A simple methodology for quantification of Nicotine and major solvents in electronic cigarette

Abstract

An analytical method was developed for the parallel quantitation of both nicotine (Nic) and the two key solvents (propylene glycol (PG) and vegetable glycerin (VG)) in e-cigarette (EC) liquids before vaping and from aerosols after vaping. For the analysis of EC refill solutions, samples were diluted by about 100 times in methanol. The aerosol samples (generated by a modified international puffing protocol) were on the other hand initially collected on Cambridge filter pads (CFP) and extracted with methanol. Both types of samples were then analyzed by gas chromatography-flame ionization detector (GC-FID) together with the mass change tracking (MCT) procedure introduced in our earlier study. The recovery of all three target components (Nic/PG/VG) in both EC liquid and aerosol samples was assessed after spiking Nic at four different concentrations (2, 5, 10, and 20 mg g-1) to the e-solutions (prepared in laboratory at three different PG:VG mass ratios of 10:0, 5:5, and 0:10). The method recoveries in e-liquid samples of Nic, PG, and VG were 96.0±1.0, 96.0±1.2, and 101.4±6.9%, respectively, while those in aerosol samples were slightly lower, viz., 94.7±5.6, 85.5±3.0, and 91.4±15.7%, respectively. The amount of VG and Nic in e-liquids had a significant influence on emission factors of PG, VG, and Nic. The detection limit values (ng) were 0.36 (Nic), 0.72 (PG), and 8.15 (VG) for liquid samples, and 0.51 (Nic), 0.96 (PG), and 3.99 (VG) for aerosol samples. Overall, this method was reliable enough to determine each target in both liquid and aerosol samples. The main ingredients used in e-liquid formulations (PG, VG, and Nic) in a total of 16 retail e-liquids (one half with or without Nic)) were analyzed by the developed analytical method. The measured Nic concentrations in e-liquids varied in a range of 5.7 to 14.7 mg g-1 which differed up to 9.0% from the declared label concentrations (two tailed P = 0.5424 at 0.05 confidence level). The concentrations of Nic and PG in vaped aerosol samples were lower (by average of 12.7% and 17.4%, respectively) than those in e-liquid samples while it was opposite in case of VG (1.95% higher on average). The composition (w/w) of 16 retail e-liquids was variable: PG + VG (82.6 to 94.9%, n=16), nicotine (0.68 to 1.63%, n=8), and unidentified compounds (water, flavors, etc.) (5.1 to 16.2%, n=16). For the corresponding vaped aerosols, the results were: PG + VG (75.4 to 92.1%, n=16), Nic (0.57 to 1.47%, n=8), and unidentified compounds (water, flavors, etc.) (7.86 to 24.0%, n=16). The relative proportion of unidentified compounds in vaped aerosols was two times higher than those in e-liquids. The mean nicotine vaping emission factor (39.6 μg puff-1) was about two times lower than that of a Kentucky 2R4F reference cigarette (75 μg puff-1). The measured e-cigarette vaping emission factors varied in a range of 22.5-61.5 μg puff-1 (Nic, n=8), 1.04-2.45 mg puff-1 (PG, n=16), and 1.35-2.09 mg puff-1 (VG, n=16).