ANALYTICAL ATOMIC SPECTROSCOPY

Transcription

1 ANALYTICAL ATOMIC SPECTROSCOPY

2 MODERN ANALYTICAL CHEMISTRY Series Editor: David Hercules University of Georgia ANALYTICAL ATOMIC SPECTROSCOPY By William G. Schrenk PHOTOELECTRON AND AUGER SPECTROSCOPY By Thomas A. Carlson In preparation MODERN FLUORESCENCE SPECTROSCOPY Edited by Earl L. Wehry A Continuation Order Plan is availab!e for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher.

3 ANALYTICAL ATOMIC SPECTROSCOPY William G. Schrenk Kansas State University Manhattan, Kansas PLENUM PRESS NEW YORK AND LONDON

4 Library of Congress Cataloging in Publication Data Schrenk, William G Analytical atomic spectroscopy. (Modern analytical chemistry) Includes bibliographies and index. 1. Atomic spectra. I. Title. QD96.A8S37 543' ISBN-13: e-isbn-13: : / Plenum Press, New York Softcover reprint of the hardcover 1 st edition 1975 A Division of Plenum Publishing Corporation 227 West 17th Street, New York, N.Y United Kingdom edition published by Plenum Press, London A Division of Plenum Publishing Company, Ltd. Davis House (4th Floor), 8 Scrubs Lane, Harlesden, London, NW1 0 6SE, England All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher

5 To the women in my life Bertha, Ellen, Sara, and Sue

6 Preface This textbook is an outgrowth of the author's experience in teaching a course, primarily to graduate students in chemistry, that included the subject matter presented in this book. The increasing use and importance of atomic spectroscopy as an analytical tool are quite evident to anyone involved in elemental analysis. A number of books are available that may be considered treatises in the various fields that use atomic spectra for analytical purposes. These include areas such as arc-spark emission spectroscopy, flame emission spectroscopy, and atomic absorption spectroscopy. Other books are available that can be catalogued as "methods" books. Most of these books serve well the purpose for which they were written but are not well adapted to serve as basic textbooks in their fields. This book is intended to fill the aforementioned gap and to present the basic principles and instrumentation involved in analytical atomic spectroscopy. To meet this objective, the book includes an elementary treatment of the origin of atomic spectra, the instrumentation and accessory equipment used in atomic spectroscopy, and the principles involved in arc-spark emission, flame emission, atomic absorption, and atomic fluorescence. The chapters in the book that deal with the methods of atomic spectroscopy discuss such things as the basic principles involved in the method, the instrumentation requirements, variations of instrumentation, advantages and disadvantages of the method, problems of interferences, detection limits, the collection and processing of the data, and possible applications. Since the book is intended to serve as a textbook, principles are stressed. Detailed methods of analysis for specific elements are not included. It is the hope of the author, however, that the presentation of basic information is sufficiently detailed so the students can develop their own methods of analysis as needed. Included in the textbook are several appendixes that should be valuable to the student as well as to atomic spectroscopists. These include a compilation of frequently used spectroscopic terms and units, tables of sensitive vii

7 viii PREFACE spectral lines of 70 elements abridged from National Bureau of Standards publications, absorbance values and the Seidel function calculated from percentage transmittances, and a table of elemental detection limits for flame emission and atomic absorption spectroscopy. The author wishes to acknowledge the assistance of a number of people in the preparation of this book. Dr. W. G. Fateley, Head, Department of Chemistry, Kansas State University, was most encouraging, cooperative, and helpful. Dr. Clyde Frank, The University ofiowa, was of great assistance in planning the text and in reading the manuscript. Dr. Lorin Neufield, Tabor College, Hillsboro, Kansas, Dr. S. E. Valente, Regis College, Denver, Colorado, Dr. Delbert Marshall, Ft. Hays Kansas State College, and Dr. Ron Popham, Chairman, Department of Chemistry, Southeast Missouri State College, Cape Giraudeau, Missouri, all have read and aided in the revision of certain chapters. All those mentioned above, including Dr. Frank, are former graduate students of the author. Mr. Allan Childs, a graduate student in chemistry, aided in preparing a number of the spectral plates used as illustrations in the text and Mr. Truman Waugh of the Kansas Geological Survey, Lawrence, Kansas, was very helpful with the preparation of Appendix IV, which shows wavelength positions of some 50 elements together with a reference iron spectrum. Ms. Diane Janke and Ms. Jane Adams were the most cooperative of typists and Steven Wallace made the line drawings. Their help is most appreciated.

