イオン対抽出分配比および分配比とイオン選択性電極電位の関係の基礎電気化学的理解

Abstract

Equations were derived for the quantitative expressions of distribution ratios, D, in ion pair extractions of a cation, i+, with a counter ion, x- from water, W, to organic, O, in the absence and presence of a special complexing neutral ligand, Y, in O by using standard transfer free energies of i+ and x- from W to O, ion pair formation constants of i+ with x- in W and O, the stability constant of the complex, (iYp)+, in O and the ion pair formation constant of (iYp)+ with x- in O. The D calculated by substituting the constants determined by electrochemical methods into the derived equations agreed very well with those obtained experimentally by the ion pair extraction, which means that the extraction processes assumed in the derivation of the equations have been reasonable. Distribution . ratios in ion pair extraction were connected quantitatively to the potentials, EISE, and selectivity coefficients, Kpotj, at an ion selective electrode, ISE, of liquid membrane type, taking into account that all of EISE, Kpotij and D could be expressed physicochemically by using standard Galvani potential differences (or standard free energies ) for ion transfers from W to the ISE membrane, M, or O, stability constants of complexes with a neutral ligand in M or O and formation constants of ion pairs with coexisting counter ions in M or O. Theoretical equations derived from the relations between EISE and Kpotij and D were verified experimentally.