The Stereoisomers of Menthol in Selected Tobacco Products. A Brief Report

INTRODUCTION: Menthol has long been an important flavorant in tobacco products, and both its historical and present uses are topics of increasing debate. Menthol can exist in eight different stereoisomeric forms (as four enantiomeric pairs) that possess different sensory properties. As regards use in tobacco products, the open scientific literature and available industry documents focus on the D-menthol and l-menthol enantiomeric pair, and in particular on l-menthol, but are ambiguous about the actual importance of D-menthol in tobacco products. This study provides the first openly available measurements regarding the stereoisomeric forms of menthol as found in selected United States sub-brands of smokeless tobacco (SLT), cigarettes, and cigarette smoke. METHODS: Gas chromatography/mass spectrometry (GC/MS) was applied using a "chiral" GC column to separate and determine the forms of menthol present in headspace air above various samples of United States sub-brands of SLT, cigarette filler material, and cigarette smoke particulate matter. Additional GC × GC/Time-of-flight mass spectrometry measurements were also made. RESULTS: The dominant form of menthol by far in any of the samples was l-menthol. CONCLUSIONS: For the selected cigarettes and SLT products tested from the U.S. market, the only form of menthol found was l-menthol. Other forms may be present in products that were not tested. No evidence was found of thermal racemization upon smoking of l-menthol to a d+l mixture.