Evaluation of distribution ratio in ion pair extraction using fundamental thermodynamic quantities

Abstract

Equations were derived for the quantitative expressions of distribution ratios, D M, in ion pair extractions of a cation, M +, with a counter ion, X −, from water, W, to an organic solvent, O, in the absence and presence of a special complexing neutral ligand, L, in O by using standard transfer free energies of M + and X − from W to O, ion pair formation constants of M + with X − in W and O, the stability constant of the complex, (ML) +, in O and the ion pair formation constant of (ML) + with X − in O. The D M values calculated by substituting the constants determined by electrochemical methods into the derived equations agreed very well with those obtained experimentally by ion pair extraction, which means that the extraction processes assumed in the derivation of the equations was reasonable.