Cd 2+ transfer across water/1,2-dichloroethane microinterfaces facilitated by complex formation with 1,10-Phenanthroline

Abstract

The transfer of Cd 2+ facilitated by 1,10-Phenanthroline (phen) was investigated at the microinterface of two immiscible electrolyte solutions, hosted by a 25 μm diameter orifice of a micropipette. Cyclic voltammetry (CV) was employed to examine the transfer in the conditions of the ligand (organic phase) in excess and Cd 2+ (aqueous phase) in excess. In these conditions, asymmetric (peak-shaped in the forward scan and steady state in the backward scan), and reversible steady state (for the two scan directions) voltammograms were observed. The dependence of half-wave potential on the ligand concentration suggested that the equilibrium was effectively displaced towards a 1:3 (Cd 2+:ligand) stoichiometry, with a formation constant, β 3 = 3.9 × 10 29. The diffusion coefficients of Cd 2+ in the aqueous solution and those of phen, Cd(phen) 3 2+ in organic phase were evaluated to be 6.5 × 10 −6, 5.8 × 10 −6, and 5.1 × 10 −6 cm 2 s −1 respectively, using CV.