Abstract
Voltammetric methods are frequently used to study complexation reactions in aqueous solutions. Peak currents i p and peak potentials U p recorded as functions of metal and ligand concentrations may be used to calculate complex stoichiometrics, stability constants and complexation capacities of natural waters. In order to enable a correct interpretation of the measured values it is necessary to investigate the dissociation of complex species at the electrode surface, their diffusion coefficients and adsorption reactions. We studied the interactions between fulvic acid (FA) and Pb2+-ions in aqueous solutions and at the mercury electrode surface using cyclic voltammetry (CV). Solutions containing FA at natural concentrations and the chelating ligands NTA and EDTA were titrated with Pb. Titration curves were recorded by differential pulse anodic stripping voltammetry (DPASV) and differential pulse cathodic stripping voltammetry (DPCSV). The problems arising in the interpretation of conventional DPASV-titration curves obtained in natural fresh waters are discussed. A new procedure based on DP CSV-measurements is presented and recommended for the detection of those ligands forming inert complexes.
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