ELUCIDATION OF THE OSCILLATION OF THE POTENTIAL DIFFERENCE ACCOMPANIED BY ION TRANSFER AT A LIQUID LIQUID OR LIQUID MEMBRANE INTERFACE USING ION-TRANSFER VOLTAMMETRY

Oscillations of the potential difference at the interface between an aqueous solution (W) containing MgSO4 as a supporting electrolyte (SE) and an organic solution (Org) containing a dilute ion i+ and a coexisting salt, j+.Y-, as Se were investigated by forcing the transfer of i+ at the interface through an applied current. The Org employed were Cs+ +tetrapentylammonium tetraphenylborate (TPenA+.TPhB-) in nitrobenzene (NB), tetramethylammonium ion + TPenA+.TPhB- in NB, H+ +tetraphenylarsonium dipicrylaminate (TPhAs+.DPA-) in 1,2-dichloroethane (DCE), etc. The necessary conditions for the oscillation were confirmed to be identical to those for the appearance of the maximum in the voltammogram (or polarogram) for the transfer of i+ at the interface. By referring to the voltammogram and the electrocapillary curve at the interface and taking into account the ion pair (i+.Y-) formation equilibrium in Org, such characteristics of the oscillation as the amplitude, period, pulse width and range of the applied current available for the oscillation were elucidated; a mechanism for the oscillation is proposed. The important roles of the adsorption-desorption of i+.Y- at the interface and the dissociation of the desorbed i+.Y- were emphasized. The result at the W/Org interface is associated with the oscillation of the potential at the liquid membrane.