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

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) = -(CH 2)(10)-: 8, -(CH2)(12)-: 9, -(CH2)(2)(OCH2CH2)(3)-: 10) were character ized by electrochemical measurement to elucidate the effect of the len gth of the alkyl group of alkoxycarbonyl substituents on Na+ selectivi ty. To obtain excellent Na+ selective ionophores, introduction of shor t chain alkyl groups rather than long chain ones, such as a decyl grou p, and maintenance of sufficient solubility of the calix[4]arene deriv atives in the membrane solvent are required concurrently. Among the ca lix[4]arenes tested, (ethoxycarbonyl)methoxy]-p-tert-butylcalix[4]aren e 2, and the diethyl-didecyl mixed ester type derivative 7 are the bes t ionophores for a Na+ selective electrode. On the other hand, sodium selectivity of the bridged type derivative 9 is comparable or even sup erior to that of the known bis(12-crown-4).