Practical examples on traceability, measurement uncertainty and validation in chemistry Vol 1 [Vol 1, Second edition] 9789279120213

Table of contents :
TABLE OF CONTENTS
Introduction
How to use the Book
About the Authors
Chapter 1 Analysis of Gold Alloys by Flame AtomicAbsorption Spectrometry
Chapter 2 Determination of Calcium in Serum bySpectrophotometry
Chapter 3 Determination of Radium in Waterby a-Spectrometry
Chapter 4 Determination of Polar Pesticides by LiquidChromatography Mass Spectrometry
Chapter 5 Determination of Ammonium in Water by ContinuousFlow Analysis (CFA) and Spectrometric Detection
Appendix 1 TrainMiC® Exercises (‘white pages’)
Appendix 2 Briefing of the trainees on the example session

Citation preview

Producing reliable measurements in analytical chemistry can be rather demanding. Some would say an uphill struggle. Comparable to mountain walking. Hard work, but then the satisfaction of reaching the top is absolutely great. And so is the view. As with all human endeavour, it always helps to know what you are doing, thus theoretical knowledge forms the basis. Likewise in analytical chemistry. Understanding the measurement science, the metrology, is important. That is why in the international standard ISO/IEC-17025 “General requirements for the competence of testing and calibration laboratories” section five deals with technical requirements such as traceability, validation and uncertainty. The European Life Long Learning Programme TrainMiC®, created in 2001, produced material for teaching the theory. As excellence in theory does not necessarily mean mastering practice, a need for developing practical examples later arose. This is what you can find in this book, which is intended as a first of a series of such compilations. Inspired by the NORDTEST “Trollbook”, we also decided to have a mascot. For each volume, a different one, which would be taken from the treasure of European fairy tales and legends. For this first volume, the fairy tale character of Kekec (pronounced as Kekets) was chosen. Kekec is a brave, clever and cheerful shepherd boy who lives in Slovenian mountains. He always brings good to the people that surround him and he helps those that are in trouble. And in that sense, that is what is the intention of this book. We hope it succeeds in doing so. Nineta Majcen Philip Taylor

ISBN 978-92-79-12021-3

PRACTICAL EXAMPLES ON TRACEABILITY, MEASUREMENT UNCERTAINTY AND VALIDATION IN CHEMISTRY

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The mission of the JRC is to provide customer-driven scientific and technical support for the conception, development, implementation and monitoring of EU policies. As a service of the European Commission, the JRC functions as a reference centre of science and technology for the Union. Close to the policy-making process, it serves the common interest of the Member States, while being independent of special interests, whether private or national.

Practical Examples on

Traceability, Measurement Uncertainty and Validation in Chemistry Volume 1

Edited by Nineta Majcen, Philip Taylor Authors: Ljudmila Benedik Steluta Duta Koit Herodes Monika Inkret Veselin Kmetov Allan Künnapas Ivo Leito Bertil Magnusson

Urška Repinc Philip Taylor Emilia Vassileva

EUR22791/2 EN - 2010

Practical Examples on

Traceability, Measurement Uncertainty and Validation in Chemistry Volume 1 Second edition

Edited by Nineta Majcen, Philip Taylor Authors: Ljudmila Benedik Steluta Duta Koit Herodes Monika Inkret Veselin Kmetov Allan Künnapas

Ivo Leito Bertil Magnusson Urška Repinc Philip Taylor Emilia Vassileva

The mission of the JRC-IRMM is to promote a common and reliable European measurement system in support of EU policies.

European Commission Joint Research Centre Institute for Reference Materials and Measurements Contact information Address: Retieseweg 111, B-2440 Geel, Belgium E-mail: [email protected] Tel.: +32 (0)14 571 605 Fax: +32 (0)14 571 863 http://irmm.jrc.ec.europa.eu/ http://www.jrc.ec.europa.eu/ Legal Notice Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of this publication. (XURSH'LUHFWLVDVHUYLFHWRKHOS\RX¿QGDQVZHUV WR\RXUTXHVWLRQVDERXWWKH(XURSHDQ8QLRQ Freephone number (*): 00 800 6 7 8 9 10 11 (*) Certain mobile telephone operators do not allow access to 00 800 numbers or these calls may be billed.

More information on the European Union is available on the Internet (http://europa.eu). Cataloguing data can be found at the end of this publication. /X[HPERXUJ3XEOLFDWLRQV2I¿FHRIWKH(XURSHDQ8QLRQ

JRC 59026 EUR 22791/2 EN ISBN 978-92-79-12021-3 ISSN 1018-5593 doi: 10.2787/10402 © European Union, 2010 Reproduction is authorised provided the source is acknowledged Printed in

TABLE OF CONTENTS INTRODUCTION ..................................................................................................................5 HOW TO USE THE BOOK ...................................................................................................6 ABOUT THE AUTHORS .....................................................................................................11 CHAPTER 1..........................................................................................................................17 Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry Veselin Kmetov, Emilia Vassileva CHAPTER 2..........................................................................................................................51 Determination of Calcium in Serum by Spectrophotometry Steluta Duta, Philip Taylor

CHAPTER 3..........................................................................................................................81 Determination of Radium in Water by α-Spectrometry Ljudmila Benedik, Urška Repinc, Monika Inkret

CHAPTER 4....................................................................................................................... 121 Determination of Polar Pesticides by Liquid Chromatography Mass Spectrometry Allan Künnapas, Koit Herodes, Ivo Leito

CHAPTER 5....................................................................................................................... 157 Determination of Ammonium in Water by Continuous Flow Analysis (CFA) and Spectrometric Detection Bertil Magnusson

APPENDIX 1 ..................................................................................................................... 193 TrainMiC® Exercises (‘white pages’) APPENDIX 2 ..................................................................................................................... 209 Briefing of the trainees on the example session

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Introduction If you will tell it to me, I will forget If you will show it to me, I will forget If you involve me, I will remember. Xun Zi

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12

About the Authors

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Practical examples on traceability, measurement uncertainty and validation in chemistry

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Practical examples on traceability, measurement uncertainty and validation in chemistry

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Chapter 1

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry Veselin Kmetov, Emilia Vassileva u u u u

TrainMiC example summary form (‘blue page’) A short introduction to the analytical procedure (‘slides’) All input needed to do the three exercises (‘yellow pages’) The solved exercises (‘green pages’) 17

Practical examples on traceability, measurement uncertainty and validation in chemistry

TrainMiC example summary form

I. General information about the example

18

Measurand

Mass fraction of Au in gold alloys (‰)

Example number

Ex-06

Authors of the example

Veselin Kmetov, Emilia Vassileva

Analytical procedure

Determination of gold in jewellery gold alloys by flame atomic absorption spectrometry

Customer’s requirement

U = 9 ‰ (k = 3)

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

II. Attached files

2 - Yellow

1-I

File number, type and name Ex-06-1-I-Aualloys-FAAS-2006Ver1.ppt

About the analytical procedure: short introduction

9

PART I

9

PART II Ex-06-2-Y-Aualloys-FAAS-2006Ver1.doc

PART III

3 - Green

PART IV

EX-06-3-G-Aualloys-FAAS-2006Ver1.doc

File is attached Yes No

Content of the file

Description of the analytical procedure The customer’s requirements concerning the quality of the measurement result Validation of the measurement procedure – relevant equations and measurement data Measurement uncertainty of the result – relevant equations and measurement data

Each participant receives own copy and may keep it

9 9

Establishing traceability in analytical chemistry

9

PART II

Single laboratory validation of measurement procedures

9

Building an uncertainty budget

9

Addendum 1: By spreadsheet approach

9

Addendum 2: By dedicated software

Given by the lecturer

9

PART I

PART III

Remark

9

III. History of the example Version

Uploaded on the webhotel

Short description of the change

0

April 2007

-

1 2

19

Practical examples on traceability, measurement uncertainty and validation in chemistry

A short introduction to the analytical procedure

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All input needed to do the three exercises ‘yellow pages’

Analytical procedure Determination of gold in jewellery gold alloys by Flame Atomic Absorption Spectrometry

PART I ...................................................................................................................................25 Description of the analytical procedure PART II .................................................................................................................................33 The customer’s requirements concerning the quality of the measurement result PART III ................................................................................................................................34 Validation of the measurement procedure – relevant equations and measurement data PART IV ................................................................................................................................35 Measurement uncertainty of the result – relevant equations and measurement data

24

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

PART I. Description of the analytical procedure

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Practical examples on traceability, measurement uncertainty and validation in chemistry

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Figure 3. Flow chart of the analytical procedure for determination of gold in gold alloys

26

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

Reagents  (MHUFNFODVVSD−YY+12IUHVKO\SUHSDUHGaqua regia1+CO±VDOW  PXUH$XFHUWL¿HGIURP1RQ)HUURXVMHWDOOXUJLFDOPODQWPORYGLY

Apparatus  )ODPH$WRPLF$EVRUSWLRQ6SHFWURPHWHUHTXLSSHGZLWKKROORZFDWKRGHODPSIRU JROG  'LVFUHWHVDPSOHLQWURGXFWLRQV\VWHP$6'I   %DODQFHd JFHUWL¿HG±%'6(1  +RWSODWH  PLSHWWHYDULDEOH−—LJUDYLPHWULFDOO\FKHFNHGFHUWL¿HGd LQ− —LUDQJH  9ROXPHWULFÀDVNPLODERUDWRU\JODVVZDUHFODVV$FHUWL¿HGd PLIRU ƒC  9ROXPHWULFÀDVNPLODERUDWRU\JODVVZDUHFODVV$FHUWL¿HGd PLIRU ƒC  PRO\SURS\OHQHYLDOVJ$6'IDXWRVDPSOHUNLW

Description of the analytical procedure Sample preparation procedure *ROG DOOR\ VDPSOHV DUH VWUHWFKHG WR IROLR ZLWK − PP WKLFNQHVV TKH VXUIDFH LV ZDVKHG E\   YY +12$ GU\ SLHFH RI  J DFFXUDWHO\ ZHLJKHG WR “ J LV GLUHFWO\GLVVROYHGLQWRDYROXPHWULFÀDVNRIPLE\PLIUHVKO\SUHSDUHGaqua regia TKHÀDVNLVKHDWHGRQFHUDPLFKRWSODWHIRUPLQ'XULQJWKLVSURFHVV$JSUHFLSLWDWHV DV$JCO$JCOLVGLVVROYHGE\DGGLQJRIJ1+COWRWKHFRROHGVROXWLRQDQGYROXPH LVPDGHXSWRWKHPDUNPL ZLWKXOWUDSXUHZDWHUDWƒC  TKHVROXWLRQLVGLOXWHGDGGLWLRQDOO\E\WUDQVIHUULQJJZLWKPLFURSLSHWWHWRDFRQLFDO YLDODGGLQJ1+COLQRUGHUWRNHHSWKHVROXWLRQKRPRJHQHRXVZLWK¿QDOZHLJKWRI JJUDYLPHWULFDOO\FRQWUROOHG PURFHGXUDO EODQN LV VXEMHFW WR H[DFWO\ WKH VDPH VDPSOH SUHSDUDWLRQ SURFHGXUH DV WKH DQDO\VHGVDPSOH

Calibration 6WRFNVWDQGDUGVROXWLRQZDVPDGHLQODERUDWRU\E\GLVVROXWLRQRIJ$XZLWKSXULW\ ZLWKPLaqua regiaDQG¿OOHGXSWRJZLWK1+COTZRFDOLEUDWLRQ

27

Practical examples on traceability, measurement uncertainty and validation in chemistry

