Activities of water, polymer and salt in liquid–liquid equilibria of polyvinylpyrrolidone and (NH4)2HPO4/(NH4)H2PO4 buffer using the Flory–Huggins model with Debye–Huckel and Pitzer–Debye–Huckel equations and the Osmotic virial model: Effects of pH and te

The Flory–Huggins model with two electrostatic terms (the Debye–Huckel and Pitzer–Debye–Huckel equations) and the Osmotic virial model were used to correlate the liquid–liquid equilibrium data of the aqueous solution of polyvinylpyrrolidone and diammonium hydrogen phosphate/ammonium dihydrogen phosphate buffer at various temperatures (298.15, 308.15 and 318.15 K) and pH 5 and 7. The obtained interaction parameters of models were used to calculate the activities of water, polymer and salt at three temperatures and both pH values. The deviations showed that these models can accurately correlate the activities of all species.