Acid-Base Interaction of Nicotine With Benzoic Acid in Vaping Aerosols, Studied with X-Ray Spectroscopy

HASHINI WEERARATNA, Xiaochen Tang, Oleg Kostko, Vi Rapp, Lara Gundel, Hugo Destaillats, Musahid Ahmed, Lawrence Berkeley National Laboratory

     Abstract Number: 159
     Working Group: Aerosol Chemistry

Abstract
Carboxylic acids are used as additives in electronic cigarette e-liquids to form a “salt” with nicotine, making the puffs less harsh upon inhalation. Such formulations contain 3 to 6 times higher nicotine levels than conventional e-liquids, facilitating initiation and addiction. Benzoic acid (BA) is a popular additive, normally present in a 1:1 ratio with respect to nicotine. The association of BA and nicotine in freshly emitted aerosols was studied using X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) on an instrument developed at the Advanced Light Source. Stable aerosols streams were generated from mixtures of water, propylene glycol (PG) and glycerol in different proportions, with added nicotine and BA. Particles of 50 – 1,000 nm diameter were admitted through a 200-µm nozzle aerodynamic lens system. The particle number, mass and surface concentration were determined with a Fast Mobility Particle Sizer spectrometer, an Optical Particle Sizer and an Aerodynamic Particle Sizer, in the range of 8 – 2,500 nm. In XPS, the C 1s and N 1s photoelectron spectra were recorded at a photon energy of 315 eV and 430 eV, respectively. Density Functional calculations were performed for band assignments to the photoelectron spectra. The analysis was supported by NEXAFS of the C and N edge. The relative fraction of free base and protonated nicotine were calculated from the N spectra, enabling for an assessment of the association ratio and nicotine free base fraction, by changing experimental conditions that are relevant for vaping, such as PG/glycerin ratio and the water content. Raman spectroscopy of the solutions from which the vaping aerosols were generated was used to corroborate their composition and compare and contrast to the aerosol chemistry deciphered via X-Ray spectroscopy. These results can contribute to new insights on users’ chemical uptake and passive exposures.