Potential-dependent adsorption and partitioning of ionic components at a liquid vertical bar liquid interface

In adsorption at the interface between two immiscible solutions, the adsorp tion of a substance from one phase is related to its adsorption from the ot her, when the substance is soluble in both solution phases, because of the presence of the simultaneous partition equilibrium of the substance. This i nterdependence of the adsorption and partition gives unique features to the effect of the phase-boundary potential on these three processes, particula rly when the surface-active substance is ionic. The electrical part of the adsorption Gibbs energy is a fraction of the electrical driving force for t he ion transfer from one phase to the other. A simple yet general model pro posed for the dependence of the adsorption Gibbs energy on the phase-bounda ry potential takes a form similar to the Butler-Volmer equation in electrod e kinetics and demonstrates that the adsorption becomes a maximum at the po tential around the standard ion-transfer potential of the surface active io ns. The link between the adsorption and partition has been illustrated for the partitioning of an ionic component between two immiscible solutions hav ing a certain volume ratio. The implications of this link in current-potent ial curves of ion transfer across the interface in the presence of adsorpti on have been elucidated. (C) 2001 Elsevier Science B.V. All rights reserved .