Bernhard Welz Michael Sperling

Atomic Absorption Spectrometry

Third, Completely Revised Edition

(33 WILEY-VCH Weinheim - New York - Chichester - Toronto - Brisbane - Singapore

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Bern hard We 1 z Michael Sperling

Atomic Absorption Spectrometry

6B WILEY-VCH

This Page Intentionally Left Blank

Bernhard Welz Michael Sperling

Atomic Absorption Spectrometry

Third, Completely Revised Edition

(33 WILEY-VCH Weinheim - New York - Chichester - Toronto - Brisbane - Singapore

Dr. Bcrnhard We17 In den Auen 20 D-XS690 Ilhldingcn, Germany

Dr. Michael Spcrling Rodcn\ccwerk Pcrkiim-Elmer <;mhfl Altc NuOdorIcr Str;ilk D-SSh62 <'Jlicrli ngcn

This hook was carefully produced. Ncvcrthclcs!, authors and publisher c io no t &.;irrant tlic iimIorni;ition c011-

tained therein to be frcc of errors. Readers are advised to kccp in mind that statements. data. illu\trations. procedural details or other items may inadvertently he inaccurate.

~~

First Edition 1076

Second Edition I O X 5

'l'hird Edition I999

First Reprint 2005

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Preface to the third Edition

Atomic absorption spectrometry (AAS) is today, more than 40 years after it was pro- posed by Walsh as an analytical procedure, well established in numerous fields of in- strumental analysis. Due to its high specificity and selectivity, as well as the fact that operation is relatively simple, AAS has gained its place alongside ICP OES and 1CP-MS. It is used to perform numerous routine tasks in the laboratory ranging from the determi- nation of trace contents through to major constituents. The fact that more than 1000 original papers dealing with AAS are published every year is a clear indication that there are numerous new developments over and above the routine applications.

These include new knowledge on atomization and other reaction mechanisms, im- proved analytical methods, especially in the fields of trace and ultratrace analysis, as well as in solids analysis, particularly using slurries. A major contribution has been the devel- opments in instrumentation, such as transversely-heated graphite furnaces, integrated platforms, the application of solid-state detectors, or simultaneous multielement AAS, as well as new sample introduction and on-line pretreatment techniques such as flow injec- tion. New areas of application including the analysis of ‘high tech’ materials and specia- tion analysis must also be mentioned.

To do justice to these manifold developments, this monograph has been rearranged, completely revised, and correspondingly extended. Thus, Chapter 1 on the historical development of AAS is new; in the first instance i t demonstrates the maturity of the technique and provides the historically interested reader with the background informa- tion, and in the second instance i t frees the technical chapters from historical ballast, leaving them free for a discussion of the current state of knowledge. Chapter 2 on the physical principles of AAS is also largely new; many of the topics discussed in this chapter are only inadequately treated in standard textbooks or not at all, and other topics have only been thoroughly developed in recent years.

Chapters 5, 6, and 7 are likewise new. Chapter 5 deals with procedures of measure- ment and calibration, the principles of quality control and assessment, and the basics of the statistical evaluation of the analytical results. Chapters 6 and 7 deal with automation and species analysis, and present a short review of the developments in these areas dur- ing recent years. On the other hand, the comparative chapter on other analytical proce- dures is no longer included since the recent developments in 1CP OES and ICP-MS are well beyond the scope of this monograph.

Compared to the last edition, Chapter 8 includes significantly improved knowledge on the mechanisms of atomization and interferences, particularly for GF AAS and HG AAS. Chapter 9, dealing with the individual elements, now includes information on the stability and storage of test sample and calibration solutions, as well as the deterini- nation of species. In the treatment of applications in Chapter 10 , methods no longer rele- vant, such as the determination of volatile elements by GF AAS using atomization from the tube wall with peak height evaluation, have been eliminated. On the other hand, all relevant procedures for speciation analysis are newly included.

Throughout this edition the terminology proposed by 1SO and IUPAC has been used consistently. Thus, instead of ambiguous units such as ppm, ppb, etc., we have consis-

VI Preface

tently used the IS0 units mg/L, pg/L, ng/L and mg/g, yglg, nglg, etc. We have also at- tempted to avoid concentrations quoted in percent, which nevertheless was not possible in all cases since it was not clear from the original papers whether the concentration of acids, for example, were quoted in weight or volume percent.

To establish the bibliography we applied a relational databank (PELIDAS, 0 M. Sperling) to evaluate more than 55 000 entries from the field of atomic spectros- copy using plausibility checks to guarantee the quality of the citations. For the selection of the 6500 or so citations in this monograph, next to their information content, their topicality and availability also played a role. It is clear that for such a selection subjec- tivity comes into play, even though we have always attempted to be objective; we there- fore ask for our readers’ understanding if any paper that they deem to be important is not cited.

To maintain the topicality of this monograph we have also departed from traditional methods of production. Since the entire work, including the layout, was produced on the authors’ PCs, we were able to update the contents until shortly before publication. We feel sure our readers will excuse the inadequacies of the word processor used in produc- ing the layout since these are more than compensated by the advantage of topicality.

Uberlingen, September 1998 Bernhard Welz Michael Sperling

Preface to the second Edition

In the nine years since the publication of the first edition of this monograph, atomic ab- sorption spectrometry has undergone a remarkable development. This is perhaps no entirely true for flame AAS, which nowadays is established as a routine procedure in all branches of elemental analysis, but it is certainly the case with all other techniques of AAS. Even though flame AAS had already found acceptance in many standard methods due to its reliability in the mg/L range, it is only a few years ago that considerable doubt was cast on the ability of graphite furnace and hydride generation AAS to provide cor- rect results at all in the pg/L and ng/L ranges.

The difficulties observed by many analysts using these techniques were due in part to the shortcomings of the instruments employed and in part to non-optimum application, since the significance of a number of parameters had not been recognized. In addition, the general problems of trace and nanotrace analysis had to be taken into consideration, since these newer techniques opened this concentration range to AAS.

These days, the causes of the majority of interferences and also the possibilities for their elimination are known. Even if all technical problems have not been completely solved, the way to their solution has been shown.

