Effect of Salt Addition on the Hydrophobicities of Aqueous Two-Phase Extraction System

The effect of the presence of salts of high concentration in aqueous two-phase systems as a phase-forming salt or a modifier on the hydrophobicity of the systems has been studied, employing several amino acids with various relative hydrophobicities as solutes. The hydrophobicity of the system can be expressed by HF (hydrophobic factor) in the presence of salts of high concentration and in the range of pH apart from pI of the solute. In the PEG/PK (potassium phosphate) system, an increase in pH of the system caused by selection of the ratio of K2HPO4 and KH2PO4 results in an increase in the hydrophobic factor of the system. The partition of amino acids is dominantly governed by the hydrophobic interaction in the range of pH9. In the PEG/ MgSO4 sysyem, addition of salts such as Na2SO4 and sodium phosphate considerably increases the hydrophobic factor, while LiCl decreases it. All data of HF can be correlated with a simple relation with concentration difference of PEG in the two phases, and therefore the variation of the hydrophobicity of the systems can be correlated with the variation of composition of the phase systems.