-MIPs. See Magnetic molecularly imprinted polymer nanoparticles (m-MIPs) M. rubra, 159 Macroporous resins, 26
27 MADLLME. See Microwave-assisted dispersive liquid
liquid microextraction (MADLLME) MAE. See Micelle-assisted extraction (MAE); Microwave-assisted extraction (MAE) Magnesium ammonium phosphate, 7 Magnesium precipitation, 6
7 Magnetic carbon nanotube-nickel hybrid (MNi-CNT), 166
168 Magnetic eutectic solvent (MDES), 258, 405
411 Magnetic hybrid semifiber dispersion solid phase extraction (MMHDSPE), 276
277 Magnetic ionic liquid-DLLME (MILDLLME), 114 Magnetic ionic liquids (MILs), 87, 258, 300
307, 301f application of, 305t micro extraction method, 302f procedure of 3D-IL@mGO, 307f Magnetic molecularly imprinted polymer nanoparticles (mMIPs), 136 Magnetic multiwalled carbon nanotube composites (MMWCNTs), 136 Magnetic nanomaterials, 133 Magnetic nanoparticles (MNPs), 133, 186 Magnetic resonance imaging (MRI), 135 Magnetic solid phase extraction (MSPE), 133
136, 224
225, 275
276, 276f Magnetic solvents, 87 Magnetite (Fe3O4), 136 Magnetomotive room temperature double cation IL (MRTDIL), 303f, 304

Manganese, 6
7 Manganese dioxide, 7 Manual shaking, 164 Mass spectrometer (MS), 46, 55
56, 150 Mass spectrometer-nuclear magnetic resonance (LC-NMR), 68 Matrix solid-phase dispersion, MIL dispersion liquid micro extraction (MSPD-MILDLLME), 303f, 304
307, 304f MBCA. See 4,40 -Methylene-bis-(2chloroaniline) (MBCA) MC-LR. See Microcystin-LR (MC-LR) MC-RR. See Microcystin-RR (MC-RR) MCNT. See Multiwall carbon nanotubes (MCNT) MDES. See Magnetic eutectic solvent (MDES) Mechanically agitated extraction columns, 14 Membrane extraction discs, 32 membrane-based LPME, 21 separator, 69 and solid phase extraction discs, 29 MEPS. See Microextraction in packed syringe (MEPS) Mercury, 10 Mercury discharge lamp, 54 Mercury electrode, 63 Metal voltmeter, 63
64 Metallic tellurium, 7
8 Metal
organic frameworks (MOFs), 26, 188
190 Metals chelate, 325 2-(Methacrylamido) ethyl methacrylate, 136 Methamphetamine, 21 Methanol, 159
160, 402 Methimazole, 439
440 Methyl silica, 30
31 Methyl tert-butyl ether (MTBE), 120 N-Methyl-2-pyrrolidinone (NMP), 14 1-Methyl-3-(3-(trimethoxysilyl) propyl), 279
280 1-Methyl-3-butylimidazolium hexafluorophosphate ((BMIM) (PF6)), 286 1-Methyl-3-hexylimidazolium hexafluorophosphate ((HMIM) (PF6)), 286

463

Index

1-Methyl-3-octylimidazolium hexafluorophosphate (OMIM) (PF6), 286 4-Methylacetophenone, 20, 76
77 4,40 -Methylene-bis-(2-chloroaniline) (MBCA), 152 3-Methylimidazolium hexafluorophosphate ((C8MIM) (PF6)), 230, 235 Methylimidazolium-chloride, 277 Methylimidazoliumhexafluorophosphate, 277 N-Methylpiperidine, 349 Methyltrioctylammonium thiosalicylate, 104
105 Micelle, 22 Micelle-assisted extraction (MAE), 245 Micelle-mediated extraction, 245
247, 246f Microcomputer, 45 Microcystin-LR (MC-LR), 286 Microcystin-RR (MC-RR), 286 Microextraction in packed syringe (MEPS), 137 Microextractions, SHS in, 356
376 of inorganic analytes, 365
372 maximizing extraction efficiency with SHS, 372 of organic analytes, 356
365 trends in SHS
based microextractions, 372
376 SHS-LLME, 372f, 373t, 374t Microliter-volume solvent-based extraction methods, 78 Microprecipitation method, 13 Microsized coprecipitation techniques, 10
11 Microsolid phase extraction (μ-SPE), 35, 118, 127
128, 224
225 Microwave-assisted dispersive liquid
liquid microextraction (MADLLME), 106
108 Microwave-assisted extraction (MAE), 19, 106, 156
158, 158f Microwave-assisted organic synthesis, 340 Microwave-assisted supramolecular solvent extraction, 340 Microwaves, 84, 158 MIL-DLLME. See Magnetic ionic liquid-DLLME (MIL-DLLME) MILs. See Magnetic ionic liquids (MILs)

