Kinetics of the tetraethylammonium (TEA(+)) ion transfer across the interface between an aqueous electrolyte solution (W) and the o-nitrophenyl octyl ether (o-NPOE) plasticized polyvinylchloride or the polyvinylidene difluoride supported membrane is examined by impedance spectroscopy at the equilibrium cell potential difference. Impedance data are analyzed by using the Randles-type equivalent circuit. As compared with the unsupported W \ o-NPOE interface, the polymer supported interfaces do not exhibit the enhanced differential capacity in the presence of the TEA(+) ion, while they exhibit a lower charge transfer resistance (i.e. a higher rate constant of ion transfer). It is shown that these differences can be due to mechano-electric oscillations, which are related to capillary waves at the liquid \ liquid interface. An equivalent electrical circuit involving these oscillations comprises an internal ac voltage source in series with the interfacial capacity having the same frequency but the opposite sign to the applied voltage. At a polymer supported interface, the mechano-electric oscillations are likely to be suppressed, and the Randles-type equivalent circuit becomes a realistic representation. A revision of the previous impedance analysis of the TEA(+) ion transfer across the unsupported W \ o-NPOE interface yields kinetic data which are consistent with the present results. The ion transfer rate constant still shows a correlation with the viscosity of the organic phase.