SEMIINTEGRAL ANALYSIS IN CYCLIC VOLTAMMETRY - DETERMINATION OF SURFACE EXCESS AND CONCENTRATION IN THE PRESENCE OF WEAK ADSORPTION AND THIN-FILMS

Semiintegral analysis is used as an effective method for determining surface coverage (i.e., initial surface excess, GAMMA*) from voltammetry in the presence of weak adsorption. Both GAMMA* and bulk concentration (C*) can be determined from the semiintegration of a single voltammogram. The approach is illustrated using p-benzoquinone (p-BQ) where the adsorption and diffusion response are indistinguishable, characteristic of weak adsorption. A surface excess of 3 nmol/cm2 was determined via semiintegration and confirmed using chronocoulometry. Advantages and disadvantages of the method relative to chronocoulometry are discussed. The semiintegral analysis approach is extended to cases where the electrode surface is covered by a thin film where the thickness is sufficiently small so that num transfer within the film is not significant (i.e., thickness much less than (2Dt)1/2). Preconcentration of redox species in the film will result in an apparent initial surface excess, similar to adsorption. When the film is in contact with species in solution, the response will contain diffusional and nondiffusional components, analogous to the response observed for adsorption in the presence of species in solution. Simulations are used to demonstrate that semiintegral analysis may be used to determine the concentration within the film and partitioning coefficients of species between the bulk and the film.