On the facilitating effect of neutral macrocyclic ligands on the ion transfer across the interface between aqueous and organic solutions Part III. Competitive facilitated ion-transfer

A theoretical equation of the reversible current -potential curves is deriv ed for the competitive ion-transfer of two kinds of cations present in an a queous (w) phase simultaneously facilitated by a macrocyclic ligand (L) pre sent in an organic (o) phase. Especially, for the two limiting cases, i.e. case (A): c(M)*(i) (j = 1, 2) much greater than c(L)* and case (B): c(L)* m uch greater than c(M)*, (where c(M)*(j) and c(L)* denote the bulk concentra tions of cation Mi in the w-phase and of L in the o-phase, respectively), s imple explicit expressions are derived and a method analyzing the facilitat ed waves is presented. Furthermore, the main part of the theoretical predic tions obtained is verified experimentally at 25 degreesC by using the ion-t ransfer-polarographic method with the electrolyte dropping electrode, for t he following four combinations: (i) competitive cations: protonated alanine and H+. L: benzo-18-crown-6 ether; (ii) Na+ and Li+, benzo-15-crown-5 ethe rs (iii) K+ and Na+, dibenzo-18-crown-6 ether, and (iv) Na+ and Ba2+, diben zo-24-crown-8 ether. (C) 2001 Elsevier Science BN. All rights reserved.