Table 5.

Chemical composition analyses of flavored EC.

E-liquid flavor	Experimental approach	E-liquid Nicotine Dose	Main findings	Reference
Menthol, Vanillin, Maltol	Particle size distribution	18 mg/ mL of nicotine	Vanillin and nicotine increase e-cigarette particle size distribution. Increasing the glycerol (VG) proportion in e-liquid increases EC particle size.	(Lechasseur et al., 2019)
Menthol	GC−MS Analysis of Liquid, Vapor, and Particulate Phases, FTIR Spectrometry	18 mg nicotine/mL	EC emissions contained acetaldehyde, acrolein, benzaldehyde, benzene, toluene, ethylbenzene, and xylene The concentrations of these chemicals increased with increasing VG composition. Benzaldehyde, naphthalene, diphenyl ether, menthol, and nicotine were also detected in the aerosol condensates.	(Ooi et al., 2019)
Strawberry, Cinnamon, Sweet cream	Hydroxyl radicals in reaction mixes were measured based on the formation of 2-hydroxyterephthalic acid (2OHTA)	3, 12, 24 and 36 mg/mL	VG e-liquids generated higher •OH levels than PG e-liquids, as did flavored e-liquids relative to nonflavored e-liquids (cinnamon>sweet cream>strawberry>non-flavored). E-vapor, combined with ascorbic acid, can also induce •OH formation. The levels of •OH in 3 and 12 mg/ml nicotine solutions were 19.6% and 10.0% lower than that in the equivalent nicotine-containing-vapor solutions. Conversely, 24 and 36 mg/ml nicotine solution induced 40% more •OH than the equivalent e-vapor solutions.	(Son et al., 2019)
51 flavors	Mass spectrometry	5% nicotine	At least one flavoring chemical was detected in 47 of 51 unique flavors tested. Diacetyl was detected above the laboratory limit of detection in 39 of the 51 flavors tested, ranging from below the limit of quantification to 239 μg/EC. 2,3-Pentanedione and acetoin were detected in 23 and 46 of the 51 flavors tested at concentrations up to 64 and 529 μg/EC, respectively.	(Allen et al., 2016)
Mango, Banana, Tobacco, Cappuccino, Chocolate, Bubblegum, Peppermint, Cinnamon, Cherry, Apple	GC-MS		Vanillin was the most frequently detected flavoring chemical. It was found in banana, tobacco, cappuccino, chocolate, bubblegum, and cinnamon. Chocolate and cinnamon e-liquids had the most complex flavoring profile, with 14 and 15 flavoring peaks, respectively. Tobacco flavor had the least complex flavoring profile with only 2 peaks.	(Ween et al. 2020b)