VWDQGDUGVDUHREWDLQHGLQSRO\SURS\OHQHYLDOVDIWHUIXUWKHUGLOXWLRQRIJDQGJ IURPVWRFNVWDQGDUGVROXWLRQZLWKSURFHGXUDOEODQNVROXWLRQWRJJUDYLPHWULFDOO\ FRQWUROOHG  TKHVHOHFWHGFDOLEUDWLRQUDQJHUHFDOFXODWHGIRUDQDO\VHGDOOR\FRUUHVSRQGVWRWKHUDQJH ±FDUDWV TKHFDOLEUDWLRQVWDQGDUGVDUHVXEMHFWWRWKHVDPHVDPSOHSUHSDUDWLRQSURFHGXUHDVWKH DQDO\VHGVDPSOHTKHH[DFWPDWFKLQJRIVDPSOHDQGVROXWLRQXVHGIRUFDOLEUDWLRQDOORZV WRDYRLGWKHLQÀXHQFHRIPDWUL[HIIHFWRQREWDLQHGVLJQDOV

Atomic absorption measurement *ROG LV GHWHUPLQHG E\ DLU VHJPHQWHG GLVFUHWH LQWURGXFWLRQ ÀDPH DWRPLF DEVRUSWLRQ VSHFWURPHWU\ $6'I)$$6  XVLQJ EUDFNHWV FDOLEUDWLRQ IQ RUGHU WR LPSURYH WKH UHSHDWDELOLW\ RI DEVRUSWLRQ PHDVXUHPHQWV WKH IROORZLQJ H[SHULPHQWDO FRQGLWLRQV DUH UHVSHFWHG  :RUNLQJ ZLWK WKH EHVW 6I*1$L12I6( UDWLR DFFRUGLQJ WKH VFHGDVWLF FXUYHV VLJQDOVQHDUDEVRUEDQFHXQLWV DQGLQYHU\QDUURZFRQFHQWUDWLRQLQWHUYDO− ȝJJ ZLWKOLQHDUUHVSRQVHDFFRUGLQJWKH%HHU¶VORZ  RHPRYLQJ  WKH GULIW E\ DVSLUDWLRQ ZDVKLQJ VROXWLRQ EHWZHHQ LQMHFWLRQV DQG DSSOLFDWLRQRIVWDQGDUGVDPSOHVWDQGDUGVHTXHQFH6WBVDPSOHB6W   $XWR]HURSHUIRUPDQFHEHIRUHHYHU\LQMHFWLRQ  $SSO\LQJVLJQDOVPRRWKLQJDQGHQVHPEOHVXPPDWLRQ IQVWUXPHQWDOSDUDPHWHUVDUHGHVFULEHGLQTDEOH 6LJQDOVDUHDFFXPXODWHGLQWKHVDPSOLQJVHW6WBVDPSOHB6W E\SUHFLVHWLPHFRQWURO V DQGDUHVPRRWKHGE\PHDQVRIH[WHUQDOGDWDWUHDWPHQWVRIWZDUH6LJQDOSUR¿OHV DUHVXPPDWHGDVHQVHPEOHVIURP1UHSOLFDWHVRIWKHVDPSOLQJVHWIRUWKH6WVDPSOHDQG 6WUHVSHFWLYHO\DQGIRUHDFKRIWKHPDQHQVHPEOHSVHXGRSODWHDXSUR¿OHLVREWDLQHG TKHVWDEOHSODWHDXSDUWV RIVXPPDWHGHQVHPEOHVLVXVHGIRUFDOLEUDWLRQDQGTXDQWLWDWLYH FDOFXODWLRQV6WDQGDUGXQFHUWDLQW\RIWKHVLJQDOVUHSHDWDELOLW\ZDVFDOFXODWHGDVVWDQGDUG GHYLDWLRQRIDEVRUEDQFHPHDVXUHGLQWKHSODWHDXSDUWV 

28

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

Table 1. Instrumental parameters for ASDI-FAAS determination of Au FAAS parameters

Values

ASDI parameters

Au spectral line [nm] Au spectral slit [nm]

242.8 0.7

Ql- aspiration rate 6.4 mL min-1 checked by BDW Injection time 5 s; Injection volume ≈ 0.530 μL

Au hollow cathode lamp current [mA]

10

Washing time 10 s; Total replicate time 15 s

Air/C2H2 units Observation high [mm]

50/18 6

Smoothing Savitzky-Golay 24 points Ensemble summation N signal profiles

Working range μg g-1 Deuterium BG corrector

37−43 OFF

Pseudo plateau 3 s Sampling mode (St1 _ sample _ St2 ) × N

Readings – points [s]

50

Total time for one set 66 s

29

Practical examples on traceability, measurement uncertainty and validation in chemistry

Calculations Concentration of initial standard solution made up from pure gold C_ Au 999.9 =

m_ pureAu × Au_ purity G _100

× 104

C_ Au 999.9

FRQFHQWUDWLRQRILQLWLDOVWDQGDUGVROXWLRQPDGHXSIURPSXUHJROG>μJJ@

m_ pureAu

PDVVZHLJKHGRISXUHJROG>J@

GB

PDVVRIWKHVROXWLRQLQWKHYROXPHWULFÀDVNPDGHXSWRJZLWK 1+CO>J@

Au− purity

WKHSXULW\RIJROGVWDWHGLQWKHFHUWL¿FDWH>@



FRQYHUVLRQ IDFWRU IURP  WR ȝJ J ȡ §  HTXDOLVHG IRU VWDQGDUG DQG VDPSOHVLQ1+CO

Concentration of calibration standard solutions C _ St1 = C Au _999.9 ×

G _100

C _ St 2 = C Au _999.9 ×

G_0.43 G _100

C _ St1 C _ St 2

CRQFHQWUDWLRQRI$XZRUNLQJVWDQGDUGVROXWLRQV>ȝJJ@ CBStIRUORZȝJJ DQGCBStIRUKLJKȝJJ 

C Au _999.9

CRQFHQWUDWLRQRI$XVWDQGDUGVROXWLRQ$X>ȝJJ@SUHSDUHGIURP SXUHJROG

G_0.37 G_0.43 G_100

30

G_0.37

MDVVHVRIWKHLQLWLDO$XVWDQGDUGVROXWLRQWUDQVIHUUHGIRUWKHSUHSDUDWLRQ RIFDOLEUDWLRQVROXWLRQVCBStȝJJ RUCBStȝJJ >J@JRU JUHVSHFWLYHO\ MDVV RI JUDYLPHWULFDOO\ FRQWUROOHG FDOLEUDWLRQ VWDQGDUG VROXWLRQV DIWHU DGGLQJ1+COLQSRO\SURS\OHQHYLDOV>J@

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

Bracketing calibration Cx =

C− st1 ( A_ St 2 − A _ X ) + C− St 2 ( A− x − A− St1 ) A− St 2 − A− St1

CRQFHQWUDWLRQRI$XLQWKHDQDO\VHGVROXWLRQ>ȝJJ@

Cx

C− St 2

CRQFHQWUDWLRQ RI WKH ORZHU FDOLEUDWLRQ VWDQGDUG VROXWLRQ XVHG IRU EUDFNHWLQJFDOLEUDWLRQ>ȝJJ@ CRQFHQWUDWLRQ RI WKH KLJKHU FDOLEUDWLRQ VWDQGDUG VROXWLRQ XVHG IRU EUDFNHWLQJFDOLEUDWLRQ>ȝJJ@

A− St1

$EVRUEDQFHPHDVXUHGIRUWKHORZHUFDOLEUDWLRQVWDQGDUGVROXWLRQCB6W

A_ St 2

$EVRUEDQFHPHDVXUHGIRUWKHKLJKHUFDOLEUDWLRQVWDQGDUGVROXWLRQCB6W

C− St1

$EVRUEDQFHPHDVXUHGIRUWKHDQDO\VHGVDPSOHVROXWLRQ

A_ X

Calculation of Au mass fraction (W_‰) in analysed sample WBÅ=

1 V_ 50 1 Gvials _12 × × × Cx 1000 m_ 0.1 R GP _ 0, 4

WBÅ

¿QDOFRQFHQWUDWLRQRI$XLQWHVWHGMHZHOOHU\JROGDOOR\ZZ>Å@ YROXPHRIWKHVROXWLRQLQWKHYROXPHWULFÀDVN>PL@

V_ 50

PDVVRIDQDO\VHGDOOR\VDPSOH>J@

m_ 0.1 Gvials _12

ZHLJKWRI¿QDOVDPSOHVROXWLRQSUHSDUHGLQYLDOV>J@

GP _ 0.4

PDVVRI$XVDPSOHVROXWLRQWDNHQIURPVB>J@

R

FRUUHFWLRQIRUUHFRYHU\

Combined model equation for calculation of Au content (‰) WBÅ =

(

)

1 ⎛ V _ 50 Gvials _ 12 ⎞ CAu_999.9 GP _0.37 ( A_ St 2 − A _ X ) + GP _0.43 ( A− X − A− St1 ) 1 × × × × A− St 2 − A− St1 R G_10 1000 ⎜⎝ m _ 0.1 GP _ 0.4 ⎟⎠

31

Practical examples on traceability, measurement uncertainty and validation in chemistry

Calculation of signal standard uncertainty estimated as standard deviation u_ A =

u_ A _ one _ set N

u_ A

u_ A _ one _ set

N

32

FDOFXODWHG VWDQGDUG XQFHUWDLQW\ IURP WKH SODWHDX SDUW  V  RI WKHDEVRUEDQFHVLJQDODIWHUHQVHPEOHDYHUDJLQJRINVHWVRIVDPSOLQJ 6WBVDPSOHB6W FDOFXODWHG VWDQGDUG XQFHUWDLQW\ IURP WKH SODWHDX SDUW  V  RI WKH DEVRUEDQFH VLJQDO REWDLQHG IURP RQH VHW RI VDPSOLQJ 6W B VDPSOH B6W QXPEHURIVHWVSHUIRUPHGDQGVXPPDWHGDVHQVHPEOH

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

PART II. The customer’s requirements concerning quality of the measurement result ([SDQGHGPHDVXUHPHQWXQFHUWDLQW\Åk 

33

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART III. Validation of the measurement procedure – relevant equations and measurement data TKHSURFHGXUHKDVEHHQGHYHORSHGLQWKHODERUDWRU\WKXVDIXOOYDOLGDWLRQPXVWEH SHUIRUPHG +RZHYHUIRUWKHSXUSRVHVRIWKLVH[HUFLVHUHFRYHU\R DQGUHSHDWDELOLW\ZLOOEH FDOFXODWHGRQO\ (TXDWLRQV See Part I MHDVXUHPHQWGDWD Recovery: CXSHOODWLRQPHWKRGÅ $'I)$$6Å Repeatability: Å Å Å Å Å Å

34

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

PART IV. Measurement uncertainty of the result – relevant equations and measurement data CDOFXODWH FRPELQHG DQG H[SDQGHG XQFHUWDLQW\ k    IURP WKH IROORZLQJ PHDVXUHPHQWGDWD Input quantity

Value

Unit

Standard uncertainty

Remark

V_ 50

50

mL

0.0379

Volume of analysed solution

V_100

100

mL

0.0697

Volume of stock standard solution

m_0.1

0.1001

g

0.0002

Mass of analysed alloy sample

Gvials _12

12.0030

g

0.0008

Mass of sample solution prepared in vials

GP _ 0.4

0.4015

g

0.0009

Mass of Au sample solution taken from V_50 flask

m_ pureAu

0.1004

g

0.0002

Mass weighed of pure gold

Au_ purity

99.99

%

0.0058

The purity of gold stated in the certificate

G p _0.37 G p _0.43

0.3701 0.4302

g

0.0006

Masses of the stock Au standard solution transferred for the preparation of calibration solutions C_St1 and C_St2

