Abstract: Based on a detailed understanding of the separation efficiency of eight menthol optical isomers on different chiral and non-chiral capillary columns, a method for the quantitative determination of them was established using gas chromatography-mass spectrometry (GC-MS) after separation on tandem chiral capillary columns. The results showed that four enantiomeric pairs of menthol were separated on DB-5MS, DB-624, DB-ALC1 and DB-INNOWAX capillary columns with non-chiral stationary phase, but the D- and L-enantiomers failed to be separated from each other. The eight menthol optical isomers were successfully separated on tandem CycloSil-B and BGB-175 chiral capillary columns by virtue of the complementarity between them. Being sharp and symmetrical, the chromatographic peaks all met the requirements for separation. The response value and retention time had good stability, and the stationary phase loss was small during the separation process, causing no significant impact on menthol detection. The limit of quantification (LOQ) of the developed method was 23.0–72.9 μg/L, and the recoveries of the spiked analytes ranged from 86.0% to 116.0%. This method was successfully utilized for the separation and quantitative detection of menthol optical isomers in candy and drugs, indicating that the dominant form of menthol in the samples tested was L-menthol, and other menthol isomers were also detected at trace levels in most samples. In addition, menthol types in different samples were distinguished by menthol isomer configuration.

Key words: menthol; optical isomer; chiral separation; tandem columns