Thermodynamic Modeling of Aqueous Two-Phase Systems Composed of Macromolecules and Sulfate Salts at pH 2.0

Liquid–liquid equilibrium data of aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG) 8000 + sodium sulfate + water, PEG 8000 + ammonium sulfate + water, and PEG 8000 + magnesium sulfate + water at T = 298.15, 308.15, and 318.15 K and pH 2.0 were determined. The universal function activity coefficient (UNIFAC) model was correlated to the experimental tie-line data, and the root-mean-square deviations (RMSDs) between experimental and calculated data were considered in the calculation. The effects of temperature and cation type on the spinodal curves were evaluated. The salting-out effect was studied by the determination of the effective excluded volume (EEV). Rising temperature resulted in an increase in the biphasic region and tie-lines. Regarding the cation type, the phase-separation abilities followed the order Mg2+ > Na+ > (NH4)+. Increases in the overall composition of the systems resulted in increased tie-line lengths. The tie-line slope absolute values also tended to rise with inc...