Discrimination and evaluation of the effects of uncompensated resistance and slow electrode kinetics from the higher harmonic components of a fourier transformed large-amplitude alternating current voltammogram.

The influence of uncompensated resistance (also called the IRu effect, where I is current and Ru is uncompensated resistance) and slow electrode kinetics have been assessed for the dc and first five ac harmonics derived from Fourier transformed large-amplitude ac voltammetry. Resistance and rate constant conditions emphasized correspond to those where separation of effects attributable to either parameter is essentially impossible under conditions of dc cyclic voltammetry. Results derived from simulations and experiments demonstrate that it is relatively easy to discriminate and quantify contributions from these two effects over a wide range of values using the fourth and fifth harmonic ac components derived from single large-amplitude ac voltammetric measurement. Furthermore, these ac components also are essentially devoid of background charging current. Concepts developed initially from simulations are confirmed by experimental studies on the following: (a) the oxidation of ferrocene, in moderately resistive CH3CN and highly resistive CH2Cl2 (represents examples of IRu effect on a reversible electron-transfer process); (b) the reduction of a low 0.2 mM concentration of [Fe(CN)6]3- in the highly conductive 3 M KCl electrolyte media (case of slow kinetics with negligible IRu effect); (c) and reduction of a high 10 mM concentration of [Fe(CN)6]3- in less conductive aqueous 0.5 M KCl electrolyte media (example where the simultaneous effects of both IRu and slow kinetics need to be resolved).