POTENTIOMETRIC SELECTIVITY OF ION-SELECTIVE ELECTRODES FOR ALKALINE-EARTH ELEMENTS BASED ON PODANDS WITH PHOSPHORYL TERMINAL GROUPS

Dependence of the analytical characteristics (detection limits, DLs) a nd potentiometric selectivity K-i,j(pot)) of the ion-selective electro des (ISEs) based on phosphoryl-containing podands on the structures wa s investigated. It was demonstrated that the DL was determined by comp lex facilitated transfer energy. It was shown that the DLs of the majo rity of the ionophores weakly depend on the lipophilicity of the ionop hores. Ionophore selectivity is determined by the difference of the fa cilitated transfer energies of both test and interfering ions and by t he properties of the electrochemical system. Stability of complexes ma kes a major contribution to the energy accompanied with the transfer o f the complex and is determined by the disposition of metal-donor atom s of ionophore bonds and by other properties of the electrochemical sy stem, specifically, the dielectric permeability of the medium. Increas ing the denticity by increasing the ethyleneglycol chain number leads to the transformation of Ca/Ba to Ba/Ca-selectivity. The introduction of the two-fold excess of the sodium tetraphenylborate (mol% to ionoph ore) in membrane composition results in increasing barium selectivity for alkali and alkaline-earth elements. An ISE for the determination o f barium was prepared. (C) 1997 Elsevier Science B.V.