Polyethylene glycol acquires certain compensatory solute properties when used to form aqueous two-phase extraction systems

The polyethylene glycols are currently considered an essential class of polymers with several applications in industry, medicine, and biology. The aqueous two-phase (ATP) extraction based on polyethylene glycol (PEG) and certain salts have gained the attention for further usage in protein purification as a simple and cheap technique; however, it is still under development. In this paper, the formation of ATP systems by PEG as a model polymer and sodium sulfate was studied focusing on (1) some of the conditions under which the polymer may have definite compensatory solute properties, and (2) the analysis of the crystallization degree and the conditions for forming di and triphasic systems. The results demonstrate that the polymer in some systems may have inherent compensatory solute-like behavior which becomes evident under certain conditions, including the type of the other solute molecules, solvent type, concentration, and pH of the system.