Racemization of S-(−)-nicotine during smoking and its relationship with pyrolysis process

The enantiomeric composition of nicotine in tobacco and cigarette smoke was analyzed by heart-cutting multidimensional gas chromatography (MDGC). The R-(+)-nicotine content of the total nicotine in cigarette smoke ranged from 2.6 to 3.6%, although essentially no R-(+)-nicotine was detected in tobacco. To investigate the formation mechanism of R-(+)-nicotine during the smoking process, S-(−)-nicotine reagent and tobacco were pyrolyzed by a micro-furnace pyrolyzer, and the chirality of nicotine in pyrolyzate was determined on-line by MDGC. The results showed that, no matter whether nicotine was pure or on tobacco, the racemization of S-(−)-nicotine was synchronous with pyrolytic decomposition. This work supports the hypothesis in the literature that the high temperatures involved in the smoking process are the main force for the racemization of nicotine. The MDGC system was composed of a pre-column of DB-1 (30 m × 0.25 mm i.d. × 0.25 μm film thickness) and a chiral column of DB-Cyclodex-B (60 m × 0.25 mm i.d. × 0.25 μm film thickness); FID and NPD were used as monitoring and analytical detectors.