Thus, as well as the flame technique, the graphite furnace, hydride generation, and cold vapor techniques are nowadays of equal significance. The major field of application of these newer techniques is in trace, nanotrilce and ultratrace analysis. Each of these techniques has its own atomizer, its own specific mechanisms of atomization and inter-

Preface V11

ference, and of course its own preferred field of application. In this second edition, these three techniques are thus treated separately whenever this appears expedient.

This made it necessary to substantially revise numerous chapters. Chapter 3 now deals only with atomizers, their historical development, and their specific characteristics for each technique. A new chapter 8 has been introduced in which the mechanisms of atomization and the interferences for each technique are discussed in detail. Additionally, typical interferences and their elimination are mentioned. A general discussion and clas- sification of interferences is presented in chapter 7. Application of the Zeeman effect for background correcttion is also treated in detail in this chapter. This treatment includes the theoretical aspects of the method, the various configurations, and their advantages and disadvantages. In the chapters on individual elements and specific applications, the various techniques are, wherever applicable, weighed against each other.

A discussion on trace and nanotrace analysis has also been newly introduced, since the newer techniques of AAS are among the most sensitive methods for elemental analy- sis. Solids analysis is also treated since this has become possible with the graphite fur- nace technique. A section on environmental analysis has been included in the chapter on specific applications, and topical questions on the analysis of air, waste water and sew- age sludge are addressed.

Ainong associated analytical methods, atomic emission spectrometry employing an inductively coupled argon plasma is discussed especially, since it is frequently regarded as a competitive technique to flame AAS. However, a broad treatment of this theme is outside the scope of this book.

Graphite furnace atomic emission spectrometry has also received attention even though, like atomic fluorescence spectrometry, it is rarely used in practice.

Finally, terms, nomenclature and units of measurement have been brought into line with the latest international standards - a fact reflected in the changed title of this mono- graph. Of particular help in this respect was my work on the committee of material test- ing within the German Institute of Standardization. This committee was chaired by Dr. Hans Massinann, who, until his death, worked on the completion of DIN 5 1 401 and who also made valuable suggestions for the second edition of this book - a fact greatly appre- ciated.

I should also like to thank those readers who wrote to me pointing out errors in the first edition; they have made valuable contributions to improving this work. I should particularly like to thank Sir Alan Walsh who drew my attention to a number of errors and who proposed numerous improvements and more precise definitions.

The numerous new diagrams were prepared with the customary care by Mr. E. Klebsattel who receives my grateful thanks. I should also like to thank Mr. J. Storz for designing the cover.

This book is the English-language version of its German forerunner “Atomabsorp- tionsspektrometrie” (formerly “Atom-Absorptions-Spektroskopie”) which is now in its third edition. As for the first edition the translation has been very capably carried out by Christopher Skegg to whom I extend my thanks.

Meersburg, May 1985 Bernhard Welz

VIII Preface

Preface to the first Edition

It was very convenient that the translation of my book into the English languagee was undertaken just as I was completing the second German edition. Therefore, all the latest developments and publications could be incorporated directly in the English edition

Usually, years go by between the publication of the original book and the completion of a translation which, therefore, typically does not represent the latest state. Here, how- ever, the translation could be published about a year after the original German edition. This is of special importance for the rapidly growing field of furnace atomic absorption which was hardly known a few years ago when the first edition of my book was pub- lished. In the meantime it has found worldwide acceptance among analysts.

So, to all my friends and colleagues who have been involved in the translation and completion of this book, I would like to express my thanks for the time that they have spent and for all the effort that they have put into it so that it could be published so early. Last not least, I want to express my pleasure that my book on Atomic Absorption Spec- troscopy has been accepted for translation into English. I hope that it will prove a stimu- lus to atomic absorption spectroscopy and will help analysts and spectroscopists in their daily work,

Meersburg, March 1976 Bernhard Welz

Contents

1 The Historical Development of Atomic Absorption .................................

1 . 1 1.2 1.3 1.4 1.5 1.6 1.7 1.7. I I . 7.2 1.7.3 1.7.4 1.8 1.8.1 1.8.2 1.8.3 1.9

The Early History ........................................................ Sir Alan Walsh and the Period 1952-1962 The Development of Spectral Radiation Sources ........................ Single-beam, Double-beam, Single-channel, Multi-channel .......

Burners and Flames ..................................................... Electrothermal Atomizatio .................. Boris L'vov and the Graph Walter SIavin and the ST The Two-step Atomizer . Graphite Tubes and Othe

..................

The Non-specific Attenuation of Radiation .................................

.................. Chemical Vapor Generation ... The Cold Vapor Technique ..........................................................

Analysis of Solid Samples ..........................................

The Hydride-Generation Technique ............... Further Techniques of Chemical Vapor Generation ....................

2 Physical Principles ......................................................................................

2.1 2.1.1 2.1.2 2.1.3 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.4 2.5 2.5.1 2.5.2 2.5.3 2.6

Atomic Structure and Spectra ...................................................... Atomic Structure . ...................................... Atomic Spectra ............................................................................. Selection of the Spectral Lines ...................................

.................. Thermal Equilibrium ..............

Natural Line Width ..................

Self-absorption and Convolution of the Various Broadening Mechanisms ................. Hyperfine Structure ............................. Measuring the Absorption .............. The Absorption Coefficient ......................................... The Beer-Lambert Law ................ Deviations from the Linearity o f t The Zeeman Effect .

..................

......................

3 Spectrometers ..................... ......................................

3.1 Radiation Sources ........................................ 3.1.1 Line Sources ........................... .............................. 3.1.2 Continuum Sources ......................................................................

1

1 3 7

12 IS 20 27 27 35 38 41 47 47 49 55 56

63

63 63 63 65 69 74 75 76 77 80 81 83 86 86 89 92 96

I03

103 103 1 1 0

X Contents

3.2 3.3 3.3.1 3.3.2 3.4 3.4.1 3.4.2 3.4.3 3.5 3.6 3.7 3.8 3.8.1 3.8.2 3.8.3 3.8.4

The Radiation Train .............................................. Dispersion and Separation of the Radiation .................................

