Effect of the supporting electrolytes on voltammetry at liquid/liquid microinterfaces between water and nitrobenzene, 1,2-dichloroethane or 1,6-dichlorohexane

The transfers of the ions of tetraalkylammonium picrates (-methyl, -ethyl, -propyl, -butyl), from water (W) to nitrobenzene (NB), 1,2-dichloroethane (DCE) or 1,6-dichlorohexane (DCH), have been studied by voltammetry at liquid/liquid microinterfaces. Electrochemistry is possible in the absence of supporting electrolytes in both phases, even in the less dissociating solvents, DCE and DCH, when the concentration of the picrate is lower than 10−3 M, the main difficulty however being the lack of reference electrodes. Without an electrolyte in the organic phase, the limiting current for an ionic transfer from the solvent to water is two times the diffusion current, due to the migration. This is not the case when the transferring ions are in water where an adventitious electrolyte is always present. Comparing voltammetry of the ion transfers with and without electrolytes has shown that ion-pairing in DCE and DCH influences the partition of the salts, which has been confirmed by some spectrophotometrical measurements. As a consequence, the partition potential scales derived from experiments performed in DCE and DCH in the presence of electrolytes are conditional.