In other words, the eliquid will be entirely VG well before the e-liquid reservoir is depleted. The predicted percent of e-liquid remaining at full VG enrichment in the model is fairly insensitive to starting volume in the e-liquid but is sensitive to starting PG:VG ratio and temperature, as expected. Thus, a user may be inhaling high relative concentrations of acrolein and other predominant VG products in the aerosol for a significant amount of time during the e-liquid cartridge or reservoir lifespan.The vaping process for e-cigarettes is complex and dynamic, possibly more so than currently appreciated. Coil temperature, puff duration, and PG:VG ratio all significantly affect both theaerosol production and the composition. Most of the mass that was lost from the e-liquid could be accounted for as PG and VG. Furthermore, volatile/semivolatile compounds dominated the total aerosol. Caution should be exercised when collecting particles with dense filter material or with overloaded filters for studying the particle phase, as the semivolatiles can be trapped and interpreted as particulates. In general, the chemical mechanisms for forming carbonyls appear to be well understood, and consistent with the numerous insights gained from interpreting the carbonyl mass yield as normalized by aerosol mass. Some exceptions include acetone, for which there may be a radical pathway from VG not currently accounted for, and acetaldehyde, for which there may be a thermal pathway from PG. Importantly, drying room the user’s exposure to toxic carbonyls such as acrolein may change during the vaping process, and the user may be exposed to high relative content of VG and its degradation products as the e-liquid is depleted.

These findings support the need for further research into aerosol composition and toxicology as a function of the e-cigarette puffing life cycle, in addition to e-liquid composition, puffing regimen, and vaping device operational conditions.The unexpected outbreak of e-cigarette or vaping-associated lung injury was reported nationwide starting in September 2019, causing more than 2800 hospitalizations and 60 deaths. The specific biological mechanisms of EVALI, as well as the chemical causes, are still under investigation. Emerging evidence shows that EVALI is associated with vaping tetrahydrocannabinol containing e-liquid cartridges that were obtained on the black market. Although adverse health effects of vaping THC cartridges have been found to include abdominal pain, nausea, chest pain, shortness of breath, and acute respiratory distress, they have not to date been fatal. The sudden deaths and hospitalizations from EVALI are, instead, strongly linked to a compound called vitamin E acetate , the chemically-stable esterified form of vitamin E . VEA is thought to be used as a cutting agent in THC cartridges because it has a similar viscosity to THC oil, so that the adulteration will not be visually evident. FDA labs confirmed that VEA was present in 81% of THC-containing vaping cartridges confiscated from 93 EVALI patients. VEA was also found in the bronchoalveolar fluid samples from 48 of 51 patients, but not found in samples from the healthy comparison control group. The VEA fraction in vaping cartridges confiscated from EVALI patients range from 23% – 88%. The interaction between aerosolized VEA with lung surfactant, the toxicity of VEA thermal degradation products, or other components in the vaping aerosol of extracted THC oil have been hypothesized to explain the association of VEA to EVALI. It should be noted that there is currently not sufficient evidence to rule out the contribution of other diluents, flavoring additives, pesticide residues, or other ingredients found in THC cartridges.

It’s also not known if VEA has a synergistic effect with THC oil components that may lead to EVALI. A limited number of recent research publications has focused on either the physical and chemical properties, or the biological effects of the vaping aerosol from VEA. DiPasquale et al.observed VEA was capable of reducing the elastic properties of pulmonary surfactant and thus cause lung dysfunction by alveolar collapse or atelectasis. Lanzarotta et al. found evidence for hydrogen bonding between VEA and THC in both vaping aerosol and unvaped e-liquid, suggesting they may synergistically cause EVALI. Wu et al. showed that the toxic gas ketene, as well as carcinogenic alkenes and benzene are generated from the thermal degradation of VEA. RiordanShort et al. found that pure VEA starts to decompose at an incubation temperature of 240 °C and identified over 40 kinds of thermal degradation product at an incubation temperature of 300 °C, 30 of which are carbonyls and acids. However, the experiments of Riordan-Short was done under heated headspace sampling as a surrogate vaping environment, instead of a real vaping environment in an e-cigarette tank with metal coil, where temperature gradients exist due to localized coil heating. Furthermore, different coil material and surface area will have different effects on thermal degradation chemistry. Jiang et al. reported a total of 35 toxic byproducts during the vaping of commonly used diluents including VEA; over 25 of them are carbonyl compounds. Compared to VEA, there is less research available on the vaping chemistry of THC oil extracts and other cannabinoids due to DEA regulations, even though the metabolism of THC has been well studied.Meehan-Atrash et al. hypothesized that THC emits similar thermal degradation products to terpenes given their terpenoid backbone; however, terpenes are also found in cannabis plants and can be used as additives in e-liquids, such that the degradation products may be difficult to distinguish from THC. It was also found that vaping and dabbing cannabis oil including terpenes may cause exposure to concerning degradants such as methacrolein, benzene, and methyl vinyl ketone.

