Sol−Gel Method for the Matrix of Chloride-Selective Membranes Doped with Tridodecylmethylammonium Chloride

An organic−inorganic hybrid sol−gel matrix was used as host for tridodecylmethylammonium chloride (TDMAC), which is an ionophore for chloride. The sol−gel precursor was prepared by the reaction of (3-isocyanopropyl)triethoxysilane with 1,4-butanediol. On mixing with TDMAC, the sol-state precursor slowly gelled, to give a TDMAC-containing membrane. The performances of the sol−gel membrane-based electrodes were compared to those of TDMAC-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with an optimum ratio of TDMAC:sol−gel precursor (0.1:3 by weight) showed very stable baseline potential. The response slope toward chloride was approximately 55 mV/decade between 10 -4 and 5 × 10 -1 M Cl - at room temperature. Moreover, selectivity toward chloride over salicylate and other lipophilic anions was improved, deviating from the Hofmeister selectivity pattern which is observed in most dissociated charged carrier-based potentiometric membrane sensors. The selectivity coefficients measured by the separate solution method in 0.01 M MES buffer, pH 5.5, were log = 0.6, log = −1.6, and log = −0.6.