465 J. Electronnal. Chem., 266 (1989) 465-469 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands Preliminary note Steady state current for ion transfer reactions at a micro liquid/liquid interface J.A. Campbell and H.H. Girault Department of Chemistry, University of Edinburgh, Wesr Mains Road, Edinburgh EH9 3JJ, Scotland (Great Britain) (Received 22 May 1989) INTRODUCTION The advantages of microelectrodes in electrochemistry, both for the study of fast charge transfer reactions, and for investigations in resistive media have been widely reported [ 11. Charge transfer reactions across the Interface between Two Immiscible Electro- lyte Solutions (ITIES) which include ion transfer, assisted ion transfer and electron transfer reactions are generally fast (10e3 < k” < 10-l cm s-‘) and the measure- ment of reliable kinetic data for these processes is largely hampered by the high resistivity of the organic phase. For this reason, the use of micro ITIES offers advantages in circumventing most of the difficulties generally encountered with larger interfaces where planar diffusion mass transport dominates. The first method proposed to obtain a micro ITIES was to support the interface at the tip of a micropipette similar to those used in electrophysiology for intracellu- lar measurements. In this case, however, it was shown that an asymmetric diffusion field prevailed comprising a linear component inside the pipette and a radial component outside [2]. This first approach permitted the study of charge transfer with solvents of low permittivity such as 1,2-dichloroethane but kinetic studies had to rely on a model derived from the computer simulation of this asymmetric mass transport regime [3]. The only kinetic studies at micropipettes which could be analysed following the methodology generally used at solid microelectrodes were pseudo-first order bimolecular reactions where the concentration of the reactant inside the pipette was in excess compared to that of the reactant outside. With this approach the mass transport was controlled by the radial diffusion of the reactants and products outside the pipette. In this way it was possible to study ion/ionophore interfacial complexation reactions [4] such as M+(aq) + C(org) + CM+(org) 0022-0728/89/$03.50 0 1989 Elsevier Sequoia S.A.