STUDIES ON THE PHASE BOUNDARIES AND THE SIGNIFICANCE OF IONIC SITES OF LIQUID MEMBRANE ION-SELECTIVE ELECTRODES

Attenuated total reflectance infrared spectroscopy (ATR-IR) has been u sed to study the cation permselectivity of liquid-membrane ion-selecti ve electrodes (ISEs). All spectroscopic evidence was found to agree wi th the interpretation of permselectivity as being due to complete excl usion of counter-ions from the boundary phase. Compared to ATR-IR, opt ical second harmonic generation (SHG) has an even more pronounced surf ace sensitivity. It has been demonstrated to be a promising new techni que for the study of ISE response mechanisms, as it allows one to obse rve the actual phase boundary. On the other hand, further potentiometr ic evidence for the influence of ionic sites on the emf response was f ound, both by a study of membranes free of ionic sites as well as by t he investigation of leaching processes at poly(vinyl chloride) membran es. Finally, the use of a photoresponsive crown ether ionophore allowe d the determination of emf response characteristics in relation to the ionophore concentration without any changes in the membrane compositi on.