Analysis of E-cigarette Liquids and Aerosols by NMR Spectroscopy: Compositions, Boiling Points, and Degradation Profiles

Electronic cigarettes (e-cigarettes) are an increasingly popular tobacco product used by ~3% of adults and 21% of 12th grade students (as reported for the prior 30-days in surveys) in the United States in 2018. As of 2019, this number went up to ~25% for 12th grade students. Due to how quickly e-cigarettes gained popularity and the rapid design changes that have ensued, there has not been enough time to accurately assess the effects of e-cigarettes, particularly for long-term use. The liquids used in e-cigarettes (e-liquids) can degrade when vaped in an e-cigarette, so understanding the variables that can modulate degradation is useful for harm-reduction strategies. It is also useful to analyze various aspects of nicotine in e-liquids as this could influence the addictiveness of a product. This dissertation contains four manuscripts that broadly cover two categories of questions. 1) In order to evaluate the variables that can contribute to degradation in e-cigarettes, a) the boiling points (i.e. aerosolization temperatures) of propylene glycol (PG) + glycerol (GL) mixtures were determined (+ additives) and b) the effect of sucralose on aldehyde and hemiacetal formation via solvent degradation was explored. 2) Nicotine in e-liquids was analyzed in terms of a) protonation state (i.e. free-base vs monoprotonated), b) acid/nicotine ratio, and c) concentration, because these variables can alter the impact and addictiveness of a product. Primary findings in the four manuscripts include: 1) the boiling points of PG + GL mixtures were determined and ranged from 188.6 °C (PG) to 292 °C (GL). Parameterizations were determined using the Gibbs-Konovalov theorem so that the boiling point of a PG/GL mixture can be calculated for any PG/GL ratio. Mixture boiling points were also evaluated with additives (2.5 mol% water, 5 mol% water, and 3 mol% nicotine). Added water decreased the boiling points of all mixtures tested, and added nicotine decreased the boiling points of some PG/GL mixtures. 2) The addition of sucralose to e-liquids resulted in more aldehyde and hemiformal production via degradation when vaporized in an e-cigarette compared to identical sucralose-free e-liquids vaped under identical conditions. Sucralose was determined to be unstable to the vaping conditions in the e-cigarettes tested, and its degradation products then enhanced degradation of the solvents PG and GL. In manuscripts 3) and 4), the ratio of free-base nicotine relative to monoprotonated nicotine (αfb) was determined for a number of commercially available e-liquids including bottles ( salt nicotine and non-salt\u22 nicotine), JUUL pods, and other JUUL-alikes/pods. Traditional e-liquids/pods and salt nicotine e-liquids/pods were evaluated for αfb, acid/nicotine ratio, and nicotine concentration. αfb ranged from 0.00 to 0.98 for all commercial e-liquids tested, acid/nicotine ratio ranged from 0 to 4.03 by mol, and nicotine concentrations ranged from 3 to 62 mg/mL for tested e-liquids. Over time, e-liquid manufacture has shifted from low nicotine concentration/high αfb content to higher nicotine concentration/lower αfb content (i.e. salt nicotine, such as JUUL and others), which results in a product that remains easily inhalable due to the reduced harshness, despite the relatively high nicotine content