Electronic cigarettes: overview of chemical composition and exposure estimation

Electronic cigarettes (e-cigarettes) are advertised to tobacco users as a tool to decrease cigarette consumption and to reduce toxic exposure associated with conventional tobacco smoking. Little is known about the compounds contained in such products, their exposure and long-term health effects.

Methods
NMR spectroscopy was used to ascertain the content of several constituents of e-cigarette liquids including nicotine, solvents and some bioactive flavour บุหรี่ไฟฟ้า. Risk assessment was based on probabilistic exposure estimation and comparison with toxicological thresholds using the margin of exposure (MOE) approach.

Results
In 54 samples of e-cigarette liquids, the average nicotine content was 11 mg/ml. Only 18 from 23 samples were confirmed as nicotine-free samples and in one e-cigarette liquid nicotine was not detected while being declared on the labelling. Major compounds of e-cigarette liquids include glycerol (average 37 g/100 g), propylene glycol (average 57 g/100 g) and ethylene glycol (average 10 g/100 g). Furthermore, 1,3-propanediol, thujone and ethyl vanillin were detected in some samples. The average exposure for daily users was estimated as 0.38 mg/kg bw/day for nicotine, 8.9 mg/kg bw/day for glycerol, 14.5 mg/kg bw/day for 1,2-propanediol, 2.1 mg/kg bw/day for ethylene glycol, and below 0.2 mg/kg bw/day for the other compounds. The MOE was below 0.1 for nicotine, but all other compounds did not reach MOE values below 100 except ethylene glycol and 1,2-propanediol.

An electronic cigarette (e-cigarette) is a part of an emerging class of electronic nicotine-delivery systems. These devices aerosolize nicotine (if contained) and produce a vapour that emulates that of tobacco cigarettes but purportedly has fewer traditional toxins than secondhand smoke [1]. The อะตอมบุหรี่ไฟฟ้า about these products and availability of e-cigarettes on the Internet, including in Web searches, virtual user communities and online shops has increased dramatically in recent years [1,2], however, only few studies have been dedicated so far to the qualitative composition and toxicological characterization of these products [3,4].

Some studies have found very inconsistent nicotine contents in some products regarding the labelling, i.e., e-cigarette liquids advertised as containing no nicotine may contain the substance and, in contrast, some products did not contain nicotine despite its presence being labelled [13,15]. Therefore, our study was principally aimed to develop a reliable and simple analytical tool based on NMR spectroscopy to control the absence/presence of nicotine in e-cigarette liquids. However, as the scope of quantitative NMR lies beyond quantification of a single analyte in a given matrix [21,22], we expanded our methodology also for the determination of other major compounds in e-cigarette liquids (solvents and flavour compounds). The procedure was then applied to analyse a large sample collection (n = 54) of e-cigarette liquids that have been bought over the Internet. Finally, the exposure of the consumer is estimated based on the analytical results and a toxicological assessment is provided.