Attention:

Certain features of Sigma-Aldrich.com will be down for maintenance the evening of Friday August 18th starting at 8:00 pm CDT until Saturday August 19th at 12:01 pm CDT.   Please note that you still have telephone and email access to our local offices. We apologize for any inconvenience.

Chiral GC Analysis of Carvone Enantiomers in Essential Oils

By: Leonard M. Sidisky, Reporter US Volume 32.1

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.

Table 1. GC Conditions

column:
oven:
inj. temp.:
detector:
carrier gas:
injection:
Astec CHIRALDEX G-TA, 30 m x 0.25 mm I.D., 0.12 µm (Product No. 73033AST)
40 °C (1 min), 2 °C/min to 170 °C (15 min)
250 °C
FID, 250 °C
helium, 25 cm/sec (set @ 110 °C)
wet needle, 100:1 spl

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.

Standard Containing D- and L-Carvone

Figure 1. Standard Containing D- and L-Carvone

 

Caraway Seed Essential Oil

Figure 2. Caraway Seed Essential Oil

 

Caraway Seed Essential Oil (Spiked with L-Carvone)

Figure 3. Caraway Seed Essential Oil (Spiked with L-Carvone)

 

Dill Seed Essential Oil

Figure 4. Dill Seed Essential Oil

 

Dill Seed Essential Oil (Spiked with L-Carvone)

Figure 5. Dill Seed Essential Oil (Spiked with L-Carvone)

 

Native Spearmint Essential Oil

Figure 6. Native Spearmint Essential Oil

 

Native Spearmint Essential Oil (Spiked with D-Carvone)

Figure 7. Native Spearmint Essential Oil (Spiked with D-Carvone)

 

Scotch Spearmint Essential Oil

Figure 8. Scotch Spearmint Essential Oil

 

Scotch Spearmint Essential Oil (Spiked with D-Carvone)

Figure 9. Scotch Spearmint Essential Oil (Spiked with D-Carvone)

 

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.

Legal Information

Astec and CHIRALDEX are registered trademarks of Sigma-Aldrich Co. LLC

Materials

     

 References

  1. Ravid, U.; Putievsky, E.; Katzir, I.; Weinstein, V.; Ikan, R., Chiral GC analysis of (S)(+)- and (R)(-)-carvone with high enantiometric purity in caraway, dill and spearmint oils. Flavour and Fragrance Journal 1992, 7, 280-292.