STUDY OF THE BEHAVIOR OF CALIX[4]ARENE-BASED SODIUM-SELECTIVE ELECTRODES BY MEANS OF ANOVA

Two ethylamide and two butyl ester calix[4]arene ionophores differing by the presence of a tert-butyl group in the upper lipophilic rim were used to construct liquid membrane ISEs with two solvents (dibutyl seb acate and dibutyl phthalate). Their behavior toward sodium ion was tes ted in terms of detection limit (DL), sensitivity (S, mV/pNa), and sel ectivity toward protons and alkali and alkaline earth metal ions. In o rder to clarify the role of the structural parameters in the behavior of the ionophores, each of these response variables was tested with a multifactor ANOVA with interactions, using four classification factors : (i) nature of the polar part of the lower rim, (ii) presence of the tert-butyl group in the upper rim, (iii) dielectric constant of the or ganic solvent, and, for selectivity, (iv) nature of the interfering io n. It was found that amides show a higher selectivity toward other alk ali metal ions and a lower DL and S than the corresponding esters. Fur thermore, the presence of the tert-butyl group in the upper rim increa ses both S and the selectivity toward alkali metals and decreases the DL, especially for esters; however, for calcium ion, it increases the selectivity of amide membranes and decreases that of the ester membran es. The major effects of a higher dielectric constant of the solvent a re decreases in the selectivity toward alkaline earth ions and the DL and S of amide calixarenes. Hypotheses are proposed for the interpreta tion of the data.