Le Hung

Le Hung presented a general theoretical approach for calculating the Galvani potential Ajyj at the interface of two immiscible electrolyte solutions, e.g., aqueous (w) and organic solvent (s) [25]. Le Hung s approach allows the calculation of when the initial concentration (Cj), activity coefficients (j/,) and standard energies of transfer of ions (AjG ) are known in both solutions. 

According to Le Hung, one deals, in general, with a system composed of two liquid immiscible phases containing 7 ions this can be described as follows ... 

Using Eqs. (7), (13), and (14), Le Hung derived the general dependence describing the difference of Galvani potentials between the phases w and s ... 

The above equation allows the calculation of Galvani potentials at the interfaces of immiscible electrolyte solutions in the presence of any number of ions with any valence, also including the cases of association or complexing in one of the phases. Makrlik [26] described the cases of association and formation of complexes with participation of one of the ions but in both phases. In a later work [27] Le Hung extended his approach and also considered any mutual interaction of ions and molecules present in both phases. Buck and Vanysek performed the detailed analysis of various practical cases, including membrane equilibria, of multi-ion distribution potential equations [28,29]. 

The few cases of Le Hung s equation, for practically important and simple systems, are discussed below. 

Interfaces of the type in Scheme 8 are used as liquid ion-selective electrodes. It is apparent that they constitute a special case of distribution systems reversible in regard to two or more ions. Here, Le Hung s equation, (16) and (17), allows quantitative evaluation of the influence of the presence of other ions on the selectivity of these systems. 

The degree of polarizability of system can be found from the data calculated by Le Hung [25] with the use of Eqs. (16) and (17). In the equilibrium state of the interphase between the solutions of 0.05 M LiCl in water and 0.05 M TBATPhB in nitrobenzene, the concentrations of Li and CL in the organic phase lower than 10 M, and the concentrations of TBA and TPhB in the aqueous phase are about 3 x 10 M each [3]. These concentrations are too low to establish permanent reversible equilibria. They are, however, significantly higher compared to those of the components present in the mercury-aqueous KF solution system [20]. 

Kakiuchi performed a very important analysis of the distribution potential in the small systems [14,31]. Using the general Le Hung approach, he discussed the behavior of Aj e at its extreme, when r 0 or oo. 

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