Atomic Absorption Spectroscopy. International Atomic Absorption Spectroscopy Conference

151 Pages·1970·3.129 MB·English

by  R. M. Dagnall and G. F. Kirkbright (Eds.)

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
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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.