G_10

10.0321

g

0.0008

Mass of calibration standard solutions

A− St1 A_ St 2

0.5203 0.6041

AU

0.0010 0.0011

Absorbance measured for calibration standard solutions

AX

0.5488

AU

0.0011

Absorbance measured for the analysed sample solution

R

1.002

-

0.0025

Recovery

35

Practical examples on traceability, measurement uncertainty and validation in chemistry

The solved exercises ‘green pages’

TrainMiC Exercises Analytical procedure Determination of gold in jewellery gold alloys by flame atomic absorption spectrometry

EXERCISE 1: Establishing traceability in analytical chemistry EXERCISE 2: Single laboratory validation of measurement procedures Part I: General issues Part II: Parameters to be validated Part III: Some calculations and conclusions

EXERCISE 3: Building an uncertainty budget Addendum I: By spreadsheet approach Addendum II: By dedicated software

36

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

ESTABLISHING TRACEABILITY IN ANALYTICAL CHEMISTRY EXERCISE 1. Specifying the analyte and measurand Analyte

Gold

Measurand

Gold mass fraction in jewellery alloys after aqua regia dissolution

Units

‰ (g/1000 g)

2. Choosing a suitable measurement procedure with associated model equation Measurement procedure Type of calibration

standard addition

standard curve

internal standard

Model equation 1. Standard solutions 1.1. Stock standard solution - prepared from pure gold C Au _999.9 =

m− pureAu × Au_ purity G _100

× 104

1.2. Calibration standard solutions C _ St1 = C Au _999.9 ×

G p_0.37 G_ 100

C _ St 2 = C Au _999.9 ×

G p_0.43 G_ 100

2. Bracketing calibration Cx =

C− St1 ( A_ St 2 − A_ X ) + C− St 2 ( A− x − A− St1 ) A− St 2 − A− St1

3. Calculation of Au content (W_‰) in analysed sample W _0 =

1 V_ 50 Gvials _12 1 × × Cx × 1000 m_ 0.1 GP _ 0.4 R

4. Calculation of signal standard uncertainty u_ A =

u_ A _ one _ set N

37

Practical examples on traceability, measurement uncertainty and validation in chemistry

5. Calculation of recovery R=

Wobserved Wref

6. Combined model equation for calculation of Au mass fraction (‰) WBÅ =

1 ⎛ V_ 50 Gvials _ 12 ⎞ m− pureAu × Au purity × × 104 × × 1000 ⎜⎝ m_ 0.1 GP _ 0.4 ⎟⎠ G_100 × V _100 ×

(G

P _0.37

( A_ St 2 − A _ X ) + GP _0.43 ( A− X − A− St1 ) A− St 2 − A− St1

)× 1

R

V _ 50

YROXPHRIDQDO\VHGVROXWLRQ>PL@

V _100

YROXPHRIVWRFNVWDQGDUGVROXWLRQ>PL@

m_ 0.1

PDVVRIDQDO\VHGDOOR\VDPSOH>J@

Gvials _12

PDVVRIVDPSOHVROXWLRQGLOXWHGLQYLDOV>J@

GP _ 0.4

PDVVRI$XVDPSOHVROXWLRQWDNHQIURPVBÀDVN>J@

m_ pureAu Au_ purity G p _0.37 or G p _0.43 G_100

PDVVZHLJKHGRISXUHJROG>J@ WKHSXULW\RIJROGVWDWHGLQWKHFHUWL¿FDWH>@ PDVVHV RI WKH VWRFN $X VWDQGDUG VROXWLRQ WUDQVIHUUHG IRU WKH SUHSDUDWLRQRIFDOLEUDWLRQVROXWLRQV6WDQG6W>J@ PDVVRIFDOLEUDWLRQVWDQGDUGVROXWLRQV>J@

A− St1 DQG A_ St 2 AX

DEVRUEDQFHPHDVXUHGIRUFDOLEUDWLRQVWDQGDUGVROXWLRQVDQG

R

UHFRYHU\

DEVRUEDQFHPHDVXUHGIRUWKHDQDO\VHGVDPSOHVROXWLRQ

3. List the input quantities according to their influence on the uncertainty of the result of the measurement (first the most important ones). At this point, your judgement should be based on your previous experience only.

38

1

Recovery – 28.5 % to the expanded uncertainty

2

Absorption of analysed gold sample − contributing 19.8 % to the expanded uncertainty

3

Mass of analysed gold sample − contributing 11.8 % to the expanded uncertainty

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

4

Mass of stock solution taken for the preparation of first standard solution − contributing 12.1 % to the expanded uncertainty

5

Volume of the analysed solution – contributing 3.4 % to the expanded uncertainty

4. List the reference standards needed and give also the information regarding traceability of the reference value For the analyte 1

Name/Chemical Formula/Producer:

2

Name/Chemical Formula/Producer:

Pure Gold − certified by Non-Ferrous Metallurgical Plant Plovdiv − Bulgaria

For the other input quantities 1

Quantity/Equipment/Calibration: e.g. mass/balance/calibrated by NMI, U = xx (k = 2), see also data yellow sheet

Balance – calibrated by NMI

2

Quantity/Equipment/Calibration:

Volumetric flask − class A quality

3

Quantity/Equipment/Calibration:

Absorbance − relative measurement. Not direct part of the traceability chain.

5. Estimating uncertainty associated with the measurement Are all important parameters included in the measurement equation?

Yes

Other important parameters are:

Within-lab reproducibility

No

6. How would you prove traceability of your result? 1

Comparing the results with independent method (cupellation)

39

Practical examples on traceability, measurement uncertainty and validation in chemistry

7. Any other comments, questions…

40

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

SINGLE LABORATORY VALIDATION OF MEASUREMENT PROCEDURES EXERCISE

PART I: GENERAL ISSUES 1. Specify the measurement procedure, analyte, measurand and units The measurement procedure

Analysis of gold alloys by AAS

Analyte

Gold

The measurand

Gold in jewellery alloys containing gold 14 ± 0.5 carats after aqua regia dissolution

Unit

‰

2. Specify the Scope Matrix

Gold in 5 % NH4Cl

Measuring range

37-43 μg g-1

3. Requirement on the measurement procedure Intended use of the results:

Quality of products from precious metals alloys LOD LOQ Repeatability

Mark the customer’s requirements and give their values

Within-lab reproducibility Measurement uncertainty

9‰

Trueness Other-state

4. Origin of the measurement procedure VALIDATION New in-house method

Full

Modified validated method

Partial

Official standard method

Confirmation/Verification

41

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART II: PARAMETERS TO BE VALIDATED

5. Selectivity/Interference/Recovery Where yes, please give further information e.g. which CRM, reference method CRM/RM: analysis of available CRM or RM Further information: Spike of pure substance Pure gold 99.99 % certified from non-ferrous metallurgical plant Plovdiv, Bulgaria Compare with a reference method Comparison with cupellation method Selectivity, interferences

Test with different matrices

Other – please specify Test for recovery with RM jewellery gold alloy marked 585

6. Measuring range Linearity Upper limit LOD LOQ

7. Spread – precision Repeatability Reproducibility (within lab) Reproducibility (between lab)

8. Robustness Variation of parameters

42

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

9. Quality control Control charts Participation in PT schemes

10. Other parameters to be tested Working range and testing of homogeneity of variances Recovery Residual standard deviation Standard deviation of the method Coefficient of variation of the method

43

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART III: SOME CALCULATIONS AND CONCLUSIONS

11. Calculation of parameters requested by the customer Parameters requested to be validated

Calculations

LOD LOQ Repeatability

2.4 ‰

Within-lab reproducibilty Trueness Measurement uncertainty

8.3 ‰ (k = 3)

Other - please state Recovery

1.0002 ± 0.0025

12. Does the analytical procedure fulfil the requirement(s) for the intended use? Parameter

(the same as stated in question 3)

Value obtained during validation

The requirement is fulfilled Yes/No

9 ‰ (k = 3)

8.3 ‰ (k = 3)

yes

Value requested by the customer

LOD LOQ Repeatability Within-lab reproducibility Trueness Measurement uncertainty Other

The analytical procedure is fit for the intended use: Yes

No

For measurement uncertainty and traceability refer to the corresponding reportsheets

44

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

BUILDING AN UNCERTAINTY BUDGET EXERCISE 1. Specify the measurand and units Measurand

Gold mass fraction in jewellery alloys after aqua regia dissolution

Unit

‰ (g/1000 g)

2. Describe the measurement procedure and provide the associated model equation Measurement procedure: *ROG DOOR\ VDPSOHV DUH VWUHWFKHG WR IROLR ZLWK − PP WKLFNQHVV TKH VXUIDFH LV ZDVKHG E\   YY +12$ GU\ SLHFH RI  J DFFXUDWHO\ ZHLJKHG WR  J LV GLUHFWO\GLVVROYHGLQWRDYROXPHWULFÀDVNRIPLE\PLIUHVKO\SUHSDUHGaqua regia TKHÀDVNLVKHDWHGRQFHUDPLFKRWSODWHIRUPLQ'XULQJWKLVSURFHVV$JSUHFLSLWDWHV DV$JCO$JCOLVGLVVROYHGE\DGGLQJRIJ1+COWRWKHFRROHGVROXWLRQDQGYROXPH LVPDGHXSWRWKHPDUNPL ZLWK%':DWƒC  TKH VROXWLRQ LV GLOXWHG DGGLWLRQDOO\ E\ WUDQVIHUULQJ  PL ZLWK PLFURSLSHWWH WR D FRQLFDOYLDODGGLQJ1+COLQRUGHUWRNHHSWKHVROXWLRQKRPRJHQHRXVZLWK¿QDO ZHLJKWRIJJUDYLPHWULFDOO\FRQWUROOHG PURFHGXUDO EODQN DQG JROG UHIHUHQFH PDWHULDO DUH VXEMHFW WR H[DFWO\ WKH VDPH VDPSOH SUHSDUDWLRQDQGPHDVXUHPHQWSURFHGXUHVDVWKHDQDO\VHGVDPSOH

Model equation: 1. Concentration of initial standard solution made up from pure gold C Au 999.9 =

m pureAu × Au purity G _100

× 104

C _ St 2 = C Au _999.9 ×

G_0.43 G _100

2. Concentration of calibration standard solutions C _ St1 = C Au _999.9 ×

G_0.37 G _100

3. Bracketing calibration Cx =

C− St1 ( A_ St 2 − A_ X ) + C− St 2 ( A− x − A− St1 ) A− St 2 − A− St1

4. Calculation of Au mass fraction (W_‰) in analysed sample WBÅ =

1 V_ 50 1 Gvials _ 12 × × × Cx 1000 m_ 0.1 R GP _ 0.4

45

Practical examples on traceability, measurement uncertainty and validation in chemistry

5. Calculation of signal standard uncertainty u_ A =

u_ A _ one _ set N

6. Calculation of recovery R=

Wobserved Wref

7. Combined model equation for calculation of Au mass fraction (‰) WBÅ =

(

)

1 ⎛ V _ 50 Gvials _ 12 ⎞ CAu_999.9 GP _0.37 ( A_ St 2 − A _ X ) + GP _0.43 ( A− X − A− St1 ) 1 × × × × A− St 2 − A− St1 R G_100 1000 ⎜⎝ m _ 0.1 GP _ 0.4 ⎟⎠

3. Identify (all possible) sources of uncertainty Uncertainty of concentration of reference solutions Uncertainty of measurements of absorption of standard and sample solutions Mass of analysed gold sample Volume of the analysed solution Recovery Other: Other:

