Chiral GC Analysis of Carvone Enantiomers in Essential Oils

Using Astec^® CHIRALDEX^® G-TA Capillary GC Columns

Introduction

D-Carvone and L-carvone are enantiomeric compounds that have very different smells. These mirror image compounds provide very different aroma notes. D-Carvone is the major compound found in caraway seed essential oil, and a large component of dill seed essential oil. L-Carvone is one of the major compounds found in spearmint essential oils. Resolving the enantiomers of carvone is a difficult application that requires the use of a chiral capillary GC column to perform the separation. In this study, we demonstrate the separation of D- and L-carvone enantiomers in samples of caraway seed, dill seed, native spearmint and scotch spearmint essential oils using an Astec CHIRALDEX G-TA capillary GC column.

The Astec CHIRALDEX G-TA is a 2,6-di-o-pentyl-3-trifluoroacetyl derivatized gamma cyclodextrin capillary GC column that has the highest selectivity for oxygen containing compounds like alcohols, ketones, acids, aldehydes and lactones. This stationary phase is the first choice of the Group 1 chiral stationary phases that typically utilize surface interactions as one of the primary separation mechanisms.

Experimental

A mixture of D- and L-carvone, with the L-enantiomer in excess concentration, was first analyzed on the Astec CHIRALDEX G-TA column to determine the elution pattern of the compounds. The GC analysis conditions are summarized in Table 1. Peak identification of the carvone enantiomers was done by injecting neat individual D- and L- carvone samples.

Caraway seed, dill seed, native spearmint and scotch spearmint essential oil samples were each evaluated as neat oils to determine their fingerprint profiles and to identify the native carvone enantiomer peak. Caraway seed and dill seed essential oils were then spiked with L-carvone, and both spearmint essential oils were then spiked with D-carvone. All four spiked samples were reevaluated to determine if the spiked enantiomer could be resolved from the natural occurring carvone enantiomer present in the oil.

Results and Discussion

Figure 1 demonstrates that the D-carvone enantiomer elutes before L-carvone. Figures 2, 4, 6 and 8 show the chromatograms resulting from analysis of neat samples of caraway seed, dill seed, native spearmint and scotch spearmint essential oils. Spiked sample chromatograms are shown in Figures 3, 5, 7 and 9, and show that the spiked enantiomer is resolved and can be identified. This demonstrates the chiral selectivity of the Astec CHIRALDEX G-TA capillary GC column.

Conclusion

The data presented here demonstrates the 30 m x 0.25 mm I.D., 0.12 µm Astec CHIRALDEX G-TA capillary GC column can be used to resolve D- and L-carvone enantiomers in neat essential oils with the D-carvone enantiomer eluting prior to the L-carvone enantiomer.

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