ONE-COMPONENT ROOM-TEMPERATURE VULCANIZING-TYPE SILICONE-RUBBER BASEDCALCIUM-SELECTIVE ELECTRODES

New calcium-selective membranes for all-solid-state ion sensors are de veloped with a highly adhesive one-component room temperature vulcaniz ing-type silicone rubber (RTV-1-type SR) matrix. The membranes are for mulated with 21.6 wt % bis(2-ethylhexyl) adipate, 0.3 wt % tetradodecy lammonium tetrakis(p-chlorophenyl)berate (ETH 500), 0.1 wt % potassium tetrakis(p-chlorophenyl)borate, and 0.8 wt % calcium-selective neutra l carrier ETH 129 or ETH 1001. Plasticizer added to the RTV-1-type SR matrix not only decreases the bulk membrane resistance but also increa ses the solubility of electroactive components incorporated in the mem brane without significantly deteriorating its adhesive strength, It is found that the lipophilic salt ETH 500 remarkably enhances the calciu m selectivity of ETH 129 or ETH 1001 ligands in the SR matrix; the sel ectivity coefficients (K-ca2+(pot) by separate solution method, where j = Li+, Na+, K+, or Mg2+) for the optimized membranes were below 10(- 5), Potentiometric characteristics of planar-type Ag electrodes coated with optimized RTV-1-type SR membranes, e.g., response slope 29.0 +/- 0.5 mV/decade, detection limit below 5.0 x 10(-7) M alpha(Ca2+), and 2-3 mV of potential drift per day, were virtually the same as those of the corresponding poly(vinyl chloride) membrane-based conventional el ectrodes, but with greatly enhanced sensor-to-sensor reproducibility a nd lifetime (3-9 weeks).