Formation of Free Radical Oxidants in the Aerosols Produced from Vaping Different Nicotine Salts in Electronic (e-) Cigarettes
NICHOLAS ROBERTSON, Lillian Tran, Guodong Rao, Haylee Hunsaker, Elizabeth Chiu, Brett Poulin, Amy Madl, Kent Pinkerton, R. David Britt, Tran Nguyen, University of California, Davis
Abstract Number: 552
Working Group: Aerosol Chemistry
Abstract
Recently, high concentrations of organic acids have been added to the nicotine in electronic (e-) cigarettes to produce nicotine salts, which reduces the bitter and harsh sensation of vaping freebase nicotine. We investigated whether organic acids in nicotine salt e-liquids may alter the redox environment within the e-cigarette by interacting with trace metals in the e-liquid, which may impact free radical formation within the aerosol. Aerosol formation and production of free radicals from a fourth-generation e-cigarette device were investigated with 2 wt.% nicotine salt solutions composed of eight organic acids used in commercially available e-liquids: benzoic acid, salicylic acid, lactic acid, levulinic acid, succinic acid, malic acid, tartaric acid, and citric acid. Additionally, results from benzoate nicotine salt e-liquids with nicotine to benzoic acid ratios of 1:2 (pH 4), 1:1 (pH 7), and 2:1 (pH 8) were compared to those from freebase nicotine e-liquid. The radical yields of each aerosolized e-liquid were quantified by spin-trapping and electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of free radicals in the various nicotine salt aerosols mirrored those of reactive oxygen species (ROS) generated by the Fenton reaction. Benzoic acid, citric acid, and tartaric acid were the only nicotine salts examined that produced a notable ROS yield. E-liquids containing salicylic acid, lactic acid, levulinic acid, succinic acid, and malic acid produced less ROS than the 2 wt.% freebase nicotine e-liquid, suggesting organic acids may both facilitate and hinder the production of ROS. Results from this study have important implications for ROS-mediated health outcomes that may be of interest to vaping consumers, manufacturers, and regulatory agencies.