Resolution of racemic γ-lactone flavors on Chiralpak AD by packed column supercritical fluid chromatography

The chiral separation by packed column supercritical fluid chromatography (pSFC) has pronounced advantages due to its enhanced efficiency and reduced solvent consumption. Seven racemic γ-lactones (γ-C6–γ-C12) which are important flavor and fragrance substances were successfully resolved in less than 15 min each using an analytical scale pSFC. Baseline or near baseline separations were achieved for γ-C8–γ-C12. The polysaccharide chiral stationary phase (CSP) of Chiralpak AD and the organic modifier of isopropanol were used. The separation conditions were optimized by systematically investigating the effect of varying the percentage of isopropanol in the mobile phase, column temperature, column pressure, and flow rate of the mobile phase. The optimum separations of the seven γ-lactones were achieved mostly at sub-critical conditions. For these compounds the length of the 4-alkyl chain exhibited a determined influence on the enantioselectivity. Among the series of γ-lactones studied, the largest selectivity factor and the largest resolution factor were both observed with the 4-pentyl derivative (γ-C9).