Voltammetric measurements were used to investigate the transfer of a series of semi-hydrophobic ions across the interface between an aqueous electrolyte solution and the o-nitrophenyl octyl ether (o-NPOE) plasticized polyvinylchloride (PVC) membrane. Standard ion transfer potentials were evaluated which are comparable with those inferred from measurements at a water \ o-NPOE interface. It is concluded that the presence of PVC has a rather small effect on the ion transfer thermodynamics, which is probably due to very weak interactions between PVC and o-NPOE or ions present.