Mini solid phase extraction column system, 28 MIPs. See Molecularly imprinted polymers (MIPs) MISPE. See Molecularly imprinted solid phase extraction (MISPE) MIT. See Molecular imprinting technology (MIT) Mixer-settling equipment, 14 MMHDSPE. See Magnetic hybrid semifiber dispersion solid phase extraction (MMHDSPE) MMWCNTs. See Magnetic multiwalled carbon nanotube composites (MMWCNTs) MNi-CNT. See Magnetic carbon nanotube-nickel hybrid (MNiCNT) MNPs. See Magnetic nanoparticles (MNPs) MOFs. See Metal
organic frameworks (MOFs) Molecular chemistry, 319 Molecular imprinting technology (MIT), 193
194 Molecular recognition, 320 Molecularly imprinted polymers (MIPs), 33, 118, 128, 134, 186, 188 Molecularly imprinted solid phase extraction (MISPE), 33, 137
138 Molybdenum, 16 Monochromator, 52, 59, 61
62 Morus species, 438
439, 438f MRI. See Magnetic resonance imaging (MRI) MRTDIL. See Magnetomotive room temperature double cation IL (MRTDIL) MS. See Mass spectrometer (MS) MSAμE. See Multisphere AμE (MSAμE) MSPD-MIL-DLLME. See Matrix solidphase dispersion, MIL dispersion liquid micro extraction (MSPD-MILDLLME) MSPE. See Magnetic solid phase extraction (MSPE) MTBE. See Methyl tert-butyl ether (MTBE) Multicommutation flow system, 19 Multisphere AμE (MSAμE), 128
129

Multiwall carbon nanotubes (MCNT), 432 Multiwalled carbon nanotube supported microsolid phase extraction (MWCNT-μ-SPE), 128 Multiwalled carbon nanotubes (MWCNTs), 98, 186
187, 195, 197f, 369 MWCNT-μ-SPE. See Multiwalled carbon nanotube supported microsolid phase extraction (MWCNT-μ-SPE) MWCNTs. See Multiwalled carbon nanotubes (MWCNTs) MWCNTs-COOH. See Carboxyl multiwall carbon nanotubes (MWCNTs-COOH)

N NAAT. See Nanoporous array anode titanium (NAAT) NADESs. See Natural deep eutectic solvents (NADESs) Nanoclusters (NCs), 88 Nanomaterials, 34, 174 Nanoparticles (NPs), 88 application in separation, 195
198 Nanoporous array anode titanium (NAAT), 277, 278f Nanotechnology, 33
34 NAPA. See N-Acetylprocainamide (NAPA) Naphthalene, 29 Naproxen, 175
176 National environmental methods index (NEMI), 215
216, 222f Natural deep eutectic solvents (NADESs), 240
241 NCs. See Nanoclusters (NCs) Nebulizers, 59 NEMI. See National environmental methods index (NEMI) Net-shaped platinum electrode, 63 Neurological disorders, 369
370 Neutron-activation analysis, 8
9 New generation separation and preconcentration methods, 75
76 application of CNT and nanoparticles in separation, 195
198 CPE, 153
154

464 New generation separation and preconcentration methods (Continued) DLLME, 160
164 high-diffusion liquids, 155
156 historical development and overview, 149
150 HPT and nonhyphenated chromatographic techniques, 150 LPME, 76
117 MAE, 157
158 modern techniques of isolation and/or preconcentration, 170
195 ATPE, 176
185 D-μ-SPE, 186
190 LPME, 170
176 SBSE, 190
195, 194f new-generation solid phase extraction methods, 117
138 DMSPE, 138 immunoaffinity solid phase extraction, 136
137 MEPS, 137 MISPE, 137
138 MSPE, 133
136 SBSE, 132
133 SPME, 117
131 PLE, 156
157 SFE, 159
160 SFODME, 164
169 USAEME, 151
153 VMAE, 159 New-generation solvents, 224
251 amphiphilic solvents, 245
251 DESs, 239
245 ILS, 229
239 SSGs, 225
229 SUPRAS, 245
251 Newton’s model, 50
51 Ni(II)-diethyldithiocarbamate, 12 Niobium, 16 Nitrated-PAHs (nitro-PAHs), 164
166 nitro-PAHs. See Nitrated-PAHs (nitroPAHs) Nitrogen gas (N2), 251
252 NMP. See N-Methyl-2-pyrrolidinone (NMP) NMR. See Nuclear magnetic resonance spectrometry (NMR) Noble metal nanoparticles, 88 Noncovalent forces, 320

Index

Nonhyphenated chromatographic techniques, 150 Nonprotic solvents, 402 3-(Nonyl-or decyl-) dlmethylammonlojpropyl sulfate, 23 Norfloxacin, 190 Nortriptyline (NRT), 190 NPs. See Nanoparticles (NPs) NRT. See Nortriptyline (NRT) Nuclear magnetic resonance spectrometry (NMR), 49
50, 54
55, 150 13 C NMR, 54
55

