Effect of Amino Acids on the Phase Behavior of Aqueous Biphasic Systems Composed of 1-Butyl-3-methylimidazolium Tetrafluoroborate and Sodium Citrate

Ionic liquids (ILs) based aqueous biphasic systems (ABSs) have been successfully applied to the extraction and purification of biomolecules. Although much research has focused on the effect of ILs on the phase formation, there are few reports that describe the phase behavior of quaternary IL-based ABS systems using amino acids (AAs) as additives. Here, 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 mim]BF 4 ) formed an ABS with sodium citrate (Na 3 C 6 H 5 O 7 ) with the aid of AAs. The phase behavior and physical properties of the ABS were investigated at 298 K. The capacity of the AA to create the ABS (area of biphasic region) increases with increasing in solubility and decrease with the molecular weight of the ILs and follows the trend glycine >  l -alanine ≈  l -lysine >  l -threonine >  l -proline ≈  l -arginine > none. Moreover, the pH of the top and bottom phases containing l -proline as additive are nearly neutral; l -threonine, glycine, and l -alanine result in mildly acidic environments, while l -arginine and l -lysine provide basic pH conditions. The results show that the effects of the addition of the AAs can be considerable and important in the simulation, design calculation and pH control of ABS for efficient separation and extraction processes.