UNION INTERNATIONALE DE LA CHIMIE PURE ET APPLIQUEE avec LA SOCIETE DE LA CHIMIE ANALYTIQUE et L'INSTITUT DE PHYSIQUE ET LA SOCIETE DE PHYSIQUE DE LONDRES SPECTROSCOPIE ATOMIQUE D'ABSORPTION Conférences plénières presentees à la CONFERENCE INTERNATIONALE DE SPECTROSCOPIE ATOMIQUE D'ABSORPTION à Sheffield, R.U. 14-18 Juillet 1969 Edité par R. M. DAGNALL et G. F. KIRKBRIGHT LONDRES BUTTERWORTHS INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY in conjunction with THE SOCIETY FOR ANALYTICAL CHEMISTRY and THE INSTITUTE OF PHYSICS AND THE PHYSICAL SOCIETY ATOMIC ABSORPTION SPECTROSCOPY Plenary Lectures presented at the INTERNATIONAL ATOMIC ABSORPTION SPECTROSCOPY CONFERENCE held at Sheffield, U.K. 14-18 July 1969 Edited by R. M. DAGNALL and G. F. KIRKBRIGHT L O N D ON BUTTERWORTHS ENGLAND: BUTTERWORTH & CO. (PUBLISHERS) LTD. LONDON: 88 Kingsway, WC2B 6AB AUSTRALIA: BUTTERWORTH & CO. (AUSTRALIA) LTD. SYDNEY: 20 Loftus Street MELBOURNE: 343 Little Collins Street BRISBANE: 240 Queen Street CANADA: BUTTERWORTH & CO. (CANADA) LTD. TORONTO: 14 Curity Avenue, 374 NEW ZEALAND: BUTTERWORTH & CO. (NEW ZEALAND) LTD. WELLINGTON: 49/51 Bailance Street AUCKLAND: 35 High Street SOUTH AFRICA: BUTTERWORTH & CO. (SOUTH AFRICA) LTD. DURBAN: 33/35 Beach Grove The contents of this book appear in Pure and Applied Chemistry, Vol. 23. No. 1 (1970) Suggested V.B.C. number 543.422 (063) © International Union of Pure and Applied Chemistry 1970 International Standard Book Number 0 408 70119 6 Printed in Great Britain by Page Bros (Norwich) Ltd., Norwich INTRODUCTION The second International Conference concerned with atomic absorption spectroscopyt was organized jointly by the Society for Analytical Chemistry (U.K.) and the Institute of Physics and the Physical Society (U.K.). The Conference was held at the University of Sheffield, U.K., between 14 and 18 July 1969, with more than 450 delegates in attendance. The conference subject matter dealt with all aspects of atomic absorption spectroscopy as well as recent developments in atomic flame emission and atomic fluorescence spectroscopy. Eight plenary lecturers presented invited papers and fifty six contributed papers were delivered. These papers were read in sessions devoted to fundamental developments, metallurgical and biological applications of atomic absorption spectroscopy, atomic fluorescence spectroscopy, develop- ments in instrumentation, theoretical aspects and chemical and physical interference effects. Two open discussion meetings provided the oppor- tunity for delegates to discuss the desirability, nature and venue of future conferences and to make proposals concerning nomenclature in atomic absorption spectroscopy. A well attended general meeting immediately before the close of the conference took the form of a forum at which problems in atomic absorption spectroscopy and the future of the technique were discussed by the plenary lecturers and delegates. It is evident from the material contained in the invited and contributed lectures, and the views presented in the discussions which followed, that interest in analytical flame spectroscopy is still expanding rapidly. The recent developments in atomic fluorescence spectroscopy and the renaissance of analytical flame atomic emission spectroscopy indicate that these techniques must be viewed as complementary to atomic absorption spectroscopy. Which of these tech- niques is preferable for a particular analysis will depend on the nature of both the elements to be determined and the matrix. It is clear from the plenary and contributed papers that much current research work is being devoted to the development of non-flame sample cells for atomic spectro- scopy. Recent promising developments suggest that these devices will be of great utility in atomic absorption and fluorescence spectroscopy. This volume contains the texts of seven of the eight invited plenary lecturers. Unfortunately the manuscript of the lecture presented by Professor V. A. Fassel (U.S.A.) was not available for publication. R. M. DAGNALL G. F. KlRKBRIGHT Co-Chairmen, Technical Committee t The first conference was held in Prague, Czechoslovakia, August 1967. ORGANIZING COMMITTEE Chairman: J.B.DAWSON Vice-Chairman: K.M.BILLS Secretary: D. MOORE Treasurer: G. NICKLESS Asst Secretary: Mrs M. WHITEHOUSE Conference Secretary: Miss P. HUTCHINSON R. M. DAGNALL G. F. KIRKBRIGHT W. T. ELWELL W. R. NALL G. I. GOODFELLOW R. J. W. POWELL W. J. PRICE TECHNICAL COMMITTEE Co-Chairmen: R. M. DAGNALL, G. F. KIRKBRIGHT R. LOCKYER R. WHITE A. TOWNSHEND P. WILDY EXHIBITION COMMITTEE R. J. W. POWELL J. B. HEADRIDGE R. MURTON LOCAL COMMITTEE Chairman: W. R. NALL Secretary: D. G. HEYWOOD B. BAGSHAWE P. H. SCHOLES J. B. HEADRIDGE Miss R. SALES D. P. HUBBARD D. SWINBURN ACKNOWLEDGEMENTS The Conference Organizing Committee wish to express their thanks to the University of Sheffield for accommodating the Conference and to the City of Sheffield for its hospitality. The following firms generously agreed to act as Guarantors : Albright & Wilson & Co. Ltd. Beckman Instruments British Drug Houses (Glaxo Charity Trust) British Petroleum British Titan Products C.Z. Scientific Instruments Esso Petroleum Evans Electroselenium Hopkin & Williams & Co. Ltd. V. A. Howe & Co. Ltd. Imperial Chemical Industries Imperial Metal Industries Johnson Matthey & Co. Ltd. Perkin-Elmer Corporation Rank Precision Industries (Hilger & Watts) Shell Chemical Company Southern Analytical Ltd. Pye Unicam Ltd. THE APPLICATION OF NEW TECHNIQUES TO SIMULTANEOUS MULTI-ELEMENT ANALYSIS A. WALSH Division of Chemical Physics, C.S.I.R.O. Chemical Research Laboratories, P.O. Box 160, Clayton, Victoria, Australia 3168 ABSTRACT The application of atomic absorption methods to simultaneous multi-element analysis is generally difficult, since