A range of flavoring molecules are used in electronic cigarette liquids (e-liquids), some of which have been shown to form cyclic acetal adducts with e-liquid solvent components propylene glycol (PG) and vegetable glycerine (VG). The objective of this study was to identify the range of flavoring molecules which form adducts in e-liquid products. Common e-liquid flavoring molecules (N = 36) from a range of chemical class groups were exposed to PG, VG, or methanol and analyzed by GC-MS over a time frame of 4 weeks to identify possible reaction products. Adduct formation was observed, with 14 of the flavoring molecules reacting with methanol, 10 reacting with PG, and 10 reacting with VG. Furfural PG and VG acetals, valeraldehyde PG and VG acetals, veretraldehyde PG and VG acetals, p-anisaldehyde PG and VG acetals, and piperonal VG acetal were confirmed for the first time. Adducts formed by reaction with ketone-containing flavoring molecules were also observed for the first time. The presence of these acetals was confirmed in 32% of commercial e-liquid products analyzed (N = 142). This study has established a range of flavoring molecules which are able to react with solvent components PG and VG in e-liquids under standard storage conditions. These newly identified adducts need to be further assessed to determine their toxicological safety.

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Introduction: A range of flavouring molecules are used in electronic cigarette liquids (e-liquids), some of which have been shown to form cyclic acetal adducts with e-liquid solvent components propylene glycol (PG) and vegetable glycerine (VG). The objective of this study was to identify the range of flavouring molecules which form adducts in e-liquid products. Methods: Common e-liquid flavouring molecules (N=36) from a range of chemical class groups were exposed to PG, VG or methanol and analysed by GC-MS over a timeframe of 4 weeks to identify possible reaction products. Results: Adduct formation was observed, with 14 of the flavouring molecules reacting with methanol, 10 reacting with PG and 9 reacting with VG. Where cyclic PG acetals formed, two diastereoisomeric peaks were observed in GC-MS chromatograms, compared to four peaks for VG acetals. All aldehyde-containing flavouring molecules analysed were reactive with PG, VG and methanol. Adducts formed by reaction with ketone-containing flavouring molecules were identified for the first time. Conclusions: A range of adduct products with unknown toxicological safety form in e-liquids through reaction of flavouring molecules and solvent components. PG and VG acetals are likely to form when any aldehyde flavourings are present in e-liquids. PG and VG solvents may also react with ketone-containing flavouring molecules. Implications: This study has established a range of flavouring molecules which are able to react with solvent components PG and VG in e-liquids under standard storage conditions. These newly identified adducts need to be further assessed to determine their toxicological safety.

In 2019 an estimated 200 million people aged 15-64 used cannabis, making cannabis the most prevalent illicit substance worldwide. The last decade has seen a significant expansion in the cannabis vaporiser market, introducing cannabis vaporisation as a common administration method alongside smoking and ingestion. Despite reports of increased prevalence of cannabis vaporisation there has been little research into the use of these devices. To remedy the current dearth of data in this area this study utilised an anonymous online survey of individuals who self-reported past cannabis vaporisation. The respondents (N=557) were predominantly young (<35 years) and male. Most (91.4%) stated they had ever vaped dry herb cannabis, 59.1% reported vaporisation of cannabis oil or liquids, and 34.0% reported vaporisation of cannabis concentrates. This study identifies the types of vaporisation devices (including brands and models) employed by cannabis vapers, as well as the vaporisation temperatures and puff durations commonly used for dry herb, cannabis liquids and cannabis concentrates. To the best of our knowledge, this is the first time the usual operating temperatures of these vaporisation devices and user specific consumption patterns such as puff duration have been reported for cannabis vaping. This information will allow for more realistic experimental conditions in research settings.