The kinetics of the ion transfer across the liquid|liquid interface is studied by means of a thin film-modified electrode in combination with square-wave voltammetry. The thin film-modified electrode consists of an edge plane pyrolytic graphite electrode covered with a thin film of a water immiscible electroinactive organic solvent containing a neutral redox probe and a suitable electrolyte. The overall electrochemical process, proceeding as a coupled electron-ion transfer reaction, is controlled either by the electron transfer across the graphite electrode|organic solvent or by the ion transfer across the organic solvent|aqueous electrolyte interface. The theoretical model enabling to distinguish the rate limiting step is developed. The theory is used to measure the kinetics of ClO4-,NO3-, Cl-, SCN-, Na +, K+, (CH3)4N+, and (C4H9)4N+ across the water|nitrobenzene interface utilizing lutetium bis(tetra-tert- butylphthalocyaninato) as a redox probe. © 2005 Elsevier B.V. All rights reserved.