engleski

Electroanalysis of trace metals in water samples

There is a growing necessity to determine the levels of trace metals in the environment. Even in low concentrations ecotoxic metals may present a severe hazard to the normal functioning of the aquatic ecosystem. They are not biodegradable and are involved in biogeochemical cycles by which they are concentrated in sediment biota. Trace metal species in waters are distributed under different physicochemical forms (i.e. simple inorganic species, organic, labile and inert complexes and metal ions adsorbed onto a variety of solid and colloidal particles). Variation in the speciation of an element will affect its bioavailability. Thus, not only total concentration, but also metal speciation measurements are required to understand and predict the role and the fate of ecotoxic trace metals in aquatic systems. Special attention will be paid to the analytical procedure due to the complexity and the composition of the aquatic systems (fresh, saline and brackish waters), and the large number of possible artefacts in the trace metal analysis (i.e. contamination, losses by adsorption, change of speciation due to coagulation of colloids or microbialy activity, etc.). Recent development of electrochemical techniques enables analysis of a large number of water samples with minimum perturbation of the composition of the sample. This is highly needed for reliable trace metal speciation of aquatic symples. Design of appropriate probes and experimental procedure is still a challenging task. Electrochemical analyses are very sensitive, specific and reproducible and at the same time allow simultaneous determinations of several elements even at the levels below 10-9 M. They are also capable of discriminating, by their very basic principle, between mobile dissolved forms (i.e., free metal ions and labile complexes with size smaller than a few nanometers) and colloidal/particulate trace metal forms. The former can be obtained by direct measurements in raw natural water while the latter can be obtained by subtraction from total metal concentrations measured in raw and filtered (or better sedimented to minimize artefacts) acidified samples. Moreover, electrochemical instrumentation may be computerized and the analytical procedure can be automated. Despite all these analytical and technical capabilities, most of the development reported until now deal with on-line automatic voltammetric analyzers for laboratory or field measurements. Amongst the analytical tools available, the potentiality of electrochemical techniques for trace metals analysis and with significant advantages for trace metals speciation in natural water samples will be demonstrated and discussed in details.

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