POLYMERIC MEMBRANE SODIUM-SELECTIVE ELECTRODES BASED ON CALIX[4]ARENE IONOPHORES

Six kinds of tetra alkylester type calix[4]arene derivatives, (R(1) = R(2) = CH3: 1, C2H5: 2, C3H7: 3, n-C4H9: 4, t-C4H9: 5, n-C10H21: 6), a diethyl-didecyl mixed ester type (R(1) = C2H5, R(2) = C10H21: 7), and three kinds of lower rim bridged types (R(1) = C2H5, R(2)-R(2) = -(CH2)(10)-: 8, -(CH2)(12)-: 9, -(CH2)(2)(OCH2CH2)(3)-: 10) were characterized by electrochemical measurement to elucidate the effect of the length of the alkyl group of alkoxycarbonyl substituents on Na+ selectivity. To obtain excellent Na+ selective ionophores, introduction of short chain alkyl groups rather than long chain ones, such as a decyl group, and maintenance of sufficient solubility of the calix[4]arene derivatives in the membrane solvent are required concurrently. Among the calix[4]arenes tested, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-tert-butylcalix[4]arene 2, and the diethyl-didecyl mixed ester type derivative 7 are the best ionophores for a Na+ selective electrode. On the other hand, sodium selectivity of the bridged type derivative 9 is comparable or even superior to that of the known bis(12-crown-4).