ION-SELECTIVE CHARGE SEPARATION AT THE PHASE-BOUNDARY OF IONOPHORE-INCORPORATED LIQUID MEMBRANES AS STUDIED BY OPTICAL 2ND-HARMONIC GENERATION

Optical second-harmonic generation (SHG) in various plasticized poly(v inyl chloride) (PVC)-based ion-selective membranes was observed, The S HG signal from the ionophore-incorporated membranes in contact with an aqueous solution of selective cation chloride salts generally increas ed with increase of the cation concentration and then levelled off. Th is result was explained by the formation of oriented and therefore SHG -active cation-ionophore complexes at the membrane surface. The fact t hat the membrane potential and SHG signal changed in parallel revealed that the observed membrane potentials were primarily governed by SHG- active oriented complex cations at the membrane surface. The effect of the ionophore structures and their cation selectivities on the SHG re sponses was also examined and discussed. (C) 1997 Elsevier Science B.V .