Reciprocal Linear Dispersion ..........................

Background Correction with Continuum Sour

Background Correction with High Current Pulsing The Detection of Radiation ..................................... The Modulation of Radiation ............................ Simultaneous Spect

Measured Quantitie

Baseline Offset Correction ....................................

Spectral S 1 i tw i dth .........................................................

The Measurement and Correction of' Background Attenuation ...

Background correction Utilizing the Zeeman ..................

Data Acquisition and Output ..................

Signal Handling ....................... ............................

Integrated Absorbance .... .....................................

..............................

4 Atomizers and Atomizer Units ...................................................................

4.1 4.1.1 4.1.2 4.1.2.1 4.1.2.2 4.1.3 4.1.3.1 4.1.3.2 4.1.3.3 4.1.3.4 4.2 4.2.1 4.2.2 4.2.2.1 4.2.2.2 4.2.2.3 4.2.2.4 4.2.2.5 4.2.3 4.2.4 4.2.5 4.2.6 4.2.7 4.2.7.1 4.2.7.2 4.2.7.3 4.2.8

Flame Atomization .. ............................................. Spectroscopic Flame ............................ Nebulizer-Burner Systems .................................... Burner Heads .................. ..................................... Nebulizers and Spray Ch ................................. Special Introduction Techniques for the Measuremen

.......................

............................ Flow Injection ......................... Hydraulic High Pressure Nebulization .................. Electrothermal Atomization .....................................

Graphite Atomizers .. ............................................. ............................

Profiled Tubes ............................................ Platforms ......................... .....................................

.............................................. Temporally and Spatially Isothermal Atomizers ......................... Heating Rate and Temperature Program . ....................... Protective Gas and Purge Gas .............................................. Metal Atomizers ...................... ............................

.....................................

............................

i10 i13 115 119 I20 121 123 133 136 138 I39 142 I43 144 146 147

149

149 150 154 154 156 I66 166 I67 167 169 170 171 175 175 178 179 182 183 185 188 192 I93 197 I97 198 200

Simultaneous Multielement Determinations ................................ 202

Contents XI

203 4.3.1 Systems for Che Vapor Generation ........................... 203

203

4.3 Chemical Vapor Generation . ................................

4.3.1 . 1 Batch Systems .... ....................................................... 4.3.1.2 Flow Systems .......................... ........................................... 206 4.3. 4.3. 4.3. 4.3. 4.3. 4.3.

. 2.1 Continuous flow systems .................................. ........... 206

. 2.2 Flow injection systems ............ ........................................... 208

. 3 Materials for Containers and Tubing ........................... 212

. 2.3

. 2.4 Gas-liquid separators (GLS) ............................. On-line sample preparation ...............................................

. 4 Special Apparatus for CV AAS ........................................ 4.3.2 Collection and Preconcentration ... ........................... 215

4.3.3 Atomization Units ............................ ..................... 217

........................... 218

4.3.2.1 Preconcentration of Mercury ... 4.3.2.2 Preconcentration of Hydrides ..

4.3.3.1 Absorption Cells for CV AAS 4.3.3.2 Atomization Units for HG AAS .......

5 The Individual Steps of an Analytical Method ......................................... 221

5.1 5.1.1 5.1.2 5.1.3 5.2 5.2. I 5.2.2 5.2.2. I 5.2.2.2 5.2.2.3 5.2.2.4 5.2.2.5 5.2.3 5.2.3.1 5.2.3.2 5.2.3.3 5.2.3.4 5.2.3.5 5.3 5.3. I 5.3.2 5.3.3 5.4 5.4.1 5.4.1.1 5.4.1.2 5.4.2

Sampling and Sample Preparation ............................

Sample Pretreatment ........................ ........................... Measurement, Calibration, Evaluation ............................. Samples and Measurement Solution ............................ Calibration ......... ...............................

Bracketing Technique ....................... ............................

Reference Element Technique ........................................ Selection of the Calibration Function and Its Quality of Fit ........ Evaluation ......................... ................................ Evaluation Function and Sensitivity ............................ Precision ............ ........................... Limits of Detecti

Trueness ............................ ................................

............................... Sample Conservation and Storage ....................................

Analyte Addition Technique ............................................

Optimizing Instruments an ............................

Determining Smalier Concertrations or Masses ................ Determining Higher Analyte Content ............................

Spectral Interferences ....................... ............................

Recognizing Interferences ...... .......................................

Interferences in AAS ............................ Classification of Interferences ................................

Non-spectral Interferences ...............................

222 222 223 226 229 229 234 235 238 239 241 242 244 245 246 252 256 261 263 263 267 271 274 274 274 281 283

XI1 Contents

5.4.3 Avoiding and Eliminating Interference ............................ 5.4.3.1 Eliminating Spectral Interferences ...................................

Elimination of Non-specttral Interferences ..................................

Methods Development and Validation .............................

5.4.3.2 5.5 5.5.1

Methods Development, Quality Control and Quality Assessment

............................ 5.5.2 Internal Quality Control ..................

6 Mechanization and Automation .................................................................

6.1 6.2 6.3 6.4 6.5 6.5.1 6.5.2 6.5.3 6.6 6.7 6.8

Flow Injection .................. ............................................ Automatic Transport and Change of Measurement Solutions ..... Automatic Addition of Reagents or Calibration Solutions Automatic Dilution .......................... ............................ Automatic Separation and Preconcentration .................... FI On-line Sorbent Extraction ............................................ FI On-line Precipitation FI On-line Solvent Extr

Automatic Setup and Opti On-line Sample Pretreatment ..........................

Automatic Data Handling ............... ............................

7 Speciation Analysis .......................... ...........................................

7.1.1 The Hydride-generation Technique ............................ 7.1 Non-chromatographic Separation Techniques .............................

7.1.2 7.2 Chromatographic Separation Techn 7.2.1 7.2.2 7.2.3

Preconcentration on Packed Columns ..............................

Gac Chromatographic (GC) Separation .......... Liquid Chromatographic (HPLC) Separation ..............................

