Voltammetry of tetraalkylammonium picrates at water∣nitrobenzene and water∣dichloroethane microinterfaces; influence of partition phenomena

A microinterface between two immiscible phases (micro ITIES), established by a microchannel (internal diameter: 50 μm, length: 15 μm) drilled through a polyimide thin plate, gives reproducible voltammograms for the transfer of charges. As expected for such a microinterface, the regime for mass transport depends on the scan rate of voltammetry, low scan rates being characterized by steady-state currents corresponding to radial diffusion; faster sweeps give rise to conventional cyclic voltammograms, from linear diffusion. This has been used as an electrochemical method for the study of tetraalkylammonium picrates at interfaces between water and immiscible solvents (nitrobenzene, 1,2-dichloroethane). The partition of Me4NPi, Et4NPi, Pr4NPi, and Bu4NPi at the W∣NB and W∣DCE interfaces is clearly illustrated by voltammetry under steady-state conditions, allowing the measurement of Gibbs energies and interfacial potentials for the transfer of the ions from water to NB. When the organic solvent is DCE, the estimation of ionic interactions is risky in such a poorly dissociating medium; the microhole interface works well however, showing the influence of the medium on solvation of the cations and on the extraction of the picrates.