The use of ionic liquid as a mobile phase modifier in analytical supercritical fluid chromatography for the separation of flavonoids

Due to the low viscosity of carbon dioxide, supercritical-fluid chromatography (SFC) allows higher flow rates with lower back pressure. Generally, analytical SFC could provide much faster and more efficient separation compared to conventional chromatographic methods. However, the non-polar characteristic of supercritical carbon dioxide (scCO2) has limited the applicability of SFC in the separation of hydrophobic compounds. Ionic liquids (ILs), with attractive features including a wide range of solubility, miscibility, and low vapor pressure, may offer a possibility to improve SFC separation. In this work, an analytical SFC method using IL as mobile phase modifier was developed for the separation of six flavonoid aglycones, and 1-butyl-3-methyl imidazolium-based ILs were tested and compared as mobile phase additives. The results demonstrated the addition of ILs into SFC mobile phase could significantly improve the resolution of flavonoid aglycones, and the selectivity changed probably based on the hydrogen-bonding interaction.