Akihiro Uehara

Evaluation of Gibbs free energy for the transfer of a highly hydrophilic ion from an acidic aqueous solution to an organic solution based on ion pair extraction

Abstract A method to determine the standard Gibbs free energy for the transfer, ΔG°tr, of a highly hydrophilic metal ion from an aqueous solution, W, in the presence of high concentration of H+ to an organic solution, O, was proposed based on the theoretical consideration of the distribution process of ions between W and O. The usefulness of the proposed method was verified experimentally by comparing ΔG°tr of Mg2+ determined by the method with that obtained by voltammetry for the ion transfer at the W|O interface. The O examined were nitrobenzene (NB) and 1,2-dichloroethane (DCE). By applying the proposed method, ΔG°tr of NpO2+, UO22+, NpO22+ and PuO22+ from an acidic W to NB were determined.

Some factors in the voltammetric measurement of ion transfer at the micro aqueous | organic solution interface

Abstract In order to expand the application of voltammetry to ion transfer at the micro aqueousxa0|xa0organic (Wxa0|xa0O) solution interface, factors essential for the measurement of voltammograms were investigated systematically by cyclic voltammetry. The effects of the dimension of the microhole, concentrations of supporting electrolytes in W and/or O and kinds of O on the characteristics of the voltammograms were investigated using micro interfaces formed in microholes made through thin polyester films set between O and W. When chloroform was used as O and the ratio of the radius to depth of the microhole was large, a well defined voltammogram for the transfer of an ion such as the tetraethylammonium ion from W to O could be observed even when the supporting electrolytes in W were as dilute as 5×10−5 M. Organic solvents of low relative dielectric constant, e, and alcohols were found to be applicable to voltammetry at the micro Wxa0|xa0O interface as O in addition to those used in voltammetry with a conventional interface. Formal potentials for transfers of various ions at interfaces between W and O of low e and alcohols were determined.

Characteristics of voltammograms for ion transfer through a membrane

Abstract Digital simulation was performed to obtain a better understanding of the characteristics of the voltammogram for ion transfer from one aqueous solution, W1, to another, W2, through a membrane, M, which was obtained by scanning the potential difference between W1 and W2 and measuring the current between W1 and W2 under the condition that W1, M and W2 contain sufficient concentrations of supporting electrolytes. When one kind of objective ion, P + , was present in the membrane system in addition to supporting electrolyte ions, the number of current peaks observable in the voltammogram depended on phase(s) where P + was added. When P + is added to W1, M, W1 and W2 or W1, M and W2, 1, 2, 2 or 3 pairs of positive and negative current peaks were observed. When P + was added to W1 and an anion, X − , which transfers more easily than supporting electrolyte ions at the Mxa0∣xa0W2 interface was added to W2, the peak potentials due to the transfer of P + at the W1xa0∣xa0M interface coupled with the transfer of X − at the Mxa0∣xa0W2 interface and the peak separation between the positive and negative current peaks, Δ E p , depended on the ratio of concentrations of P + and X − , even though the transfers of P + and X − at the interfaces were reversible. The peak current was not proportional to the concentration of P + unless the concentration of X − was much larger than that of P + . The reasons for the above-mentioned results were elucidated by considering complementary transfers of ions at the W1xa0∣xa0M and Mxa0∣xa0W2 interfaces.