Three areas related to Polymer Membrane Ion-Selective Electrodes were investigated. The first two concered (1) their application to analysis of organic cations and pharmaceuticals, and (2) the use of electrochemically polymerized films for potentiometric sensors. The third area focused on the development of a computer controlled data acquisition system for studying Ion Transport at the Interface of Two Immiscible Electrolyte Solutions (ITTIES). Coated wire Polymer Membrane Ion-Selective Electrodes (PMISEs) based on dinonylnapthalenesulfonic acid (DNNS) were prepared for several alkylammonium ions and pharmaceuticals. Selectivity coefficients and other operational characteristics were predictable from calculated distribution constants. Specifically, Log k ᵖᵒᵗ(i)(j) values increased linearly with carbon number in a homologous series of alkylammonium ions. Among cations of the same carbon number, interference increased tenfold with each additional substitution in going from quaternary, tertiary, secondary and primary alkylammonium ions. Addition of hydrophilic subtituent groups to cyclohexylammonium interferents further diminished electrode response. Electrodes for several important pharmaceuticals, namely cocaine, methamphetamine, methadone, protriptyline, cimetidine, lidoflazine, verapamil, acebutalol, diltiazem, and nicardipine, displayed nearly theoretical response down to micromolar concentrations. Their selectivity was consistent with calculated distribution constants. Selectivity was independent of sensitivity, suggesting that the magnitude of each was determined by the distribution of both the free cation and the association complex of this cation with DNNS. The polymerization of phenol derivatives onto copper rendered the resulting films responsive to counter-ions of the electroactive species present in the polymerization medium. Those incorporating Aliquat 336 (tricaprylmethylammonium chloride) showed response to various anions, while others prepared using a sulfonated phenol derivative (m-hydroxybenzenesulfonic acid) responded to tributylammonium. The films had short lifetimes due to poor adhesion to the copper substrate. Construction of a computer controlled data acquisition system provided a rapid method for obtaining electrocapillary data simultaneously with the current-scan polarogram. The system was evaluated by observation of ion-transfer of a variety of alkylammonium ions.