NEWER METHODS FOR THE SPECTROCHEMICAL ANALYSIS OF SOLUTIONS

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NEWER METHODS FOR THE SFECTROCHENICAL ANALYSIS OF SOLUTIONS

A Dissertation SUBMITTED TO THE GRADUATE COUNCIL OF WAYNE UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE DEPARTMENT OF CHEMISTRY

by Robert E. Mosher

Detroit, Michigan 19h9

Ofry.i' 0

*^V3RAr?y o} WAYME. UNIVERSITY I

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PREFACE

Review of the literature reveals that spectrochemical analysis of solutions per se has not been satisfactorily solved. In most cases the emission spectrographs technique yields data of questionable accuracy. In consequence of these difficulties attempts have been made to evaporate and pelletize solutions preparatory to employment of arc or spark excitation. Probably the most commonly used procedure is to drop the solution to be analyzed into a paraffindipped craterized carbon electrode, which is then thoroughly dried before electrical excitation. Diffusion of the various cations through electrode surface material, usually necessitates burning of the whole sample by arc technique, which is less easily manipxtlated than spark procedures. These procedures are time-consuming, allow the possible introduction of impurities, and deal primarily with solids. A portion of this thesis describes the successful use of a rotating disc electrode manufactured by the Applied Research Laboratories and modified in this laboratory for purposes of direct quantitative solution analysis of magnesium-bearing ores. The numerous difficulties concerning time, precision and accuracy of emission spectrographic analysis of solutions were overcome through this device. A more limited quantitative spectrochemical analysis of solutions may be achieved by flame excitation. A part of this thesis treats the use of the newly-developed Beckman flame photometer and its use in the successful quantitative analysis of sodium and potassium in human plasma and urine as 'well as the quantitative estimation of low concentrations of calcium in magnesium-bearing ores. ii

A critique of

flame band and line spectra is presented with experimental evidence of instrumental characteristics and factors affecting specific elemental intensities.

iii

TABLE OF CONTENTS Preface

Page ii

.

List of Tables

vii

List of Illustrations.

vi

Section I: Flame Photometry Chapter I. HISTORICAL REVIEW

1

II. DESCRIPTION OF THE BECKMAN FLAME PHOTOMETER

11

III. INSTRUMENTAL VARIABLES

Hi

A. Consideration of Gases

lU

B. Spray Chamber

15

C. Atomizer

16

D. Burner Assembly

16

E. Types of Spectra.

1?

F. Solution Variables

18

G. Comments

.

20

IV. PROCEDURES FOR THE SOLUTION ANALYSIS OF HUMAN PLASMA AND URINE FOR SODIUM AND POTASSIUM

21

V. DISCUSSION AND RESULTS

26

VI. PROCEDURES FOR THE SOLUTION ANALYSIS OF MAGNESIUM—BEARING ORES FOR CALCIUM

35>'

VII. DISCUSSION AND RESULTS

38

Section lis Spectrography VIII. INTRODUCTION AND HISTORICAL REVIEW IX. INSTRUMENTATION

.

X. APPARATUS AND SPECTROGRAPHS! CONDITIONS iv

b5 U6

XI. PROCEDURES FOR THE SOLUTION ANALYSIS OF MAGNESIUM-BEARING ORES FOR CALCIUM, IRON AND ALUMINUM

U8

XII. DISCUSSION AND RESULTS

£l

BIBLIOGRAPHY

££

BIOGRAPHICAL STATEMENT

58

v

LIST OF ILLUSTRATIONS Figure I.

The Beckman Flame Photometer

II.

Atomizer, Spray Chamber and Burner Assembly

III.

Snectrum of Natural Gas Flame from 800 to 1200 MU.)

IV.

Spectrum of Natural Gas Flame from 305 to 317 MU. )

V.

Oxygen Maxima Curves for Sodium

VI.

Oxygen Maxima Curves for Potassium

VII.

Oxygen Maxima Curves for Calcium

)

VIII. Resolution of a Potassium Doublet IX.

Typical Flame Spectra

X.

Relation Between Concentration of Standard and Intensity Values

XI.

Flame Spectrum of Sodium and Calcium

XII.

