Quasireversible Maximum in Cathodic Stripping Square-Wave Voltammetry

Abstract

Square-wave voltammetry of the cathodic stripping processes exhibits maximum response for a quasireversible redox reaction. This phenomenon, known as a “quasireversible maximum” is explored for kinetic measurements of this class of redox reactions. The apparent reversibility of a redox reaction, together with the position of the quasireversible maximum, depend on the single complex kinetic parameter K, which is defined through the standard rate constant, diffusion coefficient of the ligand and frequency of the SW signal. Critical values of the kinetic parameter Kmax are theoretically calculated for different values of the transfer coefficient α and amplitudes of the signal. If the frequency which corresponds to the quasireversible maximum is experimentally obtained, the standard rate constant of the investigated redox reaction could be estimated. Standard rate constant can be defined either in units cm s–1, which is the same as for a redox reaction of a dissolved redox couple, or only in s–1, which is typical for a redox reaction of an adsorbed redox couple. This feature shows that cathodic stripping redox reactions are an important class of redox reactions which can be regarded as an intermediate form between the redox processes of adsorbed and dissolved redox couple.