4. Evaluate values of each input quantity

46

Input quantity

Value

Unit

Remark

V _ 50

50

mL

Volume of analysed solution

V _100

100

mL

Volume of stock standard solution

m_ 0.1

0.1001

g

Mass of analysed alloy sample

Gvials _12

12.0030

g

Mass of sample solution prepared in vials

GP _ 0.4

0.4015

g

Mass of Au sample solution taken from V_50 flask

m− pureAu

0.1004

g

Mass weighed of pure gold

Au_ purity

99.99

%

The purity of gold stated in the certificate

G p _0.37 ; G p _0.43

0.3701; 0.4302

g

Masses of the stock Au standard solution transferred for the preparation of calibration solutions C_St1 and C_St2

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

G_100

10.0321

AU

A− St1 ; A_ St 2

0.5203; 0.6041

AU

AX

0.5488

AU

R

1.002

-

Mass of calibration standard solutions Absorbance measured for calibration standard solutions Absorbance measured for the analysed sample solution Recovery

5. Evaluate the standard uncertainty of each input quantity Input quantity

Standard uncertainty

Unit

Remark

V _ 50

0.0379

mL

Volume of analysed solution

V _100

0.0697

mL

Volume of stock standard solution

m_ 0.1

0.0002

g

Mass of analysed alloy sample

Gvials _12

0.0008

g

Mass of sample solution prepared in vials

GP _ 0.4

0.0009

g

Mass of Au sample solution taken from V_50 flask

m− pureAu

0.0002

g

Mass weighed of pure gold

Au_ purity

0.0058

%

The purity of gold stated in the certificate

G p _0.37 ; G p _0.43

0.0006; 0.0006

g

Masses of the stock Au standard solution transferred for the preparation of calibration solutions C_St1 and C_St2

G_10

0.0008

g

Mass of calibration standard solutions

A− St1 ; A_ St 2

0.0010; 0.0011

AU

AX

0.0011

AU

R

0.0025

Absorbance measured for calibration standard solutions Absorbance measured for the analysed sample solution Recovery

6. Calculate the value of the measurand, using the model equation Å

7. Calculate the combined standard uncertainty (uc) of the result and specify units Using:

MDWKHPDWLFDOVROXWLRQ

6SUHDGVKHHWDSSURDFK

CRPPHUFLDOVRIWZDUH

47

Practical examples on traceability, measurement uncertainty and validation in chemistry

Input quantity

Value

Standard uncertainty

Unit

Remark

W_‰

583.5

2.8

‰

Au mass fraction in jewellery alloys

8. Calculate expanded uncertainty (Uc) and specify the coverage factor k and the units Åk 

9. Analyse the uncertainty contribution and specify the main three input quantities contributing the most to Uc 1

Recovery – contributing 37.6 % to the expanded uncertainty

2

Absorption of analysed gold sample − contributing 26.1 % to the expanded uncertainty

3

Mass of analysed gold sample − contributing 14.9 % to the expanded uncertainty

10. Prepare your uncertainty budget report “ Åk   WKHUHSRUWHGXQFHUWDLQW\LVDQH[SDQGHGXQFHUWDLQW\FDOFXODWHGXVLQJDFRYHUDJHIDFWRURI k ZKLFKJLYHVDOHYHORIFRQ¿GHQFHRIDSSUR[LPDWHO\

48

Analysis of Gold Alloys by Flame Atomic Absorption Spectrometry

Further readings

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Practical examples on traceability, measurement uncertainty and validation in chemistry

Addendum I. Measurement uncertainty calculation: spreadsheet approach (Excel)

Chapter 2

Determination of Calcium in Serum by Spectrophotometry Steluta Duta, Philip Taylor u u u u

TrainMiC example summary form (‘blue page’) A short introduction to the analytical procedure (‘slides’) All input needed to do the three exercises (‘yellow pages’) The solved exercises (‘green pages’) 51

Practical examples on traceability, measurement uncertainty and validation in chemistry

TrainMiC example summary form

I. General information about the example

52

Measurand

Concentration of calcium in human serum (mg dL-1)

Example number

Ex-10

Authors of the example

Steluta Duta, Philip Taylor

Analytical procedure

Standard WHO procedure

Customer’s requirement

Standard WHO procedure

Determination of Calcium in Serum by Spectrophotometry

II. Attached files

3 - Green

2 - Yellow

1-I

File number, type and name Ex-10-1-ICa-serumPhotometry2006-Ver1.ppt

Ex-10-2-YCa-serumPhotometry2006-Ver1.doc

Ex-10-3-GCa-serumPhotometry2006-Ver1.doc

File is attached Yes No

Content of the file

About the analytical procedure: short introduction

9

PART I

Description of the analytical procedure

9

PART II

The customer’s requirements concerning the quality of the measurement result

9

PART III

Validation of the measurement procedure – relevant equations and measurement data

9

PART IV

Measurement uncertainty of the result – relevant equations and measurement data

9

PART I

Establishing traceability in analytical chemistry

9

PART II

Single laboratory validation of measurement procedures

9

Bulding an uncertainty budget

9

Addendum 1: By spreadsheet approach

9

PART III

Addendum 2: By dedicated software

Remark

Given by the lecturer

Each participant receives own copy and may keep it

9

III. History of the example Version

Uploaded on the webhotel

0

April 2007

Short description of the change

1

53

Practical examples on traceability, measurement uncertainty and validation in chemistry

A short introduction to the analytical procedure

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54

Analysis of GoldofAlloys Determination Calcium by Flame in Serum Atomic by Spectrophotometry Absorption Spectrometry

([SHULPHQWDOSURWRFRO SUHSDUHEXIIHUUHDJHQWVS+  DQG FRORXUUHDJHQWV SUHSDUH&DVWRFN VROXWLRQÎ FDOLEUDQWV 6DPSOH VHUXPQRVDPSOHWUHDWPHQW  0,;ZDWHUVWGFRORXU UHDJ VDPSOH LQFXEDWHDWƒ&IRUPLQ &DOLEUDWLRQFKHFNOLQHDULW\ EODQNWR]HUR LQWHUSRODWLRQÎ 2QHSRLQWFDOLEUDWLRQ FKHFN4& EHWZHHQGD\VSUHFLVLRQ

55

Practical examples on traceability, measurement uncertainty and validation in chemistry

All input needed to do the three exercises ‘yellow pages’

Analytical procedure Determination of concentration of calcium in serum by molecular absorption spectrometry. The quality of the results should comply with the requirements in the WHO procedure

PART I ...................................................................................................................................57 Description of the analytical procedure PART II .................................................................................................................................60 The customer’s requirements concerning the quality of the measurement result PART III ................................................................................................................................61 Validation of the measurement procedure – relevant equations and measurement data PART IV ................................................................................................................................62 Measurement uncertainty of the result – relevant equations and measurement data

56

Determination of Calcium in Serum by Spectrophotometry

PART I. Description of the analytical procedure

Laboratory task COLQLFDO ODERUDWRU\ KDV WR GHWHUPLQH FDOFLXP FRQFHQWUDWLRQ LQ KXPDQ VHUXP VDPSOH DULYLQJLQWKHLUODERUDWRU\IWLVWKHFDVHZKHQRQO\WKHDQDOLWLFDOSDUWLVFRQVLGHUHGWKH ODERUDWRU\KDVQRWUHVSRQVLELOLW\KRZVDPSOHLVWDNHQSUHSDUHGWUDQVSRUWHG TKH ODERUDWRU\ VKRXOG HYDOXDWH WKH DQDO\WLFDO SURFHGXUH UHOLDELOLW\ ZLWKLQ ODERUDWRU\ UHSURGXFLELOLW\ TKHUHSRUWHGUHVXOWVVKRXOGFRPSO\ZLWKWKHFOLQLFDOLQWHUSUHWDWLRQWKH H[SHFWHGQRUPDOUDQJHRIFDOFLXPFRQFHQWUDWLRQLQVHUXPLV±PJGL

Principle of the measurement method TH[WH[WUDFWIURP:RUOG+HDOWK2UJDQL]DWLRQ:+2 −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

Analytical procedure Serum sample preparation and storage 1RVHUXPSUHSDUDWLRQLVSHUIRUPHGE\WKHODERUDWRU\LQFKDUJHZLWKWKHDQDO\WLFDOZRUN 6HUXP VDPSOH DULYHV LQ WKH ODERUDWRU\ DIWHU VHSDUDWLRQ IURP WKH EORRG FHOOV GXULQJ WKHSUHDQDO\WLFDOVWHSSHUIRUPHGE\DQRWKHUGHSDUWPHQW+DHPRO\VHGDQGKHSDULQLVHG VDPSOHVDUHXQVXLWDEOHIRUWKLVPHWKRG CDOFLXPLQVHUXPLVVWDEOHIRUKDWURRPWHPSHUDWXUH−°C RQHZHHNDW−°C DQGIRUDORQJHUSHULRGXSWRPRQWKVDW−°C

Reagents $MP%XIIHUS+ IQPLRI$MPUHDJHQWDGGPLRIGLVWLOOHGZDWHUDQGPL[$GMXVWWKHS+WR ZLWK+CO1DQGPDNHXSWRPLZLWKGLVWLOOHGZDWHU6WRUHLQWKHUHIULJHUDWRULQD EURZQFRORXUHGJODVVERWWOH6WDEOHIRUWKUHHZHHNV

57

Practical examples on traceability, measurement uncertainty and validation in chemistry

CRORXUUHDJHQWV $GG  PL FRQFHQWUDWHG +CO WR D  PL YROXPHWULF ÀDVN FRQWDLQLQJ DERXW  PL RIGLVWLOOHGZDWHUTUDQVIHUPJ2FUHVROSKWKDOHLQFRPSOH[RQHSRZHULQWRLWPL[WR GLVVROYHTKHQDGGPJRIK\GUR[\TXLQROLQHGLVVROYHDQGWKDQPDNHXSWR PLZLWKGLVWLOOHGZDWHU6WRUHLQDEURZQFRORXUHGJODVVERWWOHDWURRPWHPSHUDWXUH− °C 6WDEOHIRUDERXWRQHPRQWK CDOFLXPVWDQGDUGVROXWLRQV Stock calcium standard solution CDOFLXPFDUERQDWHLVGULHGDW°CIRUK$OORZWRFRROLQDGHVLFDWRU'LVVROYH PJRIGULHGFDOFLXPFDUERQDWHLQPLRIGLVWLOOHGZDWHUWDNHQLQDPLYROXPHWULF ÀDVNDQGDGGPL+COFRQFML[WRGLVVROYHDQGPDNHXSWRPLZLWKGLVWLOOHG ZDWHU6WRUHLQEURZQERWWOHDWURRPWHPSHUDWXUH−°C 6WDEOHIRUPRQWKVTKH FDOFLXPFRQFHQWUDWLRQLQWKLVVROXWLRQLVPJGL Calibration calcium standard solutions TKH FDOLEUDWLRQ FDOFLXP VWDQGDUG VROXWLRQV DUH SUHSDUHG E\ GLOXWLRQ RI VWRFN FDOFLXP VWDQGDUGVROXWLRQLQWRIRXUPLYROXPHWULFÀDVNVWUDQVIHUDQGPLRI VWRFNFDOFLXPVWDQGDUGVROXWLRQDQGGLOXWHHDFKWRPLZLWKEHQ]RLFDFLGTKHZRUNLQJ VWDQGDUGVFRQWDLQ666DQG6PJGLFDOFLXPUHVSHFWLYHO\ 6WRUHLQEURZQERWWOHVDWURRPWHPSHUDWXUH−°C 6WDEOHIRUPRQWKV

