Analytical approaches for investigation of partially identified leachables in ENDS

Electronic nicotine delivery systems (ENDS), or e-cigarettes, are battery-powered devices that produce an aerosol for inhalation by heating e-liquid. E-liquid is typically composed of propylene glycol (PG), vegetable glycerin (VG), nicotine salt, and is contained within a container closure system (CCS), such as a prefilled pod or disposable device. These container closure systems are commonly manufactured with materials such as plastics, elastomers, glass, metals, etc., which have the potential to leach unintended chemical compounds into the e-liquid. Given that these leachable compounds may transfer to the aerosol during consumer use, the United States Food and Drug Administration (U.S. FDA) requires ENDS manufacturers to conduct extractable and leachable (E&L) studies to assess potential safety risks. One significant challenge in leachable studies for ENDS products is that e-liquid naturally changes over time, forming trace degradants and reaction products despite the materials used in the container closure system. Because leachable studies often utilize non-targeted, highly sensitive, analytical methods to investigate changes over time, the origin of a compound observed during the aging process can be difficult to ascertain when compounds are not observed in extractable studies. In this work, a case study was presented in which five partially identified, data-deficient, leachable compounds were reported following 12 months of room temperature storage of unflavored e-liquid in a JUUL2 pod container closure system that were not observed in extractable studies or in initial unaged samples. An experiment was conducted where unflavored e-liquid was artificially aged outside the JUUL2 pod, and all five of the data-deficient compounds were observed. Additional experiments using isotopically labelled primary ingredients confirmed that four of the five studied organic compounds were derived from nicotine, and the fifth was derived from benzoic acid. The analytical approaches outlined in this work provided a technique to determine whether select organic compounds observed in long term leachable studies were derived from the container closure system.