O OA. See Oleic acid (OA) Ochratoxin A (OTA), 128, 249
250 1-Octanol, 20
21 Octanol-based SUPRAs, 329 1-Octyl-3-methylimidazolium chloride (C8MIm-Cl), 111 Octylguanidinium chloride (C8Gu-Cl), 111 OES. See Optical emission spectrometer (OES) Offline SFE-SFC-MS/MS technology Ofloxacin, 190 Olbyzacin, 439 Oleic acid (OA), 416 Olive oil, 411 ˚ (A ˚ ngstrom), 50
51 1A Online flow injection coprecipitation system, 11
12 Online preconcentration and analysis methods, 11
12 Online supercritical SFE liquid mass spectrometry, 432, 432f Optical emission spectrometer (OES), 214 Optical probe, 90
91 Organic carbon dioxide, 426 chelating agents, 13
14 extraction solvents, 15 SHS for extraction of organic analytes, 356
365 solvents, 85 species, 2
3 Oscillograph, 66 Oscillographic polarography, 66 OTA. See Ochratoxin A (OTA) OX-MWCNTs. See Oxidized MWCNTs (OX-MWCNTs)

Oxalate precipitation, 9 Oxidized monoterpenes, 434
435 Oxidized MWCNTs (OX-MWCNTs), 195
198 Oxy-PAHs. See Oxygenated-PAHs (Oxy-PAHs) Oxygenated organic solvents, 325
326 Oxygenated-PAHs (Oxy-PAHs), 164
166

P PA. See Polyacrylate (PA); Procainamide (PA) Pa-SDME. See Parallel-single-drop microextraction (Pa-SDME) Packaged cartridges, columns, or discs, 29 PAD. See Pulsed amperometric detection (PAD) Paeonol, 84 PAHs. See Polycyclic aromatic hydrocarbons (PAHs) PAM. See Pentamidine (PAM) PAN. See 1-(2-Pyridylazo)-2-naphthol (PAN) PANI. See Polyaniline (PANI) Paper chromatography, 46 Parallel-single-drop microextraction (Pa-SDME), 92, 175 Patent Blue V, 152 pBA. See Poly(butyl acrylate) (pBA) PBBs. See Polybrominated biphenyls (PBBs) PC. See Phycocyanin (PC) PCBs. See Polychlorinated biphenyls (PCBs) PCDDs. See Polychlorinated dibenzop-dioxins (PCDDs) PCP. See Pentachlorophenol (PCP) PCR. See Polymerase chain reaction (PCR) PCV2 Cap protein. See Porcine circovirus type 2 Cap protein (PCV2 Cap protein) PDMS. See Polydimethylsiloxane (PDMS) PDMS-OH. See Hydroxyl-terminated poly-dimethylsiloxane (PDMSOH) PEEK. See Polyetheretherketone (PEEK) PEG. See Polyethylene glycol (PEG)

Index

PEG600MO. See Polyethylene glycol 600 monooleate (PEG600MO) Penalty points (PPs), 219, 223t Pencil lead, 120 Pentachlorobenzene, 99 Pentachlorophenol (PCP), 136 Pentamidine (PAM), 33 Pentane, 17, 159
160 Pequi oil, 435
436 Per-methyl-hydroxypropylβ-cyclodextrin (PMHP-β-CD), 23
24 Percentage relative standard deviation (%RSD), 356 Perfluorinated solvents, 382 Periodic mesoporous organosilica-IL (PMO-IL), 300 Perkin-Elmer instrument, 53
54 PEs. See Phthalate esters (PEs) PGC. See Porous graphitic carbon (PGC) pH equation, 65 Phen. See Phenanthroline (Phen) Phenanthrene, 16, 29 Phenanthroline (Phen), 11
12, 188 Phenazopyridine, 439
440 Phenpropatrin, 433 1-Phenyl-1,2-propanedione-2oximethiosemicarbazone (PPDOT), 371 Phenylalanine (Phe), 135 Phosphor scope, 56
57 Phosphorescence, 56 Phosphoric acid determination, 6
7 Phosphoroscrope, 56
57 Phosphorus, 56
57 Photoacoustic spectrometry, 46 Photodetectors, 52 Photodiode array UV-Vis absorbance, 150 Photomultiplier tube (PMT), 53, 59
60 Phthalate esters (PEs), 190
193 Phycocyanin (PC), 440 PIL. See Polymerized ionic liquid (PIL) Pipette-tip solid phase extraction (PTSPE), 236
237, 237f Plackett
Burman design program, 86
87, 367, 372 Plasma emission spectroscopy, 61 PLE. See Pressurized liquid extraction (PLE)

PMHP-β-CD. See Per-methylhydroxypropyl-β-cyclodextrin (PMHP-β-CD) PMMA. See Poly(methyl methacrylate) (PMMA) PMO-IL. See Periodic mesoporous organosilica-IL (PMO-IL) PMT. See Photomultiplier tube (PMT) Pneumatic nebulizers, 59 Polar solvents, 225
226 Polarity, 399, 400t, 402 ChCl-glycerol mixtures, 401t pH values, 401f Polarography, 66 Poly(4-vinylpyridineco-ethylene glycol dimethacrylate) (Poly (VPco-EDMA)), 131 Poly(butyl acrylate) (pBA), 68 Poly(butyl methacrylate), 68 Poly(ethylene glycol dimethacrylate/ graphene oxide) (EDMA/GO), 130 Poly(ethylene glycol dimethacrylate)/ graphene composite, 131 Poly(methyl methacrylate) (PMMA), 68 Poly(oxyethylene) (7.5) nonyl-phenyl ether, 23 Poly(vinylimidazole-divinylbenzene), 129
130 Poly(VPco-EDMA). See Poly(4vinylpyridineco-ethylene glycol dimethacrylate) (Poly(VPcoEDMA)) Polyacrylate (PA), 193
194 Polyaniline (PANI), 120
121, 236 Polybrominated biphenyls (PBBs), 104 Polychlorinated biphenyls (PCBs), 27
28, 120
121 Polychlorinated dibenzo-p-dioxins (PCDDs), 247 Polycyclic aromatic hydrocarbons (PAHs), 22, 82, 102, 115
116, 128, 131, 216
217, 307, 356, 432 Polydimethylsiloxane (PDMS), 118
120, 130, 132
133, 135, 190
193 Polyetheretherketone (PEEK), 21, 82 Polyethylene glycol (PEG), 118, 180
182 Polyethylene glycol 600 monooleate (PEG600MO), 23
24