Instrumentation $SKRWRPHWHURUVSHFWURSKRWRPHWHULVXVHGLQWKHYLVLEOHUDQJHLQWH[WLWLVFDOOHGVSHFWUR SKRWRPHWHUTKH LQVWUXPHQWDO SHUIRUPDQFHV VSHFWUDO UDQJH − QP DEVRUEDQFH DFFXUDF\DW$TKHLQVWUXPHQWKDVWKHDEVRUEDQFHVFDOHDVDFRQFHTXHQFHIRU FRQFHQWUDWLRQPHDVXUHPHQWVWKHFDOLEUDWLRQJUDSKVKRXOGEHHVWDEOLVKHGE\ODERUDWRU\ LWVHOI

Experimental protocol TKHH[SHULPHQWDOVWHSVRIWKHPHDVXUHPHQWSURFHGXUHDUHGHVFULEHGLQWKHWDEOHEHOORZ DGH¿QHGYROXPHVRIFDOLEUDWLRQVROXWLRQVDQGVHUXPVDPSOHPL DUHPL[HGZLWK PLRIFRORXUUHDJHQWML[HGWKDQZLWKPLRIEXIIHUVROXWLRQ

58

Blank

S5

S7.5

S10

S12.5

Serum

QC

Distilled water (mL)

0.1

-

-

-

-

-

-

Standard (mL)

-

0.1

0.1

0.1

0.1

-

-

Serum/QC (mL)

-

-

-

-

-

0.1

0.1

Determination of Calcium in Serum by Spectrophotometry

Colour reagent (mL)

Buffer solution (mL)

2.0

2.0

2.0

2.0

Mix

well

2.0

2.0

Mix

well

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

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Calculation of result TKHIROORZLQJHTXDWLRQLVLQGLFDWHGLQ:+2SURFHGXUH cCa = ( Ax A−10 ) × 10 >PJGL@

ZKHUHcCD−FRQFHQWDWLRQRIFDOFLXPLQVHUXPVDPSOH  Ax−DEVRUEDQFHRIVHUXPVDPSOH A−−DEVRUEDQFHRIWKHFDOLEUDWLRQVROXWLRQPJGL

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59

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART II. The customer’s requirements concerning quality of the measurement result according to WHO* Clinical interpretation:1 CDOFLXPFRQFHQWUDWLRQLQVHUXP−PJGL−QRUPDOUDQJH CDOFLXPFRQFHQWUDWLRQLQVHUXP−PJGL−SDWKRORJLFDOUDQJH



:RUOG+HDOWK2UJDQL]DWLRQ

60

Determination of Calcium in Serum by Spectrophotometry

PART III. Validation of the measurement procedure – relevant equations and measurement data Within-laboratory reproducibility (between day precision) Model equation CRHI¿FLHQWRIYDULDWLRQC9 5

∑ (c

i , obs

1

CV =

− cQC

)

2

n ( n − 1)

× 100

cQC

CV

FRHI¿FLHQWDVYDULDWLRQ>@

cREV

REVHUYHGFDOFLXPFRQFHQWUDWLRQLQQCVHUXPLQiWKGD\i − >PJGL@

cQC

WDUJHWFDOFLXPFRQFHQWUDWLRQLQQCVHUXP>PJGL@

n

QXPEHURIUHSURGXFLEOHPHDVXUHPHQWV

Measurement data Input quantity

Value ± standard deviation (3 replicates) 1st day:

ci,obs (i = 1−5) day 3 replicates/day

8.990 ± 0.057

rd

3 day:

9.210 ± 0.105

4th day:

9.230 ± 0.086

5th day:

9.110 ± 0.120

cQC

8.24−10.52

n

5

Unit

9.16 ± 0.05

mg dL-1

9.280 ± 0.021

nd

2 day:

Mean value ± standard deviation

9.38 ± 0.38

mg dL-1 no units

CV = 

61

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART IV. Measurement uncertainty of the result: relevant equations and measurement data2 IV.1. Preparation of standard solutions2 IV.1.1 Preparation of calcium stock standard solution, cstock

(

cstock = ( m × M Ca × P ) × 100 / V500 × M CaCO3

)

cVWRFN

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m

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MCD

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V

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MCDC2

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MHDVXUHPHQWGDWD Input quantity

Value

Standard uncertainty

Unit

m

625.0

0.2

mg

MCa

40.078

0.002

g mol-1

P

0.9999

0.0058

mass fraction

V500

500.00

0.15

mL

MCaCO3

100.0869

0.0024

g mol-1

IV.1.2 Preparation of calibration standard solutions, ci: ⎛ V ⎞ ci = cstock × ⎜ i ⎟ ⎝ V100 ⎠

cVWRFN

CRQFHQWUDWLRQRIFDOFLXPVWRFNVROXWLRQ>PJGL@

Vi

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V

9ROXPHRIFDOLEUDWLRQVROXWLRQ>PL@

ZKHUH Vi VVVVFRUUHVSRQGLQJWRci = cccc

+HUH\RXPD\DOVRZDQWWRLQFOXGHWKHUHOHYDQWFHUWL¿FDWHV



62

Determination of Calcium in Serum by Spectrophotometry

MHDVXUHPHQWGDWD Input quantity

Value

Standard uncertainty

Unit

cstock

50.05

0.02

mg dL-1

Vi

20.000

0.043

mL

V100

100.000

0.058

mL

IV.2 Calibration – one point calibration MRGHOHTXDWLRQc±WKHSRLQWRIFDOLEUDWLRQVWDQGDUGVROXWLRQ 

(

)

cx = c−10 Ax − Ablank / ( A−10 − Ablank )

cx c Ax A AEODQN

CRQFHQWUDWLRQRIVHUXPVDPSOHIURPFDOLEUDWLRQGDWD>PJGL@ CRQFHQWUDWLRQRIFDOFLXPFDOLEUDWLRQVROXWLRQPJGL >PJGL@ $EVRUEDQFHFRUUHVSRQGLQJWRVHUXPVDPSOH $EVRUEDQFHFRUUHVSRQGLQJWRFDOLEUDWLRQVROXWLRQPJGL $EVRUEDQFHFRUUHVSRQGLQJWREODQNVROXWLRQ

MHDVXUHPHQWGDWD Input quantity

Value

Standard uncertainty

Unit

c_10

10.000

0.023

mg dL-1

Ax

0.323

0.004

no units

A-10

0.338

0.002

no units

Ablank

0.052

0.004

no units

IV.3 Calculation of calcium concentration in serum sample cCD V ⎛ ⎞ c cCa = cx × ⎜ f V ⎟ x ⎝ int ⎠ VI VLQW

FDOFLXPFRQFHQWUDWLRQLQVHUXPVDPSOH>PJGL@ FRQFHQWUDWLRQRIVHUXPVDPSOHIURPFDOLEUDWLRQGDWD>PJGL@ YROXPHRIVHUXPVDPSOHXQGHULQYHVWLJDWLRQ>PL@ LQWDNHYROXPHIURPVHUXPVDPSOH>PL@

MHDVXUHPHQWGDWD Input quantity

Value

Standard uncertainty

Unit

cx

9.486

0.303

mg dL-1

Vf

0.100

0.002

mL

Vint

0.100

0.002

mL

63

Practical examples on traceability, measurement uncertainty and validation in chemistry

The solved exercises ‘green pages’

TrainMiC Exercises Analytical procedure Determination of calcium concentration in human serum by molecular absorbtion (spectro)photometry The quality of results should comply with WHO procedure requirements

EXERCISE 1: Establishing traceability in analytical chemistry EXERCISE 2: Single laboratory validation of measurement procedures Part I: General issues Part II: Parameters to be validated Part III: Some calculations and conclusions

EXERCISE 3: Building an uncertainty budget Addendum I: By spreadsheet approach Addendum II: By dedicated software

64

Determination of Calcium in Serum by Spectrophotometry

ESTABLISHING TRACEABILITY IN ANALYTICAL CHEMISTRY

1. Specifying the analyte and measurand Analyte

Calcium

Measurand

Total concentration of calcium in human serum

Units

mg dL-1

2. Choosing a suitable measurement procedure with associated model equation Measurement procedure

To determine the calcium concentration in human serum, a serum sub-sample is mixed with reagent colour and buffer solution, according to WHO standard operation procedure. The absorbance of calcium calibration solutions and serum sample are measured by visible spectrophotometry at 540 nm. From the calibration data the concentration of calcium in human serum is calculated.

Type of calibration

standard curve

standard addition

internal standard

Model equation: calcium concentration in serum ⎛V ⎞ cCa = ⎡⎣( m × M Ca × P ) × 100 / V500 × M CaCO3 ⎤⎦ × (Vi / V100 ) × ⎡⎣( Ax − Ablank ) / ( A−10 − Ablank )⎤⎦ × ⎜ f V ⎟ ⎝ int ⎠

(

)

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Practical examples on traceability, measurement uncertainty and validation in chemistry

3. List the input quantities according to their influence on the uncertainty of the result of the measurement (first the most important ones). At this point, your judgement should be based on your previous experience only. 1

Matrix effect - recovery

2

Instrumental signal (absorbance)

3

Concentration of standard solutions - purity of CaCO3

4

Volume of the glassware (pipettes, volumetric flasks)

5

Mass

4. List the reference standards needed and state the information regarding traceability of the reference value For the analyte 1

Name/Chemical Formula/Producer:

CaCO3 purity, Merck, min. 99.99 %

2

Name/Chemical Formula/Producer:

CaCO3 molar masses/IUPAC

For the other input quantities 1

Quantity/Equipment/Calibration: e.g. mass/balance/calibrated by NMI, U = xx (k = 2), see also data yellow sheet

Absorbance/(Spectro)photometer/Calibrated against traceable optical standard (i.e. PTB)

2

Quantity/Equipment/Calibration:

Volume/Laboratory glassware (pipettes, volumetric flasks/calibrated by manufacturer (i.e. Hirschmann Laborgerate )

3

Quantity/Equipment/Calibration:

Mass/Analytical balance/calibrated by manufacturer against traceable mass standards

5. Estimating uncertainty associated with the measurement

66

Are all important parameters included in the model equation?

Yes

Other important parameters are:

Matrix effect

No

Determination of Calcium in Serum by Spectrophotometry

6. How would you prove traceability of your result? 1

Via traceable calibration data

2

Via traceable volumetric measurements

3

Via traceable mass measurements

7. Any other comments, questions…

67

Practical examples on traceability, measurement uncertainty and validation in chemistry

SINGLE LABORATORY VALIDATION OF MEASUREMENT PROCEDURES PART I: GENERAL ISSUES 1. Specify the measurement procedure, analyte, measurand and units

The measurement procedure

To determine the calcium concentration in human serum, a serum sub-sample is mixed with reagent colour and buffer solution, according to WHO standard operation procedure. The absorbance of calcium calibration solutions and serum sample are measured by visible spectrophotometry at 540 nm. From the calibration data the concentration of calcium in human serum is calculated.

