2002 Volume 51 Issue 12 Pages 1103-1119
The distribution process of an objective ion (iz+) with a counter ion (xz-) between water (W) and an organic solution (O) was assumed as that iz+ and xz- transfer at the W|O interface individually, depending on their own standard Gibbs free energies (ΔG0tr) for the transfer from W to O and maintaining the electroneutrality of both phases. Also, theoretical equations were derived for the quantitative expression of the distribution ratios. (D) of iz+ in both the absence and presence of a special complexing neutral ligand (Y) in O. The derived equations were composed of ΔG0tr of iz+ and xz-, ion pair formation constants (Kip) of iz+ with xz- in W and O, the stability constant (Kst) of the complex [(iYp)z+] in O and Kip of (iYp)z+ with xz- in O. The D calculated using the derived equations and constants such as ΔG0tr, Kip and Kst, which were determined with the aid of voltammetry for the transfer of the ion at the W|O interface and conductometry, agreed well with the D determined experimentally by ion pair extraction. This fact means that the distribution process assumed in the present work is reasonable. Based on a theoretical consideration of the distribution process mentioned above, a method to determine ΔG0tr of highly hydrophilic metal ions, which could not be determined by previous methods, was proposed. The D and the selectivity in the distribution (Γi,j) at the W|O interface were connected quantitatively to the potential (EISE) and selectivity coefficient (Kpoti,j) at an ion selective electrode (ISE) of the liquid membrane type while taking into account that not only D and Γi,j, but also EISE and Kpoti,j could be expressed by using ΔG0tr, Kst and Kip when the ISE membrane was regarded as O.
