Quantitative insights into major constituents contained in or released by electronic cigarettes: Propylene glycol, vegetable glycerin, and nicotine.

Generally, the liquid used in electronic cigarettes (E-cigarettes), which is also called E-liquid, is composed of propylene glycol (PG), vegetable glycerin (VG), and nicotine, with many other miscellaneous ingredients. E-liquid is consumed mainly in the form of aerosol via inhalation by the e-cigarette user. The amount and composition of the aerosol generated during its consumption depend on various factors. In this study, the three major constituents (PG, VG, and nicotine) of E-cigarettes were analyzed in both liquid and aerosol samples from 50 commercial products. Their concentrations in the liquid (and aerosol at 3.4 V) samples were 538 (4 6 7), 482 (4 4 9), and 8.75 mg g-1 (7.91 mg g-1), respectively. The nicotine levels in the E-liquids measured in this study were normally 1.2 times greater than those specified by the manufacturers. Furthermore, the amount of liquid consumed increased proportionally as the voltage of the E- cigarette increased. The consumption rate of VG increased as the voltage of the E-cigarette increased, whereas that of PG and nicotine decreased. The results of our study confirm that the amounts of PG and VG generated through the use of E-cigarettes are noticeably larger than those from other tobacco products (such as traditional tobaccos and heat-not-burn products), although no such trend was evident in case of nicotine.