Drops of nitrobenzene and 1,2-dichloroethane containing only 0.1 mol l(-1) decamethylferrocene (dmfc) are attached to the surface of a paraffin-impregnated graphite electrode (PIGE) and immersed into various aqueous electrolytes. The oxidation of dmfc and the reduction of the cation dmfc(+) are enabled by the simultaneous transfers of anions between the aqueous electrolyte and the organic solvents. The reaction starts at the three-phase junction. A linear relationship is observed between the mid-peak potentials of cyclic voltammograms of dmfc and the standard Galvani potential differences of the anions, and the influence of the anion concentration on the intercepts of these straight lines is explained. The standard Gibbs energies of transfer of acetate anions and dmfc(+) cations on the water / nitrobenzene interface are estimated as: DeltaG(tr.Ac-) (0.nb -->w) = -33.4 kJ mol(-1) and DeltaG(tr,dmfe+) (0,nb -->w) =35 +/- 2 kJ mol(-1), respectively.