Spectrochemical trace analysis for metals and metalloids

791 Pages·1996·35.363 MB·English

by  R Lobinski, Z Marczenko

Editor's Preface
I am proud to bring to you, as the first volume under my editorship of
this series, a treatise of enormous value and broad scope.
It has never been more true than today that the more we learn about
the composition of matter, of the environment, and of biological
systems, the more we will understand how chemistry controls function.
It has become evident that trace and ultratrace analysis remain
challenging, and that without a proper and deep understanding of each
step in a method, it is possible to be in error. A thorough reading of the
first two sections of this volume, and selected reading in the third
section, prepare the chemist in all aspects of modern inorganic trace
and ultratrace analysis for metals and metalloids. Indeed, the book has
pedagogical value. Rarely do modern instrumental analysis texts
venture in any depth beyond the physics surrounding the actual
measurement.
The information in this volume on sample preparation, and on
selected metal determinations, is a boon to the industrial, government,
or academic chemist with teaching or training responsibility.
S.G. Weber
xxi
Authors' Preface
The development of trace inorganic analysis is a response by analytical
chemists to the increasing concerns about the role of elements at low
concentrations in the environment, biology, medicine, industrial qual-
ity control and other fields. Whereas classical analysis has dealt with
sample components exceeding the 0.01% concentration level, for trace
analysis those at levels between 0.1 and 100 fig g-l (ppm) are interest-
ing. The determination of concentrations below 0.1 g g' is termed
extreme trace (ultratrace) analysis.
The increasing requirements in terms of sensitivity, sample through-
put, precision and accuracy of analysis are driving the development of
novel and more effective analytical techniques. The most important
group are spectrometric techniques which only in few cases can be
matched by electrochemical methods. Spectrometric techniques are
based on a correlation of the intensity of an element-specific signal
observed in an electromagnetic or mass spectrum with the concentra-
tion of the element in the sample. They are divided according to the
origin (and wavelength) of the spectrum used for quantification into
molecular or atomic absorption, emission and fluorescence spectrome-
try, X-ray fluorescence, a-, A-, and y-spectrometry and mass spectrome-
try. Further subdivisions are often made according to how the spectrum
is generated (atomization, excitation or activation). The most important
spectrometric techniques include atomic absorption spectrometry
(AAS), atomic emission spectrometry (AES) and mass spectrometry
(MS); the latter two are usually associated with excitation in an induc-
tively coupled plasma (ICP). Their rapid development contributed to a
decline of the role of spectrophotometry and X-ray fluorescence (XRF)
in trace analysis in recent years (insufficient sensitivity) and neutron
activation analysis (the need of access to a nuclear reactor).
xxiil
It must be emphasized that, except for some sophisticated instru-
mental techniques, the lower concentration levels in real samples are
not accessible but are after the sample decomposition and/or a chemical
separation/preconcentration of the analytes from the matrix prior to
measurement. More or less complex spectrochemical procedures are
still dominant in the majority of academic, industrial and commercial
analytical laboratories and enjoy a unique and widely recognized role
in the certification of candidate reference materials and secondary
laboratory standards. A deep understanding of these methods is a
prerequisite of successful analysis. In particular this applies to the
awareness of contamination risk which is omnipresent in trace and
ultratrace analysis.
This book discusses analytical methods that combine a chemical
sample treatment step (e.g. decomposition, separation and preconcen-
tration, matrix modification) with a spectrometric technique, applied to
the determination of metals and metalloids (As, B, Sb, Se, Si and Te) at
trace and ultratrace levels. Analytical techniques for surface analysis
or for direct bulk analysis (e.g. instrumental activation analysis, XRF,
ablation MS techniques) are not included unless preceded by a chemical
sample processing step. In principle, the book covers analytical chemis-
try of stable nuclides only, but some important long-lived naturally
occurring isotopes (U, Th, Tc) and anthropogenic environmental con-
taminants (239'240Pu, 247Np) have been included. Particular attention is
given to the analysis for the chemical species in which the element is
present in the analyzed material (speciation).
The overview of current spectrochemical techniques used in elemen-
tal trace analysis should enable an analyst, facing the task of analyzing
a sample type that he or she has never analyzed before, to reach a
decision which instrumental technique to choose and how to handle the
sample starting from sampling and decomposition, through separation
and preconcentration, until the final determination step. A thorough
critical survey of the literature for the last ten years (1985-1994)
specifies analytical characteristics likely to be achieved and gives refer-
ences to source articles in peer-reviewed journals.
