BACKGROUNDThe aqueous two-phase extraction (ATPE) based on organic solvent and inorganic salt was considered a promising method in the extraction, enrichment, and purification field. Ionic liquids (ILs) used as additives to the aqueous two-phase system (ATPS) can improve the extraction yield. RESULTSIn this study, seven ILs were added to the ethanol/ammonium sulfate ATPS and used for the salting-out extraction (SOE) of sinomenine from Sinomenium acutum. The IL [C(2)OHmim]FeCl4 was screened as the optimal additive, then the influencing factors IL amount, ethanol concentration, salt concentration, and temperature were investigated. The maximum extraction efficiency of 96.4% was obtained under the following conditions: 23.06wt% ethanol concentration, 27.28wt% (NH4)(2)SO4 concentration, 4.0wt% [C(2)OHmim]FeCl4 and 40(degrees)C temperature. Moreover, the components in the SOE system can be recycled after extraction. CONCLUSIONThus, this ATPS had lower cost and higher extraction ability, and it is feasible to scale up using a small amount of ILs. This system can also be used in the extraction of some other important active compounds from natural plant resources. (c) 2017 Society of Chemical Industry