SELECTIVE ION-TRANSPORT IN ACETONITRILE ACROSS THE IONOPHORE-IMMOBILIZED POLYMER MEMBRANES USED AS THE SENSOR OF THE ION-SELECTIVE ELECTRODES

A conductometric study was carried out concerning the selective ion transport of alkali and alkaline earth metal ions, mainly in acetonitrile (AN), across a membrane of polyacrylamide (PAA) coupled to such ionophores as tetraethylene glycol monododecyl ether, hexaethylene glycol monododecyl ether, dibenzo-18-crown-6, and cryptand222B. A sintered glass filter membrane was impregnated with PAA-ionophores and the conductivity of the solution of one side of the membrane was measured in order to monitor the ion transport across the membrane from the opposite side. Alkali and alkaline earth metal ions could pass across the ionophore-free PAA membrane, but the ions were entrapped in the PAA-ionophore membranes. Tetraethylammonium and perchlorate ions, however, could pass across both the PAA and the PAA-ionophore membranes. The entrapped ions could pass across the PAA-ionophore membranes if a complexing reagent was added to the solution on one side of the membrane by forming complexes with the reagent. The limiting equivalent conductivities and the ion association constants of (Li-12C4)+ClO4-, (Li-Cryp22)+ClO4-, (K-DB18C6)+ClO4-, (K-Cryp222)+ClO4-, (Mg-12C4)2+2ClO4-, (Ba-DB18C6)2+2ClO4-, (Ba-Cryp22)2+2ClO4-, and (Ba-Cryp222)2+2ClO4- were determined. The limiting equivalent conductivities were used to compare the relative conductivity values among different species obtained the conductometric measurements of ion transport across the membrane.