Current–potential curves for liquid ∣ liquid microinterfaces with no added supporting electrolyte in the water phase

Abstract

Equations describing steady-state voltammograms have been derived for ion transfer at liquid ∣ liquid microinterfaces with no supporting electrolyte in the aqueous phase. The effect of the absence of any added supporting electrolyte on limiting current, half-wave potential and shape of the current–potential curves is derived theoretically and verified experimentally. Ion-transfer voltammetry across a water ∣ nitrobenzene microinterface with no supporting electrolyte in the aqueous phase has been employed for the determination of standard Gibbs energies of ion partition (in kJ mol −1) of relatively hydrophilic ions such as Tl + (19.7), K + (22.4), Ag + (26.0), Na + (31.5), Li + (35.5) and H + (34.4). The data obtained agree well with those obtained previously by voltammetry and extraction measurements. With respect to the paper of Quinn et al. (J. Electroanal. Chem. 460 (1999) 149), it is assumed that measurements without a supporting electrolyte in the aqueous phase are useful in systems with a relatively high polarity of the organic phase, e.g. the system water ∣ nitrobenzene. The decisive prerequisite is that the ions of interest in the aqueous phase are transferred sufficiently before the hydrophobic ion of the reverse sign of the charge number in the organic phase.