8 Contents Chapter 1 Historical Introduction I. Early Developments 2. The Newtonian Era. 3. The Early 1800's (to Kirchhoff and Bunsen). 4. The Later 1800's 5. Arc and Spark Excitation. 6. Flame Emission Spectroscopy. 7. Atomic Absorption Spectroscopy. 8. Atomic Fluorescence Spectroscopy Selected Reading I \0 Chapter 2 The Origin of Atomic Spectra. I. The Nature of Electromagnetic Radiation 2. Early Concepts. 3. The Balmer Equation. 4. From Balmer to Bohr Spectral Line Series for Hydrogen 4.2. Energy Level Diagrams. 5. Modifications of the Bohr Theory Selection Rules for nand k(f) 5.2. Atoms with Two Valence Electrons 5.3. Selection Rules and the Schrodinger Equation 6. Alkali Metal Atom Spectra 6.1. Doublet Structure of Alkali Metal Spectra 6.2. Electron Spin. 7. Alkaline Earth Atomic Spectra II II ix

9 x 8. Spectral Series and Spectroscopic Term Symbols 9. Zeeman and Stark Effects 10. Spectral Line Intensities Statistical Weight The Boltzmann Distribution Factor II. Transition Probabilities-Oscillator Strengths 12. Spectral Linewidths. 13. Atomic Fluorescence 14. Metastable States-Laser Action Laser Action 15. Molecular Spectra (Band Spectra) Selected Reading CONTENTS Chapter 3 Filters, Prisms, Gratings, and Lenses 1. Filters 1.1. Absorption Filters 1.2. Interference Filters 1.3. Circular Variable Filters. 2. Prisms 2.1. Dispersion of a Prism 2.2. Resolving Power of a Prism Prism Materials 2.4. Types of Prisms 3. Interferometers. 4. Diffraction Gratings 4.1. Dispersion of a Grating Resolving Power of a Grating 4.3. Production and Characteristics of Gratings 4.4. Grating Replicas Concave Gratings 4.6. Holographic Gratings 4.7. Echelle Gratings 5. Lenses 5.1. Uses of Lenses 5.2. Lens Defects Selected Reading Chapter 4 Spectrometers. 1. Prism Spectrometers 1.1. The Cornu Prism Spectrometer

10 CONTENTS 1.2. The Littrow Spectrometer Plane Grating Spectrometers The Ebert Spectrometer The Czerny-Turner Spectrometer The Two-Mirror, Crossed-Beam, Plane Grating Spectrometer The Double-Grating Spectrometer Concave Grating Spectrometers The Rowland Spectrometer The Paschen-Runge Spectrometer The Eagle Spectrometer The Wadsworth Spectrometer The Grazing Incidence Spectrometer The Seya-Namioka Spectrometer Vacuum Spectrometers Direct Reading Spectrometers Selection of a Spectrometer Adjustment and Care of Spectrometers Vertical Adjustment of the Entrance Slit Focusing the Entrance Slit Prism Instruments Grating Instruments Final Adjustments General Care of Spectrometers. 96 Selected Reading 97 xi Chapter 5 Accessory Equipment for Arc and Spark Spectrochemical Analysis 99 I. The Spectrometer Slit The Hartmann Diaphragm 10 I 3. The Step Filter Rotating Sectors Excitation Sources The Direct Current Arc The Alternating Current Arc The Electric Spark The Plasma Arc The Laser Source Multiple Source Units Arc and Spark Stands 114

11 xii 6.1. Special Assemblies for the Arc-Spark Stand The Stallwood Jet The Petry Stand Rotating Disk Electrode Device 7. Order Sorters 8. Densitometers and Comparators. 9. Miscellaneous Accessory Equipment 9.1. Electrodes. Selected Reading CONTENTS Chapter 6 Recording and Reading Spectra 125 I. The Photographic Process Characteristics and Properties of the Photographic Emulsion The Characteristic Curve 1.3. The Reciprocity Law 1.4. The Intermittency Effect The Eberhard Effect Graininess and Granularity Resolving Power Spectral Sensitivity Processing of Spectroscopic Films and Plates The Developing Process Hadamard Transform and Fourier Transform Spectroscopy Light-Sensitive Phototubes Spectral Response Designation General Characteristics of Multiplier Phototubes Solar Blind Phototubes Resonance Detectors Vidicon Detectors 145 Selected Reading 146 Chapter 7 Qualitative and Semiquantitative Arc-Spark Emission Spectrochemical Analysis Sample Excitation Wavelength Measurements Line Identification by Wavelength Measurement Comparison Spectra 151