465 Polyisoprene acetate (PPA), 404 Polymerase chain reaction (PCR), 301
302 Polymeric resins, 27 Polymerized ionic liquid (PIL), 118, 269
270, 270f Polyols, 402 Polyoxyethylene-(n)-nonylphenyl ether (PONPE), 23 Polypropylene glycol 400 (PPG 400), 404 Polystyrene-divinylbenzene (PS-DVB), 26 Polytetrafluoroethylene (PTFE), 29 Polythiophene/graphene oxide (PTh/ GO), 125
126 PONPE. See Polyoxyethylene-(n)nonylphenyl ether (PONPE) Porcine circovirus type 2 Cap protein (PCV2 Cap protein), 180 Porous graphitic carbon (PGC), 26 Porous membrane-protected μ-SPE. See Microsolid phase extraction (μ-SPE) Porous polymeric sorbents, 26 Porphyrins, 23 Portable XRF device, 214 Potentiometry, 65 Potentiostat, 63
64 PPA. See Polyisoprene acetate (PPA) PPDOT. See 1-Phenyl-1,2propanedione-2oximethiosemicarbazone (PPDOT) PPG 400. See Polypropylene glycol 400 (PPG 400) PPs. See Penalty points (PPs) Preconcentration factors, 359
360 methods, 3
35 Preference ranking organization method for enrichment evaluation (PROMETHEE), 217
218 Premix nebulizer burner, 59 Pressure variation in-syringe DLLME (PV-IS-DLLME), 163, 163f Pressurized liquid extraction (PLE), 19, 156
157 influential factors, 157f Pressurized liquid extraction, 156
157 Prism, 50, 61

466

Index

Procainamide (PA), 30
31 PROMETHEE. See Preference ranking organization method for enrichment evaluation (PROMETHEE) Prometryn, 30
31 Propranolol, 439
440 Proton NMR, 54
55 PT-SPE. See Pipette-tip solid phase extraction (PT-SPE) PTFE. See Polytetrafluoroethylene (PTFE) PTh/GO. See Polythiophene/ graphene oxide (PTh/GO) Pulse nebulizers, 59 Pulsed amperometric detection (PAD), 66
67 Pulsed-wave mode (PWM), 151 PV-IS-DLLME. See Pressure variation in-syringe DLLME (PV-ISDLLME) PWM. See Pulsed-wave mode (PWM) Py-SPME. See Pyrolysis-dynamic solid phase microextraction (PySPME) Pyrethroid residues, 433 1-(2-Pyridylazo)-2-naphthol (PAN), 22, 87, 365 Pyroelectric detectors, 54 Pyrolysis-dynamic solid phase microextraction (Py-SPME), 126
127 Pyrolytic acid, 14

Recorder, 61 Reduced graphene oxide (rGO), 236 Reductive coprecipitation method, 10 Relative standard deviation (RSD), 9
10, 163, 404
405 Response surface methodology (RSM), 360, 437 Restricted access materials (RAMs), 26, 331 rGO. See Reduced graphene oxide (rGO) Rhizoma coptidis, 362
363 Room temperature ILs (RTILs), 229
230, 269 Rotating can phosphor scope (RCP), 56
57 Rotating disk phosphorescence (RDP), 56
57 Rotating platinum electrode (RPE), 66
67 Rotating-disc sorbent extraction (RDSE), 35, 118, 130, 224
225 RPE. See Rotating platinum electrode (RPE) RSD. See Relative standard deviation (RSD) RSM. See Response surface methodology (RSM) RTILs. See Ionic liquids at room temperature (RTILs); Room temperature ILs (RTILs) Rubidium, 51

Q

S

Quality-by design (QbD), 214
215 Quantas, 59
60 Quantitative analyses, 45 Quartz prism spectrograph, 52 Quaternary ammonium salts, 180
182, 385

SA-SFODME. See Surfactants SFODME (SA-SFODME) SAE-VA-μ-SPE. See Vortex-assisted porous membrane-protected microsolid phase extraction (SAE-VA-μ-SPE) SALDI-MS. See Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) Sampling frequency, 11
12 Sampling systems for analytical instruments, advancement in, 70
71 SBA. See Sulfobenzoic acid (SBA) SBME. See Solvent bar microextraction (SBME) SBSE. See Stir-bar sorptive extraction (SBSE)

