Cation effect on the (PEG 8000Â +Â sodium sulfate) and (PEG 8000Â +Â magnesium sulfate) aqueous two-phase system: Relative hydrophobicity of the equilibrium phases

The partitioning of four dinitrophenylated (DNP-) amino acids in aqueous two-phase systems of (polyethylene glycol (PEG)-8000 + sodium sulfate) and (polyethylene glycol (PEG)-8000 + magnesium sulfate) in five different tie-lines was experimentally determined at T = 298.15 K. The Gibbs energy of transfer of a methylene group between the two phases was calculated from the measured partition coefficients. This characterizes the relative hydrophobicity of the equilibrium phases. Values of ΔG∗(CH2) were in range from (−0.674 to −1.012) kJ · mol−1. A comparison of both systems was carried out. The results show that the cation type has a strong influence on the amino acids partitioning process. The largest relative hydrophobicity was noted for the ATPS system formed by sodium sulfate. This showed to be a better system for the separation.