Enantioseparation of nornicotine in tobacco by ultraperformance convergence chromatography with tandem mass spectrometry

Nornicotine, an alkaloid constituent of tobacco, is a precursor to the carcinogen N-nitrosonornicotine that is produced during the curing and processing of tobacco. Accumulating evidence reveals that nornicotine enantiomers have different neurochemical and behavioral effects. In the present study, an accurate and rapid method was developed for the enantioseparation of (R)-(+)-nornicotine and (S)-(-)-nornicotine enantiomers in tobacco by ultra-performance convergence chromatography with tandem mass spectrometry. Chromatographic conditions were investigated to achieve the optimal resolution of two enantiomers. Results indicated that (R)-(+)-nornicotine and (S)-(-)-nornicotine could be separated within 5 min when ammonium hydroxide was added into the cosolvent, and the best resolution (Rs = 4.76) was achieved on a immobilized cellulose tris-(3,5-dichlorophenylcarbamate) chiral stationary phase. The proposed method was validated and was finally applied to analyze the compositions of (R)-(+)-nornicotine and (S)-(-)-nornicotine in three typical types of tobaccos (flue-cured, burley, and oriental). It was found that, enantiomer fraction of nornicotine (the proportion of (S)-(-)-nornicotine in the nornicotine pool) in burley tobacco samples was relatively high and constant compared with flue-cured and oriental tobaccos. The effective and rapid enantioseparation of nornicotine may help the understanding of alkaloid metabolites in different tobacco varieties and may also benefit pharmacological studies of alkaloid enantiomers.