GC Separation .. ................................................ The Coupling of Hydride-generation, Preconcentration, and

8 The Techniques of Atomic Absorption Spectrometry .............................

8.1 8.1.1 8.1.1 . 1 8.1.1.2 8.1.1.3 8.1.1.4 8 . 1 . 1.5 8.1.2 8 . I . 2.1 8.1.2.2 8.1.2.3 8.1.2.4 8.1.2.4.1 8.1.2.4.2

The Flame Technique ...................................... Atomization in Flames ..... The Process of Volatilization .......... The Process of Dissociation ............................................. Deviations from Equilibrium .......... ............................. The Kinetic Aspect ............................... The Solvent Effect ........... .............................................

................................. ............................

................................................ ................... ............................

Spatial-distribution Interferences ....................

The volatilization of particles .......................... Solute-volatilization Interferences ...............................................

Reactions during volatilization ............................................. ............

285 285 287 290 291 294

297

297 300 30 1 302 305 306 313 315 316 3 I7 318

323

324 324 324 326 326 329

332

335

335 335 336 337 339 340 341 342 342 343 345 346 346 348

8.1.2.4.3 8 . I .2. 4.4 8.1.2.5 8 . I .2. 5.1 8.1.2.5.2 8.2 8.2.1 8.2.2 8.2.2.1 8.2.2. I . 2 8.2.2.1.2 8.2.2.1.3 8.2.2.1.4 8.2.2.2 8.2.2.2.1 8.2.2.2.2 8.2.2.3 8.2.2.3.1 8.2.2.3.2 8.2.2.3.3 8.2.2.3.4 8.2.2.4 8.2.2.4.1 8.2.2.4.2 8.2.2.4.3 8.2.3 8.2.3.1 8.2.3.2 8.2.3.3 8.2.3.4 8.2.3.5 8.2.3.6 8.2.3.7 8.2.3.8 8.2.3.9 8.2.3.10 8.2.3.1 1 8.2.3.12 8.2.3.13 8.2.4 8.2.4.1 8.2.4.1.1 8.2.4.1.2 8.2.4.1.3 8.2.4.2

Contents

The alkaline-earth elements .............. The flame effect ........................................................................... Vapor-phase Interferen Dissociation interferences ........................................ Ionization interferences ........................................... The Graphite Furnace Technique ...... The Atomization Signal ... ........................................... Methods to Elucidate .................... Atomic and Molecular Spectrometric Techniques ....................... Pyrolysis and attomization curves ................................................ Time-resolved signals .............................................. Molecular absorption . ........................................... Time-resolved and spa measurements Techniques for Investigating the Gas Phase ................................ ETV-F AAS and ETV Mass spectrometric (MS) investigations .................. Techniques for Investigating the Condensed Phase ..................... The use of radiotracers ...................... Electron microscopy ... ........................................... X-ray diffracttion analysis (XRD) .... Miscellaneous techniques of surface analysis ..........

Arrhenius diagrams ........................... ................................... High-temperature equilibria calculations ..................................... Monte Carlo simulation techniques .. Atomization Mechanisms ......................................... The Alkali Metals ......................................... ...................... The Alkaline-earth Elements .................................. Yttrium and the Ra Vanadium, Chromi Manganese and the The Noble Metals ................................ Zinc and Cadmium Aluminium and Boron . ............................................. Gallium, Indium, Thallium .......................................................... Silicon, Germanium, Tin ...........................................

..

........................

......................

Derived Procedures and Techniques ............................................

......................

...................... .......................... .......................

...................... Selenium ...................................................... ............................................

The STPF Concept ...... ........................................... Chemical modification ...................... ........................ Isothermal atomization ............................................. Control of the atmosphere in the atomizer Spectral lnterferences ...............................................

. .

......................

XI11

350 355 357 358 358 361 362 366 367 367 368 372 373 377 377 377 379 379 380 381 381 383 383 384 384 384 387 387 389 390 392 394 395 395 399 400 402 404 406 409 409 410 415 416 418

8.2.4.3 Non-spectral Interferences ........................................................... 424

XIV Contents

8.2.4.3.1 8.2.4.3.2 8.2.4.3.3 8.2.5 8.3 8.3.1 8.3.1,l 8.3.1.2 8.3. I .3 8.3.1.4 8.3.1.5 8.3.2 8.3.2.1 8.3.2.2 8.3.2.3 8.3.3 8.3.3.1 8.3.3.2 8.3.3.2.1 8.3.3.2.2 8.3.3.2.3 8.3.3.3 8.3.3.3.1 8.3.3.3.2 8.4 8.4.1 8.4.2 8.4.3 8.4.3.1 8.4.3.2

Classification of non-spectral interferences ................................. Interference mechanisms .................. ..... .._... Avoiding non-spectral interferences ............. ..................... Absolute Analyses ..... ........... The Hydride-generation Technique ............ Generation and Transport of the Hydride ....................................

Driving the Hydride

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

..................... Non-heated Flame-in-t

Interferences .... . . .. . . . . . . . . . . . . . . . . . ......................................

Interferences caused by concomitants ..................... ...... .....

Interferences in the Atomizer ........................................... Quartz tube atomizers ...... ....................................

The Cold Vapor Technique ................................................

Interferences . . . . . . . . . . . . . . . . . . . . . . . . . ..................................

9 The Individual Elements.. ................................................

9.1

9.3 Arsenic (As) ................................................ 9.4 ..................... .................................... 9.5 9.6 .................................................. 9.7 Boron (B) ............................. .................................... 9.8 Cadmium (Cd) ............................................. ...................... 9.9 9. 10 Cesium (Cs) .................................................. 9.11 Chromium (Cr).. ................................................ 9.12 Cobalt (Co) ........................... ......................................

9.2 Antimony (Sb) .................. ....................................

9.13 Copper(Cu) ..............................................................................

424 425 428 432 434 434 434 435 436 437 439 440 440 442 45 I 454 455 45 5 455 456 46 1 463 463 468 469 469 47 1 473 473 474

477

479 482 483 486 488 589 490 492 493 495 496 499 500

Contents xv

9.14 9.15 9.16 9.17 9.18 9.19 9.20 9.21 9.22 9.23 9.24 9.25 9.26 9.27 9.28 9.29 9.30 9.3 I 9.32 9.33 934 9.35 9.36 9.37 9.38 9.39 9.40 9.4 1 9.42 9.43 9.44 9.45 9.46 9.47 9.48 9.49 9.50 9.5 1 9.52 9.53 9.54 9.55 9.56 9.57 9.58 9.59

Gallium (Ga) .......................................................................... .....................................................

