Direct analysis of free-base nicotine in tobacco leaf by headspace solid-phase micro-extraction combined with gas chromatography/mass spectrometry
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A little nicotine in tobacco leaf is non-ionized, which is also known as free-base nicotine (FBN). The dynamic equation existed between FBN and ionized nicotine can easily change with water content, temperature and pH value. In this study, a method of the direct quantitative analysis for FBN in tobacco leaf by using headspace solid-phase micro-extraction, combined with gas chromatography/mass spectrometry, was developed. The optimum conditions for analysis method, including sample forms, SPME fiber type, pre-equilibrium temperature, pre-equilibrium time, extraction temperature and extraction time, were investigated in detail. Under the optimized conditions, the linear range of the method was 1 mg/mL–100 mg/mL, with a correlation coefficient (r) of 0.9977 and a detection limit of 0.84 μg/g, the repeatability (expressed as relative standard deviation) was 3.35 %, and the recovery of this method was between 99.56 % and 99.80 %. The uncertainty budget was finally done according to the “Guide to the Expression of Uncertainty in Measurement,” and the relative expanded uncertainty was 7.1 % with coverage factor k = 2. This method may be reliable and convenient for tobacco control.
KeywordsFree-base nicotine Tobacco leaf Direct analysis HS-SPME
The authors are grateful for tobacco samples kindly provided by Dr. Duan Yanqing. We also thank Mr. Li Shijie for determination of water contents of tobacco samples. This study was financially supported by Yunnan Tobacco Industry Co., Ltd. (2016GY01 and 2017CP06).
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