the various elements to be determined may require not only the use of different flame lengths but also different fuel mixtures. However, the use of resonance detection, selective modulation and flame fluorescence, either individually or collectively, in conjunction with one or more flames, permits the development of simple multi-element systems which can be successfully applied to some important classes of analytical problem. Measurement of the intensity of the resonance radiation produced by illumi- nating atomic vapours generated by cathodic sputtering offers a possible approach to the direct simultaneous determination of several elements in metals and alloys. INTRODUCTION During recent years increasing attention has been directed to the develop- ment of atomic absorption spectrophotometers for the simultaneous deter- mination of several elements1-3. These efforts have had only limited success, as may be illustrated by the fact that of the ten thousand atomic absorption spectrophotometers now in operation throughout the world, probably less than fifty are capable of making simultaneous determinations of two or more elements. The reasons for the difficulty in designing multi-channel instruments suitable for application to a wide range of analytical problems have been discussed in detail elsewhere3, and may be summarized as follows: (a) One set of working conditions can only be used over a concentration range of about 1:10 if precise results are to be obtained; (b) for several elements the number of absorption lines available for measurement is extremely small, and the two most sensitive lines may give sensitivities varying by more than 1:100, so that a range of absorption path lengths and/or sample dilutions becomes necessary if analyses over a wide concentration range are required ; (c) the optimum fuel mixture varies from element to element; (d) the height of the absorption path above the burner which gives minimum chemical inter- ference also varies from element to element; (e) all channels must be kept in correct wavelength adjustments, and this may require more stringent control of room temperature than is necessary for the successful operation of a single-channel instrument. 1 P.A.C.-23/1-B A. WALSH There are, of course, many analytical problems for which one absorption path in a given flame can be used for the determination of several elements and in such cases the design of a multi-channel instrument is straightforward. In general, however, this is not so and at the present time the prospects for developing a multi-channel instrument of wide applicability do not appear to be promising. This paper describes four approaches to the problem which my colleagues and I have studied in an attempt to overcome some of the diffi- culties listed above. MULTI-CHANNEL SPECTROPHOTOMETERS EMPLOYING RESONANCE DETECTORS The multi-channel instrument described below was the outcome of the successful application of resonance detectors in single-channel instruments for the routine determination of magnesium, calcium, copper and nickel and described in recent publications by J. V. Sullivan et αί*~Ί. It has been demon- strated that for these elements the techniques can yield results of the same precision and accuracy as those obtainable by conventional atomic absorption spectrophotometers employing optical monochromators for the isolation of atomic resonance lines. The factors determining the design and performance of atomic absorption spectrophotometers incorporating resonance detectors have been discussed in detail in a recent review8. The outstanding characteristic of a resonance detector is that it cannot be put out of adjustment by changes in room tem- perature and pressure, and it is virtually unaffected by mechanical vibrations. The use of resonance detectors in multi-channel instruments thus offers a solution to the problem of maintaining each channel correctly 4tuned' to the resonance wavelength(s). My colleagues D. C. McDonald, P. Lloyd and J. V. Sullivan have collabor- ated with C. Macliver and D. Sampey (Sampey Exploration Services, Western Australia) in the design and construction of an instrument for the simultaneous determination of copper, silver, nickel, zinc, lead and cobalt in ores. The general layout of the instrument is shown in Figure 1. The light sources are on the right and the resonance detectors on the left. In operation, the lid of the instru- ment covers and makes light-tight the compartment housing the detectors. The resonance radiation from the six detectors falls on six photomultiplier tubes below the detectors. The amplifiers, power supplies and read-out systems of the six channels are housed beneath the optical system. Figure 2 shows a close-up of the burner and light sources. The perforations in the burner top are so arranged as to provide the appropriate absorption path length and an adequate width for each element. The optical system for each channel can be arranged to select the optimum height above the burner. High-intensity hollow-cathode lamps9 are used as light sources for the determination of zinc and nickel, whilst conventional hollow-cathode lamps are used for copper, silver and lead channels. Sputtering-type detectors are used for all channels except zinc and lead, for which a thermal type detector has proved superior. No combination of lamp and detector has yet given a satisfactory signal-to-noise ratio for the determination of cobalt. Using the type of burner illustrated in Figure 2 it has only been possible to use an air-propane flame. It is advisable to use an air-acetylene flame in 2 Figure 1. Six-channel atomic absorption spectrophotometer incorporating resonance lamps as monochromators. Figure 2. Arrangement of light sources and burner in six-channel spectrophotometer.