Determination of 4 Tobacco-Specific N-Nitrosamines in E-Cigarette Liquid and Aerosol by HPLC-MS/MS

A method was established for determination of 4 tobacco-specific N-nitrosamines (TSNAs) in e-cigarette liquid and aerosol by HPLC-MS/MS, including NNN, NAB, NAT and NNK. Analytes in 1 g of e-cigarette liquid was extracted by 20 mL of 0.1 mol·L^-1 ammonium acetate solution containing 50 μL of mixed internal standard solution ultrasonically for 30 min and then filtered through a 0.2 μm PTFE filter. 20 puffs of aerosol realeased at maximum power were collected by a 44 mm diameter Cambridge filter, and the TSNAs in aerosol were extracted by the same method as e-cigarette liquid. The analytes were fixed on an Agilent Eclipse Plus C₁₈ RRHD chromatographic column at 60℃, and mixed solutions of 0.01 mol·L^-1 ammonium formate solution and acetonitrile solution containing 0.025% (φ) formic acid with the different volume ratios were used as mobile phase for gradient elution at flow rate of 0.3 mL·min^-1. A tandem mass spectrometer equipped with ESI⁺ was used for detection under multi-reaction monitoring (MRM) mode. Four deuterated reagents of TSNAs were used as internal standards for quantitative analysis. The results showed that linear relationships between mass concentrations of 4 TSNAs and the ratios of their corresponding peak areas to those of internal standards were kept in the same range of 0.010-5.0 μg·L^-1. Detection limits (3S/N) were 0.002-0.015 ng·g^-1 (e-cigarette liquid) and 0.001-0.008 ng/20 puffs (aerosol) respectively; RSDs (n=5) of the determined values for the intra-day were 0.78%-1.5% (e-cigarette liquid) and 0.96%-2.5% (aerosol) respectively; RSDs (n=5) of the determined values for inter-day were 1.3%-2.1% (e-cigarette liquid) and 4.9%-6.3% (aerosol) respectively. The spiked recovery test was made on actual samples at the 3 concentration levels, giving results of recovery in the ranges of 90.7%-103% (e-cigarette liquid) and 92.0%-108% (aerosol) respectively. This method was used to analyze 14 actual samples, with maximum detectable amounts of NNN, NAT, NNK and NAB in e-cigarette liquid of 40.57, 31.94, 11.22, 8.33 ng·g^-1 and in aerosol of 6.40, 5.03, 1.89, 1.28 ng/20 puffs.