Resolution of Enantiomers by Supercritical Fluid Chromatography with Cellulose Tris(phenylcarbamate) Coated on Silica Gel

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Abstract
The solvent characteristics of super- and subcritical carbon dioxide for the chromatographic resolution of enantiomers (tarns-stilbene oxide) by chiral cellulose tris(phenylcarbamate) were investigated by altering the pressure (10, 15, 20, and 40 MPa), the temperature (0, 25, and 40 °C), and the concentrations of the modifiers. Among methanol, ethanol, and 2-propanol used as modifiers, methanol is the most effective in terms of the resolution of enantiomers, though 2-propanol gives a slightly high value for the separation factor. When the concentration of alcohol increases, the capacity ratio decreases substantially, but the separation factor decreases only a little. At 40 °C, an increase in pressure results in a decrease in the capacity ratio and a slight increase in the separation factor. These pressure effects may be attributed to the enhanced solubilities of both the solute and the modifier with an increase in the mobile-phase density. The temperature is the most effective variable for the separation factor of enantiomers; it increases as the temperature lowers. Therefore, the resolution becomes higher at 0 °C (subcritical conditions) than at 40 °C on the basis of the same analysis time.