ELECTROCHEMICAL STUDIES OF COPPER AND LEAD COMPLEXATION BY FULVIC-ACID .2. A CRITICAL COMPARISON OF POTENTIOMETRIC AND POLAROGRAPHIC MEASUREMENTS

Amperometric titrations of copper and lead with fulvic acid (FA) extracted from the River Tamar, southwest England, were carried out in 0. 1 M NaClO//4 at pH values in the range 6. 0-6. 5. The complexation capacities estimated were 25-50% of those measured in comparable potentiometric titrations for copper, and 0-7% for lead. While calculations indicate that much of the discrepancy can be explained by lability of the metal-FA complexes, analysis of the peak potential shifts during the titrations and of pseudopolarograms provides strong evidence for interference by irreversible processes at the electrode surface. Furthermore, pronounced differences in behavior were encountered in reverse titrations of FA into organic-free metal solutions.