| Depletive stripping chronopotentiometry (SCP), a new, recently developed electroanalytical technique, has been investigated and evaluated in terms of metal speciation in aqueous samples containing dissolved organic compound (DOC). The effect of stripping current on metal determination has been studied, as well as that of deposition time and stirring speed on diffusion layer thickness. At low stripping current and high stirring speed, depletive condition can be attained and linear diffusion may be approached at a Static Mercury Drop Electrode (SMDE). Scanned Stripping Chronopotentiometry (SSCP) has been applied to simple homogeneous complexes, e.g. cadmium and lead with pyridine-2, 6-dicarboxylic acid, nitrilo-triacetic acid and the stability constants have been validated by comparison with those obtained from Pseudopolarography (Scanned Stripping Voltammetry, SSV) under the same experimental conditions. The results determined by both techniques are in good agreement with the literature values. SSCP has been further exploited in metal complexation in the presence of heterogeneous fulvic acid (FA), a kind of humic substances which is one of the largest fractions of dissolved organic matter (DOM) in aquatic systems. The stability constants, heterogeneities and diffusion coefficients of complexes of Cd(II), Pb(II) and Zn(II) with FA have been determined by SSCP and Pseudopolarography for comparison. Besides, I pioneered efforts to apply SCP to real samples, in which the effect of dilution of Copper Cliff Mine effluent water samples (Sudbury, Ontario) with tap water on the average conditional stability constants of DOC of zinc and cadmium was investigated by complexometric titration followed by SCP. Compared with similar work reported in the literatures, the results of SCP are reasonable. Depletive stripping chronopotentiometry (SCP) may offer more reliable information on metal speciation compared with stripping voltammetry (SV) because of its elimination or reduction of secondary effects. |
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