Analytical solution for the facilitated ion transfer at the interface between two immiscible electrolyte solutions via successive complexation reactions in any voltammetric technique: Application to square wave voltammetry and cyclic voltammetry

Abstract

Simple, analytical and explicit expressions are presented for the I/E response, interfacial concentrations and concentration profiles for the reversible ion transfer at ITIES of an ion undergoing several equilibrium complexation reactions in both the aqueous and the organic phase. Semi-infinite planar diffusion and excess of ligand in the organic phase have been assumed. These equations are valid for any multipotential step technique, and for any value of the diffusion coefficient for all the species involved. The I/E expressions of cyclic voltammetry and cyclic square wave voltammetry are deduced as particular cases of these equations. An in-depth study of the evolution of the concentration profiles of the free and complexed ion with different parameters of interest has been made, and some interesting conclusions are drawn about the magnitude of their Nernst and δ99 diffusion layer thicknesses. The morphology and behavior of the cyclic and square wave voltammograms in response to changes in the equilibrium complexation constants and in the diffusion coefficients ratio are also studied. Based on these studies, simple methods for the quantitative determination of the equilibrium constants and/or de diffusion coefficients are proposed. The application of these equations to the experimental study of the transfer of decylammonium facilitated by the presence of dibenzo-18-crown-6 (DB18C6) in the membrane has been carried out.