R R. P. Cuspidati, 159 Radiation sources, 52 RAMs. See Restricted access materials (RAMs) RCP. See Rotating can phosphor scope (RCP) RDP. See Rotating disk phosphorescence (RDP) RDSE. See Rotating-disc sorbent extraction (RDSE)

SC-DHFHS-LPME. See Solvent cooling-assisted dynamic hollow-fiber-supported headspace liquid phase microextraction (SC-DHFHSLPME) SC-SF-SLDME procedure, 168, 169f SCD. See Segmented-array charge
coupled detector (SCD) Schiff base ligand, 372 SCMNPs. See Silica-coated magnetic nanoparticles (SCMNPs) SCSE. See Stir-cake sorptive extraction (SCSE) SDME. See Single-drop microextraction (SDME) SDME/GC-MS procedure, 85 SDS. See Sodium dodecyl sulfate (SDS) Segmented-array charge
coupled detector (SCD), 60 Selenium (Se), 9
10 Self-assembly, 337 Semiautomatic dynamic HS-LPME technique, 83
84 Separation methods, historical development of, 3
35 Sequential flow injection analysis (SIA), 19 Sequential injection system (SI system), 108 Sesame oil, 411 SF. See Supercritical fluid (SF) SFC. See Supercritical fluid chromatography (SFC) SFC-NMR. See Supercritical fluid chromatography-nuclear magnetic resonance (SFC-NMR) SFE. See Supercritical fluid extraction (SFE) SFE-NMR. See Supercritical fluid extraction-nuclear magnetic resonance (SFE-NMR) SFE-SUPRAS. See Supercritical fluid extraction-supramolecular solvents (SFE-SUPRAS) SFEAP. See Supercritical fluid chromatography assisted by pressing (SFEAP) SFOD. See Solidification of floating organic droplet (SFOD) SFODME. See Solidified floating organic drop microextraction (SFODME)

Index

SHDS. See Switchable-hydrophilicity dispersive solvent (SHDS) Short-chain alcohols, 399 SHS. See Switchable-hydrophilicity solvents (SHS) SHS-LLME method. See Solvent
liquid
liquid microextraction method (SHSLLME method) SI system. See Sequential injection system (SI system) SIA. See Sequential flow injection analysis (SIA) SIL. See Stable isotope labeling (SIL) Silica, 188 silica-based sorbents, 26 sol, 188 Silica-coated magnetic nanoparticles (SCMNPs), 134
135 Silicon carbide, 54 Silicotungstic acid, 7
8 Silver (Hg21), 368
369 Silver bromide precipitation, 6
7 Silver nanoparticles (AgNPs), 187 Simplified D-μ-SPE, 188 Single-drop microextraction (SDME), 19, 76
92, 79f, 150, 224
225, 229
230, 270, 286
287, 333 applications, 82
92 CFME, 82 DI-SDME, 80
81 HS-SPME, 81
82 modes of, 173f three-phase, 82 Single-potential amperometry, 66
67 Single-walled carbon nanotubes (SWCNTs), 186
187, 195, 197f Size exclusion chromatography, 47 Slotted quartz tube (SQT), 371 Sodium chloride (NaCl), 360 Sodium dodecyl sulfate (SDS), 19
20, 329 Sodium methyl chloride (SOX-MeCl), 434
435 Solar spectrum, 51 Sol
gel processes, 193
194 Solid phase dynamic extraction (SPDE), 35, 118, 224
225 Solid phase extraction (SPE), 5, 26
27, 30, 135, 149, 229 Solid phase extraction/ microextraction methods historical development of, 24
35

sorbents in, 27f Solid phase membrane tip extraction (SPMTE), 98
99 Solid phase microextraction (SPME), 5, 19, 35, 75
76, 117
131, 150, 209, 214, 229, 236f, 240f, 270, 274
280, 279f. See also Liquid phase microextraction (LPME) application of ILs in, 281t graphene oxide
coated stainless steel wire, 280f polyacrylate fibers, 439 Solidification of floating organic droplet (SFOD), 106
108 Solidified floating organic drop microextraction (SFODME), 22, 76, 115
117, 116f, 164
169, 170f application, 167t organic solvent in, 166t SC-SF-SLDME procedure, 168, 169f ultrasonic-assisted supramolecular based on, 166f Solvent bar microextraction (SBME), 99, 172
173 Solvent cooling-assisted dynamic hollow-fiber-supported headspace liquid phase microextraction (SC-DHFHSLPME), 100 Solvent selection guidelines (SSGs), 225
229 physicochemical properties, 226t properties and environmental risk ranking, 227t Solvent-based liquid
liquid microextraction (SsLLME), 250
251 Solvent
liquid
liquid microextraction method (SHSLLME method), 357, 372f analytes preconcentrated with, 374f Solvents, 161, 381
382 extraction system, 325
327 of transition metal dithiocarbamates, 8 power, 429 Sonication, 151, 164 sonication-based extractions, 155
156 SOX-MeCl. See Sodium methyl chloride (SOX-MeCl) Soxhlet method, 155
156

