Analytical Graphite Furnace Atomic Absorption Spectrometry: A Laboratory Guide

291 Pages·1997·8.8 MB·English

by  Dr. Gerhard Schlemmer, Dr. Bernard Radziuk (auth.)

Analytical
Graphite
Furnace Atomic
Absorption
Spectrometry
A Laboratory Guide
Gerhard Schlemmer
Bernard Radziuk
Birkhäuser Verlag
Basel • Boston • Berlin
Authors
Or. Gerhard Schlemmer
Or. Bernard Radziuk
Bodenseewerk Perkin-Elmer GmbH
Postfach 101164
0-88662 Überlingen
Germany
Library of Congress Cataloging-in-Publication Data
Schlemmer, Gerhard:
Analytical graphite furnace atomic absorption spectrometry: a laboratory guide / Gerhard
Schlemmer, Bernard Radziuk.
p. cm
Includes bibliographical references and index.
ISBN 978-3-0348-7578-3
1. Atomic spectroscopy. I. Radziuk, Bernard. 11. Title.
QD96.A8S365 1999
543' .0858--dc21 99-13388
Deutsche Bibliothek Cataloging-in-Publication Data
Schlemmer, Gerhard:
Analytical graphite furnace atomic absorption spectrometry: a laboratory guide / Gerhard
Schlemmer; Bernard Radziuk. - Basel; Boston; Berlin : Birkhäuser, 1999
ISBN 978-3-0348-7578-3
The publisher and editor can give no guarantee for the information on drug dosage and
administration contained in this publication. The respective user must check its accuracy by
consulting other sources of reference in each individual ca se.
The use of registered names, trademarks etc. in this publication, even if not identified as such,
does not imply that they are exempt from the relevant protective laws and regulations or free
for general use.
This work is subject to copyright. All rights are reserved, whether the whole or part of the
material is concerned, specifically the rights of translation, reprinting, re-use of illustrations,
recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data
banks. For any kind of use permission of the copyright owner must be obtained.
© 1999 Birkhäuser Verlag, PO Box 133, CH-401 0 Basel, Switzerland
Softcover reprint of the hardcover 1st edition 1999
Printed on acid-free paper produced from chlorine-free pulp. TCF
00
Cover design: Gröflin Graphic Design, Basel
ISBN 978-3-0348-7578-3 ISBN 978-3-0348-7576-9 (eBook)
DOI 10.1007/978-3-0348-7576-9
987654321
Table of contents
Prefaee ............................................ IX
11
AAS: a simple and rugged system for traee and
ultratraee elemental analysis .......................... . 1
1.1 The physical background .................... . ... . . 2
1.2 Light sources, their properties and how to obtain maximum
intensity and lifetime .. ... .. ... .... .... .. ... .. ... . 5
1.3 Monochromators, polychromators and other optical
components: from lines to plane .................... 10
1.4 Detectors in AAS: the revolution has just begun ... .... . 14
1.5 Improving selectivity: about light modulation, photon
integration, continuum sources and magnetic fields ..... 17
1.6 A little bit about flames and a lot more about
graphite furnaces for generation of atom clouds .. .... . 30
1.6.1 Safety aspects and laboratory prerequire-
ments for graphite furnace systems ............. 36
Important terms and units for analytical atomic
speetrometry ....................................... 43
2.1 Sensitivity and characteristic mass: the way to
check your spectrometer . .... .... .... .. . ... .. .. . .. 44
2.2 Precision or detection limit: what's the name
of the game? ..... .... ... ... .. ..... ............. 46
2.3 Working range of graphite furnace AAS:
linear and nonlinear curves and ways to
linearize nonlinear functions .. .... ... .. .. .. .. . ..... 51
2.4 Calibration in AAS or: never underestimate
the importance of the standard .. ................... 54
v
Analytical Graphite Furnace Atomic Absorption Spectrometry
2.5 Effects and interferences: the harmless and
the dangerous effects of matrix ... .... .. . .. .. . ..... . 58
2.6 Means and methods to provide quality
assurance in AAS 61
11
Even theory can be fun: the exciting growth of
knowledge in electrothermal AAS ....................... 67
3.1 History of graphite furnaces ..... ... .. .. .... ........ 67
3.2 Empirieal observations: the stability of the
