Reverse pulse polarography of labile metal + macromolecule systems with induced reactant adsorption: theoretical analysis and determination of complexation and adsorption parameters

Abstract

A model for the interpretation of reverse pulse polarography (RPP) in metal macromolecular ligand systems is developed, including both adsorption of the macromolecule and the induced adsorption of the metal ion. The following basic assumptions are made: reversible charge transfer at a stationary planar electrode (static mercury drop electrode), labile complex, large excess of ligand compared with the total metal concentration, formation of a 1:1 complex and diffusion coefficients for ligand and complex species different from that of the free metal ion. Equations for the limiting current I lim and for the RPP full wave are deduced for both linear and Langmuirian adsorption. It is found that adsorption does not modify the expressions for I lim valid for the case without adsorption. Thus the stability constant K can be determined. In contrast, adsorption influences the shape and position of the RPP full wave. In the case of linear adsorption, an analytical expression has been deduced which relates the adsorption parameter K ML 1 to Δ E 1 2 values, thus allowing the calculation of K ML 1 from RPP waves. This method has been applied to experimental results obtained for the Cd(II) polymethacrylate system.