Interpretation of speciation measurements on labile metal–macromolecular systems by voltammetric techniques

Abstract

Phenomena such as non-ligand excess, adsorption and heterogeneous or non-independent complexation models are discussed in order to improve the interpretation of the plots of the normalized limiting currents (Φ)versus the total ligand concentration in speciation studies. It is shown that under ligand excess conditions, all complexation models behave like the homogeneous and independent model. This result enhances the reliability of stability constants obtained under excess conditions using an equilibrium relationship between formal species. The convenience of Φversus total metal concentration plots in order to detect the mentioned phenomena and to obtain quantitative information about the complexation and adsorption processes from the limiting Φ value at low metal concentrations is emphasized. Finally, it is shown that non-ligand excess conditions with their corresponding interpretative framework are required for heterogeneity studies.