CONSISTENCY OF VOLTAMMETRIC METAL SPECIATION IN LATEX PARTICLE DISPERSIONS

Differential pulse polarography (DPP) and, especially, differential pu lse anodic stripping voltammetry (DPASV) were applied to the study of the binding of Cd(II) by polystyrene latex particles. Some complicatio ns that arose in previous voltammetric studies of different heavy meta l + polystyrene latex systems at low concentrations of the metal ion w ere considered. The problem consisted basically of noticeable differen ces between the stability constants computed from current data and tho se obtained from potential data. The results show that the metal-to-li gand ratio is a key parameter for understanding such problems, and tha t these could be related to the presence of a small minority of strong complexing sites. Complications derived from association-dissociation kinetics and/or from non-excess of ligand also might be involved. The various possibilities are discussed and some qualitative consideratio ns and general guidelines are given, especially to define criteria to test the reliability of voltammetric measurements on heavy metal + col loid systems.