12 CONTENTS 4. Spectral Charts Wavelength Tables Some Special Problems and Techniques of Spectrochemical Qualitative Analysis Spectral Line Interferences Spectral Band Interferences Arc Continuum Interference Increasing Spectral Line Intensities Semiquantitative Spectrochemical Analysis Determination of a Concentration Level The Harvey Method of Semiquantitative Spectrochemical Analysis Matrix Effects The Wang Method of Semiquantitative Spectrochemical Analysis Some Special Spectrochemical Problems Microsamples Microarea Sampling. 166 Selected Reading 167 xiii Chapter 8 Quantitative Spectrochemical Analysis 169 I. Some General Considerations The Internal Standard Spectroscopic Buffers Excitation of the Sample Selection of Spectral Lines Comparison Standards Sample Preparation Emulsion Calibration and Analytical Working Curves Emulsion Calibration The Emulsion Calibration Curve The Working Curve Construction of a Typical Analytical Working Curve The Calculating Board. 192 II. Background Correction Multielement Analysis with Direct Read-Out Types of Samples Liquid Samples Metallic Samples Powder Samples 197

13 xiv Organic Samples Special Samples. 14. Some Special Techniques Fractional Distillation Carrier Distillation Transfer Methods 14.4 Laser Methods Controlled Atmospheres Cathode Layer Excitation Gases Radioactive Samples IS. Time-Resolved Spectroscopy Time-Resolving Components Some Characteristics of Time-Resolved Spectra Analytical Applications 16. Chemical Preparation of Samples. 17. Applications of Spectrochemical Analysis Metals and Alloys Geology Oils and Water Plants and Soils Men and Animals Environmental Studies Some Other Applications Selected Reading CONTENTS I Chapter 9 Flame Emission Spectroscopy. I. Flame Emission Instrumentation Requirements. 2. The Analytical Flame Burners and Aspirators 2.2. Fuel-Oxidant Control 3. The Excitation Process in the Flame 3.1. Flame EmIssion Spectra. 4. Flame Emission Interferences 4.1. Spectral 4.2. Ionization Cation-Anion Interferences Cation-Cation Interferences 4.5. Oxide Formation Chemiluminescence

14 CONTENTS 4.7. Physical Interferences Control of Interferences Spectral Ionization Interference Control Cation-Anion Interference Control Control of Oxide Interference Control of Physical Interference Simultaneous Multielement Analysis Analytical Treatment of Data Establishment of a Working Curve Background Correction Sample Bracketing The Method of Standard Additions 241 Selected Reading 242 xv Chapter 10 Analytical Atomic Absorption Spectroscopy The Atomic Absorption Process Instrumentation Requirements Radiation Sources Hollow Cathode Lamps High-Intensity Lamps Multiple-Element Lamps Demountable Lamps Gaseous Discharge Lamps Electrodeless Discharge Lamps Flame Emission Sources Continuous Sources Production of the Atomic Vapor Nebulization of the Sample Ultrasonic Nebulization Flame Systems Fuels and Oxidants Atomic Distribution in Flames Non-Flame Absorption Cells Hollow Cathodes L'vov Furnace W oodriff Furnace Delves Cup Carbon Rod Analyzers Tantalum Boat Analyzer 273

15 xvi CONTENTS 6.7. Other Non-Flame Cells Special Systems Monochromators Detectors Resonance Detection Amplifiers Read-Out Devices 284 II. Interferences in Atomic Absorption Spectral Interferences Ionization Interferences Chemical Interferences Interferences with Flameless Sampling Control of Interferences Spectral Interference Control Ionization Interference Control Chemical Interference Control Flame Temperature Fuel-to-Oxidant Ratio Flame Region Releasing and Chelating Agents Chemical Separations Background Correction Analytical Treatment of Data The Working Curve Analytical Procedures Simultaneous Multielement Analysis. 297 Selected Reading 298 Chapter 11 Atomic Fluorescence Spectroscopy Theoretical Basis of Analytical Atomic Fluorescence Spectroscopy Advantages and Limitations of Atomic Fluorescence Instrumentation Excitation Sources Hollow Cathode Lamps Metal Vapor Lamps Electrodeless Discharge Lamps Continuous Sources Laser Sources The Sample Cell. 307

16 CONTENTS 4.1. Total-Consumption Aspirator Burners Laminar Flow Burners Non-Flame Sample Cells Monochromators Interferences in Atomic Fluorescence Spectral Interferences Chemical Interferences Physical Interferences Analytical Procedures The Analytical Working Curve Organic Solvents Detection Limits Sample Preparation Applications and Future Developments 317 Selected Reading 318 xvii Appendix I. Some Basic Definitions, Physical Constants, Units, and Conversion Factors. 319 Appendix II. Spectral Lines, Arranged by Wavelength, with gf and Intensity Values. 321 Appendix III. Spectral Lines, Arranged by Elements, with gfand Intensity Values 337 Appendix IV. Spectral Charts 347 Appendix V. Absorbance Values Calculated from Percentage Transmittances 353 Appendix VI. Numerical Values of the Seidel Function 355 Appendix VII. Four-Place Logarithm Table 357 Appendix VIII. Detection Limits by Flame Emission and Atomic Absorption 361 Appendix IX. Periodic Table of the Elements 365 Appendix X. Relative Atomic Weights 367 Author Index 369 Subject Index 371