Effects of Common e-Liquid Flavorants and Added Nicotine on Toxicant Formation during Vaping Analyzed by ¹H NMR Spectroscopy

Abstract

A broad variety of e-liquids are used by e-cigarette consumers. Additives to the e-liquid carrier solvents, propylene glycol and glycerol, often include flavorants and nicotine at various concentrations. Flavorants in general have been reported to increase toxicant formation in e-cigarette aerosols, yet there is still much that remains unknown about the effects of flavorants, nicotine, and flavorants + nicotine on harmful and potentially harmful constituents (HPHCs) when aerosolizing e-liquids. Common flavorants benzaldehyde, vanillin, benzyl alcohol, and trans-cinnamaldehyde have been identified as some of the most concentrated flavorants in some commercial e-liquids, yet there is limited information on their effects on HPHC formation. E-liquids containing flavorants + nicotine are also common, but the specific effects of flavorants + nicotine on toxicant formation remain understudied. We used 1H NMR spectroscopy to evaluate HPHCs and herein report that benzaldehyde, vanillin, benzyl alcohol, trans-cinnamaldehyde, and mixtures of these flavorants significantly increased toxicant formation produced during e-liquid aerosolization compared to unflavored e-liquids. However, e-liquids aerosolized with flavorants + nicotine decreased the HPHCs for benzaldehyde, vanillin, benzyl alcohol, and a “flavorant mixture” but increased the HPHCs for e-liquids containing trans-cinnamaldehyde compared to e-liquids with flavorants and no nicotine. We determined how nicotine affects the production of HPHCs from e-liquids with flavorant + nicotine versus flavorant, herein referred to as the “nicotine degradation factor”. Benzaldehyde, vanillin, benzyl alcohol, and a “flavorant mixture” with nicotine showed lower HPHC levels, having nicotine degradation factors <1 for acetaldehyde, acrolein, and total formaldehyde. HPHC formation was most inhibited in e-liquids containing vanillin + nicotine, with a degradation factor of ∼0.5, while trans-cinnamaldehyde gave more HPHC formation when nicotine was present, with a degradation factor of ∼2.5 under the conditions studied. Thus, the effects of flavorant molecules and nicotine are complex and warrant further studies on their impacts in other e-liquid formulations as well as with more devices and heating element types.

Assessing toxicant emissions from e-liquids with DIY additives used in response to a potential flavour ban in e-cigarettes

“…The data on carbonyl and phenol emissions showed mixed observations with increase in some emissions and decrease in others for the same e-liquid condition. This could be attributed to the different mechanisms of formation during e-cigarette operation,26 27 or to coil variability in triplicate measurements that can mask the impact of liquid ingredients on emissions 28. Also, focusing on toxicants that are mainly formed from PG/G degradation23 24 29 may lead to overlooking other degradation pathways, as in the case of sucralose leading to chloropropanols 28 30.…”

Profiling flavourings in strawberry‐flavoured e‐liquid using headspace‐gas chromatography–mass spectrometry

“…The composition of e‐liquids has been analysed previously by high‐performance liquid chromatography (HPLC), for example, to identify carbonyls in toxic chemicals like formaldehyde 20 . Peyton et al used 1 H NMR spectroscopy to investigate the effect of both nicotine and flavourings on toxicant formation during vaping and found that the presence of such compounds could enhance PG and VG degradation 21 . GC‐MS allows the direct analysis of volatiles and has been widely demonstrated to be a viable method for e‐liquids 12,22–26 .…”

“…20 Peyton et al used 1 H NMR spectroscopy to investigate the effect of both nicotine and flavourings on toxicant formation during vaping and found that the presence of such compounds could enhance PG and VG degradation. 21 GC-MS allows the direct analysis of volatiles and has been widely demonstrated to be a viable method for e-liquids. 12,[22][23][24][25][26] This technique offers the separation capability of chromatography, required as liquids increasingly contain more complex flavouring components, and the identification abilities of MS. Coupling of GC-MS with a headspace (HS) analyser has the additional benefit of direct sample introduction of the vapour, formed above the e-liquid on heating.…”

Determination of Glycerol, Propylene Glycol, and Nicotine as the Main Components in Refill Liquids for Electronic Cigarettes

“…The most common determination methods are based on gas chromatography in combination with different detectors, either flame ionization [18][19][20] or mass spectrometry [21,22]. Some of the techniques for the determination of glycerol, propylene glycol, and nicotine are based on proton nuclear magnetic resonance ( 1 HNMR) [23][24][25]. Despite these efforts, to the best of the author's knowledge, there is no method that uses liquid chromatography coupled with mass spectrometry (LC-MS) or tandem mass spectrometry (LC-MS/MS) in determination of nicotine, propylene glycol, and glycerol.…”