Objective To develop a method for detecting nicotine and cotinine in hair by hydrophilic interaction chromatography tandem mass spectrometry.

Methods Hair samples were hydrolyzed in sodium hydroxide solution before extraction with dichloromethane. The samples were blown to dry with nitrogen and dissolved with mobile phase. The filtrate of the samples was injected into a chromatographic-mass spectrometry system for analysis. The separation was performed by a hydrophilic column, with which methanol-0.1% ammonia was used as the mobile phase. The quantitative detection of Nicotine and Cortinine was carried out with electron spray ionization-triple quadrupole mass spectrometry. The established method was used for detecting nicotine and cotinine in 602 hair samples of pregnant women and 31 hair and urine samples of volunteers.

Results A standard curve was drawn for the established method of hydrophilic liquid chromatography tandem mass spectrometry. Good linearity was obtained for detecting nicotine and cotinine in the range of 0.030-100.000 μg/L, with a detection limit (MDL) of 0.007 6 μg/g and 0.004 4 μg/g, respectively. The inter-day and intra-day precisions reached a level of less than 10%. The recoveries of the spiked samples ranged from 81.0% to 102.0%. About 0.020-0.260 μg/g nicotine and 0.004 8-0.069 0 μg/g cotinine were detected in the pregnant women without exposure to secondhand smoking (SHS), compared with 0.029-0.350 μg/g nicotine and 0.005 6-0.085 0 μg/g cotinine in those exposed to SHS. Nicotine and cotinine were also found in the hair and urine samples of volunteers, which were correlated with smoking (P < 0.05). A dose-response relationship were found between smoking and hair nicotine.

Conclusion The proposed method is accurate and sensitive for detecting nicotine and cotinine in hair samples. Hair nicotine can be a specific biomarker for assessing exposure to tobacco smoking.