467 SPDE. See Solid phase dynamic extraction (SPDE) SPE. See Solid phase extraction (SPE) Spectrofluorometer, 61
62 Spectrometer/spectrophotometer, 61 Spectroscopy, 49
62, 150 AFS, 61
62 atomic absorption spectroscopy, 57
59, 58f atomic emission spectroscopy, 59
61 EMR sources, 50t IR spectrometry, 53
54 luminescence spectroscopy, 56
57, 57f MS, 55
56 NMR spectrometry, 54
55 plasma emission spectroscopy, 61 UV-Vis spectroscopy, 50
53 Spherocarb adsorbents, 28 Spin interaction mechanism, 54
55 Spinacia oleracea, 188 Spirulina platensis, 440 SPME. See Solid phase microextraction (SPME) SPMTE. See Solid phase membrane tip extraction (SPMTE) Spot test, 46 SPS. See Switchable-polarity solvents (SPS) Sputtering, 58
59 SQT. See Slotted quartz tube (SQT) SRSE. See Stir-rod sorptive extraction (SRSE) SS-LPME. See Switchable solventbased liquid phase microextraction (SS-LPME) SSGs. See Solvent selection guidelines (SSGs) SsLLME. See Solvent-based liquid
liquid microextraction (SsLLME) SSs. See Switchable solvents (SSs) Stable isotope labeling (SIL), 106
108 Stainless steel, 58
59 Static-SDME. See Direct immersion single-drop microextraction (DI-SDME) Steam distillation method, 434 Stir-bar sorptive extraction (SBSE), 19, 129
130, 132
133, 150, 190
195, 194f, 224
225 application, 196t

468 Stir-bar sorptive extraction (SBSE) (Continued) extraction mode of, 195f Stir-cake sorptive extraction (SCSE), 35, 118, 129
130, 224
225 Stir-rod sorptive extraction (SRSE), 35, 118, 130
131 Styrene
divinylbenzene Amberlite XAD-2 resin, 27
28 Subcritical hot water extraction (SWE), 257
258 Sulfobenzoic acid (SBA), 271 Sulfuric acid, 16, 357 Supercritical carbon dioxide, 426
427, 429 Supercritical fluid (SF), 159 Supercritical fluid chromatography (SFC), 49, 426 Supercritical fluid chromatography assisted by pressing (SFEAP), 434, 435f, 436 Supercritical fluid chromatographynuclear magnetic resonance (SFC-NMR), 68 Supercritical fluid extraction (SFE), 19, 155
156, 159
160, 256, 425
426 extraction of pyrethroid residues, 433f Supercritical fluid extraction-nuclear magnetic resonance (SFENMR), 69 Supercritical fluid extractionsupramolecular solvents (SFESUPRAS), 439 Supercritical fluids, 256
258, 382, 425 application of SFE, 441t in drug and biological sample, 439
440 in environment, 430
433 extraction of pyrethroid residues, 433f in foods and herbs, 433
439 instrumentation, 427
429 mechanism and kinetic, 429
430 phase diagram of gases, 425f properties, 426
427, 427t Superheated water, 257
258 Superspeed HPLC, 49 Supramolecular chemistry, 319
320, 321f, 324f, 338 Supramolecular restricted access solvents (SUPRASs), 19,

Index

112
113, 174, 245
251, 246f, 248f, 319
325, 323f, 439 components, 331 efficiency, 337 emergence of supramolecular chemistry, 321f environment, 338 formation mechanism of SUPRAS phase, 329
331 historical development of supramolecular chemistry, 324f integrated use of SUPRAS with nanomaterials, 339 in liquid
liquid microextraction, 338
339 microwave-assisted SUPRAS extraction, 340 molecular extraction types, 338 preparation, 327
329 in separation and preconcentration methods, 331
337 solvent extraction system, 325
327 SUPRAS-assisted silver nanoparticles, 342 temperature-assisted SUPRAS extraction, 341
342 thermodynamics, 337
338 trends, 342 ultrasonic-assisted SUPRAS extraction, 339 vortex assisted SUPRAS extraction, 340
341 SUPRASs. See Supramolecular restricted access solvents (SUPRASs) Surface-assisted laser desorption/ ionization mass spectrometry (SALDI-MS), 176 Surfactant-based extraction. See Cloud-point extraction (CPE) Surfactants, 152 Surfactants SFODME (SA-SFODME), 164 SWCNTs. See Single-walled carbon nanotubes (SWCNTs) SWE. See Subcritical hot water extraction (SWE) Switchable solvent-based liquid phase microextraction (SS-LPME), 174
175, 365 Switchable solvents (SSs), 19 future, 376f, 377

analytes preconcentrated with SHS-LLME, 374f SHS. See Switchable-hydrophilicity solvents (SHS) Switchable-hydrophilicity dispersive solvent (SHDS), 358 Switchable-hydrophilicity solvents (SHS), 251
258, 252f, 348
349 applications of, 353
354 in large-scale extractions, 354
356 liquid phase micro extraction, 255f LPME and micro sampling FAAS analysis stages, 256f in microextractions, 356
376, 376f MILs, 258 supercritical fluids, 256
258 superheated water, 257
258 synthesis and chemistry, 349
353, 352t phase separation, 354f SHS synthesis by purging CO2, 350f tertiary amines solvents tested, 351t Switchable-polarity solvents (SPS), 348 Switched-off nonionic liquid, 348 Synergic extraction, 325
326 Synthetic polymers, 26 Syringe-assisted D-μ-SPE, 186
187

