Trace metal speciation studies

After a brief introduction on terminology, this overview summarizes the experimental and theoretical modelling methods applied in trace metal speciation studies, emphasizing the dissolved fraction as defined by 0.95 pm filtration. The experimental approach comprises interactions with organic - and inorganic ligands, speciation schemes, biological experiments and interactions with particles and colloids. 

Different approaches in trace metal speciation studies (with some examples). 

Trace metal speciation studies in natural waters using ACSV The high sensitivity and selectivity of ACSV makes this technique very suitable for trace metal speciation studies. ACSV has consequently been used for this purpose in river, lake, ground, and sea... 

Interest in trace element speciation studies in natural waters has increased considerably during the last decade. It has become apparent that data on total concentrations of any element rather than on individual well defined chemical entities, are often inadequate to identify transport mechanisms, ultimate fate and toxicity of particular elements to organisms. A study of the different trace metal species and their relative distribution will assist in understanding the chemical processes that take place in the highly reactive estuarine zone and in the open sea. These processes include the rate at which chemical processes take place, the participation in geochemical processes (precipitation/dissolution, adsorption/desorption). 

Mackey, D.3., 1982. An investigation of the suitability of amberlite XAD-1 resin for studying trace metal speciation in seawater. Mar. Chem., 11 169-181. 

Niirnberg, H.W., 1983. Voltammetric studies on trace metal speciation in natural waters. Part II Application and conclusions for chemical oceanography and chemical limnology. In G.G. Leppard (ed.), Trace Element Speciation in Surface Waters. Plenum, New York, pp. 211-230. 

Studies involving trace metal speciation in soil solutions require the values of stability or association constants of complexes of the trace metals with a number of inorganic and organic ligands which exist in these environments. Much of these data can be obtained readily from published compilations ( -7 ). However, experimental data on association constants for complexes of the trace metals with ligands such as 063, ... 

ICP-MS was found to be compatible with LC for the trace metal speciation. The role of ICP-MS in trace element speciation studies at the FSL was described (Crews et al., 1987). The characteristics of LC-ICP-MS for the study of metalloprotein species were assessed and the chromatographic efficiency of ICP-MS was found to be similar to that obtained with a UV detector (Dean et al., 1987). Information about the chemical nature of trace elements from food can be obtained by first treating the foods in vitro with enzymes to broadly simulate the action of enzymes in the gastrointestinal tract (Crews et al., 1988). The soluble components can be separated by size exclusion chromatography (SEC) and an estimate of their molecular size obtained. By coupling SEC... 

In the last few decades many studies have been carried out to evaluate the distribution of dissolved trace metals in sea water (12, 119 122) and more recently studies of metal speciation have been reported (24, 33, 34, 108 110, 123). However, few data sets are available for the Southern Ocean (124—133), and studies of trace metal speciation are limited to a few papers (35, 57, 69, 134). 

Moldovan, M., Kmpp, E.M., Holliday, A.E., and Donard, O.F.X. (2004) High resolution sector field ICP-MS and multicollector ICP-MS as tools for trace metal speciation in environmental studies a review. J. Anal. At. Spectrom.,... 

The technique can be used to measure concentrations in the range 10 6-10 9M and as such is eminently suitable for the determination of trace metal impurities of recent years it has found application in the analysis of semiconductor materials, in the investigation of pollution problems, and in speciation studies. 

Model Studies. In model studies of adsorption, one deals with simple, well-defined systems, where usually a single well-characterized solid phase is used and the composition of the ionic medium is known, so that reactions competing with the adsorption may be predicted. It is not a trivial problem to compare the results from such model studies with those from field studies, or to use model results for the interpretation of field data. In field studies, a complex mixture of solid phases and dissolved components, whose composition is only poorly known, has to be considered competitive reactions of major ions and trace metal ions for adsorption may take place, and the speciation of the trace metal ions is often poorly understood. In order to relate field studies to model studies, distribution coefficients of elements between the dissolved and solid phases are useful. These distribution coefficients are of the following form ... 

In 2006, Lobinski et al.1 reported on the imaging and speciation analysis of trace elements to study the element distribution, oxidation state, metal site and metal structure in biological environments using mass spectrometric techniques (LA-ICP-MS, SIMS, MALDI-MS) and non-mass-spectrometric techniques such as micro-PIXE (proton induced X-ray emission), XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) -the latter two techniques are very sensitive due the use of a more intense synchrotron beam.1... 

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