STUDIES ON PERMSELECTIVITY AT THE PHASE-BOUNDARY OF ION-SELECTIVE LIQUID MEMBRANES BY OPTICAL PHENOMENA AS PROBES FOR PHASE-BOUNDARY POTENTIALS

Cation permselectivity at the phase boundary of ionophore-incorporated liquid membranes was studied by optical phenomena as probes for phase -boundary potentials in order to understand the response mechanism of liquid membrane-type ion-selective electrodes (ISEs) at the molecular level. In the first study, optical second-harmonic generation (SHG) at various plasticized poly(vinyl chloride) (PVC)-based ion-selective me mbranes was observed, and the existence of SHG-active, oriented cation complexes at the membrane surface was shown. By examining the correla tion between the SHG and potentiometric responses, the observed SHG in tensity was assumed to be a measure of the charge density at the very membrane surface. In the second study, lipophilic derivatives of photo responsive azobis (benzo-15-crown-5) were used as a molecular probe an d the photoinduced changes in the potentiometric responses were observ ed. As a result, it was found that the photoinduced change in the pote ntiometric response behavior depends on the change in the number of pr imary cations permselectively extracted into the membrane side of the interface. These studies proved the necessity to investigate the inter facial phenomena which arise at the membrane surface in addition to th ermodynamic considerations in order to understand the response mechani sm of liquid membrane-type ISEs.