The book is composed of three parts: general principles and charac-
teristics of analytical methodologies (Part I), practical issues of sample
treatment and multielement analysis (Part II) and determination of
individual elements (Part III). Part I discusses general aspects of
successive steps of an analytical procedure from sampling and sample
decomposition (acid attack, fusion, decomposition in gas streams) in
xxiv
simple and assisted (microwave, ultrasonic, pressure) systems, through
separation and preconcentration (extraction, volatilization, coprecipita-
tion, sorption and chromatographic techniques) to instrumental deter-
mination techniques (spectrophotometry and spectrofluorimetry,
atomic absorption, emission and fluorescence, X-ray, nuclear and mass
spectrometric techniques). Emphasis is placed on automated sample
processing - flow injection analysis (FIA) and the rapidly developing
field of analytical chemistry of metal and metalloid moieties (speciation
and hyphenated techniques). The last chapter of Part I, devoted to
accuracy in trace analysis, discusses various quantification techniques,
sources of errors and the role of certified reference materials (CRMs) for
method validation. The chief objective of Part I is to present principles,
analytical characteristics and possible interferences of modern spectro-
chemical techniques and to direct the reader to relevant monographs,
edited works, topic and tutorial reviews, written by leading experts in
the related fields. Part I should give the reader a global view on modern
analytical spectrochemistry and enable him or her to establish the
relevance and suitability of a given analytical method for the analytical
task to be solved, and to estimate its chance of success.
Part II is devoted to practical aspects of initial sample handling and
multielement trace analyses of different types of real samples: environ-
mental, geological, biological and clinical, and inorganic and organic
industrial materials. Both the cases of direct analysis following a
chemical sample decomposition and those involving multielement sepa-
ration and preconcentration using extraction, hydride generation and
sorption are discussed. Each chapter contains several tables summariz-
ing procedures for multielement analysis of real samples and certified
reference materials available for method validation.
Part III contains 54 alphabetically arranged monographic reviews on
spectrochemical trace analysis for individual elements. Each chapter
gives basic information on analytico-chemical properties of the element
which is followed by an overview of methods for its separation, precon-
centration, and instrumental detection. Particular attention is given to
practical issues, difficulties and quality assurance during the analysis
of real samples. Each chapter contains tables summarizing the key
steps of the procedures developed for the trace element determination
and the detection characteristics reported.
The book contains ca 5000 carefully selected references, in general
not older than 1985. Strong preference is given to full papers in peer-re-
viewed English-language journals, but for elements which are pertinent
xxv
in geochemistry, environmental or biomedical fields a number of refer-
ences from specialized field-related journals are given. In our opinion,
these references together with those cited therein give a sufficiently
extensive coverage of the topic. For a more comprehensive survey, the
reader is advised to consult the periodic reviews in Analytical Chemis-
try and Journalo fA nalytical Atomic Spectrometry which were not cited
anywhere in the book.
Ryszard Lobifiski
Zygmunt Marczenko
xxvi
List of abbreviations
AAS atomic absorption spectrometry
ADL absolute detection limit
AES atomic emission spectrometry
AFS atomic fluorescence spectrometry
APDC ammonium pyrrolidinedithiocarbamate
ASV anodic stripping voltammetry
BPHA n-benzoyl-n-phenylhydroxylamine
5-Br-PADAP 2-(5-Br-2-pyridylazo)-5-diethylaminophenol
CF continuous flow
CCP capacitively coupled plasma
CGC capillary gas chromatography
copptn. coprecipitation
conc. concentrated
CP cetylpyridinium ion (or its salt)
CTA cetyltrimethylammonium ion (or its salt)
CV cold vapour
DAM diantipyrylpropylmethane
DBDTC dibenzyldithiocarbamate
DBA DBDC dibenzylammonium dibenzyldithiocarbamate
DCP direct current plasma
DDTC diethyldithiocarbamate
DEE diethyl ether
detn. detection
dil. diluted
diln. dilution
dissoln. dissolution
DIPE diisopropyl ether
DL detection limit
DMF dimethylformamide
DMSO dimethylsulphoxide
DTC dithiocarbamate
DTPA dithiophosphoric acid
xxvii
ED energy dispersive
EDL electrodeless discharge lamp
EDTA ethylenediaminetetraacetic acid (di-Na salt)
EGTA ethyleneglycolbis(2-aminoethyl ether-NVNN'N'-tetraacetic acid)
EI electron ionization
eln. elution
ETA electrothermal atomization
ETV electrothermal vaporization
evapn. evaporation
extrn. extraction
FAAS flame atomic absorption spectrometry
FAB fast atom bombardment
FAES flame atomic emission spectrometry
FI flow injection
FIA flow injection analysis
FLU spectrofluorimetry
FPD flame photometric detection
GC gas chromatography
GD glow discharge
GF graphite furnace
HCL hollow cathode lamp
HDEHP di(2-ethylhexyl)phosphoric acid
HMA HMDTC hexamethyleneammonium hexamethylenedithiocarbamate
