Analytical Sciences

Prediction of the Standard Gibbs Energy of Ion Transfer across the 1,2-Dichloroethane/Water Interface

Akiyoshi YAMADA, Erina YOSHIDA, Kazuo EDA, and Toshiyuki OSAKAI

Department of Chemistry, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan

The standard Gibbs energy of ion transfer at the 1,2-dichloroethane/water interface (ΔG_tr°^,W→O) was determined for 26 organic cations and 24 anions by means of ion-transfer voltammetry with a micro oil/water interface. Based on the data sets, a theoretical analysis was performed with the non-Bornian solvation model, in which the solvation energy of an organic ion is evaluated from local electric fields on the surface of the ion. The semi-empirical equations thus obtained are available for relatively accurate prediction of ΔG_tr°^,W→O for organic ions. The mean absolute error was 1.9 or 3.1 kJ mol⁻¹ for cations or anions, respectively, corresponding to the error of ∼20 or ∼30 mV in the standard ion-transfer potential. In this paper, energy decomposition has been performed to discuss different contributions to ΔG_tr°^,W→O from the “hydrated” (strongly charged) and positively and negatively charged “non-hydrated” (moderately charged) surfaces as well as from the hydrophobic interaction (cavity formation energy).

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