characteristie mass mo ... ..... .. .... .. . ... .. .. ..... 75
3.3 The dynamie temperature behaviour of a
Massmann-type furnace and a Transversely
Heated Graphite Atomizer .. .. ... . ... .. ... .. . .. . .. . 77
3.4 Chemieal reactions in a gas phase at elevated
temperatures enclosed by graphite ....... ........... 79
3.5 The influence of tube wall and platform on
the atomization pulse . .. .. ... .. .. .. . .. .. . .. . ..... 80
3.6 Statistieal model ... . ... .... .. .. ... ... ... ... .. ... . 83
3.7 Graphite is an impressive material - but
somehow and sometimes it is still black magie . .. . .. ... 84
;I
Developing a method in GFAAS ........................ 93
4.1 Basie checks or "o.k., the whole thing is doing
wh at it's supposed to" .. .. . ... ................... . 94
4.1.1 Automatie checks on modern instruments ........ 94
4.1.2 Spectrometer .. ... ......... ................ 94
4.1.3 Graphite furnace .. ... .. . ... . ... ... .. ... ... .. 96
4.1.4 Blank and reference solutions including
modifier ..... .. ... ... ... . ... ... .. .. . ... .. . 97
4.1.5 Characteristic mass ... . .. .... . .. . .. . .. . .. ... . 99
4.1.6 Simultaneous multielement GFAAS .... ........ . 99
4.2 Screening may be sufficient and may save a
lot of time and annoyance ....... . .. . .. . .. .. . .. . .. . 102
4.3 Systematie development of a GFAAS method:
accuracy, precision, speed, long term stability .......... 103
4.3.1 Basie considerations ........... .............. 104
VI
Table of contents
4.3.2 Drying .......................... . ......... 106
4.3.3 Pyrolysis ................................... 109
4.3.4 Atomization ............................... 112
4.3.5 Analytical quality and long term stability ........ 115
4.3.6 Speed ........................... . ........ 117
4.4 Chemical modifiers: the spectroscopist's box of tricks 119
4.4.1 Modifiers which influence the thermal
stability or the chemical activity of the
the matrix (matrix modifiers) .................. 120
4.4.2 Modifiers which thermally stabilize the
analyte element(s), or "Eureka! There is
a universal modifier!" from the vantage
point of 12 years after its introduction .......... 124
4.4.3 Using modifiers properly ..................... 127
4.4.4 Modifiers which are active in combination
with the graphite surface in the solid phase ...... 133
The first step is sam pie pretreatment ................... . 141
5.1 Using the right method for sampie pretreatment
is half the analysis .............................. . 142
5.2 Autosampiers, the universal sampie management
systems ........................................ 152
5.3 A liquid is not necessarily a prerequirement:
about solids and slurries ........................... 158
5.4 Ways to separate matrix and preconcentrate
analyte ........................................ 166
5.5 Analyte in gaseous molecular form: horror
or benefit? ..................................... 174
Use and abuse of microprocessors ...................... . 189
6.1 A peak will tell you more than 1000 numbers ......... . 190
6.1.1 What do we see on the screen? ............... . 191
Blank firings ............................ . 192
Absorbance by analyte only ..... . .......... . 195
Background only ........................ . 201
6.2 Everything you need may be in your PC's memory ...... 207
VII
Analytical Graphite Furnace Atomic Absorption Spectrometry
6.3 Check functions and quality control . ........ . .... . ... 209
6.3.1 Calibration: range, precision, recovery .. .... . .... 210
6.3.2 Quality control sampies: accuracy and
long term stability of results .... ..... .. .. .. .. .. 211
6.3.3 Accuracy of the entire analytieal procedure . .. .... 212
6.4 What's to be done with all the data? . ... .. . .. ... .. .. . 214
• Patience Clever's exciting voyage through the world of matrices and
challenging analyses ................................. 221
7.1 Utlra pure water and chemieals ........ . .. . ... .... .. 221
7.1.1 Keeping contamination under control ... . ..... . . 224
7.1.2 Optimization of the photometrie noise .. ...... .. 226
7.1.3 Graphite furnace time/temperature programs .. .. . 226
