Portland State University. Department of Chemistry
David H. Peyton
Term of Graduation
Date of Publication
Master of Science (M.S.) in Chemistry
1 online resource (xvii, 105 pages)
Electronic cigarettes (e-cigarettes) are the most commonly used tobacco products among adolescents with ~11 and ~3% of high school and middle school students reporting past 30 day use in 2021 according to the Centers for Disease Control and Prevention (CDC), respectively. Furthermore, greater than ~80% of high school and middle school e-cigarette consumers use flavored e-liquids. Consumers can be exposed to variable toxicant levels upon e-liquid aerosolization, depending on the composition of the e-liquid, type of e-cigarette, e-cigarette settings, and other customizations.
E-liquids are typically composed of a carrier solvent (propylene glycol (PG) and glycerol (GL)), flavorants, and nicotine. PG and GL can degrade thermally upon aerosolization to produce formaldehyde, acetaldehyde, and other harmful and potentially harmful constituents (HPHCs). Flavorants can alter the e-liquid composition before and after aerosolization. Aldehyde flavorants react with PG and GL to form flavorant-PG and -GL acetals that transfer into the aerosol and have unique toxicity profiles. Aerosolized e-liquids with flavorants can contain higher HPHC levels compared to those without. However, there is limited information on the effects of nicotine and other common e-liquid additives on 1) the toxicant levels in aerosolized PG+GL e-liquids with and without flavorants and 2) the kinetics of aldehyde flavorant-PG and -GL acetal formation in e-liquids.
This thesis contains two manuscripts that cover 1) the effects of flavorants and flavorants+nicotine on PG+GL e-liquid degradation and 2) the kinetics of aldehyde flavorant-acetal formation in e-liquids with different solvents and common additives.Study 1) showed that aerosolized e-liquids with trans-cinnamaldehyde, benzyl alcohol, vanillin, benzaldehyde, and a "flavorant mixture" (mixture of the four flavorants) contained increased HPHC levels compared to those without. Flavored e-liquids aerosolized with nicotine decreased HPHC formation for benzyl alcohol, vanillin, benzaldehyde, and a "flavorant mixture", but increased HPHC formation for trans-cinnamaldehyde compared to flavored e-liquids without nicotine. The effect of nicotine on flavored e-liquid degradation was complex and requires further study with different flavorants and e-cigarettes.
The following study 2) revealed that trans-cinnamaldehyde-, benzaldehyde-, and vanillin-acetals formed at a faster rate and higher yield in GL versus PG. GL formed a 5- and 6-member ring acetal, but PG only formed a 5-member ring acetal. Acetalization was inhibited by water and nicotine (an acetalization product and base, respectively), but catalyzed by benzoic acid in PG e-liquids. Lastly, flavorant-PG acetal formation was delayed in flavored PG e-liquids with nicotine, even when benzoic acid was 2-, 4-, and 10-fold greater than the nicotine concentration. The kinetics of additional aldehyde flavorant-acetal and ketone flavorant-ketal formation should be explored in the future due to their unknown toxicity profiles.
© 2022 Paul Joseph Kerber
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Kerber, Paul Joseph, "NMR Analyses of Flavored E-cigarette Liquids Before and After Aerosolization" (2022). Dissertations and Theses. Paper 6192.