Determination of rate constants of ion transfer kinetics across immiscible electrolyte solutions

Abstract

The rotating diffusion cell was used to study ion transfer across the interface between two immiscible electrolyte solutions. Tetrabutylammonium was chosen as the transferring cation and lithium chloride as the supporting electrolyte in aqueous phase. Tetrabutylammonium tetrakis-(4-fluorophenyl)-borate in 2-nitrophenyl-octylether was used as the organic electrolyte solution supported in the porous membrane. The quasi-steady state current–voltage curves were measured both by applying potential steps and by imposing a slow potential sweep. The analysis of experimental results was based on the comparison with the theoretical current–voltage curves and on the Koutecky–Levich plots. The apparent electrical resistance at low applied potentials was also considered. Some experimental limitations which make the rotating diffusion cell suitable only for a limited range of values of the standard rate constant to be determined were identified. In particular, it was shown that the method requires an accurate evaluation of the different contributions to the ion permeability. Nevertheless, an estimation of the rate constant for ion transfer in the system studied was obtained.