Analysis of [3′,3′-d2]-nicotine and [3′,3′-d2]-cotinine by capillary liquid chromatography–electrospray tandem mass spectrometry

A selective and sensitive LC/MS/MS assay was developed for the quantification of d2-nicotine and d2-cotinine in plasma of current and past smokers administered d2-nicotine. After solid phase extraction and liquid–liquid extraction, HPLC separation was achieved on a capillary hydrophilic interaction chromatography phase column. The analytes were monitored by tandem mass spectrometry with electrospray positive ionization. Linear calibration curves were generated for d2-nicotine (0.03–6.0 ng/ml plasma) and d2-cotinine (0.15–25 ng/ml plasma). The lower limits of quantitation were 0.15 ng/ml and 0.25 ng/ml for d2-nicotine and d2-cotinine, respectively. The coefficient of variation was 3.7% for d2-nicotine and 2.5% for d2-cotinine. The method was applied to two ongoing studies of d2-nicotine metabolism in prior and current smokers. Preliminary analysis of a subset of subjects from these studies detected a significantly lower rate of nicotine conversion to cotinine by past smokers compared to current smokers.