HPLC high performance liquid chromatography
HR high resolution
ICP inductively coupled plasma
ID isotope dilution
INAA instrumental neutron activation analysis
LEI laser-enhanced ionization
LA laser ablation
LC liquid chromatography
LI laser induced
LTA low temperature ashing
MIBK methyl isobutyl ketone
MIP microwave-induced plasma
MS mass spectrometry
MT metallothionein
NAA neutron activation analysis
ND non-dispersive
NTA nitriloacetic acid
oxidn. oxidation
oxine 8-hydroxyquinoline, 8-quinolinol
PAN 1-(2-pyridylazo)-2-naphthol
PAR 4-(2-pyridylazo)resorcinol
PVC polyvinyl chloride
PDA photodiode array
xxviii
PE polyethylene
PGM platinum group metals
phen phenanthroline
pptn. precipitation
ppb parts per billion
ppm parts per million
ppt parts per trillion
PIXE proton-induced X-ray emission
QF quartz furnace
redn. reduction
REE rare earth elements
RF radiofrequency
RI resonance ionization
RNAA radiochemical neutron activation analysis
sepn. separation
SFC size-exclusion chromatography
SIM single ion monitoring
SPE solid phase extraction
STPF stabilized temperature platform furnace
TE transuranium elements
TI thermal ionization
T-i-OA tri-i-octylamine
TMDTC tetramethylenedithiocarbamate
TOA tri-n-octylamine
TOF time of flight
TOMA trioctylmethylammonium
TOPO tri-n-octylphosphine oxide
TPA tetraphenylarsonium
TPAO tetraphenylarsonium oxide
TPP triphenylphosphine
TPPO triphenylphosphine oxide
Tris tris(hydroxymethyl)aminomethane
TTA 2-thienoyltrifluoroacetone
TXRF total reflection X-ray fluorescence
VIS spectrophotometry (photometry) in the visible range
volatn. volatilization
WD wavelength-dispersive
XRF X-ray fluorescence
ZAAS Zeeman atomic absorption spectometry
xxix
Chapter 1
Sampling
According to IUPAC, a sample is defined as a portion of material se-
lected from a larger quantity of material [1]. Sampling is defined as the
total of activities which end with the acquisition of the test portion
(actual subject of analysis). Sampling starts by taking an increment (an
individual portion of material collected by a single operation of a sam-
pling device). The collection of one or more increments or units initially
taken from a population represents a primary sample which on division
and reduction gives rise to a reduced sample of a mass approximating
that of the final laboratory sample. The laboratory sample is the one the
analyst has the first contact with. The final stage of sampling consists
of the selection, removal and preparation of analytical portions from the
laboratory sample and is usually performed in the analytical laboratory.
IUPAC recommends that the term "sample" should not be used after
analytical operations on a homogeneous test portion have begun.
A prerequisite for a test (analytical) sample is its being homogeneous.
The homogeneity (heterogeneity) denotes the degree to which a constitu-
ent is uniformly distributed throughout a quantity of material. A material
may be homogeneous with respect to one analyte or property but hetero-
geneous with respect to another. The degree of heterogeneity is the
determining factor of sampling error. Homogeneity may be considered
to have been achieved when the sampling error of the processed portion
is negligible compared to the total error of the measurement system [1].
Meaningful analytical results can only be achieved if the test sample
is representative, i.e. adequately represents the population of material
from which it was drawn. A statistical sampling plan (a predetermined
procedure for the selection, withdrawal, preservation, transportation
and preparation of the portions to be removed from a population as,
samples) is intended to minimize the difference between the properties
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as estimated from a sample and the actual properties of the lot, within
practical constraints. Precautions necessary to avoid changing the char-
acteristics of the sample (contamination, moisture loss or gain) should
be considered during sample collection and storage.
Sampling should be considered as an integral step of chemical analy-
sis. Many errors (especially contamination [2]) are committed at this
stage and often remain undetected as the analytical chemist is not
involved in either the design or the implementation phase of sampling.
The analyst must have a perception of the uncertainty involved in
sampling as often the analytical methodology is not the limiting factor.
Unless the history of the sample is known the analyst is advised not to
spend his or her time analysing it. The theory and practice of sampling
have been extensively discussed [1-7]. Practical considerations regard-
ing particular sample types are discussed in Part II.
REFERENCES
1 W. Horowitz, Pure Appl. Chem., 62 (1990) 1193.
2 F.M. Garfield, J. Assoc. Off. Anal. Chem., 72 (1989) 405.
3 R. Smith and G.V. James, The Sampling of Bulk Materials. RSC, London,
1981.
4 B. Kratochvil, D. Wallece and J.K. Taylor, Anal. Chem., 56 (1984) 113R.
5 B.W. Woodget and D. Cooper, Samples and Standards. Wiley, London,
1987.
6 G.E. Baiulescu, P. Dumitrescu and P.Gh. Zugrvescu, Sampling. Ellis
Horwood, Chichester, 1991.
7 P.M. Gy, Sampling of Heterogeneous and Dynamic Materials Systems.
Theories of Heterogeneity, Sampling and Homogenizing. Elsevier, Amster-
dam, 1992.
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