Effect of 873090 Filter on Calcium and Sodium Spectrum

XIII. Influence of Iron, Aluminum and Magnesium on Calcium Emission XIV.

Rotating Disk Electrode

XV.

Working Curve for Iron

XVI.

Working Curve for Aluminum)

)

)

XVII. Working Curves for Calcium)

vx

(

LIST OF TABLES Table

Page

I. Additions °** Sodium as Chloride to Analyzed Pooled Plasma#.,.

27

II. Additions of Potassium as Chloride to Analyzed Pooled Plasma -

27

III. Effect of Gelatin on Intensity in Sodium Measurements......

28

IV. Effect of Gelatin on Intensity in Potassium Measurements..•.

29

V. Sodium and Potassium Values of 72 Normal Plasma Samples Analyzed Spectrographically and Flame Photometrically........

31

VI* The Combined Effect of Magnesium, Iron and Aluminum on Calcium Intensity

hZ

VII. Additions of Known Amounts of Calcium to an Analysed Magnesite Sample

U3

VIII. Comparison of Caley-Elving and Flame-Photometric Methods for CaO.

U3

3X. Spectrographic Analyses of Ilagnesite

^1

X. Recoveries of Known Amounts of Calcium, Iron and Aluminum from Magnesite

53

XI. Replicate Analyses of a Magnesite Ore.

vii

SECTION I FLAKE PHOTOMETRY

CHAPTER I HISTORICAL REVIEW It has long been known that elements subjected to high temperatures induced by electrical or other means emit characteristic spectra, the intensity of which is a function of concentration. This phenomenon has been utilized for the qualitative detection and more recently for the quantitative estimation of numerous elements in both free and combined states, Bunsen and Kirchoff are credited with the initial discovery in i860"*" that solutions containing alkalies and alkaline earth metals, respectively, give rise to characteristic colors when injected into a gas flame. This finding was soon utilized as a method of detecting elements of these groups. Even today it is an accepted technique for visually identifying sodi\im, potassium, calcium, strontium, barium and several other elements. The first serious study of the spectra of colored flames is recorded in a series of very interesting papers published by Hemsalech and de VFatteville in the early part of this cent\^ry.^,^,^,*' 1, Kirchoff, C-., and Bunsen, R., Pogg. Ann. 110: 16 (i860), 2, Hemsalech, G. A., and de Vfatteville, C., Compt. Rend. lUU: 1338-UO (1907). 3, Ibid., ll£: 1266 (1907). U. Ibid.1 1U6: 7U8-51 (1908). 5. Ibid., 1U6: 859-62 (1908). 6*

Ibid., 1U6: 962-65 (1908).

7. Ibid., Ik6: 1389-92 (1908). 8«

Ibid., 1U9: 1112-15 (1909).

9* Ibid., l£0: 329-32 (1?10).

2 These workers observed that on passing a high frequency spark between two metallic electrodes and blowing the finely-powdered metal formed into a high-temperature flame, light of various wave lengths was emitted.

They proved that the wave lengths emitted were characteristic

of the metallic electrodes and that the spectra produced were identical with spectra obtained by exciting these metals electrically#

Most of

their work concerns the use of metallic electrodes such as calcium, copper and iron, however, an apparatus was eventually developed in which non-conducting materials could be studied. reviewed by De Grsjnont in 1923*^

This work was

He suggested that the methods of

Hemsalech and de Watteville might find application in the qualitative analysis of minerals.

He later observed that although several minerals

could be analyzed satisfactorily, there were many which did not lend themselves to this technique. It was not until 1929 that further refinements in the detection and measurement of flame spectra were made.

Lundegardh

2

at this time

became interested in the applications of flame spectra to various chemical problems and is generally credited as being the pioneer in this field.

Using a controlled acetylene-oxygen flame source and a

suitable aspirating and atomizing unit through which solutions could be delivered at a uniform rate to the flame, Lundegardh studied the spectra of over thirty elements by passing the light emitted by these elements to the grating of a conventional spectrograph and

1. De Gramont, A., Bull, soc. chim. 33: 1693 (1923)* 2. Lundegardh, H., Die Quantitative Spektralanalyse der Elemente (Jena: Gustav Fischer, I, 1929; II, 1935).