Gold (Au) .................. ..................

Indium (In) .... ................ .......................... Iodine (I) ............................................................................. Iridium (Ir) ................................................................... Iron (Fe) .................... ..................... Lanthanum (La) and the Rare-earth Elements (REE) .................. Lead (Pb) ................... Lithium (Li) ..................................................................................

Hafnium (Hf) ................................................................................

......................................

Molybdenum (Mo) .... ................

Niobium (Nb) .... ................ ...................... Nickel (Ni) ......................................................................

Non-metals ...................................................................... ...................................................................

.................. Phosphorus (P) ........................................................................

................ .....................

................................................................... ................

Rubidium (Rb) ............................................................................. Ruthenium (Ru) ......... Scandium (Sc) .................................................................

Silicon (Si) ................ ................

Sodium (Na) .............. Strontium (Sr) ............................................

Silver (Ag) ..............................................................................

................ ......................................... Tantalum (Ta) ...............

Tellurium (Te) ........... .................................. Thallium (TI) ........................................................................ Tin (Sn) .................... ......................................... Titanium (Ti) ...........................................

................................................................... .............................

Vanadium (V) ............................................................... ................ .........................................

................... Zirconium (Zr) ...............................................

502 503 504 506 506 508 508 510 512 516 519 520 522 523 529 531 533 534 535 537 538 538 54 I 542 542 544 545 546 547 551 553 554 555 556 557 557 558 559 561 565 567 567 568 569 570 572

XVT Contents

10 Applications of AAS .................................................................................... 575

10.1 10.1.1 10.1.2 10.1.3 10.1.4 10.1.5 10.2 10.2.1 10.2.2 10.2.3 10.2.4 10.2.5

10.2.6 10.3 10.3.1 1 0.3.1 . 1 10.3.1.2 10.3.1.3 10.3.1.4 10.3.1.5 10.3.1.6 10.3.1.7 10.3.2 10.3.2.1 10.3.2.2 10.3.2.3

10.3.2.4 10.3.3 10.3.3.1 10.3.3.2 10.3.3.3 10.3.3.4 10.3.3.5 10.4 10.4.1 10.4.2 10.4.3 10.4.4 10.5 10.5.1 10.5.2 10.5.3

Body Fluids and Tissues ....... The Electrolytes .................................

Industrial Hygiene and Toxicolog .......................

The Analysis of Tissues .......................................... Biological Materials ..............................................

..........................................

Trace Elements .............................................................................

Therapeutically Admi

Sampling and Sample Pretreatment ............................................. Digestion Procedures Determination Procedures for F AAS .......................................... Determination Procedures for GF AAS ....................................... Digestion Procedures for Analytical Techniques Using Chemical Vapor Generation .........................................................

Environmental Analysis ...............................................................

Sampling and Sample Co Methods for F AAS .......................................... Methods for GF AAS ............................................ Methods for HG A Methods for CV AAS ......

Speciation Analysis ............................

Water Analysis ................ .......................

....................... Methods of Speciation Analysis ...................................................

Selective Extraction of Individual Constituents and Bonding Forms ................ ...................... Speciation Analysis in Sol Coal. Ash. Dust. and Air ... Sampling Dusts ..................................... .... Digestion Procedures ...................................................................

Speciation Analysis ......... .......................................... Rocks. Minerals. Ores ........................................... .... Digestion Procedures .......................................... Direct Determination .... Extraction and Preconcentration Procedures ............................... The Direct Analysis of Solid Samples ......................................... Crude Oil and Petroleum Products ........................ Origin-specific Elements and Contamination in Crude Oil .........

Wear Metals and Lubricating Oils ...............................................

ges ................. ..........................................

The Direct Analysis of Solid Samples and Slurries ..................... Methods for the Determination of Mercury .................................

....

Additives to Fuels, Lubricating Oils, and Grease ....

575 577 581 598 608 610 614 616 616 623 628

640 648 655 656 657 658 662 672 675 676 68 1 682 682 682

688 691 694 695 697 699 700 702 703 703 705 708 710 711 712 716 719

Con tents XVIl

10.5.4 10.6 10.6.1 10.6.1.1 10.6.1.2 10.6. I . 3 10.6.1.4 10.6.1 . 5 10.6.1.6 10.6.2 10.6.2. I 10.6.2.2 10.6.2.3 10.6.2.4 10.6.2.5 10.6.2.6 10.6.2.7 10.6.2.8 10.7 10.7.1 10.7.2 10.7.3 10.7.4 10.7.5 10.7.5. I 10.7.5.2 10.7.6 10.7.7 10.7.8 10.7.9 10.7.10 10.7.1 1 10.8 10.8.1 1 0.8.2

Rubber and Plastics ............................................... Metallurgical Samples .................................................. Iron. Steel and Ferrous Alloys ......... ....................... Digestion Procedures Direct Determination Separation and Preconcentration Procedures ........ The Application of G The Application of HG AAS .................... Direct Analysis of Solid Samples ................................................

...............

Non-ferrous Metals and Alloys ... Light Metals and Alloys ................................................... Lead, Tin, and Lead-Tin Alloy Copper and Copper Alloys ...... Nickel, Chromium, Cobalt, Manganese and their Alloys ............

Ultrahigh-purity Metals ..... Noble Metal Analysis ........ ................................... Electrolytic Baths .................................................. Miscellaneous Industrial Products ............................................... The Analysis of Glass ............................... Ceramic Materials, Superconductors ........................................... Cement and its Raw Materials . Chemicals ................................................................... Pharmaceuticals and Cosmetics ................................................... Determination of Metallic Active Ingredients and lmpurities ..... Indirect Determination of Organic Active Ingredients ................ Catalysts ....................................... ....................... Semiconductors ................................................................. Nuclear Materials ... Fertilizers, Fungici Paints, Varnishes, Pigments ......................................................... Papers, Textiles, Leather ............... Multidisciplinary Applications ..........................................

