How to cite this paper: Kudo, Y., et al. (2014) − , into the two diluents were also determined with the determination of K ex . From comparison of these K D,Pic values with those standardized, interfacial potential differences (∆φ eq ) at extraction equilibria were evaluated. Then, using these ∆φ eq values, relations of the experimentally-determined logK ex± or logK ex values with their electrochemically-standardized ones were precisely discussed. Consequently, it was indicated that logK ex± should be expressed as a function of ∆φ eq .