ANALYTICAL AND KINETIC INVESTIGATIONS OF TOTALLY IRREVERSIBLE ELECTRON-TRANSFER REACTIONS BY SQUARE-WAVE VOLTAMMETRY

The influence of slow electron transfer on the analytical performance of square-wave voltammetry is considered from an experimental viewpoint. The magnitude, shape and position of the square-wave response depends on the degree of reversibility and also the value of the transfer coefficient (alpha). The dimensionless square-wave peak current of 0.93 (for nE(sw) = 50 mV, n-DELTA-E(s) = 10 mV) for a reversible system decreases to 0.39 for totally irreversible slow charge transfer when alpha = 1.0 and decreases monotonically to zero as alpha goes to zero. Although a further increase in square-wave step height has only a small effect and an increase in amplitude has a moderate effect on the square-wave response when the system is Nernstian, sensitivities can be dramatically increased, at least fivefold, with the proper choice of these parameters for irreversible systems. To illustrate these points the reduction of two compounds, N-acetylpenicillamine thionitrite (alpha = 0.46) and tert-butyl hydroperoxide (alpha = 0.08) were examined.