Characterization of electronic cigarette liquid ingredients using combinatorial techniques: Solubility of chemicals used in formulations is critical to the study of health effects

The use of electronic cigarettes (a.k.a. the act of ‘vaping’) is considered an alternative method for nicotine uptake compared to traditional cigarettes. ‘E-cigarettes’ are battery powered devices that allow users to heat an ‘e-liquid’ into an aerosol, which is then inhaled. E-liquids or ‘e-juices’ are composed of an active ingredient (e.g., nicotine), solvents, water, and flavoring additives. Due to the variety among composition, it is difficult to study the physicochemical characteristics of all ingredients present in the native e-liquid as well as emissions formed in the heating processes. It is hypothesized that some ingredients, as well as degradants of vaped e-liquids, are cytotoxic. Before cytotoxicity can be measured, however, the solubility of each ingredient and ingredient mixtures ought to be systematically assessed to aid in health effects testing and used to predict potency. The purpose of this project is to provide solubility assessments of e-liquid binary mixtures containing prevalent diluents and flavoring additives. The following three steps were used in the experimental design: (1) literature review of the current knowledge of e-liquid toxicity, (2) miscibility assessment of binary mixtures of three common flavoring additives, and (3) preliminary characterization of e-liquid formulations with recommendations for future work. Results indicated that binary mixtures dissolved more readily in reverse osmosis (RO) water than in cell culture media. Miscibility decreased as a result of increasing flavoring additive concentration regardless of dilution in RO water or cell culture media. Nuclear magnetic resonance (NMR)spectroscopy showed minor spectral changes indicating possible degradant formation when comparing native versus heated samples. In the near future, aerosolized samples should be collected and analyzed via mass spectrometry.