Enantioseparation of napropamide by supercritical fluid chromatography: Effects of the chromatographic conditions and separation mechanism

Supercritical fluid chromatography (SFC) is already used for enantioseparation in the pharmaceutical industry, but it is rarely used for the separation of chiral pesticides. Comparing with high performence liquid chromatography, SFC uses much more environmnetal friendly and economic mobile phase, supercritical CO₂. In our work, the enantioseparation of an amide herbicide, napropamide, using three different polysaccharide‐type chiral stationary phases (CSPs) in SFC was investigated. By studying the effect of different CSPs, organic modifiers, temperature, back‐pressure regulator pressures, and flow rates for the enantioseparation of napropamide, we established a rapid and green method for enantioseparation that takes less than 2 minutes: The column was CEL2, the mobile phase was CO₂ with 20% 2‐propanol, and the flow rate was 2.0 mL/min. We found that CEL2 demonstrated the strongest resolution capability. Acetonitrile was favored over alcoholic solvents when the CSP was amylose and 2‐propanol was the best choice when using cellulose. When the concentration of the modifiers or the flow rate was decreased, resolutions and analysis times increased concurrently. The temperature and back‐pressure regulator pressure exhibited only minor influences on the resolution and analysis time of the napropamide enantioseparations with these chiral columns. The molecular docking analysis provided a deeper insight into the interactions between the enantiomers and the CSPs at the atomic level and partly explained the reason for the different elution orders using the different chiral columns.