Microelectrode voltammetry for studying host-guest complexation equilibria. An analysis of the possibilities of the method

Abstract

The use of microelectrode voltammetry in the study of host-guest complexation is described. A digital simulation approach to describe the complexation as a second-order CE mechanism for any kinetic condition is proposed. For a completely mobile equilibrium, the constant can be determined by the very simple relationship ( I 1/ I 1,0) = (1 + D r K[L] b)/(1 + K[L] b), where I 1/ I 1,0 is the ratio of the limiting current in the presence and absence of the host species, D r is the ratio of the diffusion coefficients of the complex and the guest species, K is the equilibrium constant and [L] b is the bulk equilibrium concentration of the host species. Advantage is gained from the linear dependence of the limiting current on the diffusion coefficient of the reactant which allows an enlargement of the measurement range. The potential applicability of the method to electroinactive guest species was also explored by using it in a competitive procedure. Agreement was found between the theoretical results and those relative to the ferrocenecarboxylic acid + β-cyclodextrin and ferrocenecarboxylic acid + p-nitrophenol + β-cyclodextrin systems in aqueous solution at pH 9.2.