Analyte

Calcium

The measurand

Total calcium concentration in human serum

Unit

mg dL-1

2. Specify the scope Matrix

Human serum

Measuring range

1.0−12.0 mg dL-1

3. Requirement on the measurement procedure Intended use of the results

Calcium concentration in serum result is intended to be used for clinical interpretation Parameters to be validated

Value requested by the customer

LOD LOQ Repeatability Mark the customer’s requirements and give their values

Within-lab reproducibility Trueness Measurement uncertainty Other-state

68

8 % as CV, by WHO procedure 2 % as CV, the actual state-of-art

Determination of Calcium in Serum by Spectrophotometry

4. Origin of the measurement procedure VALIDATION New in-house method

Full

Modified validated method

Partial

Official standard method

Confirmation/Verification

69

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART II: PARAMETERS TO BE VALIDATED

5. Selectivity/Interference/Recovery Where yes, please give further information e.g. which CRM, reference method CRM/RM: analysis of available CRM or RM Further information: ROCHE-Control serum type Precipath U Spike of pure substance

Compare with a reference method

Selectivity, interferences

Test with different matrices

Other – please specify

6. Measuring range Linearity Upper limit LOD LOQ

7. Spread – precision Repeatability Reproducibility (within lab) Reproducibility (between lab)

8. Robustness Variation of parameters

70

Determination of Calcium in Serum by Spectrophotometry

9. Quality control Control charts Participation in PT schemes

10. Other parameters to be tested Working range and testing of homogeneity of variances R squared Residual standard deviation Standard deviation of the analytical procedure Coefficient of variation of the analytical procedure Measurement uncertainty

71

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART III: SOME CALCULATIONS AND CONCLUSIONS

11. Calculation of parameters requested by the customer Parameters requested to be validated

Calculations

LOD LOQ Repeatability 5

∑ (c

i , obs

1

Within-lab reproducibilty

CV =

− cQC

)

2

n ( n − 1) cQC

× 100 = 1.27 %

Trueness Measurement uncertainty Other - please state

12. Does the analytical procedure fulfil the requirement(s) for the intended use? Parameter

Value requested by the customer (the same as stated in question 3)

Value obtained during validation

The requirement is fulfilled Yes/No

1.27 %

YES

LOD LOQ Repeatability Within-lab reproducibility

8 % as CV, by WHO procedure 2% as CV, the actual state-of-art

Trueness Measurement uncertainty Other

The analytical procedure is fit for the intended use: Yes

No

For measurement uncertainty and traceability refer to the corresponding sheets 72

Determination of Calcium in Serum by Spectrophotometry

BUILDING AN UNCERTAINTY BUDGET

1. Specify the measurand and units Measurand

Total calcium concentration in human serum

Unit

mg dL-1

2. Describe the measurement procedure and provide the associated model equation Measurement procedure TRGHWHUPLQHWKHFDOFLXPFRQFHQWUDWLRQLQKXPDQVHUXPDVHUXPVXEVDPSOHLVPL[HG ZLWKUHDJHQWFRORXUDQGEXIIHUVROXWLRQDFFRUGLQJWR:+2VWDQGDUGRSHUDWLRQSURFHGXUH TKH DEVRUEDQFH RI FDOFLXP FDOLEUDWLRQ VROXWLRQV DQG VHUXP VDPSOH DUH PHDVXUHG E\ YLVLEOH VSHFWURSKRWRPHWU\ DW  QP )URP WKH FDOLEUDWLRQ GDWD WKH FRQFHQWUDWLRQ RI FDOFLXPLQKXPDQVHUXPLVFDOFXODWHG

Model equation: calcium concentration in serum ⎛V ⎞ cCa = ⎡⎣( m × M Ca × P ) × 100 / V500 × M CaCO3 ⎤⎦ × (Vi / V100 ) × ⎡⎣( Ax − Ablank ) / ( A−10 − Ablank )⎤⎦ × ⎜ f V ⎟ ⎝ int ⎠

(

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Practical examples on traceability, measurement uncertainty and validation in chemistry

3. Identify (all possible) sources of uncertainty Uncertainty of concentration of reference solutions Uncertainty of measurements of peak area Method bias Matrix effect Other: Uncertainty of absorbance measurements Other: Uncertainty of volume measurements

4. Evaluate values of each input quantity Input quantity

Value

Unit

m

625.0

mg

MCa

40.078

g mol-1

P

0.9999

mass fraction

V500

500.00

mL

MCaCO3

100.0869

g mol-1

Vi

20.000

mL

V100

100.000

mL

Ax

0.323

no units

A-10

0.338

no units

Ablank

0.052

no units

Vf

0.100

mL

Vint

0.100

mL

Remark

5. Evaluate the standard uncertainty of each input quantity

74

Input quantity

Standard uncertainty

Unit

m

0.2

mg

MCa

0.002

g mol-1

P

0.0058

mass fraction

V500

0.15

mL

MCaCO3

0.0024

g mol-1

Remark

Determination of Calcium in Serum by Spectrophotometry

Vi

0.043

mL

V100

0.058

mL

Ax

0.004

no units

A-10

0.002

no units

Ablank

0.004

no units

Vf

0.002

mL

Vint

0.002

mL

6. Calculate the value of the measurand, using the model equation ⎛V ⎞ cCa = ⎡⎣( m × M Ca × P ) × 100 / V500 × M CaCO3 ⎤⎦ × (Vi / V100 ) × ⎡⎣( Ax − Ablank ) / ( A−10 − Ablank )⎤⎦ × ⎜ f V ⎟ ⎝ int ⎠

(

)

cCD PJGL

7. Calculate the combined standard uncertainty (uc) of the result and specify units Using:

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Input quantity

Value

Standard uncertainty

Unit

m

625.0

0.2

mg

MCa

40.078

0.002

g mol-1

P

0.9999

0.0058

mass fraction

V500

500.00

0.15

mL

MCaCO3

100.0869

0.0024

g mol-1

Vi

20.000

0.043

mL

V100

100.000

0.058

mL

Ax

0.323

0.004

no units

A-10

0.338

0.002

no units

Ablank

0.052

0.004

no units

Vf

0.100

0.002

mL

Vint

0.100

0.002

mL

CRPPHUFLDOVRIWZDUH

Remark

ucCD  PJPRO

75

Practical examples on traceability, measurement uncertainty and validation in chemistry

8. Calculate expanded uncertainty (Uc) and specify the coverage factor k and the units U(cCa) = k u (cCa) = 0.606 [mg dL-1], k = 2

9. Analyse the uncertainty contribution and specify the main three input quantities contributing the most to Uc 1

Volume serum measurements

2

Concentration of serum sample from calibration data

10. Prepare your uncertainty budget report

76

Determination of Calcium in Serum by Spectrophotometry

Further readings

 Guide to the Expression of Uncertainty in Measurement *8M  VW HG   *HQHYH6ZLW]HUODQG  EurachemCitac Guide C* Qualtifying Uncertainty in Analytical Measurement QGHG   6WDQGDUG RSHUDWLRQ SURFHGXUH IRU COLQLFDO FKHPLVWU\ 'HWHUPLQDWLRQ RI FDOFLXP E\ FDOFLXPRFUHVROSKWDOHLQFRPSOH[RQHPHWKRGKWWSZZKRVHRUJ  6 LLQNR 8 gUQHPDUN DQG R .HVVHO (YDOXDWLRQ RI PHDVXUHPHQW XQFHUWDLQW\ LQ FOLQLFDOFKHPLVWU\*(RIMIRMM  -.UDJWHQCDOFXODWLQJVWDQGDUGGHYLDWLRQVDQGFRQ¿GHQFHLQWHUYDOVZLWKDXQLYHUVDOO\ DSSOLFDEOHVSUHDGVKHHWWHFKQLTXHAnalyst −

77

Practical examples on traceability, measurement uncertainty and validation in chemistry

Addendum I: Measurement uncertainty calculation: spreadsheet approach (Excel) Preparation of the standard solution

78

Determination of Calcium in Serum by Spectrophotometry

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Practical examples on traceability, measurement uncertainty and validation in chemistry

Calibration

Calculation of calcium concentration in serum sample 

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Chapter 3

Determination of Radium in Water by a-Spectrometry Ljudmila Benedik, Urška Repinc, Monika Inkret u u u u

TrainMiC example summary form (‘blue page’) A short introduction to the analytical procedure (‘slides’) All input needed to do the three exercises (‘yellow pages’) The solved exercises (‘green pages’) 81

Practical examples on traceability, measurement uncertainty and validation in chemistry

TrainMiC example summary form

I. General information about the example

82

Measurand

Activity concentration of Ra-226 in water (Bq L-1) (by α-spectrometry)

Example number

Ex-08

Authors of the example

Ljudmila Benedik, Urška Repinc, Monika Inkret

Analytical procedure

Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometric sources J.C. Lozano, F. Fernandez and J.M.G. Gomez, Journal of Radioanalytical and Nuclear Chemistry 223 (1997) 1−2, 133−137

Customer’s requirement

Directive 98/83/EC on the quality of water intended for human consumption

Determination of Radium in Water by α-Spectrometry

II. Attached files

1-I

File number, type and name EX-08-1-I-Ra226-waterAS-2006-Ver1.ppt

Content of the file About the analytical procedure: short introduction

2 - Yellow

PART I

PART II EX-08-2-Y-Ra226-waterAS-2006-Ver1.doc PART III

3 - Green

PART IV

Description of the analytical procedure The customer’s requirements concerning the quality of the measurement result Validation of the measurement procedure – relevant equations and measurement data Measurement uncertainty of the result – relevant equations and measurement data

File is attached Yes No

9 9 9 9

Establishing traceability in analytical chemistry

9

PART II

Single laboratory validation of measurement procedures

9

Building an uncertainty budget

9

Addendum 1: By spreadsheet approach Addendum 2: By dedicated software

9

PART III

Given by the lecturer Each participant receives own copy and may keep it

9

PART I

EX-08-3-G-Ra226-waterAS-2006-Ver1.doc

Remark

9

III. History of the example Version

Uploaded on the webhotel

0

April 2007

Short description of the change

1

83

Practical examples on traceability, measurement uncertainty and validation in chemistry

A short introduction to the analytical procedure

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Analysis of GoldofAlloys by in Flame Atomic Absorption Spectrometry Determination Radium Water by α-Spectrometry

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Analysis of GoldofAlloys by in Flame Atomic Absorption Spectrometry Determination Radium Water by α-Spectrometry

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All input needed to do the three exercises ‘yellow pages’

Analytical procedure Determination of activity concentration of Ra-226 in drinking water. The quality of the results should comply with the requirements in the revised Directive 98/83/EC on the quality of water intended for human consumption

PART I ..................................................................................................................... 89 Description of the analytical procedure PART II .................................................................................................................... 96 The customer’s requirements concerning the quality of the measurement result PART III ................................................................................................................... 97 Validation of the measurement procedure – relevant equations and measurement data PART IV ................................................................................................................... 98 Measurement uncertainty of the result – relevant equations and measurement data

88

Determination of Radium in Water by α-Spectrometry

PART I. Description of the analytical procedure

)RUWKHGHWHUPLQDWLRQRIRDLQZDWHUWKHIROORZLQJSXEOLVKHGSURFHGXUHLVXVHG Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometric sources -CLR]DQR))HUQDQGH]DQG-M**RPH] -RXUQDORIRDGLRDQDO\WLFDODQG1XFOHDUCKHPLVWU\223 −−

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Practical examples on traceability, measurement uncertainty and validation in chemistry

Figure 4. Experimental protocol for determination Ra-226 in water

3. Apparatus             

90

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Determination of Radium in Water by α-Spectrometry

4. Reagents              

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×

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9.2 Alpha spectrometer efficiency determination İĮGHW RRD6WG PRD6WG tRD6WG mRD66 ARD66

94

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Determination of Radium in Water by α-Spectrometry

9.3 Activity concentration of Ra-226 in the sample (Bq L-1) A Ra-226

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× eα det

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Practical examples on traceability, measurement uncertainty and validation in chemistry

PART II. The customer’s requirements concerning quality of the measurement result Extract from the Directive 98/83/EC, Draft annex 2005/04/20 on the quality of water intended for human consumption Reference concentration for radioactivity in drinking water* Origin

Nuclide

Reference concentration

Natural

Ra-226

0.5 Bq L-1

 This table includes the most common natural and arti¿cial radionuclide Reference concentrations for other radionuclides can be calculated using the dose coef¿cients for adults laid down in Annex III Table A of Directive 96/29/Euratom or more recent information recognised by the competent authorities in the Member State, and by assuming an intake of 730 litres per year.