Archeological Fin

Hard and Refractory Metal

........................

Forensic Analysis ....

Bibliography ......................................................................................................

Index ......................................................................................................

722 724 724 7 25 726 727 728 729 730 73 1 731 732 733 736 738 739 740 741 742 742 744 746 748 752 752 754 755 759 762 763 765 766 768 768 7 69

771

907

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Abbreviations and Acronyms

The following abbreviations and acronyms are used in this monograph:

AA AAS A/D (conversion) AES AFM ANOVA APDC AsB ASV BC BCR BERM

BG BOC BPTH CARS CCD CE CF CGC CI CID CPG CRA CRM CSIRO

CT CV AAS DAL DBT DCTA DDAB DDC DDTC DDTP DESe DIBK DIN

acetylacetone atomic absorption spectrometry analog-to-digital Auger electron spectroscopy atomic force microscopy analysis of variance ammonium pyrrolidine dithiocarbamate arsenobetaine anode stripping voltammetry background correction; background corrector Bureau Commun de RCfCrence, Belgium International Symposium for Biological and Environmental Reference Materials borosilicate glass baseline offset correction 1,5-bis~phenyl-(2-pyridyl)methylene] thiocarbohydrazide coherent anti-Stokes Raman spectroscopy charge coupled device concentration efficiency continuous flow capillary gas chromatography consumptive index charge injection device controlled pore glass carbon rod atomizer certified reference material Commonwealth Scientific and Industrial Research Organization (Australia) cryotrapping cold vapor AAS dialkyl-lead dibutyltin I ,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid didodec yl-dimethy lammonium-bromide diethyldithiocarbamate dieth y ldithiocarbainate dimethoxydithiophosphate diethylselenium di-isobutyl ketone Deutsches lnstitutfiir Normung (German Standards Institute)

xx Abbreviations and Acronyms

DMA DMF DMSe DMSO DPTH DTC DTP EDL EDTA EDX EF EG

EMP EPA ESCA ET AAS ETV ETV-ICP-MS

F AAS FANES FEP FG FI FI A FID FIMS FIT FWHM GAP GC GF AAS GLP GLS HCL HG AAS HGA H MA- HMDTC HMDTC HPLC IAEA IBMK ICP ICP-MS

diinethyl arsonate dimethylformamide dimethylselenium dimethylsulfoxide 1,5-bis(di-2-pyridylmethylene)thiocarbonhydra~one dithiocarbamate dithiophosphoric acid electrode discharge lamp ethylendiamine-tetraactic acid energy-dispersive X-ray spectrometry enrichment factor polycrystalline electrographite (also Er-ussungsgrenze in Section 5.2.3) electron microprobe Environmental Protection Agency (U.S.A.) electron spectroscopy for chemical analysis electrothermal AAS electrothermal vaporization electrothermal vaporization inductively coupled plasma mass spectrometry flame AAS furnace atomic non-thermal excitation spectrometry fluorinated engineering polymers (perfluoro-ethylene-propylene) flint glass flow injection flow injection analysis flame ionization detector flow injection mercury system (Perkin-Elmer) flame-in-tube (non-heated quartz tube atomizer with flame) full width at half maximum good analytical practice gas chromatography (also glassy carbon in Chapter I ) graphite furnace AAS good laboratory practice gas-liquid separator hollow cathode lamp hydride-generation AAS longitudinally-heated graphite atomizer (Perkin-Elmer) hexamethyleneammonium-hexamethylenedithincarbamate hexamethylenedithiocarbamate high performance liquid chromatography International Atomic Energy Authority (Austria) isobutyl methyl ketone inductively coupled plasma inductively coupled plasma mass spectrometry

Abbreviations and Acronyms XXI t

instrument limit of detection instrumental neutron activation analysis infrared (wavelength range > 800 nm) International Organization for Standardization International Union of Pure and Applied Chemistry knotted reactor liquid chromatography laser-dispersion time-of-flight mass spectrometry laser-enhanced atomic fluorescence spectrometry limit of detection limit of quantitation monobuty ltin methylmercury methyltin microwave induced plasma monomethylarsonate monomethyltin mass spectrometry neutron activation analysis bis(2-hydroxyethy1)dithiocarbamate sodium salt National Institute of Standards and Technology (U.S.A.) non-linearity nitrilotriacetic acid optical emission spectroscopy 1 -(2-pyridylazo)-2-naphthol 4-(2-pyridylazo)resorcinol pol ycarbonate mixed modifier of palladium nitrate and magnesium nitrate polyethylene poly(ethyleneterephtha1ate) perfluoroalkoxy plastics pyrolytic graphite polyimides particle [proton] induced X-ray emission spectroscopy 1 -phenyl-3-methyl-4-benzoyl-5-pyrazolone photomultiplier tube polypropylene pol ysulfone pol ytetratluoroethy lene polyurethane polyvinyl chloride physical vapor deposition quartz tube furnace with a small flame burning i n it quartz tube atomizer Rutherford backscattering spectroscopy

ILOD INAA 1R IS0 IUPAC KR LC LD-TOF-MS LEAFS LOD LOQ MBT MeHg MeT MIP MMA MMT MS NAA NaHEDC NlST NL NTA OES PAN PAR PC Pd-Mg PE PET PFA PG PI PIXE PMPB PMT PP PSF PTFE PU PVC PVD QF QTA RBS

