| This dissertation presents the fundamental studies on ion-selective membrane by the sandwich membrane method and new material for making ionsensing membranes.; In this dissertation, the method has been used to determine complex formation constants and pKa values of neutral or charged ionophores and chromoionophores, obtain the information on the stoichiometry of the ion-ionophore complex, compare different plasticizers and polymer matrices, elucidate the extent of ion pair formation, evaluate the upper detection limit of ion-selective electrodes, determine the extent of extraction of dissociated electrolyte into the membrane, and assess the mobility of free and covalently immobilized ionophores in the membrane phase.; A methyl methacrylate and decyl methacrylate (MMA-DMA) copolymer has been used to fabricate plasticizer-free ion-selective membranes. The copolymer matrix showed good mechanical properties for preparing ion-selective membranes and optode thin films. The material was evaluated in ionophore-free cation and anion exchanger membranes as well as in membranes containing different ionophores. These MMA-DMA membranes showed excellent selectivity similar to the corresponding plasticized PVC membranes. This makes MMA-DMA a potentially superior choice over alternative membrane matrices reported in the literature and a promising platform for the establishment of covalently immobilized membrane components. A derivative of a known Ca2+-selective ionophore, ETH 129, was synthesized to contain a polymerizable acrylic moiety (AU-1) and covalently grafted into MMA-DMA polymer matrix via a simple one-step homogeneous polymerization method. It exhibited mechanical properties similar to the blank MMA-DMA polymer. Electrodes, containing only MMA-DMA-AU-1 and cation exchanger, exhibited a Nernstian response towards calcium with selectivity over Na +, K+, and Mg2+ that was comparable to electrodes containing free AU-1 dissolved in the MMA-DMA matrix. The segmented sandwich membrane technique was utilized to assess the binding constant of free and covalently bound ionophores to calcium, and to study their diffusion coefficients in the membrane phase. Diffusion was greatly diminished for the bound ionophore. Optical sensing films with the new copolymer matrix, unblended and blended with plasticizer and PVC, showed functional optical responses that are suitable for the physiological assessment of calcium at neutral pH. Response times were found to be very rapid (on the order of 2 min) with the blended polymer film system. The new derivative AU-1 can form complex with calcium and magnesium ions individually with different stoichiometric ratios. (Abstract shortened by UMI.)... |