7.1.4 Recoveries .. .. ...... ... ....... .. .. .... ... .. 227
7.1.5 Detection limits .. ..... .... .... . .... . .. . ... .. 227
7.2 Surface water, mineralized water, sea water
and waste water .. .. .. ... ... .... .... .... .... .. . .. 233
7.3 Sediments, soils and sludges .. ... . ... ... .. . .. . .. .. .. 240
7.4 Plants and other biologieal tissue .. ... ... .. .. .... .. . . 243
7.5 Clinieal sampies .... . .... ... ...... .............. .. 246
7.6 Oil and fat .. .. .. ... .. ... .. . ... . ... . .... . ... .... 253
7.7 Clean sampies which are difficult to dissolve:
the analysis of slurries .. .. .. .. .. .. ... ... ... ... ... . 257
Subject index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. 263
VIII
Preface
"One should rather go horne and mesh a net than jump into the pond and dive far
fishes"
(Chinese proverb)
Recognizing the precise analytical question and planning the analysis according
ly is certainly the first prerequisite for successful trace and ultratrace determina
tions. The second prerequisite is to select the method appropriate to the analyti
cal specification. The method itself consists of a set of available tools. The third
prerequisite is that analysts and operators know the methods weH enough to
enjoy challenging themselves as weH as the methods and are rewarded by the joy
of high-quality data, fast and economical results and the conviction of having the
analytical job under control. This skill is known among analysts or operators
working with an exciting new and sometimes complicated analytical technique
but is gradually lost on ce a technique becomes "mature" and a routine tool.
Unfortunately, laboratory managers often do not allow sufficient training time
for their analysts and technicians for "routine" techniques and thus miss an
opportunity for motivating their co-workers and obtaining the full benefit of the
equipment.
Graphite furnace atomic absorption spectrometry (AAS) is one of the mature
analytical techniques wh ich is seen as a routine method in most laboratories.
More than 10,000 furnaces are operated in elemental trace and ultratrace analy
ses in laboratories around the world today. Although most of these probably do
provide acceptable analytical data, only a few are challenged in the sense men
tioned above. Having been involved in instrumental research and development, in
the curricula of training courses, in the support of graphite furnace AAS, and in
the development of analytical methods based on this technique for more than 15
years, we are convinced that - apart from being a routine tool - modern graphite
furnace AAS is a fascinating analytical technique with much future potential. We
IX
hope that the "Laboratory Guide" will help to impart the joy of using, playing
with and challenging modern graphite furnace AAS to our readers.
Überlingen, 21 February 1999
Gerhard Schlemmer
Bernard Radziuk
x
AAS: a simple and rugged system for
trace and ultratrace elemental analysis
"Clever ... your ignal i noisy? .. whal's the tandard deviation of your
blank? ... what element are you running today? ... we've never done barium
before, have we? All right, 1'11 be down in aminute."
Mrs. Patience Clever aved part of the report - two hour of work - on her
laptop, grabbed her Laboratory Guide and ru hed down to the trace element
laboratory. The new multielement graphite furnace y tem wa humming and
4 peaks appeared simultane u lyon the screen. 3 peaks were symmetrie and
Gaus ian shaped with a "clean" ba eline. One signal was noisy, relatively
broad and was superimposed on a low background ignal howing approxi
mately the same sinusoidal noise as the analyte p cific ab orbance.
a 0.3 As b 0.2 Pb
~ 0.2 .~.
I: I:
"
':.",; ~.. 0.1
~ 0.1 '0":(
1 2
1 time (s) 2
time (s)
c 0.2 Cr d 0.2 Ba
'" .'".
"c "c
-."oe, 0.1 ~.. 0.1
'" '"
0:( 0:(
°O~~~'~'~2~~3---4~~5 °O~~~~2~~3~~4~~5
time (s) time (s)
Figure 1.1 Four elements in multielement mode
(a) 250 pg As, (b) 250 pg Pb, (e) 50 pg Cr; (d) 1000 pg Ba.
Analytical Graphite Furnace Atomic Absorption Spectrometry, by G. Schlemmer and B. Radziuk
© 1999, Birkhäuser Verlag Basel/Switzeriand