VOLTAMMETRIC STUDY ON THE OSCILLATION OF THE POTENTIAL DIFFERENCE AT A LIQUID/LIQUID OR LIQUID/MEMBRANE INTERFACE ACCOMPANIED BY ION TRANSFER
The oscillations of potential difference at the interface between an aqueous solution (W) containing MgSO4 as a supporting electrolyte (SE) and an organic solution (Org) containing dilute ion i+ and j ~•Y-as SE were investigated by forcing the transfer of i+ at the interface through an applied current. The Org employed were Cst + tetrapentylammonium tetraphenylborate (TPeiiA+•TPhB-) in nitrobenzene (NB), tetramethylammonium ion + TPenA}•TPhB-in NB, W + tetraphenylarsonium dipicrylaminate
... icrylaminate (TPhAs~•DPA) in 1,2-dichloroethane , etc. The necessary conditions for the oscillation were confirmed to be identical to those for the appearance of the maximum in the voltammogram 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, and a mechanism for the oscillation is proposed. The important roles of the adsorptiondesorption of i+•Y-at the interface and the dissociation of the desorbed i+•Y-were emphasized. Key words oscillation of potential difference, ion transfer, liquid/liquid interface, adsorption of ion-pair, ion transfer voltammetry The oscillation of the potential difference or the interfacial tension at a liquid/liquid or liquid/membrane interface coupled with the ion transfer which closely relates to the electrical excitability in living organisms as well as the distribution of an ion at a liquid/liquid interface[2,3] has been extensively investigated by many authors[2, 4 -S]. Reviewing previous works, most of potential oscillations at the aqueous (W)/organic (Org) interface observed so far are accompanied with both the ion transfer across the interface and the interfacial adsorption. Therefore, the voltammetry for the ion transfer at an interface of two immiscible electrolyte solutions, VITIES, which is one of powerful methods to specify the transferring ion and to determine the amount of the ion transferred must be helpful for the elucidation of the mechanism of the oscillation. The adsorption at the W/Org interface can also be investigated by the VITIES since it causes the voltammetric maximum  . In our previous work, well-defined oscillations of the potential difference at the W/Org interface observable when the transfer of ions was forced by an applied current were introduced, and the mechanisms for the oscillations were discussed based on the results of VITIES and electrocapillary curve measurements. In the present paper, the general feature of the oscillation process will be discussed taking into account the data obtained recently together with the results given in the previous work.