Quantitative Analysis of Menthol Isomer Distributions in Selected Samples

Menthol occurs naturally in oils of the Mentha species in the (1 R, 3R, 4S)-(–) form (l-menthol), whereas synthetic menthol is available either in the same form or as a racemic mixture (d- and l-menthol). Quantitative analysis of the presence of the (1S, 3S, 4R)-(+)- form (d-menthol) is achieved by using gas chromatographic analysis on a chiral capillary column with selective ion monitoring detection. Detection of the presence of as little as 0.01 % (d-menthol in the total menthol concentration is possible with relative standard deviation values averaging around 7%. Minimal sample preparation with short sample analysis times of 30 min provide for a rapid sample turn around. This method should be applicable to the speciation of menthol in a wide variety of menthol-containing products, including cigarettes.