Standard Gibbs energies of ion transfer from water to 2-nitrophenyl octyl ether (NPOE) have been determined employing steady-state cyclic voltammetry at a microhole-supported water I NPOE microinterface. A large polarised potential range has been obtained which made the investigation of ions such as NO3-possible with tetradodecylammonium tetrakis(4-chlorophenyl)borate as the supporting electrolyte in the organic phase. The transfer of even more hydrophilic ions like Br, Cl and KI could also be observed when no supporting electrolyte was used in the aqueous phase. The standard Gibbs energies obtained, which are based on the tetraphenylarsonium tetraphenylborate assumption, are in a rather fair agreement with data reported by Samec et al. (J. Electroanal. Chem. 409 (1996) 1). Linear Gibbs energy relationships have been found for the ion transfer from water into the organic phase for the solvents 2-nitrophenyl octyl ether, nitrobenzene, 1,2-dichloroethane and o-dichlorobenzene.