Partitioning of ionic liquids in {polyethylene glycol - potassium citrate} ABS: Effect of polyethylenglycol molecular weight

Aqueous biphasic systems (ABS) are suitable for development of enviromentally friendly and biocompatible separation processes. Polyethylene glycols (PEGs) are a class of polymers widely used in typical polymer-salt ABS. However, the applicability of PEGs was faced with limitation due to the low polarity of the PEG-rich phase. To overcome this limitation, in recent years, a new approach has been proposed based on the use of ionic liquids (ILs) as adjuvants in ABS. The ILs are usually applied in ABS to modify the characteristics of the polymer-rich phase aimed at enhancing the extraction efficiency of ABS for biomolecules. In this context, the efficient application of ABS containing IL as adjuvant for preparative purposes (e.g., for separation or purification) requires the knowledge of the specific mechanism behind the partitioning of the used IL between two aqueous phases. Thus, here the effect of the polymer molecular weight on the partitioning of 1-butyl-3-methylimidazolium bromide ([C4C1im]Br) in ABS composed of PEG and potassium citrate, a common biodegradable organic salt, was evaluated at T = 298.15 K. The results obtained show that [C4C1im]Br tends to partition into the PEG-rich top phase and its tendency to the PEG-rich phase was enhanced with decreasing the PEG molecular weight