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The influence of uncompensated resistance (also called the I[R.sub.u] effect, where I is current and [R.sub.u] 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 voltammetry 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 C[H.sub.3]CN and highly resistive C[H.sub.2][Cl.sub.2] (represents examples of I[R.sub.u] effect on a reversible electron-transfer process); (b) the reduction of a low 0.2 mM concentration of [[Fe[(CN).sub.6]].sup.3-] in the highly conductive 3 M KCl electrolyte media (case of slow kinetics with negligible I[R.sub.u] effect); (c) and reduction of a high 10 mM concentration of [[Fe[(CN).sub.6]].sup.3-] in less conductive aqueous 0.5 M KCl electrolyte media (example where the simultaneous effects of both I[R.sub.u] and slow kinetics need to be resolved).

Large-amplitude sinusoidal ac voltammetric techniques, when analyzed in the frequency domain using the Fourier transform--inverse Fourier transform sequence, produce the expected dc and fundamental harmonic ac responses in addition to very substantial second, third, and higher ac harmonics that arise from the presence of significant nonlinearity. A full numerical simulation of the process, Red [arrow right] [left arrow] Ox + [e.sup.-], incorporates terms for the uncompensated resistance ([R.sub.u]), capacitance of the double layer ([C.sub.dl]), and slow electron transfer kinetics (in particular, the reversible potential (E.sub.o]), rate constant ([k.sub.0]), and charge transfer coefficient ([alpha]) from the Butler--Volmer model). Identification of intuitively obvious patterns of behavior (with characteristically different sensitivity regimes) in dc, fundamental, and higher harmonic terms enables simple protocols to be developed to estimate [R.sub.u] [C.sub.dl], [E.sub.o], [k.sub.0], and [alpha]. Thus, if large-amplitude sinusoidal cyclic voltammograms are obtained for two concentrations of the reduced species, data obtained from analysis of the recovered signals provide initial estimates of parameters as follows: (a) the dc cyclic component provides an estimate of [E.sub.o] (because the [R.sub.u] and [k.sub.0] effects are minimized); (b) the fundamental harmonic provides an estimate of [C.sub.dl] (because it has a high capacitance-to-faradaic current ratio); and (c) the second harmonic provides an estimate of [R.sub.u], [k.sub.0], and [alpha] (because the [C.sub.dl] effect is minimized). Methods of refining the initial estimates are then implemented. As a check on the fidelity of the parameters (estimated on the basis of an essentially heuristic approach that solely utilizes the dc, fundamental, and second harmonic voltammograms), comparison of the predicted simulated and experimental third (or higher) harmonic voltammograms can be made to verify that agreement between theory and experiment has been achieved at a predetermined level. The use of the heuristic pattern recognition approach to evaluate the oxidation of ferrocene at a platinum electrode (a reversible process) in the very high resistance solvent dichloromethane (0.1 M [Bu.sub.4]NP[F.sub.6]) and the reduction of [[Fe(C[N.sub.6])].sup.3-] at a glassy carbon electrode (a quasi-reversible process) in much lower resistance but higher capacitance conditions found in aqueous (0.5 M KCl) media is described and verifies the inherent advantages of employing large-amplitude sinusoidal techniques in quantitative studies of electrode processes.

Significant advantages of Fourier transformed large-amplitude ac higher (second to eighth) harmonics relative to responses obtained with conventional small-amplitude ac or dc cyclic voltammetric methods have been demonstrated with respect to (i) the suppression of capacitive background currents, (ii) the separation of the reversible reduction of [[Ru[(N[H.sub.3]).sub.6].sup.3+] from the overlapping irreversible oxygen reduction process under conditions where aerobic oxygen remains present in the electrochemical cell, and (iii) the kinetic resolution of the reversible [[Ru[(N[H.sub.3]).sub.6]].sup.3+/2+) process in mixtures of [[Fe[(CN).sub.6]].sup.3-] and [[Ru[(N[H.sub.3]).sub.6]].sup.3+] at appropriately treated boron-doped diamond electrodes, even when highly unfavorable [[Fe[(CN).sub.6]].sup.3-] to [[Ru[(N[H.sub.3]).sub.6]].sup.3+] concentration ratios are employed. Theoretical support for the basis of kinetic discrimination in large-amplitude higher harmonic ac cyclic voltammetry is provided.