Improvement on the extraction efficiency of low density lipoprotein in an ionic liquid microemulsion

A novel microemulsion is developed at room temperature with 30 mu L of sodium alginate sulfate (SAS, 0.02 mol/L), 0.005 g bis (2-ethylhexyl) succinate sulfonate (AOT) and 270 mu L of 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) ionic liquid as aqueous phase, surfactant and IL phase, respectively. The SAS/AOT/BmimPF(6) microemulsion significantly improves the extraction efficiency for low density lipoprotein (LDL). 96% LDL in a 300 mu L of PBS is selectively extracted into a same volume of microemulsion, with respect to those of 67%, 76% and 85% by BmimPF(6), H2O/AOT/BmimPF(6) microemulsion and sodium alginate (SA)/AOT/BmimPF(6) microemulsion. LDL in the SAS/AOT/BmimPF(6) microemulsion is distributed both in BmimPF(6) via hydrophobic interaction and in the "pools" of the microemulsion via electrostatic interaction with AOT and specific interaction between LDL with SAS. 83% of LDL in the microemulsion can be readily back extracted into an aqueous phase with 0.8% (m/v) of sodium dodecyl sulfate (SDS) as stripping reagent. For practical applications, LDL in human serum is selectively extracted with the microemulsion, as demonstrated by enzyme linked immunosorbent assay (ELISA) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).