T TAME. See Tert-amyl methyl ether (TAME) TAN. See 1-(2-Thiazolylazo)-2naphthol (TAN) TBAB. See Tetrabutylammonium bromide (TBAB) TBAC. See Tetrabutylammonium chloride (TBAC) TBBPA. See Tetrabromobisphenol-A (TBBPA) 2,4,6-TBP. See 2,4,6-Tribromophenol (2,4,6-TBP) TBuT. See Tributyltin (TBuT) 2,4,6-TCP. See 2,4,6-Trichlorophenol (2,4,6-TCP) TD-cGC-MS. See Thermal desorptioncapillary GC-MS (TD-cGC-MS) TDU. See Thermal desorption unit (TDU) TEAB. See Tetraethylammonium bromide (TEAB)

Index

TEAC. See Tetraethylammonium chloride (TEAC) Technique for order of preference by similarity to ideal solution (TOPSIS), 217
218 2,3,4,6-TeCP. See 2,3,4,6Tetrachlorophenol (2,3,4,6TeCP) Teepol, 15 Teflon rotating disc apparatus, 130 TEL species. See Triethyllead species (TEL species) Telephone analysis, 64
65 Temperature-assisted supramolecular solvent extraction, 341
342 Temperature-controlled ionic liquid dispersive liquid phase microextraction (TILDLME), 341
342 Temperature-induced SUPRAS, 334 Terbutryn, 30
31 Tert-amyl methyl ether (TAME), 120 Tetrabromobisphenol-A (TBBPA), 97 Tetrabutylammonium (Bu4N 1 ), 339 Tetrabutylammonium bromide (TBAB), 180
182, 404 Tetrabutylammonium chloride (TBAC), 180
182 Tetrachloromethane, 97
98 2,3,4,6-Tetrachlorophenol (2,3,4,6TeCP), 136 Tetraethylammonium bromide (TEAB), 180
182 Tetraethylammonium chloride (TEAC), 180
182, 404 Tetrafluoroborate ion, 269 Tetrahydrofuran (THF), 164, 249
250, 329 Tetramethoxysilane (TMOS), 300 Tetramethylammonium bromide (TMAB), 404 Tetramethylammonium chloride (TMAC), 404 Tetramethylammonium chloride/ urea, 404 N,N,N0 ,N0 Tetramethylethylenediamine, 349 8-Tetramethylnaphthalen-2-ol (TNO), 243 Tetrapropylammonium bromide/ urea, 404

TFMS. See Trifluoromethanesulfonate (TFMS) TGA. See Thermal gravimetric analysis (TGA) 2-Thenoyltrifluoroacetone-xylene, 16 Thermal conductivity detector, 47
48 Thermal desorption unit (TDU), 190
193 Thermal desorption-capillary GC-MS (TD-cGC-MS), 132
133 Thermal gravimetric analysis (TGA), 273, 402 Thermodynamics, 337
338 ionization, 399
401 Thermospray tandem mass spectrometry (TSP-MS-MS), 32 THF. See Tetrahydrofuran (THF) 1-(2-Thiazolylazo)-2-naphthol (TAN), 13 Thin layer chromatography (TLC), 46 Thiocyanate, 13
14 3-dimensional ionic liquid ferrite functionalized graphene oxide nanosorbent (3D-IL-Fe3O4-GO), 236
237, 238f Three-dimensional surface response (3D surface response), 367, 372 Three-electrode potentiostat, 61
62, 64 Three-liquid phase SDME, 170 Three-phase drop-based technique, 77 Three-phase HF-LPME, 172 Three-phase SDME, 20, 82 Tie line length (TLL), 178
179 TILDLME. See Temperature-controlled ionic liquid dispersive liquid phase microextraction (TILDLME) Time-of-flight mass spectrometer, 47
48 Tin (Sb), 7, 11 Titanium wires, 121
122 Titrimetry, 3
4, 45 TLC. See Thin layer chromatography (TLC) TLL. See Tie line length (TLL) TMA. See 2,4,5-Trimethylaniline (TMA) TMAB. See Tetramethylammonium bromide (TMAB) TMAC. See Tetramethylammonium chloride (TMAC) TMG. See Trimethylglycine (TMG)

