engleski

Electroanlytical methods for trace metals analysis in seawater

The main pathways of trace metals to the marine environment are direct disposal of waste waters, polluted rivers and precipitation from the atmosphere. Furthermore, metals are non-degradable constituents having a tendency to accumulate in vital oegans of many living organisms. At present, metal pollution predominantly occurs in river, estuaries, coatal zone, and closed sea basins, while metal pollution of the open ocean seems to be rather low because of a large oceanic capacity. Analytical measurements of the aquatic systems have first been confined to the determination of the total metal concentrations and metal distribution in different environmental compartments, including the aquatic one. It has been only within recent years, that reliable measurements of the total concentrations of metals of ecotoxicological significance have been performed in natural waters. This comment is especially valid for the determination of trace metals of prime environmental concern, Cd, Pb, Cu, Hg in seawater, due to their very low natural concentrations: the lower the actual dissolved metal concentration in natural water, the more critical for the ecosystem are even small anthropogenic additions of this metal into natural aquatic environment. Accurate and precise data on the overall, total concentrations of dissolved trace metals in the aquatic environment are of great significance and provide one of the prerequisites to quantify the distribution of chemical forms of metals in any type of natural waters. The concentration of heavy metal traces in the dissolved state is, as a rule, lower than in any other phase of natural water system. The dissolved state is nevertheless of central significance, because the transformation of metals to and from other phases (compartments) of natural water system occurs via this state. The technique which enables quantitative and selective determination of natural dissolved trace concentrations of Cd, Cu, Co, Ni, Hg, Pb, Tl, Zn, Bi, in, As(III) and As(VI), Cr(III) and Cr(VI) in different water types, is the voltammetric technique. It has the advantage that the measurements can be performed directly in the water samples without any pretreatment. Inherent high sensitivity of this technique is based on Faraday s low, which defines an enormous electric charge of 96.500 coulombs for one mole equivalent of reduced substances. With respect to sensitivity, low accuracy risks and low cost requirements, voltammetry is of all present techniques the most versatile analytical method for the direct and comparative determination of the total metal concentration and respectively, at the natural pH of water, for the trace metal speciation, because it is a species-sensitive method. The results obtained recently by a new hanging mercury drop electrode (HMDE) and differential pulse anodic stripping voltammetry (DPASV) for trace metal analysis, will be presented in details.

trace metal analysis; dissolved trace metals; electroanalytical methods

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