Various organic solvents were screened for recovery of Monascus
pigments from the excess IL phase after Winsor I microemulsion
extraction (Fig. 2) (ratio of organic solvent to the excess IL phase
was 1 ml to 1 g (0.8 ml)). The basic parameters of organic solvents
were also listed (Table 1). It was observed that phase separation
was not strictly related to the polarity of organic solvent. The
hydrophobic organic solvent dimethyl phthalate was miscible with
IL while tert-butanol–IL two-phase system was achieved. In IL–hydrocarbon
two-phase system, the volume of IL phase was varied
with equal or more than the original volume of the excess IL phase(
0.8 ml), which was consistent with high solubility of aromatic
hydrocarbons in IL [Bmim]PF6 while only limited solubility of IL in
hydrocarbons (n-alkanes and cycloalkanes) [21]. Based on the different
solubility of n-alkane and aromatic hydrocarbon in IL, extraction
of toluene from alkane by ILs is also reported [22]. Similar
phenomenon was also observed in IL–alcohol two-phase system,
where the solubility of IL [Bmim]PF6 in alcohols is very limited in
spite of the relatively higher solubility of alcohols in IL [23]. Thus,
the risk of contaminated IL in the organic solvent phase during
IL–organic solvent two-phase extraction had reduced markedly.
The fraction of residual Monascus pigments in the IL phase was
determined based on the phase volume of IL phase and the corresponding
absorbance of Monascus pigments at 410 nm. The result
indicated only moderate polar organic solvents, such as tert-butanol,
chloroform, and 1-octanol, exhibited a relatively strong extractive
capacity while the hydrophobic organic solvent (such as
cyclohexane) and polar solvent with low molecular dipole moment
(such as ethyl ether) had limited extractive efficiency.