Monascus pigments in the excess IL phase were further
back-extracted by various organic solvent–IL two-phase systems,
such as tert-butanol–IL two-phase system. Equal volume of excess
IL phase and tert-butanol (15 ml) were put into 50 ml scaled tube.
The mixture solution was set up at a room temperature at least 1 h
for phase separation. The mixture was separated into two phases,
where the lower one was IL phase and the upper one was tert-butanol
phase. The IL phase was further extracted by equal volume of
tert-butanol. After three times of tert-butanol–IL two-phase extraction,
the tert-butanol phases were combined. The volume and the
fraction of Monascus pigments in the combined tert-butanol phase
were determined. Based on the volume and the corresponding pigments
absorbance at 410 nm, the fraction of Monascus pigments in
the tert-butanol phase was determined.