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 (PE G)-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 determ ined, and the partition coefficients for the inorganic ions in each of the systems were investigated as a function of the difference in the concentrat ion of PEG in the two phases, Deltaw(PEG). If was found from the phase diag rams that the salting-out abilities of K+ and SO42- were lower than those o f Na+ and HPO42-, respectively. However the former ions were more effective for the extraction of oppositely charged analyte ions to the PEG-rich phas e than the latter ions when they were compared with each other under a cons tant Deltaw(PEG). On the other hand, Na+ and HPO42- were more effective tha n K+ and SO42- for the extraction of the ions which have the same charge si gn as theirs. These counter-ion and co-ion effects of the phase-forming ion s on the partition of ionic solutes are interpreted by a model regarding th e partition mechanism of ions in the presence of excess amounts of co-exist ing salts.