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ICP-OES
APPLICATIONS
The
versatility of ICP-OES makes it a good analytical technique for a wide
variety of applications.This versatility is due not only to the large
number of elements that can be determined rapidly at trace levels but
also to the wide variety of sample types that can be analyzed using
the ICP-OES technique.
In
this chapter,ICP-OES applications have been grouped into six
generalized categories:Agricultural and Foods,Biological and
Clinical,Geological,Environ-mental and Waters,Metals,and
Organics.While an exhaustive review of each of these application areas
is beyond the scope of this book,some examples of ICP-OES applications
are discussed to give the reader an idea of the types of analyses
where this technique has been used successfully.
Information regarding general application areas and specific
applications can be obtained from a number of
sources.Unfortunately,there is no one source that contains all the
information needed to perform any and all ICP-OES analyses.For general
discussions of applications,the books about ICP-OES by
Boumans;Mon-taser and Golightly;and Thompson and Walsh are very good
(see table 5-1). For reviews of the latest ICP-OES applications,see the
Fundamental and Applica-tions Reviews published in alternating years
in the journal Analytical Chemistry.The Fundamental Reviews are
categorized according to technique,e.g.,Emission Spectrometry.The
Applications Reviews are categorized according to sample Related
Drugs.The Journal of Analytical Atomic Spectrometry contains
applications reviews in its “Atomic Spectrometry
Updates”section.These reviews are a good starting place to search
for references to specific analyses reported in the chemical
literature.Also quite useful in locating literature references to
specific applications are computer data base search services,such as
CAS Online,available through various outlets.The journal Atomic
Spectroscopy also publishes a biannual bibliog-raphy of atomic
spectroscopy-related articles.
Detailed
information about specific applications can be found in a number of
sources.The ICP-OES books by Boumans and by Thompson and Walsh,while
not exhaustive references,provide detailed information on some
selected applications. Many
monographs,such as “Selected Methods of Trace Metal Analysis”by
J.C.
Van
Loon
General
applications
“Inductively Coupled Plasma Emission Spectroscopy -Part
2”,P.W.J.
M.Boumans,ed.,Chemical Analysis,Vol.90,P.J.Elving,J.D.
Winefordner,eds.,John Wiley &Sons,New York,1987.
“Inductively
Coupled Plasmas in Analytical Atomic Spectrometry”,A. Montaser and D.W.Golightly,eds.,2nd Edition,VCH
Publishers,Inc., New York,1992.
“A
Handbook of Inductively Coupled Plasma Spectrometry”,M.
Thompson
and J.N.Walsh,Blackie,Glasgow,1983.
Application
Reviews
“Fundamental
Reviews”,Analytical Chemistry 60,(1988).(published in
even-numbered years)
“Applications
Reviews”,Analytical Chemistry 59,(1987).(published in
odd-numbered years)
“Atomic
Spectrometry Updates”,Journal of Analytical Atomic Spectrometry,various
issues.
Representative
Journals
Analytical Chimica Acta
Analytical Chemistry
The Analyst
Applied Spectroscopy
Atomic Spectroscopy
Clinical Chemistry
Journal of Analytical Atomic Spectrometry
Journal of the Association of Official Analytical
Chemists
Spectrochimica Acta,Part B
Talanta
chemistry and related topics
contain the greatest amount of detailed information
about
specific analyses.Table 5-1 contains a list of several such
journals.While few organizations have the resources to subscribe to
every journal containing papers on ICP-OES application,access to these
journals is often available through univer-sity libraries and various
cooperative loan programs.
Agricultural
and Foods
The
ICP-OES technique has been applied to the analysis of a large variety
of agricultural and food materials.Types of samples include
soils,fertilizers,plant materials,feedstuffs,foods,animal tissues,and
body fluids.Analyses of these materials are required to determine
levels of essential nutrients as well as levels of toxic elements in
the materials.
Most
agricultural and food materials are generally not in the form of
dilute aqueous solutions nor are they readily soluble in distilled
water.Therefore,analyses of these materials by ICP-OES often requires
that rigorous sample preparation procedures be carried out prior to
analysis.Fortunately for the analyst,the use of modern microwave
sample digestion techniques is helping to simplify the sample
prepara-tion steps for agricultural and food materials as well as many
other sample types. Some
typical applications of ICP-OES in this area include determination of
trace metals in beer and wine;analysis of infant formula for
Ca,Cu,Fe,Mg,Mn,P,K,Na and Zn;determination of country origin of orange
juice through trace element analysis;determination of 14 elements in
peanuts;and analysis of soils for toxic metal contamination.
Biological
and Clinical
As
research reveals more information regarding the roles and behaviors of
trace elements in biological systems,ICP-OES has become an important
tool in the area of biological and clinical
applications.Determinations by ICP-OES of essential,toxic and
therapeutic trace elements are important in the medical research
laboratories as well as in the clinical and forensic lab environments.
Of
significant concern regarding trace element determinations in the
biological and
clinical
fields is the contamination of samples prior to their analysis.While
it is always
important
to consider sources of contamination when performing trace
determina-tions
in
any field,the biological and clinical area is particularly susceptible
to errors
due
to contamination originating in the sample collection and sample
preparation
steps.The
use of surgical equipment,such as scalpels,needles,scissors,and
forceps,often
contaminates the sample with trace quantities of the very elements
being
determined in the sample.For this reason,appropriate equipment should
be
used to collect,process and store biological and
clinical samples before analysis
by
ICP-OES.
