Microelectrochemical measurements at expanding droplets (MEMED): investigation of cupric ion stripping kinetics in a two-phase oil/water system

Microelectrochemical measurements at expanding droplets (MEMED) are used as a new approach for investigating the stripping kinetics of metals ions bet ween an organic phase containing an extractant ligand, which complexes the metal ion of interest, and an aqueous acid solution. The approach is illust rated with measurements of the stripping of cupric ion from 1,2-dichloroeth ane (DCE) droplets containing CuL2 (where L is the oxime ligand, Acorga P50 ) that are formed periodically through a capillary tip submerged in an aque ous receptor phase containing HCl. First-order dependences of the stripping rate constants on the bulk concentration of CuL2 in the DCE phase (5-20 mm ol dm(-3)) and HCl in the aqueous phase (0.25-2.0 mol dm(-3)) were found, w ith an effective bimolecular rate constant of (6.2 +/- 1.0)x10(-5) cm s(-1) M-1. The results obtained demonstrate that the cupric ion stripping proces s is likely to be heterogeneous, occurring at the immiscible liquid/liquid interface, with the first attack of protons on CuL2 as the rate-limiting st ep. The prospects for using MEMED more generally to investigate metal extra ction/stripping kinetics are discussed.