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 derived for the competitive ion-transfer of two kinds of cations present in an aqueous (w) phase simultaneously facilitated by a macrocyclic ligand (L) present in an organic (o) phase. Especially, for the two limiting cases, i.e. case (A): c*_Mj (j=1, 2)?c*_L and case (B): c*_L?c*_Mj (where c*_Mj and c*_L denote the bulk concentrations of cation M_j in the w-phase and of L in the o-phase, respectively), simple explicit expressions are derived and a method analyzing the facilitated waves is presented. Furthermore, the main part of the theoretical predictions obtained is verified experimentally at 25 °C by using the ion-transfer-polarographic method with the electrolyte dropping electrode, for the following four combinations: (i) competitive cations: protonated alanine and H⁺, L: benzo-18-crown-6 ether; (ii) Na⁺ and Li⁺, benzo-15-crown-5 ether; (iii) K⁺ and Na⁺, dibenzo-18-crown-6 ether; and (iv) Na⁺ and Ba²⁺, dibenzo-24-crown-8 ether.