Characterization of photopolymerized decyl methacrylate as a membrane matrix for ion-selective electrodes

Potentiometric ion-selective sensors based on photopolymerized thin films of decyl methacrylate (DMA) crosslinked with hexanedioldimethacrylate (HDDMA) are described. The electrochemical response characteristics including slopes, selectivities, resistances and response times of several DMA-based ion-selective electrodes are reported and compared to those obtained using PVC-based sensors. Sensors incorporating the nonspecific anion exchanger tridodecylmethylammonium chloride and the plasticizer dioctyl sebacate exhibit a Nernstian response to chloride with the expected Hofmeister selectivity pattern. Additional response data for potassium and carbonate selective sensors prepared with the electrically neutral ionophores valinomycin and p-decyltrifluoroacetophenone, respectively, are also presented. The effects of endogenous anionic sites arising from dissociated methacrylic acid impurities within the membrane matrix are discussed. The degree of site dissociation and its resulting contributions to the EMF response-governing equilibria are considered in detail. It is shown that such sites must be electrically compensated (via addition of adequate lipophilic cationic sites) when preparing neutral carrier based anion sensors but otherwise have no apparent effect on the sensing membranes' selectivity and performance.