Adding terpenes to THC oil led to higher levels of gas-phase products compared to vaping THC alone. Since vaping is a complex and dynamic process, a systematic understanding of the chemistry occurring during the vaping process is needed to assess potential factors that may contribute to EVALI, as well as other potential adverse health effects. In this work, a temperature controlled vaping device with accurate coil temperature measurement was used to vape e-liquids of VEA, extracted THC oil, and their mixture under typical vaping conditions consistent with the CORESTA standard. Gravimetric analysis was used to evaluate the aerosolization efficiency, while the high performance liquid chromatograph coupled with high resolution mass spectrometry was used to characterize thermal degradation products including carbonyl compounds, acids, and cannabinoids using the methods developed by Li et al. A comprehensive thermal degradation mechanism for THC and VEA are proposed, which could be useful for regulation and further research.A temperature-controlled third generation Evolv DNA 75 modular e-cigarette device with a refillable e-liquid tank and single mesh stainless steel coils was used for aerosol generation . The mod enabled variable output voltages with coil resistance of ~0.12 ohm. Evolv Escribe software was used to customize the power output in order to achieve the desired coil temperature. The coil temperatures were measured by a flexible Kapton-insulated K type thermocouple in contact with the center of the coil surface and output to a digital readout. The temperature set by the device is not truly representative of the measured coil temperature, as often, vertical farming units the device flow rate, e-liquid viscosity, and coil resistance changes will alter the relationship between applied power and output coil temperature that drives chemistry. The puff duration is 3 s with a flow rate of 1.20 ± 0.05 L/min, quantified by a primary flow calibrator , corresponding to puff volume of 60 ± 2.5 mL. The puff volume and puff duration selected in this work is consistent with e-cigarette test protocols applied to propylene glycol /vegetable glycerin based e-cigarettes.The e-liquids used for vaping in this work are: pure VEA that was used as purchased, extracted THC oil that is commercially obtained from Bio-pharmaceutical Research Company , and the mixture of the two ingredients . All THC experiments are performed at the BRC facility under an active DEA Schedule 1 license. Thecomposition analysis by gas chromatography of unvaped extracted THC oil showed that the most abundant cannabinoids are: Δ 9 -tetrahydrocannabinol , Δ9 – tetrahydrocannabinol acid and cannabigerol acid , while other cannabinoids were identified below 3% of the total peak area . Δ 8 -THC, which can be observed at 0.3 minutes after the Δ 9 isomer, was not detected in the mixture. A total of over 50% of mass in unvaped extracted THC oil remain uncharacterized, but presumably contains terpenoids and potentially other alkanes and alkenes. Three temperatures were chosen for the particle generation, with a temperature measurement deviation of 10 °F. The quantification of carbonyls is only reported at 455 °F. During the sample collection, a total of 10 puffs of aerosol with a frequency of 2 puffs/min were collected for each sample. Carbonyls, acids and cannabinoids in vaping aerosols , which represent a large portion of expected products, were collected onto 2,4- dinitrophenylhydrazine cartridges for HPLC-HRMS analysis. The consecutive sampling with three DNPH cartridges shows a collection efficiency >98.4% for carbonyl-DNPH adducts in the first cartridge. Excess DNPH is conserved in the cartridge after the collection to maximize collection efficiency.

DNPH cartridges were extracted with 2 mL of acetonitrile into autosampler vials and analyzed by HPLC-HRMS. Consecutive extractions of DNPH cartridges for samples confirmed that >97% of both DNPH and its hydrazones were extracted after the first 2 mL volume of acetonitrile. The collection efficiency for cannabinoids is unknown, since only a limited amount of THC oil was available for experiment and not for quality controlcharacterizations. The high resolution mass data of cannabinoids is only used for identification in this work. Details on the collection method are described elsewhere. Moreover, glass fiber filters were used to collect the particles, as has been done in other e-cigarette studies. The particle mass collected on filters was determined gravimetrically on a microbalance by weighing the filter mass immediately before and after puffing at different experimental conditions. The standard deviation of the gravimetric analysis after triplicate measurements was determined to be ∼20%, mainly due to variations in puffing. The sample collection and analysis were performed in triplicate.Carbonyl compounds and acids from the thermal degradation of VEA and THC were derivatized by 2,4-DNPH to form carbonyl-DNPH compounds during the collection process. The detailed mechanism and method of identification for each carbonyl were described in previous work.40 Beside DNPH adducts, HRMS has been proven to be an effective tool for the detection of cannabinoids and their oxidative products, as the phenolic hydroxyl group in cannabinoids can be ionized in both electrospray ionization positive and negative modes, while the high mass precision enables the analysis of elemental composition. Negative mode was applied for the detection in this work as both carbonyl-DNPH adducts and cannabinoids can form negative ions by deprotonation. An external mass calibration was performed using the carbonyl-DNPH standard solution immediately prior to the MS analysis, such that the mass accuracy was adjusted to be approximately 1 ppm for standard compounds, the mass calibration was then applied to a molecular formula assignment for unknown compounds. All molecular assignments were analyzed by the MIDAS v.3.21 molecular formula calculator . Carbonyl-DNPH adducts and cannabinoids in extracts solution were separated and analyzed using an Agilent 1100 HPLC with an Poroshell EC-C18 column coupled to a linear-trap-quadrupole Orbitrap mass spectrometer with an ESI source at a mass resolving power of ∼60 000 m/Δm at m/z 400. The mobile phase of LC−MS grade water with 0.1% formic acid and acetonitrile were applied in the chromatography method. The analytes were eluted over the course of 45 min at 0.27 mL/min with the following gradient program: 40% B , 50% B , 60% B , 80% B , and 40% B . After separation by chromatography, single ion chromatography of each compound were extracted for the quantification of specific carbonyl compounds based on their calibrated m/z. Formaldehyde, acetaldehyde, acetone, butyraldehyde, valeraldehyde, hexanal were quantified using the analytical carbonyl-DNPH standards. The SIC peak separation between isomers of butyraldehyde/isobutyraldehyde, valeraldehyde/isovaleraldehyde hexanal/4-methylpentanal cannot be achieved, so the concentration of all isomers were calculated as a total amount. The concentrations of glyoxal, methylglyoxal, diacetyl were calculated by an estimated ESI sensitivity as described by Li et al.40The thermal degradation of both VEA and THC was observed at the measured coil temperature of 455 ± 10 °F , which is close to temperature that VEA started to degrade in the work of Riordan-Short et al..