Aqueous three-phase systems formed by poly(vinylpyrrolidone) + poly(ethyleneglycol) + lithium sulfate + water: Phase behavior and partition data

Abstract

Aqueous three-phase systems (A3PSs) have been used to extract and separate several strategic analytes; however, there are several gaps in the characterization and theoretical principles of this technique. Therefore, an A3PS made up of 10,000 g‧mol−1 of polyvinylpyrrolidone (PVP), 10,000 g‧mol−1 of polyethylene glycol (PEG), lithium sulfate (Li2SO4), and water was characterized in this study. The results revealed that PEG, PVP, and Li2SO4 were concentrated in the top, middle, and bottom phases, respectively, whereas water was the main component in all phases. The three-dimensional coordinates of the phase composition points generated a plane with an area that increased as the difference in the phase compositions increased. The tie-plane area (TPA) decreased as the global composition and temperature decreased, indicating a strong temperature effect. Moreover, at relatively low overall concentrations, a phase inversion behavior between the electrolyte-rich phase and the PVP-rich phase was observed at 308.15 K. HE-4R dye molecules preferentially partitioned to the PVP-rich phase, and this trend increased as the TPA and temperature increased. A similar partition behavior was observed for Cu(II) ions, but they preferred to concentrate in the salt-rich phase. At relatively low overall concentrations, the Cu(II) ions promoted phase inversion at 298.15 K, a phenomenon similar to that observed in the temperature study. Thus, the phase diagram for a new A3PS was obtained, and as far as we know, this is the first work that quantitatively describes the TPA.