Effects of Phase-Forming Cations and Anions on the Partition of Ionic Solutes in Aqueous Polyethylene Glycol-Inorganic Salt Two-Phase Systems

The partition bahavior of inorganic ions in aqueous polyethylene glycol (PEG)-salt two-phase systems of different polymer and salt concentrations has been studied. Na2SO4, Na2HPO4 and K2HPO4 were used as phase-forming salts. Phase diagrams for the three aqueous PEG-salt two-phase systems were determined, and the partition coefficients for the inorganic ions in each of the systems were investigated as a function of the difference in the concentration of PEG in the two phases, ∆wPEG. It was found from the phase diagrams that the salting-out abilities of K+ and SO42- were lower than those of Na+ and HPO42-, respectively. However the former ions were more effective for the extraction of oppositely charged analyte ions to the PEG-rich phase than the latter ions when they were compared with each other under a constant ∆wPEG. On the other hand, Na+ and HPO42- were more effective than K+ and SO42- for the extraction of the ions which have the same charge sign as theirs. These counter-ion and co-ion effects of the phase-forming ions on the partition of ionic solutes are interpreted by a model regarding the partition mechanism of ions in the presence of excess amounts of co-existing salts.