469 TML species. See Trimethyllead species (TML species) TMOS. See Tetramethoxysilane (TMOS) TMSPEDA. See N-(3Trimethoxysilylpropyl) ethylenediamine (TMSPEDA) TNO. See 8-Tetramethylnaphthalen-2ol (TNO) Toluene, 97
98 1573a Tomato Leaves, and Oriental Basma Tobacco Leaves (INCTOBTL-5), 365
366 TOPSIS. See Technique for order of preference by similarity to ideal solution (TOPSIS) Total consumption burner, 59 TPhT. See Triphenyltin (TPhT) TPME. See Twin polarized microelectrode (TPME) Trace elements, 3
4 2,4,6-Tribromophenol (2,4,6-TBP), 287 Tributyltin (TBuT), 10, 132 2,4,6-Trichlorophenol (2,4,6-TCP), 136, 232
233, 287 Triethanolamine, 349 Triethylene glycol, 402 Triethyllead species (TEL species), 122
125 Trifluoromethanesulfonate (TFMS), 271 Trihexyl(tetradecyl)phosphonium tetrachloroferrate (III), 114
115 Trihexyltetradecylphosphonium tetrachlorocobalt (II), 114 N-(3-Trimethoxysilylpropyl) ethylenediamine (TMSPEDA), 235 2,4,5-Trimethylaniline (TMA), 152 Trimethylglycine (TMG), 397, 402 Trimethyllead species (TML species), 122
125 Triphenyltin (TPhT), 132 Triton X (polyoxyethylene-(n)octylphenyl ether), 23 Triton X-100, 24, 329 Triton X-114, 23
24 Trivalent cations, 7 TSP-MS-MS. See Thermospray tandem mass spectrometry (TSP-MSMS) Tungsten halogen lamp, 54 Turbulent flow burner, 59

470 Twin polarized microelectrode (TPME), 66
67 Twisters, 190
193 Two-liquid phase SDME, 170 Two-phase HF-LPME methods, 172 Tyrosine kinas inhibitors, 168

U U-shaped hollow-fiber liquid phase microextraction (U-shaped HFLPME), 99 UA-HF-LPME. See Ultrasoundassisted hollow-fiber liquid microextraction (UA-HFLPME) ¨ bermoleku¨, 323
324 U UCON, 179 Udex procedure, 14 Ultra-high-performance liquid chromatography with tandem mass spectrometer (UHPLC
MS/MS), 130 Ultra-high-performance liquid chromatography-diode-array detector (UHPLC-DAD), 247 Ultrasonic irritation, 104 Ultrasonic nebulizers, 59 Ultrasonic-assisted supramolecular SFOD, 164 solvent extraction, 339 Ultrasound (US), 437 radiation, 151 treatment, 405
411 US-assisted deep eutectic solvent LPME, 174
175 Ultrasound-assisted emulsification microextraction (USAEME), 104, 151
153, 152f applications of, 154t Ultrasound-assisted hollow-fiber liquid microextraction (UA-HFLPME), 97 Ultrasound-assisted polymer surfactant
enhanced emulsification microextraction, 152 Ultrasound-assisted solidified floating organic drop microextraction (USSFODME), 164

Index

Ultratrace, 3
4 Ultraviolet (UV) radiation, 51 spectrometry, 49
50 Ultraviolet visible spectroscopy (UVVis spectroscopy), 50
53, 52f detector, 68 EMR, 52 spectral regions, 52t, 53t Uncooled indium gallium arsenide photodiodes, 54 Undecane, 97
98 UNE-headspace ionic liquid SDME (UNE-HS/IL/SDME), 287
294, 292f United Nations World Food Programme (UNWFP), 2
3 Uranium, 23 Uranyl nitrate, 13
14 US. See Ultrasound (US) USAEME. See Ultrasound-assisted emulsification microextraction (USAEME) USSFODME. See Ultrasound-assisted solidified floating organic drop microextraction (USSFODME) UV-Vis spectroscopy. See Ultraviolet visible spectroscopy (UV-Vis spectroscopy)

V VA-IL-DLLME. See Vortex agitation for ionic liquid-based dispersive liquid
liquid microextraction (VA-ILDLLME) VA-SFODME. See Vortex mixing SFODME (VA-SFODME) Vacuum microwave-assisted extraction (VMAE), 159 VALLME. See Vortex-assisted liquid
liquid microextraction (VALLME) van der Waals forces, 320 Vaporizers, 58
59 n-Vinylpyrrolidone, 129 Viscosity, 395
396, 402 eutectic mixture of urea/ZnCl2, 397f

VMAE. See Vacuum microwaveassisted extraction (VMAE) Volta-electrometer, 61
63 Voltammetry, 65 Voltammograms, 65 Volumetry, 45 Vortex agitation for ionic liquid-based dispersive liquid
liquid microextraction (VA-ILDLLME), 106 Vortex assisted supramolecular solvent extraction, 340
341 Vortex mixing SFODME (VASFODME), 164 Vortex mixing/mixer, 97, 341f Vortex-assisted liquid
liquid microextraction (VALLME), 105
106, 107f, 340 Vortex-assisted porous membraneprotected microsolid phase extraction (SAE-VA-μ-SPE), 128

W Warm-blooded biological system, 338 Wastewater, 364
365 Water, 159
160, 382, 402 activity, 402 distillation method, 434 water-immiscible liquid SUPRAS, 339 water-induced SUPRAS, 334
335 water-sensitivity problem, 348
349 World Environment and Development Commission (WCED), 18 World Health Organization (WHO), 2
3 World Pharmacy Council (WPC), 2
3

X X-ray, 51
52

Z Zeeman effect, 54
55 Zeolite, 24
25 Zeolite imidazolate framework 8 (ZIF8), 128 Zinc (Zn), 6
7, 368
369 ZnSe-based beam splitters, 54