Determination of Consecutive Formation Constants of Complex Ions from Ion-Transfer Voltammetric Data

Abstract

Abstract The half-wave potentials of the voltammetric waves of facilitated transfer of Pb2+ ion by 1,4,7,10,13,16-hexathiacyclooctadecane across the nitrobenzene/water interface have been measured as a function of the concentration of free CH3COO− ion in aqueous phase. Using the equation of reversible half-wave ion-transfer potential, the formal formation constants of 1 : 1, 1 : 2, and 1 : 3 Pb2+–CH3COO− complexes in the aqueous medium have been determined to be 102.3 M−1, 103.0 M−2, and 104.0 M−3, respectively. A polynomial regression method for the determination of the formation constants from voltammetric data is presented. Ion-transfer voltammetry at the liquid/liquid interface can be applied advantageously to the determination of consecutive formation constants of metal complexes with a ligand in aqueous media as well as those with an ionophore in organic media.