Characterizing the Chemical Landscape in Commercial E-Cigarette Liquids and Aerosols by Liquid Chromatography-High-Resolution Mass Spectrometry

Abstract

The surge in electronic cigarette (e-cig) use in recent years has raised questions on chemical exposures that may result from vaping. Previous studies have focused on measuring known toxicants, particularly those present in traditional cigarettes, while fewer have investigated unknown compounds and transformation products formed during the vaping process in these diverse and constantly evolving products. The primary aim of this work was to apply liquid chromatography-high-resolution mass spectrometry (LC-HRMS) and chemical fingerprinting techniques for the characterization of e-liquids and aerosols from a selection of popular e-cig products. We conducted nontarget and quantitative analyses of tobacco-flavored e-liquids and aerosols generated using four popular e-cig products: one disposable, two pod, and one tank/mod. Aerosols were collected using a condensation device and analyzed in solution alongside e-liquids by LC-HRMS. The number of compounds detected increased from e-liquids to aerosols in three of four commercial products, as did the proportion of condensed-hydrocarbon-like compounds, associated with combustion. Kendrick mass defect analysis suggested that some of the additional compounds detected in aerosols belonged to homologous series resulting from decomposition of high-molecular-weight compounds during vaping. Lipids in inhalable aerosols have been associated with severe respiratory effects, and lipid-like compounds were observed in aerosols as well as e-liquids analyzed. Six potentially hazardous additives and contaminants, including the industrial chemical tributylphosphine oxide and the stimulant caffeine, were identified and quantified in the e-cig liquids and aerosols analyzed. The obtained findings demonstrate the potential of nontarget LC-HRMS to identify previously unknown compounds and compound classes in e-cig liquids and aerosols, which is critical for the assessment of chemical exposures resulting from vaping.

Figure 1:

Summary of experimental and data analysis workflows for non-target and quantitative analysis of organic compounds in e-cig liquids and aerosols.

Figure 2:

PCA score plots showing differences in chemical composition among (A) e-liquids and (B) aerosols of analyzed e-cig products. Two points for each e-liquid or aerosol are shown, each representing one analytical run.

Figure 3:

van Krevelen diagram of H/C and O/C elemental ratios for Juul, Mi-Salt (Smok) and Vuse (A) e-liquids and (B) aerosols from analyzed products, with the constraints for the condensed hydrocarbon-like compound category shown as a black rectangle.

Figure 4:

Molecular weight as a function of RT of detected compounds in aerosols of e-cig samples. Left: Juul (interval 2), Mi-Salt (Smok) (interval 1) and the PG/VG base (interval 1), highlighting predominantly lipid-like compounds determined based on multidimensional stoichiometric classification (circled). Right: Vuse (interval 1), Blu (interval 1).

Figure 5:

Plots of Kendrick mass defect as a function of molecular weight showing methylene (left) and propylene glycol (right, PPG compounds shown in red) homologous series in the PG/VG base e-liquid and aerosol.

Figure 6:

Concentrations of six compounds in commercial e-liquids and aerosols.