3

photographing the resultant spectral lines and bands. 3y this method the densities of the spectral lines become a function of the concentration of the elements present in solution. Further improvements in apparatus were reported in 1936,1 at which time Lundegardh published a detailed study of his methods and results. He reported that the high-temperature flame source was suited for quantitative work and that large amounts of foreign substances appeared to present no serious interferences. A modification in the flame 2

source of the Lundegardh-type apparatus was made by Hultgren, who constructed a combination spark-flame source. He hoped to combine the advantages of both flame and electrical excitation by this method. Little difference was found between this combined source and an ordinary high-temperature flame source. Of major significance was the observation by Hultgren that certain impurities, specifically alkali chlorides, intensified certain spectra], lines. This phenomenon was ascribed to the increased electrical conductance of flame components. The work of Hultgren was repeated by Lundegardh and Philipson in 1938*3

After an extended series of comparisons and measurements, these

workers expressed the opinion that the ordinary flame source was far superior to the "spark-in-flame" technique for the determination of all elements except magnesium, which apparently required the higher temperature of the electric spark to effect excitation. It was 1. Lundegardh, H., Lants-Hogskol. Ann. (Sweden) ^' k9 (1936). 2. Hultgren, R., J. A. C. S. j?U: 2320-28 (1932). 3» Lundegardh, H., and Philipson, T., Lants-Kflgskol. Ann. (Sweden) £: 2h9 (1938).

h

observed at this time that alkali chlorides caused an intensification of the spectral lines of aluminum, tin and lead. It was not long before the advantages of flame spectral analysis began to be explored more fully. Among the early workers we find Mitchell and Robertson,"'" who used a Lundegardh-type apparatus for the quantitative determination of calcium and strontium. In the data reported by them we find the interesting discovery that aluminum depresses the intensity of certain lines of calcium and strontium. The nature of this depression was such that a quantitative estimation of aluminum- could be made by observing the magnitude of the calcium spectral depression brought about by the foircer. In the preparation of this thesis this striking effect was observed and led to a literature search which credited Mitchell and Robertson with this finding originally. McClelland and Whalley^ studied in detail the construction of the Lundegardh apparatus with a view to its application for solution analysis. That practical uses were found is demonstrated by the work of Tate and Whalley,^ who analyzed tobacco ash for small amounts of calcium, potassium, magnesium, manganese and strontium. Mitchell,^ by using a standard which approximated the sample to be analyzed, 1. Mitchell, R. L», and Robertson, I. M., Soc. Chem. Ind. 55; 269-272 T (1936). "" 2. McClelland, J. A. C., and Whalley, H. K., J. Soc. Chem. Ind. (London) 60: 288-291 (19U1). 3. Tate, F. G. H., and Whalley, H. K., Analyst 65: 589-593 (19U0). U. Mitchell, R. L., J. Soc. Chem. Ind. (London) (1936).

267 T-269

5 quantitatively determined iron, manganese, potassium, calcium, strontium and lithium in soil extracts, plant ash and drainage waters.

1 and Cholak and Hubbard,2 the only American

Griggs and co-workers

workers to become interested in flame spectrography, did not report in the literature until I9I4I and 19UU, respectively.

The former

investigated the details of sample preparation and the latter investigated those elements susceptible to flame analysis and the attendant errors.

Both papers present analyses of such materials as

plant fluids, blood serum and urine for calcium, sodium, potassium and iron#

For these elements, an accuracy of three to five per cent was

claimed, A modification of the Lundegardh apparatus, which should be 3

mentioned for completeness, was developed by Ramage. "Ramage Flame."

It features the

In this instrument a filter-paper spill, on which has

been evaporated a fraction of a milliliter of solution, is burned in an oxygen-coal gas flame and the resulting light is resolved and measured by a Hilger Spectrograph. well as that of Mitchell,

tL

h

Further work by Steward and Harrison,

as

has shown that this method is not adequate

for the spectrochemic al analysis of several cations simultaneously. Its main advantage is that only 0.05 milliliters of solution is

1. Griggs, M. A., Johnstin, R., and Elledge, p. E., Ind. Eng. Chem,5 Anal. Ed. 13: 99 (1