Performance characteristics and methods of analysis )RU WKH IROORZLQJ UDGLRDFWLYLW\ SDUDPHWHUV WKH VSHFL¿HG SHUIRUPDQFH FKDUDFWHULVWLFV DUH WKDW WKH PHWKRG RI DQDO\VLV XVHG PXVW DV D PLQLPXP EH FDSDEOH RI PHDVXULQJ FRQFHQWUDWLRQVHTXDOWRWKHSDUDPHWULFYDOXHZLWKDOLPLWRIGHWHFWLRQVSHFL¿HG Parameter

Limit of detection

Notes

Ra-226

0.04 Bq L-1

Note 1 Note 2

Note 1: the limit of detection should be calculated according to ISO 11929-7, Determination of the detection limit and decision thresholds for ionizing radiation measurements - Part 7: Fundamentals and general applications, with probabilities of errors of 1st and 2nd kind of 0.05 each Note 2: measurement uncertainties should be calculated and reported as complete standard uncertainties, or as expanded standard uncertainties with an expansion factor of 1.96, according to the ISO Guide for the Expression of Uncertainty in Measurement (ISO, Geneva 1993, corrected reprint Geneva, 1995)

96

Determination of Radium in Water by α-Spectrometry

PART III. Validation of the measurement procedure – relevant equations and measurement data IQ WKH SUHVHQW FDVH VWXG\ PHWKRGRORJ\ IRU YDOLGDWLRQ RI PHDVXUHPHQW SURFHGXUH IRU GHWHUPLQDWLRQ RI RD LQ ZDWHU E\ ĮVSHFWURPHWU\ LV SUHVHQWHG )RU WKH FDOFXODWLRQ SDUWWKHHPSKDVLVLVRQWKHSDUDPHWHUVWKDWDUHUHTXLUHGE\WKHFXVWRPHUIQWKLVSDUWLFXODU FDVHWKHVHSDUDPHWHUVDUH  L2'  ZLWKLQODERUDWRU\UHSURGXFLELOLW\ )RUWKHSXUSRVHRIWKLVH[HUFLVHL2'LL' ZLOOEHFDOFXODWHGRQO\

Equation LLD =

tBkg

2.71 + 4.65 Bkg × ε α det × Rchem × Vsample

Measurement data Input quantity

Unit

Value

Rchem

radiochemical yield (recovery)

-

0.803

εα det

efficiency of alpha detector

-

0.2453

Bkg

peak area of background of alpha detector at the Ra-226 alpha energy

-

tBkg

time of measurement of background

s

Vsample

volume of the sample

L

97

Practical examples on traceability, measurement uncertainty and validation in chemistry

PART IV. Measurement uncertainty of the result – relevant equations and measurement data IQ WKH SUHVHQW FDVH VWXG\ PHWKRGRORJ\ IRU HYDOXDWLRQ RI PHDVXUHPHQW XQFHUWDLQW\ RI UHVXOWRIRDGHWHUPLQDWLRQLQGULQNLQJZDWHULVSUHVHQWHGRDZDVGHWHUPLQHG XVLQJĮVSHFWURPHWU\TKHQHFHVVDU\UHOHYDQWLQIRUPDWLRQZDVREWDLQHGIURPWKHPHWKRG YDOLGDWLRQ GDWD WKH TXDOLW\ FRQWURO GDWD DQG HTXLSPHQW FDOLEUDWLRQ FHUWL¿FDWHV  TKH PHWKRGRIPHDVXUHPHQWLVGHVFULEHGWRJHWKHUZLWKWKHPHDVXUHPHQWHTXDWLRQVHOHFWHG WUDFHDEOH UHIHUHQFH VWDQGDUGV DQG WKH DVVRFLDWHG PHDVXUHPHQW XQFHUWDLQW\TKH PDMRU VRXUFHVRIXQFHUWDLQW\RIWKHUHVXOWRIPHDVXUHPHQWZHUHLGHQWL¿HGDQGWKHFRPELQHG XQFHUWDLQW\ZDVFDOFXODWHGIGHQWL¿FDWLRQRIWKHPDLQXQFHUWDLQW\VRXUFHVUHSUHVHQWEDVLV IRUWDUJHWRSHUDWLRQIRUUHGXFLQJWKHPHDVXUHPHQWXQFHUWDLQW\RIWKLVGHWHUPLQDWLRQ

Equations u ( ARa-226 ) ARa-226 u ( Rchem ) Rchem

u ( eαdet ) eαdet

⎛ u (Vsample ) ⎞ ⎛ u (PRa-226 ) ⎞ ⎛ u ( eα det ) ⎞ = ⎜ +⎜ + ⎜ ⎟ ⎟ ⎟ ⎝ PRa-226 ⎠ ⎝ eα det ⎠ ⎝ Vsample ⎠ 2

⎛ u (PBa-133Std ) ⎞ = ⎜ ⎟ + ⎝ PBa-133Std ⎠

2

⎛ u (mBa-133Std ) ⎞ ⎜ ⎟ ⎝ mBa-133Std ⎠

⎛ u (mRa-226SS ) ⎞ ⎛ u (PRa-226Std ) ⎞ = ⎜ + ⎜ ⎟ P ⎝ mRa-226SS ⎟⎠ ⎝ Ra-226Std ⎠

u (ARa-226 ) = k × (ARa-226 )

98

2

2

2

2

2

⎛ u (Rchem ) ⎞ +⎜ ⎝ Rchem ⎟⎠

(

⎛ u PBa-133sample + ⎜ ⎜⎝ PBa-133sample

⎛ u (ARa-226SS ) ⎞ +⎜ ⎟⎠ ⎝ A Ra-226SS

2

)⎞⎟ ⎟⎠

2

2

(

⎛ u mBa-133sample +⎜ ⎜⎝ mBa-133sample

⎛ u ( RRa-226Std ) ⎞ +⎜ ⎟⎠ ⎝ R Ra-226Std

2

)⎞⎟ ⎟⎠

2

peak area of Ra-226 in standard disc

radiochemical yield (recovery)

efficiency of alpha detector

radium standard disc recovery

PRa-226 Std

Rchem

εα det

RRa-226Std -

-

-

-

-

peak area of Ba-133 in barium standard disc

PBa-133 Std

-

peak area of Ba-133 in the sample

PBa-133 sample

-

peak area of Ra-226

s

s

s

Bq g-1

g

g

g

L

Unit

PRa-226

time of measurement of Ba-133 in barium standard disc

time of the sample measurement (s)

tBa-133 sample

tBa-133Std

time of measurement

activity concentration of Ra-226 in standard solution

tRa-226

ARa-226 SS

mRa-226 SS

mass of added Ba-133 in barium standard disc mass of added Ra-226 in standard solution

mass of added Ba-133 in the sample

mBa-133 sample

mBa-133Std

volume of the sample

Vsample

Input quantity

Measurement data

-

-

-

12 785

5090

10 914

7516

3000

3000

300 000

2729

0.010

0.112

0.301

1.0

Value

-

-

-

113

71

104

87

-

-

-

-

0.001

0.001

0.001

0.002

(u)

Standard uncertainty

A

A

A

A

A

A

A

-

-

-

B

B

B

B

B

Type of uncertainty

X

X

X

X

X

X

X

X

normal

-

-

-

X

X

X

rectangular

Type of distribution

X

triangular

Determination of Radium in Water by α-Spectrometry

99

Practical examples on traceability, measurement uncertainty and validation in chemistry

The solved exercises ‘green pages’

TrainMiC Exercises Analytical procedure Determination of activity concentration of Ra-226 in drinking water. The quality of the results should comply with the requirement in the revised Directive 98/83/EC on the quality of water intended for human consumption

EXERCISE 1: Establishing traceability in analytical chemistry EXERCISE 2: Single laboratory validation of measurement procedures Part I: General issues Part II: Parameters to be validated Part III: Some calculations and conclusions

EXERCISE 3: Building an uncertainty budget Addendum I: By spreadsheet approach Addendum II: By dedicated software

100

Determination of Radium in Water by α-Spectrometry

ESTABLISHING TRACEABILITY IN ANALYTICAL CHEMISTRY

1. Specifying the analyte and measurand Analyte

Ra-226

Measurand

Activity concentration of Ra-226 in water (drinking, surface, waste, …)

Units

Bq L-1

2. Choosing a suitable measurement procedure with associated model equation Measurement procedure

Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometrical sources Lozano et al., Journal of Radioanalytical and Nuclear Chemistry

Type of calibration

mixed standard source

standard addition

internal standard

Model equation TKHDFWLYLW\FRQFHQWUDWLRQRIRDLQVDPSOH%TL LVFDOFXODWHGE\ A Ra-226 =

tRa-226

× eα det

PRa-226 × Vsample

×

Rchem

ARD

DFWLYLW\FRQFHQWUDWLRQRIRDLQWKHVDPSOH>%TL@

PRD

SHDNDUHDRIRD

tRD

WLPHRIPHDVXUHPHQW>V@

V

YROXPHRIWKHVDPSOH>L@

İĮGHW

FRUUHFWHGHI¿FLHQF\RIDOSKDGHWHFWRU

RFKHP

UDGLRFKHPLFDO\LHOGUHFRYHU\

Rchem =

PBa-133sample tBa-133sample × mBa-133sample

×

tBa-133Std × mBa-133Std PBa-133Std

RHFRYHU\REWDLQHGE\JDPPDVSHFWURPHWU\LVFDOFXODWHGDVIROORZV RFKHP

UDGLRFKHPLFDO\LHOGUHFRYHU\ 

P%DVDPSOH

SHDNDUHDRI%DLQWKHVDPSOH

t%DVDPSOH

WLPHRIWKHVDPSOHPHDVXUHPHQW>V@

m%DVDPSOH

PDVVRIDGGHG%DLQWKHVDPSOH>J@

P%D6WGD

SHDNDUHDRI%DLQEDULXPVWDQGDUGGLVF

101

Practical examples on traceability, measurement uncertainty and validation in chemistry

t%D6WG

WLPHRIPHDVXUHPHQWRI%DVWDQGDUGGLVF>V@

m%D6WG

PDVVRIDGGHG%DLQEDULXPVWDQGDUGGLVF>J@

$OSKDVSHFWURPHWHUHI¿FLHQF\LVFDOFXODWHGDVIROORZV İĮGHW =

tRa-226Std

PRa-226Std × mRa-226SS × ARa-226SS

×

RRa-226Std

İĮGHW

HI¿FLHQF\RIDOSKDGHWHFWRU

RRD6WG

UDGLXPVWDQGDUGGLVFUHFRYHU\

PRD6WG

SHDNDUHDRIRDRIVWDQGDUGGLVF

tRD6WG

WLPHRIPHDVXUHPHQWRIRDVWDQGDUGGLVF>V@

mRD66

PDVVRIDGGHGRDVWDQGDUGVROXWLRQ>J@

ARD66

RDDFWLYLW\FRQFHQWUDWLRQLQVWDQGDUGVROXWLRQ>%TJ@

3. List the input quantities according to their influence on the uncertainty of the result of the measurement (first the most important ones). At this point, your judgement should be based on your previous experience only. 1

Uncertainty of concentration of reference solutions

2

Uncertainty of volumes

3

Uncertainty of weighing

4

Uncertainty of measurement, using alpha and gamma detectors

4. List the reference standards needed and state the information regarding traceability of the reference value For the analyte

102

1

Name/Chemical Formula/Producer:

Standard Radionuclide Source, Analytics, SRS 67978-121

2

Name/Chemical Formula/Producer:

Ba-133 standard solution, Czech Metrological Institute, Cert. No: 931-OL-137/99

2

Name/Chemical Formula/Producer:

Ra-226 standard solution, NIST SRM 4967

Determination of Radium in Water by α-Spectrometry

For the other input quantities 1

Quantity/Equipment/Calibration: e.g. mass/balance/calibrated by NMI, U = xx (k = 2) see also data yellow sheet

Graduated and mixing cylinders, volumetric flask/with established traceability BLAUBRAND® tolerance

2

Quantity/Equipment/Calibration:

Mass/calibrated balance/with established traceability Sartorius

5. Estimating uncertainty associated with the measurement Are all important parameters included in the model equation?

Yes

Other important parameters are:

Uncertainty of measured background of detector, uncertainty of measured blank reagents (minor contributions)

No

6. How would you prove traceability of your result? 1

Analysis of matrix CRM

2

Participation in a proficiency testing scheme

3

-

7. Any other comments, questions…

103

Practical examples on traceability, measurement uncertainty and validation in chemistry

SINGLE LABORATORY VALIDATION OF MEASUREMENT PROCEDURES PART I: GENERAL ISSUES 1. Specify the measurement procedure, analyte, measurand and units The measurement procedure

Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometric sources J.C. Lozano, F. Fernandez and J.M.G. Gomez Journal of Radioanalytical and Nuclear Chemistry 223 (1997) 1−2, 133−137.

