The Evolving E-cigarette: Comparative Chemical Analyses of E-cigarette Vapor and Cigarette Smoke

Abstract

Background: E-cigarette designs, materials, and ingredients are continually evolving, with cotton wicks and diverse coil materials emerging as the popular components of atomisers. Another recent development is the use of nicotine salts in e-liquids to replicate the form of nicotine found in cigarette smoke, which may help cigarette smokers to transition to e-cigarettes. However, scientific understanding of the impact of such innovations on e-cigarette aerosol chemistry is limited.Methods: To address these knowledge gaps, we have conducted a comparative study analyzing relevant toxicant emissions from five e-cigarettes varying in wick, atomiser coil, and benzoic acid content and two tobacco cigarettes, quantifying 97 aerosol constituents and 84 smoke compounds, respectively. Our focus was the potential for benzoic acid in e-liquids and cotton wicks to form aerosol toxicants through thermal degradation reactions, and the potential for nickel–iron alloy coils to catalyze degradation of aerosol formers. In addition, we analyzed e-cigarette emissions for 19 flavor compounds, thermal decomposition products, and e-liquid contaminants that the FDA has recently proposed adding to the established list of Harmful and Potentially Harmful Constituents (HPHCs) in tobacco products.Results: Analyses for benzene and phenol showed no evidence of the thermal decomposition of benzoic acid in the e-cigarettes tested. Measurements of cotton decomposition products, such as carbonyls, hydrocarbons, aromatics, and PAHs, further indicated that cotton wicks can be used without thermal degradation in suitable e-cigarette designs. No evidence was found for enhanced thermal decomposition of propylene glycol or glycerol by the nickel–iron coil. Sixteen of the 19 FDA-proposed compounds were not detected in the e-cigarettes. Comparing toxicant emissions from e-cigarettes and tobacco cigarettes showed that levels of the nine WHO TobReg priority cigarette smoke toxicants were more than 99% lower in the aerosols from each of five e-cigarettes as compared with the commercial and reference cigarettes.Conclusions: Despite continuing evolution in design, components and ingredients, e-cigarettes continue to offer significantly lower toxicant exposure alternatives to cigarette smoking.

Non-Targeted Analysis Using Gas Chromatography-Mass Spectrometry for Evaluation of Chemical Composition of E-Vapor Products

“…Their designs have evolved from the first-generation devices (“cig-a-likes”) to devices with disposable, prefilled cartridges or “pods” and “mods” with user-controllable settings, such as wattage, voltage, and temperature control ( Zhu et al, 2014 ; Talih et al, 2017 ; FDA, 2019c ). ENDS products aerosolize the e-liquid that is typically composed of a mixture containing propylene glycol (PG), vegetable glycerol (VG), nicotine, and flavors ( Hahn et al, 2014 ; Flora et al, 2016 ; FDA, 2019c ; Cunningham et al, 2020 ).…”

Evidence From the Scientific Assessment of Electronic Cigarettes and Their Role in Tobacco Harm Reduction

“…The US FDA has identified 92 harmful or potentially harmful constituents (HPHCs) in addition to nicotine (103) and public comment was recently sought on the proposal to add a further 19 compounds to the list (104). However, to our knowledge, only one study has investigated the emissions of these additional HPHCs (22). In practice, it has been suggested that Pre-Market Tobacco Product Applications should report at least 32 compounds (66).…”

“…ECs generally do not reach temperatures higher than 250 °C during normal use or more than 350 °C under dry wicking conditions (105). However, a huge variety of devices and e-liquids exist (106) and many different puffing conditions and analytical techniques have been used to assess them (42,(107)(108)(109), but, overall, results indicate significantly lower levels of toxicants in EC aerosols than in cigarette smoke (20,22,43,44,102,110,111).…”

“…These products heat a liquid (termed e-liquid) containing ingredients that function as carriers (e.g., propylene glycol (PG) and vegetable glycerin (VG)) and may contain flavours and/or nicotine. Compared with tobacco combustion, e-liquids are heated to only around 250 °C and release an aerosol that is much less complex than cigarette smoke, having substantially fewer and lower concentrations of compounds (19)(20)(21)(22). Systematic reviews indicate substantially decreased disease risk compared with smoking through greatly reduced exposure to toxicants and carcinogens (23)(24)(25)(26)(27)(28), although the risks are not wholly eliminated nor yet fully characterised.…”

The Chemical Complexity of e-Cigarette Aerosols Compared With the Smoke From a Tobacco Burning Cigarette

“…E-cigarette aerosol studies tend to use targeted HPHC analyses ( National Academies of Sciences, Engineering, and Medicine, Health and Medicine Division, Board on Population Health and Public Health Practice, Committee on the Review of the Health Effects of Electronic Nicotine Delivery Systems, 2018 ), such as, carbonyls ( Farsalinos and Gillman, 2018 ), metals ( Williams et al, 2013 ) and major e-liquid component thermal decomposition products ( Uchiyama et al, 2020 ). A few e-cigarette studies have targeted broader ranges of HPHC emissions, Lauterbach and Laugesen (2012), Tayyarah and Long 2014 , Cunningham et al (2020) with up to 150 measurands examined ( Margham et al, 2016 ). These studies have shown considerable differences between e-cigarette aerosols and cigarette smoke, detecting fewer HPHCs in e-cigarette aerosols, and lower concentrations of those that are present.…”