A new approach to the measurement of transfer rates across immiscible liquid/liquid interfaces

The use of ultramicroelectrodes (UMEs) to induce and quantitatively measure the transport of chemical species across immiscible liquid organic/water (o/w) interfaces is considered. In this application, a disc-shaped UME located in the aqueous phase, at micrometre distances from the interface of interest, is employed to drive the transfer process, initially at equilibrium, in the direction of the aqueous phase. This is achieved by applying a potential to the UME, sufficient to electrolyse the target species at a diffusion-controlled rate. The resulting depletion in the local aqueous concentration provides the thermodynamic force for the transfer process and species crossing the interface contribute to the UME current flow, the magnitude of which depends on the transfer kinetics. The technique is illustrated with model studies on the extraction/stripping of Cu2+ hem aqueous solutions by oxime ligands in heptane and 1,2-dichloroethane (DCE).