Analyte

Ra-226

The measurand

Activity concentration of Ra-226 in drinking water

Unit

Bq L-1

2. Specify the scope Matrix

Drinking water

Measuring range

0.01–10 Bq L-1

3. Requirement on the measurement procedure Intended use of the results

Compliance to the requirements in the revised water directive 98/83/EC on the quality of water intended for human consumption Parameters to be validated

Value requested by the customer 0.04 Bq L-1

LOD LOQ Mark the customer’s requirements and give their values

Repeatability Within-lab reproducibility Trueness Measurement uncertainty Other-state

4. Origin of the measurement procedure VALIDATION

104

New in-house method

Full

Modified validated method

Partial

Official standard method

Confirmation/Verification

Determination of Radium in Water by α-Spectrometry

PART II: PARAMETERS TO BE VALIDATED

5. Selectivity/Interference/Recovery Where yes, please give further information e.g. which CRM, reference method CRM/RM: analysis of available CRM or RM Further information: Spike of pure substance spiking of samples with pure substances and calculation of recovery Compare with a reference method

Selectivity, interferences

Test with different matrices

Other – please specify

6. Measuring range Linearity Upper limit LOD LOQ

7. Spread – precision Repeatability Reproducibility (within lab) Reproducibility (between lab)

105

Practical examples on traceability, measurement uncertainty and validation in chemistry

8. Robustness Variation of parameters

9. Quality control Control charts Participation in PT schemes

10. Other parameters to be tested Working range and testing of homogeneity of variances R square Residual standard deviation Standard deviation of the analytical procedure Coefficient of variation of the analytical procedure Measurement uncertainty

106

Determination of Radium in Water by α-Spectrometry

PART III: SOME CALCULATIONS AND CONCLUSIONS

11. Calculation of parameters requested by the customer Parameters requested to be validated

Calculations LLD =

LOD

2.71 + 4.65 14.26092744 = 0.000245 Bq L-1 420 730 × 0.2453 × 0.803 × 1

LOQ Repeatability Within-lab reproducibilty Trueness Measurement uncertainty Other - please state

12. Does the analytical procedure fulfil the requirement(s) for the intended use? Parameter

Value requested by the customer (the same as stated in question 3)

LOD

0.04 Bq L-1

LOQ



Repeatability



Value obtained during validation

The requirement is fulfilled Yes/No

0.00025 Bq L-1

YES

Within-lab reproducibility



Trueness Measurement uncertainty



Other

The analytical procedure is fit for the intended use: Yes

No

For measurement uncertainty and traceability refer to the corresponding sheets

107

Practical examples on traceability, measurement uncertainty and validation in chemistry

BUILDING AN UNCERTAINTY BUDGET

1. Specify the measurand and units Measurand

Activity concentration of Ra-226 in water (drinking, surface, waste, …)

Unit

Bq L-1

2. Describe the measurement procedure and provide the associated model equation

Measurement procedure 'HWHUPLQDWLRQRIUDGLXPLVRWRSHVE\%D62FRSUHFLSLWDWLRQIRUWKHSUHSDUDWLRQRIDOSKD VSHFWURPHWULFVRXUFHV -CLR]DQR))HUQDQGH]DQG-M**RPH] -RXUQDORIRDGLRDQDO\WLFDODQG1XFOHDUCKHPLVWU\223 −−

Model equation: TKHDFWLYLW\FRQFHQWUDWLRQRIRDLQWKHVDPSOH%TL LVFDOFXODWHGE\ A Ra-226 =

108

tRa-226

×

α det

PRa-226 × Vsample

×

Rchem

ARD

$FWLYLW\FRQFHQWUDWLRQRIRDLQWKHVDPSOH>%TL@

PRD

SHDNDUHDRIRD

tRD

WLPHRIPHDVXUHPHQW>V@

V

YROXPHRIWKHVDPSOH>L@

İĮGHW

FRUUHFWHGHI¿FLHQF\RIDOSKDGHWHFWRU

RFKHP

UDGLRFKHPLFDO\LHOGUHFRYHU\ 

Determination of Radium in Water by α-Spectrometry

RHFRYHU\PHDVXUHGE\JDPPDVSHFWURPHWU\LVFDOFXODWHGDVIROORZV Rchem =

PBa-133sample tBa-133sample × mBa-133sample

×

× mBa-133Std

tBa-133Std

PBa-133Std

RFKHP

UDGLRFKHPLFDO\LHOGUHFRYHU\

P%DVDPSOH

PHDNDUHDRI%DLQWKHVDPSOH

t%DVDPSOH

WLPHRIWKHVDPSOHPHDVXUHPHQW>V@

m%DVDPSOH

PDVVRIDGGHG%DLQWKHVDPSOH>J@

P%D6WG

SHDNDUHDRI%DLQEDULXPVWDQGDUGGLVF

t%D6WG

WLPHRIPHDVXUHPHQWRI%DLQEDULXPVWDQGDUGGLVF>V@

m%D6WG

PDVVRIDGGHG%DLQEDULXPVWDQGDUGGLVF>J@

$OSKDVSHFWURPHWHUHI¿FLHQF\GHWHUPLQDWLRQLVFDOFXODWHGDVIROORZV İĮGHW =

tRa-226Std

PRa-226Std × mRa-226SS × ARa-226SS

×

RRa-226Std

İĮGHW

HI¿FLHQF\RIDOSKDGHWHFWRU

RRD6WG

UDGLXPVWDQGDUGGLVFUHFRYHU\

PRD6WG

SHDNDUHDRIRDLQVWDQGDUGGLVF

tRD6WG

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mRD66

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ARD66

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3. Identify (all possible) sources of uncertainty Uncertainty of concentration of reference solutions Uncertainty of measurements of peak area (alpha and gamma detectors) Method bias Matrix effect Other: Uncertainty of volume measurements Other: Uncertainty of weighing Other: Uncertainty of measured background of alpha and gamma detectors Other: Uncertainty of measured blank reagents, filters, discs

109

Practical examples on traceability, measurement uncertainty and validation in chemistry

4. Evaluate values of each input quantity Input quantity

Value

Unit

PRa-226

7516

-

tRa-226

300 000

s

εαdet

0.2453

-

Vsample

1.0

L

Rchem

0.803

-

Remark

5. Evaluate the standard uncertainty of each input quantity Input quantity

Standard uncertainty

Unit

PRa-226

87

-

tRa-226

0

s

εαdet

0.01392

-

Vsample

0.0020

L

Rchem

0.0142

-

Remark

Constant

6. Calculate the value of the measurand, using the model equation A Ra-226 =

A Ra-226 =

tRa − 226

PRa-226 × eα det × Vsample

7516 × 300 000 × 0.2453 × 1

×

1 Rchem

1 = 0.127 Bq L-1 0.803

7. Calculate the combined standard uncertainty (uc ) of the result and specify units Using:

110

MDWKHPDWLFDOVROXWLRQ

6SUHDGVKHHW$SSURDFK

Input quantity

Value

Standard uncertainty

Unit

PRa-226

7516

87

-

tRa-226

300 000

0

s

εαdet

0.2453

0.01392

-

Remark

CRPPHUFLDO6RIWZDUH

Determination of Radium in Water by α-Spectrometry

Vsample

1.0

0.0020

L

Rchem

0.803

0.0142

-

u ( ARa-226 ) ARa-226 u ( ARa-226 ) ARa-226

⎛ u (Vsample ) ⎞ ⎛ u (PRa-226 ) ⎞ ⎛ u ( eαdet ) ⎞ = ⎜ +⎜ + ⎜ ⎟ ⎟ ⎟ ⎝ PRa-226 ⎠ ⎝ eαdet ⎠ ⎝ Vsample ⎠ 2

2

2

2

⎛ 87 ⎞ ⎛ 0.01392 ⎞ ⎛ 0.0020 ⎞ = ⎜ + + ⎜ ⎝ 7516 ⎟⎠ ⎜⎝ 0.2453 ⎟⎠ ⎝ 1 ⎟⎠

2

2

⎛ u (Rchem ) ⎞ +⎜ ⎝ Rchem ⎟⎠

2

2

⎛ 0.0142 ⎞ +⎜ = 0.00806 ⎝ 0.803 ⎟⎠

8. Calculate expanded uncertainty (Uc) and specify the coverage factor k and the units u (ARa-226 ) = k × (ARa-226 ) U = 2 × 0.00806 = 0.016 Bq L-1

9. Analyse the uncertainty contribution and specify the main three input quantities contributing the most to uc 1

Mass of Ra-226 standard solution

2

Peak area of Ba-133 in the standard disc

3

Peak area of Ra-226 of the sample

10. Prepare your uncertainty budget report See the attached Excel calculations and calculations done using the software GumWorkbench

111

Practical examples on traceability, measurement uncertainty and validation in chemistry

Further readings

(CCRXQFLO'LUHFWLYHRI-XO\UHODWLQJWRWKHTXDOLW\RIZDWHULQWHQGHG IRUKXPDQFRQVXPSWLRQOf¿c. J. Eur. Commun.L  (CCRXQFLO'LUHFWLYH(CRI1RYHPEHUTKHTXDOLW\RIZDWHULQWHQGHG IRUKXPDQFRQVXPSWLRQOf¿c. J. Eur. Commun.L   (8R$T2M  CRXQFLO RHJXODWLRQ (XUDWRP  1R  RI  -XO\  DPHQGLQJRHJXODWLRQ(XUDWRP 1ROD\LQJGRZQPD[LPXPSHUPLWWHGOHYHOV RI UDGLRDFWLYH FRQWDPLQDWLRQ RI IRRGVWXIIV DQG RI IHHGLQJVWXIIV IROORZLQJ D QXFOHDU DFFLGHQW RU DQ\ RWKHU FDVH RI UDGLRORJLFDO HPHUJHQF\ Of¿c. J. Eur. Commun. L    (8R$T2M  (XURSHDQ CRPPLVVLRQ RHFRPPHQGDWLRQ (8R$T2M Of¿c. J. Eur. Commun. L   Guidelines for Drinking Water Quality, Recommendation YRO  QG HG   :+2*HQHYD  Guidelines for Drinking Water Quality, Recommendation YRO  UG FXUUHQW  HG LQFOXGLQJWKH¿UVWDGGHQGXP :+2*HQHYD$YDLODEOHIURPKWWSZZZZKRLQW ZDWHUBVDQLWDWLRQBKHDOWK -CLR]DQR))HUQDQGH]DQG-M**RPH]'HWHUPLQDWLRQRIUDGLXPLVRWRSHVE\ %D62FRSUHFLSLWDWLRQIRUWKHSUHSDUDWLRQRIDOSKDVSHFWURPHWULFVRXUFHVJ. Radioanalyt. Nucl. Chem.−  −