SELECTIVITY OF CALIX[4]ARENE CROWN-6 FOR CESIUM ION IN ISE - EFFECT OF THE CONFORMATION

A new series of calix-crowns were used in ion-selective electrodes with two solvents (dibutyl sebacate and o-nitrophenyl octyl ether), As ionophores, the 1,3-dimethoxy and the three different conformers of the 1,3-diisopropoxycalix[4]arene-crown-6 (i,e,, 1,3-alternate, partial cone, and cone) were considered. Their behavior toward cesium ion was studied in terms of detection limit (DL), sensitivity (S, mV/pCs), and selectivity toward protons, ammonium, alkali, and alkaline earth metal ions, The lowest DL value was obtained for membranes containing the 1,3-diisopropoxy derivative in the 1,3-alternate conformation, To correlate the analytical results with the structural properties of the ligand and with the nature of the polymeric membrane, a multifactor ANOVA with interactions was carried out on selectivities toward univalent and divalent ions, As for the alkali metal ions, a highly significant negative correlation (p < 0.01) between the pK(Cs/M)(pot), values and the ionic radius was found; in addition, for the smaller ions H+, Li+, and Na+, the four ionophores showed higher differences in selectivity than for the larger ions K+ and Rb+ as well as for alkaline earth metal ions, Better results than those previously reported with other ligands in terms of DL (5 x 10(-7) M) and pK(Cs/m)(pot) (4.46) were found for the 1,3-diisopropoxycalix[4]arene-crown-6 in the 1,3-alternate conformation.