Enhancement of long alkyl-chained imidazolium ionic liquids for the formation and extraction behaviour of PEG 600/(NH4)2SO4 aqueous two-phase system by complexing with Triton X-100

Broadening the polarity range of polymer-based aqueous two-phase systems (ATPSs) is of practical significance. Recently, ionic liquids have been used as adjuvants to modify the polarity and properties of PEG-rich phases in PEG/salt ATPSs. However, thus far, only short alkyl (containing less than 8 carbon atoms)-chained ionic liquids have been able to promote the extraction performance of ATPSs; long alkyl-chained ionic liquids have decreased the extraction performance significantly due to their distribution in the bottom phase. In the present study, we found that by complexing with Triton X-100 (TX-100), long alkyl-chained imidazolium ionic liquids [C n mim]Br (n = 10 and 12) as adjuvants were enriched in the top phase of PEG/salt ATPSs, and hence, the polarity difference of the two phases were increased. By extracting two model substances (S-mandelic acid (MA) and l -tryptophan (Trp)), it was concluded that, although the long alkyl-chained [C n mim]Br adjuvant decreased the extraction performance of the ATPS substantially, the long alkyl-chained [C n mim]Br/TX-100 complex as the adjuvant enhanced the extraction performance of the ATPS significantly. Compared with the case without an adjuvant, when the [C 12 mim]Br/TX-100 complex and the [C 10 mim]Br/TX-100 complex were used as the adjuvants, the partition coefficients of MA and Trp in the PEG 600/(NH 4 ) 2 SO 4 ATPS were increased up to 3 ∼ 4 times, much better than those with short alkyl-chained ionic liquid as the adjuvant. Moreover, the [C 12 mim]Br/TX-100 complex is more conductive to the transfer of MA into the PEG-rich phase, and the [C 10 mim]Br/TX-100 complex is more conductive to the transfer of Trp into the PEG-rich phase.