Adsorptive stripping chronopotentiometry (AdSCP). Part 2: Basic experimental features

AdSCP determines a metal ion, M, by reaction with added ligand, Lad, to form a surface active MLad which is accumulated on an electrode surface, then quantified by constant current reduction. The chronopotentiometric stripping curves for Pb(II), with xylenol orange (XO) as the added ligand, are scrutinized in the context of a recently developed theoretical framework. The experimental curves are well described by expressions for the general case of an adsorbed reactant and a dissolved product, Pb0, at a conventional mercury drop electrode. The shape of the potential/time transient is substantially influenced by convergency in the diffusion of Pb0 into the electrode volume. The mercury drop electrode lies in between the limits for a macroscale electrode (with planar diffusion) and a microelectrode (where diffusion of product is immaterial). Practical borders to the various experimental conditions are identified, e.g. in the maximum value of the stripping transition time as compared to the accumulation time, and in the strength of adsorption of PbXO to ensure a constant accumulation flux. The measured position of the E/t transient is in good agreement with that predicted on the basis of the extent of convergence together with the adsorption coefficient and the stability constant for PbXO. The suitability of the area under the dt/dE peak for obtaining the magnitude of the stripping transition time and the ensuing amount of PbXO is evaluated in detail.