A Wide Range of Flavoring–Carrier Fluid Adducts Form in E-Cigarette Liquids

Abstract

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.

Detection of the Synthetic Coolant Menthone 1,2-Glycerol Ketal in an e-Liquid and in Electronic Waterpipe Aerosols Therefrom

“…The possibility of MGK being a reaction product specifically refers to the plausible reaction between menthone and glycerol in an e-liquid to form a ketal, which would be analogous to the known reactions of aldehydes with glycerol or PG in e-liquids to form acetal products . A reaction between acetone and glycerol, for example, may explain the presence of 2,2-dimethyl-1,3-dioxolane-4-methanol (a ketal) in the aerosols generated by vaping some e-liquids, as reported by Crosswhite et al A recent investigation of selected e-liquid flavorants showed that two out of six tested ketones (none of which are menthone) reacted with glycerol to yield unidentified products that were posited to be ketals . Those findings, however, cannot be easily extended to predict the fate of menthone in e-liquids.…”

“…30 A reaction between acetone and glycerol, for example, may explain the presence of 2,2dimethyl-1,3-dioxolane-4-methanol (a ketal) in the aerosols generated by vaping some e-liquids, as reported by Crosswhite et al 31 A recent investigation of selected e-liquid flavorants showed that two out of six tested ketones (none of which are menthone) reacted with glycerol to yield unidentified products that were posited to be ketals. 32 Those findings, however, cannot be easily extended to predict the fate of menthone in eliquids. The approach in that study was to assess possible reactions in experimentally prepared solutions of ketones in glycerol, which lack the numerous components of a commercial e-liquid that potentially may favor or disfavor ketal formation�as nicotine, for example, has been reported to slow acetal formation in reactions between aldehydes and PG.…”

Chemical Analysis and Flavour Distribution of Electronic Cigarettes in Australian Schools

“…Reactions between some flavouring chemicals and the carrier fluids have been observed to form acetals in situ in e-liquids, the toxicological properties of which are similarly understudied. [11][12][13] In Australia, nicotine-containing vaping products are a Schedule 4 medicine, requiring individuals to obtain a prescription from a medical practitioner for purchase. 14 The standard for nicotine vaping products (TGO110) 15 establishes guidelines for the contents of nicotinecontaining e-cigarette products and their labelling.…”

Acetal Formation of Flavoring Agents with Propylene Glycol in E-Cigarettes: Impacts on Indoor Partitioning and Thirdhand Exposure

“…A widely neglected fact is that the flavor carbonyls can react with e-liquid solvents (e.g., PG) and form stable acetals with chemical and toxicological properties that differ from either the flavorings or the solvents. , Carbonyl PG acetals have been observed in both e-liquids and aerosols, suggesting that they remain stable during storage and persist upon inhalation by e-cigarette users. − Furthermore, a study has indicated that more than 30% of commercially available e-liquids contain detectable levels of acetal products . Given the abundance of PG in e-liquids, the acetal form can become a major form (>40%) of certain carbonyl species .…”