Composition of aerosols from thermal degradation of flavors used in ENDS and tobacco products

Abstract

Aim: The cardiovascular toxicity of unheated and heated flavorants and their products as commonly present in electronic cigarette liquids (e-liquids) was evaluated previously in vitro. Based on the results of in vitro assays, cinnamaldehyde, eugenol, menthol, and vanillin were selected to conduct a detailed chemical analysis of the aerosol generated following heating of each compound both at 250 and 750 °C. Materials and Methods: Each flavoring was heated in a drop-tube furnace within a quartz tube. The combustion atmosphere was captured using different methods to enable analysis of 308 formed compounds. Volatile organic compounds (VOCs) were captured with an evacuated Summa canister and assayed via gas chromatography interfaced with mass spectrometry (GC-MS). Carbonyls (aldehydes and ketones) were captured using a 2,4-dinitrophenylhydrazine (DNPH) cartridge and assayed via a high-performance liquid chromatography-ultra-violet (HPLC-UV) assay. Polyaromatic hydrocarbons (PAHs) were captured using an XAD cartridge and filter, and extracts were assayed using GC-MS/MS. Polar compounds were assayed after derivatization of the XAD/filter extracts and analyzed via GC-MS. Conclusion: At higher temperature, both cinnamaldehyde and menthol combustion significantly increased formaldehyde and acetaldehyde levels. At higher temperature, cinnamaldehyde, eugenol, and menthol resulted in increased benzene concentrations. At low temperature, all four compounds led to higher levels of benzoic acid. These data show that products of thermal degradation of common flavorant compounds vary by flavorant and by temperature and include a wide variety of harmful and potentially harmful constituents (HPHCs).

Keywords: Cinnamaldehyde; ENDS; eugenol; menthol; tobacco; vanillin.

Figure 1.

Structures of the parent compounds, cinnamaldehyde (a), eugenol (b), menthol (c), and vanillin (d).

Figure 2.

Diagram of the drop-tube furnace within a quartz tube used to heat flavorants.

Figure 3.

Volatile organic aromatic hydrocarbons measured in the flavorant aerosols at low (blue; 250°C) and high (red; 750°C) temperatures.

Figure 4.

Polycyclic aromatic hydrocarbons (PAH) measured in the flavorant aerosols at low (blue; 250°C) and high (red; 750°C) temperatures.

Figure 5.

Proportion of total measured organic compounds for each of the flavorants in the low (250°C) and high (750°C) temperature-generated atmospheres. Individual listed compounds were measured in the highest abundance (excluding parent flavorant).