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.

Introduction E-cigarettes are becoming increasingly popular in Australia, especially amongst the younger population. The synthetic cooling molecules WS-3 and WS-23 have been identified in e-cigarette products from the US and Europe. The extent of inclusion of these synthetic coolants in Australian e-liquids is unknown, particularly in newer disposable e-cigarettes. Methods E-cigarettes and e-liquids were purchased within Australia and anonymously donated by Australian users. Nicotine, WS-3, WS-23 and menthol were quantified in the eliquids using gas chromatography – mass spectrometry (GCMS). Results WS-23 and nicotine were detected in all of the disposable e-cigarettes with WS-23 often present in high concentrations. There was no correlation between cooling terms in the flavour name and the inclusion of cooling agents. Only three bottled e-liquids were found to contain WS-23 while none contained WS-3 above the limit of detection. Conclusions Synthetic coolants were a common addition in disposable e-cigarettes while rarely added to e-liquid bottle refills. Their inclusion in these products is reflective of trends observed in US and European ecigarette products.

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.