Study of kinetics of charge transfer across a supported liquid membrane under transient conditions

The transfer of a cation across a supported liquid membrane is studied both theoretically and experimentally during a linear potential scan. The transferring cation was originally present both in the membrane and in the flanking aqueous phases, thus working as a potential-determining ion in the system. With this set-up, the transfer kinetics of hydrophobic ions which usually determine the limits of the potential window of an ideally polarised liquid ∣ liquid interface can be studied, even if the standard potential of transfer is unknown. The probe cation studied was tetrabutylammonium, and the membrane phase was o-nitrophenyloctyl ether. The observed standard rate constant k0 took a surprisingly low value of ca. 2×10−4 cm s−1; however, this agrees with the values measured with a rotating diffusion cell under steady-state conditions. It is therefore suggested that the different values obtained with different techniques reflect the structural changes of the liquid ∣ liquid interface due to the electric current.