Atomic Absorption Spectrometry - leseprobe.buch.de · Thus, Chapter 1 on the historical development of AAS is new; in the first instance it demonstrates the maturity of the technique

Bernhard Welz Michael Sperling

Atomic Absorption Spectrometry

Third, Completely Revised Edition

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

This Page Intentionally Left Blank

Bern hard We 1 z Michael Sperling


6B WILEY-VCH

This Page Intentionally Left Blank

Bernhard Welz Michael Sperling


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.

~~

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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 proposed 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 determination 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, improved 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 developments 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 injection. New areas of application including the analysis of ‘high tech’ materials and speciation 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 information, 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 measurement 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 during recent years. On the other hand, the comparative chapter on other analytical procedures 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 relevant, 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 attempted 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 spectroscopy 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 therefore 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 absorption 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 classification 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 analysis. Solids analysis is also treated since this has become possible with the graphite furnace 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 monograph. 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, however, 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 published. 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

Documents

Atomic Absorption Spectrometry - leseprobe.buch.de · Thus, Chapter 1 on the historical development of AAS is new; in the first instance it demonstrates the maturity of the technique