XXII Abbreviations and Acronyms

REE RF RNAA ROC (model) S S-H SIN SEM SeMet SIMS SRM ss SSD SSF STM STPF

TAL TAR TBT TEL TEM TGL THF THGA

TMDTC TML TMSe TOMA T O P 0 TPG TPN (patients) TPP TTFA uv WHO XAD XPS XRD ZBC

rare earth elements radio frequency radiochemical neutron activation analysis reduction of oxides by carbon silica Smith-Hieftje high current pulsing background correction signal-to-noise ratio scanning electron microscopy selenomethionine secondary ion mass spectrometry standard reference material solid sampling solid state detector spectral shadow filming scanning tunneling microscopy stabilized temperature platform furnace (a concept for quasi isothermal atomization) tetraalkyl-lead 4-(2-thiazolylazo)resorcinol tributyltin tetraethyl-lead transmission electron microscopy temperature gradient lamp tetrahydrofuran transversely-heated graphite atomizer with integrated platform (Perkin-Elmer) tetramethylenedithiocarbamate tetramethyl-lead trimethylselenonium tri-N-octylmethylammonium trioctylphosphine oxide total pyrolytic graphite total parenteral nutrition triphen ylphosphine thenoy ltrifluoroacetone ultraviolet (wavelength range < 400 nm) World Health Organization ion exchange resin X-ray photoelectron spectroscopy X-ray diffraction analysis Zeeman-effect background correction

‘Atomic absorption spectrometry (AAS) is a sl,ec.trounal?tticul procedure ,fiw the qiiulitli- tive detection and quantitative determination of elements employing the ubsorption of’

optical radiation by free utoms in the guseous state ’ [ 150 1 1.

1 The Historical Development of Atomic Absorption Spec- trometry

1.1 The Early History

The beginning of optical spectroscopy is generally attributed to Sir ISAAC NEWTON [ 3205 1 who, in a letter to the Royal Society in 1672, described the observation that sun- light is split into various colors when it is passed through a prism. Albeit JOANNES MARCUS MARCI vON KRONLAND (1595-1667), professor of medicine at the University of Prague (Figure 1 - l ) , had already explained the origin of the rainbow o n the basis of the diffraction and scattering of light in water droplets in his book Thuumantias. Liber de urcu coelesti deyue colorum upparentium nuturu ortu et cwusis published in 1648; he can thus be looked upon as the first spectroscopist.

The history of absorption spectrometry is closely connected with the observation of sunlight [5934]. In 1802 Wollaston discovered the black lines in the sun’s spectrum. These were later investigated in detail by Fraunhofer, who assigned letters to the

Figure 1-1. Philosophy in Kronland

‘Joannes Marc and Medicine, i n Bohemia, 17

us Mai and PI Junc I

oct .)r,

or o f born

2 I The Historical Development of Atomic Absorption Spectrometry

strongest lines, starting at the red end of the spectrum with the letter A. Even nowadays it is common to refer to the ‘sodium D line’, a designation originated by Fraunhofer.

In 1820 Brewster expressed the view that these Fraunhofer lines were caused by ab- sorption processes in the sun’s atmosphere. The underlying principles of this absorption were established by KIRCHHOFF and BUNSEN 13 121-3 1241 during their systematic ex- amination of the line reversal in the spectra of alkali and alkaline-earth elements. They conclusively demonstrated that the typical yellow line emitted by sodium salts in a flame is identical to the black D line of the sun’s spectrum. The classical experimental ar- rangement is shown in Figure 1-2.

Figure 1-2. Experimental setup of KIKCHHOFF and B ~ J N S E N for investigating the line reversal in the sodium spectrum (according to [5934]). Radiation from a lamp is focused by lens 1, through the flame of a Bunsen burner B into which sodium chloride is introduced with a spatula. The radiation beam is dispersed by prism P and observed on screen S. The sodium D line appears as a black discontinuity in the otherwise continuous spectrum.

The relationship between emission and absorption was formulated by Kirchhoff in his law, which is generally valid and states that any material that can emit radiation at a given wavelength will also absorb radiation of that wavelength.

The connection between atomic structure and the interaction of atoms with radiation was established by Planck (1900) in the quantum law of absorption and emission of radiation, according to which an atom can only absorb radiation of well defined wave- length il or frequency v, i.e. it can only take up and release definite amounts of energy F :

where h is Planck’s constant and c is the speed of light. Characteristic values of t‘ and v exist for each atomic species.

On the basis of this and many other spectroscopic observations, Bohr proposed his atomic model in 1913, the fundamental principle of which is that atoms do not exist in random energy states, but only in certain fixed states which differ from each other by integral quantum numbers. Upon absorbing a quantum of energy, an atom is transformed

1.2 Sir Alan Walsh and the Period 1952-1962 3

into a particular, energy-enriched state ‘containing’ the radiation energy which has been taken up. After a period of around lO-’s to 10kx s the atom can re-emit this energy and thus return to the ground state.

Although Kirchhoff had already recognized the principle of atomic absorption i n I860 and the theoretical basis was steadily extended during the following decades, the practical significance of this technique was not recognized for a long time. Since the work of Kirchhoff, the principle of atomic absorption was mainly used by astronomers to determine the composition and concentration of metals in the atmospheres of stars. Chemical analyses were only carried out very sporadically by this technique; the deter- mination of mercury vapor did, however, acquire a degree of importance 14225, 63801 (see Section 1.8.1).

The actual year of birth of modern AAS was 1955. In that year, publications authored independently by WALSH [6135] and ALKEMADE and MILATZ [ 125, 1261 recommended AAS as a generally applicable analytical procedure.

1.2 Sir Alan Walsh and the Period 1952-1962

Even though the publications by ALKEMADE and MILATZ 1 1 25, 126) in The Netherlands and WALSH [6135] in Australia appeared in the same year, making it difficult to answer the question as to who actually rediscovered AAS, Alan Walsh (Figure 1-3) is generally recognized as the ‘father’ of modern AAS. This privilege is his just due since he cam- paigned with untiring energy against the resistance to this new idea for more than a dec- ade, spending much time to overcome the disinterest and misunderstanding. Best of all, let Alan Walsh himself describe the events and developments of the period 1952 to 1962 [ 6 1371.

‘My initial interest in atomic absorption spectroscopy was a result of two interacting experiences: one of the spectrochemical analysis of metals over the period 1939- 1946; the other of molecular spectroscopy over the period from 1946-1952. The interaction occurred early in 1952, when I began to wonder why, as in my experience,

Figure 1-3. Sir Alan Walsh.

