A dual-ionic liquid microemulsion system for the selective isolation of hemoglobin

A novel dual-ionic liquid (IL) microemulsion system is developed with IL 1-decyl-3-methylimidazolium bromide (DmimBr) as the surfactant and IL 1-butyl-3-methylimidazolium hexaflourophosphate (BmimPF(6)) as a substitute for organic solvent. The phase diagram of this dual-IL microemulsion system clearly shows the formation of a single phase within a wide range of BmimPF(6) (1.76-98.3%, wt) and in the presence of an appropriate amount of DmimBr and water. The microemulsion is characterized by means of FT-IR spectra, dynamic light scattering and molecular probe. The dual-IL microemulsion system has been demonstrated to be effective for the extraction of proteins, and exhibited an obvious improvement in extraction efficiency for hemoglobin in comparison with pure BmimPF(6). When 100 mu L microemulsion is used to extract 100 mu g mL(-1) of proteins in an equal volume of sample solution, high selective extraction of hemoglobin (Hb) has been observed at pH 5. This might be attributed to the coordination interaction between the heme group of Hb and the imidazolium cationic moiety in the ionic liquids. Hb transferred into the microemulsion can be readily recovered by back extraction with Britton-Robinson buffer at pH 12, giving rise to a recovery of 55.6%. The dual-IL microemulsion system is practically applied to the isolation of Hb from human whole blood and the SDS-PAGE indicates that hemoglobin has been selectively isolated from human blood in the presence of co-existing protein species.