Many
biological and clinical samples are either too small or contain
elemental concentrations too low for ICP-OES analysis using
conventional pneumatic sample introduction.In these cases,it is often
necessary to turn to alternate sample introduction techniques such as
ultrasonic nebulization,electrothermal vaporiza-tion, or hydride
generation,or preconcentration techniques such as ion exchange or
solvent extraction.
Examples
of ICP-OES analyses of biological and clinical samples include
determi-nations of Cr,Ni and Cu in urine;Al in blood;Cu in brain
tissue;Se in liver;Cr in feces;Ni in breast milk;B,P and S in bone;and
trace elements in oyster and tuna tissues.
Geological
Geological
applications of ICP-OES involve determinations of major,minor and
trace compositions of various rocks,soils,sediments,and related
materials.The major use of ICP-OES in this field is for prospecting
purposes.The technique is also used for applications such as
determining origins of rock formations and for marine geochemistry.
Preparation
of geological samples for analysis by ICP-OES often involves the use
of lithium metaborate fusion reactions,especially for materials
containing high levels of silica.Acid dissolutions are also commonly
used for many geological materials.
Of major concern for geological applications of ICP-OES is the
elimination of residues that may be present following acid digestion
or dissolution of a fusion bead.
Careful selection of the nebulizer used with the ICP instrument
can help to reduce problems caused by high salt and residue
concentrations. Typical
applications of ICP-OES for analysis of geological samples include
deter-mination of U in ore grade material;analysis of river sediments
for several metals; analysis of carbonate drill cores for major,minor
and trace elements;determination of rare earth elements in rock
formations;and analysis of plankton for several elements.
Environmental
and Waters
The
area of environmental analysis is quite a broad topic,covering many
different
types
of ICP-OES applications.Many of these applications,such as analyses of
soils,sediments,and
animal and plant tissues,overlap areas covered previously in
this
chapter and will not be addressed in this section.This still leaves a
number of
5-4
Concepts,Instrumentation,and Techniques.important environmental ICP-OES
applications,not the least of which are the
analyses
of various types of water.Other important environmental ICP-OES
appli-cations include analyses of sewage sludge,domestic and
industrial refuge,coal and coal fly ash,and dust and other airborne
particulates.
The
analysis of water can be the simplest of all ICP-OES
applications,depending on the type of water being analyzed and the
required measurement levels and protocols.Fresh waters generally
require only that the sample be stabilized with a mineral acid before
analysis by ICP-OES.Some waters may require filtering to remove
particulates.For analyses requiring very low detection levels,it may
be necessary to perform some kind of preconcentration step prior to
analysis.Ultra-sonic nebulizers are also useful for improving
sensitivity for such analyses.Analyses of sewage sludge,various
refuses,and coal and coal fly ash require more rigorous sample
preparation while collection of airborne particulates requires use of
air filtering techniques.
Examples
of environmental ICP-OES applications include various water quality
analyses as required by the U.S.Environmental Protection
Agency;determination of Fe,Cd,Cu,Mo,Ni,V,and Zn in
seawater;determination of phosphorus in municipal
wastewater;determination of heavy metals in inner-city dust samples;
and trace metal analysis of coal fly ash.
Metals
ICP-OES
is used widely for the determination of major,minor and trace
elemental constituents in metals and related materials.The technique
is used for analysis of raw materials,production control,and quality
control for final products as well as in the developmental lab
environment.Sample preparation is generally through acid
digestions,except for oxide materials which often require use of
fusion techniques. Analysis
of metals is also the most likely use of solid sampling techniques
such as spark or laser ablation with ICP-OES instruments.
A
particular difficulty associated with metals analysis by ICP-OES is
the potential for a large number of spectral interferences since many
metals exhibit very complex emission spectra.Use of a high-resolution
spectrometer and spectral interference correction techniques are often
required for metals analyses by ICP-OES.
Some representative applications of ICP-OES for the analysis of
metals and related materials include determination of toxic,trace and
major constituents in coal and slags;analysis of low alloy steels for
As,B,Bi,Ce,La,P,Sn and Ta;high-precision determination of Si in
steels;determination of contaminants in high-purity Al;and analysis of
superconducting materials for trace contaminants.
Concepts,Instrumentation,and
Techniques 5-5.Organics
Analysis
of organic solutions by ICP-OES is important not only for analyzing
organic-based materials such as petroleum products but also for a wide
variety of other applications.For many of the analyses from the other
application categories discussed in this chapter,it is necessary to
perform sample preparation in which the final form of the analyte is
contained in an organic solvent.For example,solvent extraction for the
purpose of preconcentrating analyte species is a widely used sample
preparation technique for ICP-OES.Also considered under the category
of organic analyses would be introduction of organic effluents and
vapors from high performance liquid chromatography (HPLC)and gas
chromatography (GC)sepa-rations.
While analysis of organics by ICP-OES is generally
straightforward,there are often some special requirements.For
example,introduction of organic matrices into the ICP discharge
usually requires that the ICP be operated at a higher RF power than is
normally required for aqueous samples.Sometimes it is also necessary
to use special nebulizers or torch injector tubes.When a peristaltic
pump is used to transport the sample to the nebulizer,special
consideration must be made regarding the chemical resistance of the
pump tubing used with respect to the organic solvent.
The analysis of used lubricating oils for trace metal content
is one of the more popular applications for organics analysis by
ICP-OES.Some other applications include analysis of solvent-extracted
geological materials for trace elemental com-position; determination
of lead in gasoline;determination of Cu,Fe,Ni,P,Si and V in cooking
oils;analysis of organophosphates for trace contaminants;and
determi-nation of major and trace elements in antifreeze.
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