4 1 The Historical Development of Atomic Absorption Spectrometry

molecular spectra were usually obtained in absorption and atomic spectra in emission. The result of this musing was quite astonishing: there appeared to be no good reasons for neglecting atomic absorption spectra; on the contrary, they appeared to offer many vital advantages over atomic emission spectra as far as spectrochemical analysis was con- cerned. There was the attraction that absorption is, at least for atomic vapours produced thermally, virtually independent of the temperature of the atomic vapour and of excita- tion potential. In addition, atomic absorption methods offered the possibility of avoiding excitation interference, which at that time was thought by many to be responsible for some of the interelement interferences experienced in emission spectroscopy when using an electrical discharge as light source. In addition, one could avoid problems due to self- absorption and self-reversal which often make it difficult to use the most sensitive lines in emission spectroscopy.’

‘As far as possible experimental problems were concerned, I was particularly fortu- nate in one respect. For several years prior to these first thoughts on atomic absorption, I had been regularly using a commercial i.r. spectrophotometer employing a modulated light source and synchronously tuned detection system. A feature of this system is that any radiation emitted by the sample produces no signal at the output of the detection system. This experience had no doubt prevented the formation of any possible mental block associated with absorption measurements on luminous atomic vapours.’

In an internal report for the period February-March 1952 Walsh suggested that the same type of modulated system should be considered for recording atomic absorption spectra. ‘Assuming that the sample is vaporised by the usual methods, e.g. flame, arc, or spark, then the emission spectrum is “removed“ by means of the chopper principle. Thus the emission spectrum produces no output signal and only the absorption spectrum is recorded.’

In the same report he continued: ‘For analytical work it is proposed that the sample is dissolved and then vaporised in a Lundegardh flame. Such flames have a low tempera- ture (2000 K) compared to arcs and sparks (5000 K) and have the advantage that few atoms would be excited, the great majority being in the ground state. Thus absorption will be restricted to a small number of transitions and a simple spectrum would result. In addition, the method is expected to be sensitive since transitions will be mainly confined to those from the ground level to the first excited state.’

The next report for the period April-May 1952 included the diagram shown in Figure 1-4 and described the first experiment as follows: ‘The sodium lamp was operated from 50 cyclesk and thus had an alternating output so that it was not necessary to use a chop- per. The D lines from the lamp were isolated-but not resolved from each other-by means of a direct vision spectroscope and their intensities were measured by means of a photomultiplier tube, the output from which was recorded on a cathode ray oscillograph. Amplification of the signal was achieved by the a.c. amplifiers in the oscillograph. With the slit-width used the signal gave full-scale deflection on the oscillograph screen. A Meker flame was interposed between the sodium lamp and the entrance slit of the spec- troscope. When a solution of sodium chloride was atomised into the air supply of the flame the signal at the oscillograph was reduced to zero. The principle of the method is therefore established.’

I .2 Sir Alan Walsh and the Period 1952-1 962 5

Figure 1-4. The first outline by Walsh for the measurement of atomic absorption from his report for April-May 1952.

In retrospect Walsh admitted to ‘optimistic naivety’; he nevertheless recalls: ‘This simple experiment gave me a great thrill, and I excitedly called John Willis, who at the time was working on infrared spectroscopy and was later to make important contribu- tions to the development of atomic absorption methods of chemical analysis. “Look,” 1 said, “that’s atomic absorption.” “So what?” was his reply, which was the precursor of many disinterested reactions to our atomic absorption project over the next few years.’

In his report for June-July 19.52 Walsh discussed the problem of recording atomic absorption spectra using a continuum source and came to the conclusion that a resolution of approximately 2 pni would be required. This was far beyond the capabilities of the best spectrometer available in his laboratory at that time. The report concluded: ‘One of the main difficulties is due to the fact that the relations between absorption and concen- tration depend on the resolution of the spectrograph, and on whether one measures peak absorption or total absorption as given by the area under the absorptiordwavelength curve.’

This realization led him to conclude that the measurement of atomic absorption re- quires line radiation sources with the sharpest possible emission lines. The task of the monochromator is then merely to separate the line used for the measurement from all the other lines emitted by the source. The high resolution demanded for atomic absorption measurements is in end effect provided by the line source.

At this point Walsh had already recognized the salient points of AAS: The use of line radiation sources, which make a high-resolution monochromator unnecessary, the princi- ple of modulation, which makes the technique selective and eliminates the radiation emitted by the atomizer, and the use of laminar flames of relatively low temperature to atomize the sample. A patent for the technique was lodged at the end of 1953 and an atomic absorption spectrometer was publicly demonstrated in Melbourne in March 1954. However, during the exhibition the instrument aroused little interest.

The last changes to the specifications for the patent were submitted in October 1954 and immediately thereafter WALSH sent his first manuscript about AAS to Spectro- chimica Acta, which was published at the beginning of 1955 [6135]. This paper was followed by others from Walsh’s group [SO101 and also from ALLAN [ 13.51 in New Zea- land and DAVID [ 14261 in Australia. Nevertheless the technique was still looked upon as a ‘scientific curiosity’ rather than a practical analytical technique.

In the meantime, Hilger and Watts had built an instrument, but since the radiation source was not modulated it could not exploit the technique. Other manufacturers later made the same mistake. WALSH [6137] recalls that ‘by 1958 there was no sign of any

6 1 The Historical Development of Atomic Absorption Specti-omelry

instrument manufacturer willing to produce the type of instrument which we thought desirable.’

WALSH then decided to arrange for the production of appropriate equipment. The necessary items were manufactured by three small companies in Melbourne and then assembled by the user. ‘As it transpired,’ he wrote (61371, ‘for the next few years the members of our research group were increasingly involved in supporting the commercial production in Australia of atomic absorption equipment. That a new type of Australian industry was eventually created was, of course, cause for much satisfaction, but it was inevitable that there was a substantial reduction in our research effort over a period of several years.’

Figure 1-5. The Perkin-Elmer Modcl 303. the first 9pectrorneter built cxclusivcly for AAS.

5000

4000

= 3000 :: cn c a, c

E, 5 2000 -

1000

I I

J

6

Figure 1-6. Sales figures for atomic absorp- 1960 1965 1970 1975 tion spectrometers during the first IS years

Year (from [6138]).