This study seeks to understand the relationship between various electronic cigarette modifications and the particle size profile of the aerosols generated by the device using a cascade impactor. The coil resistance, battery voltage, and the composition of the glycols in the e-liquid were varied to determine the impact on particle size formation. E-liquids using 12 mg/mL nicotine were evaluated as well as two e-liquids containing DOTNs, 60 mg/mL methamphetamine and methadone. Methamphetamine is a schedule II CNS stimulant with a history of smoking as a mode of administration. In recent years, arrests have been made with individuals having been found with methamphetamine inside their e-cigarette devices20. Methadone, a schedule II synthetic opioid in the same class of compounds as heroin, is primarily taken orally for opioid addiction maintenance. The liquid concentrate formulation of methadone is composed of propylene glycol, which is also a constituent in e-cigarette e-liquids21.
Reagents and supplies
Nicotine, methamphetamine hydrochloride, and methadone hydrochloride were purchased from Sigma Aldrich (St. Louis, MO). The vegetable glycerin and propylene glycol were purchased from Wizard Labs (Altamonte Springs, FL). The Kangertech replaceable atomizers were purchased from Discount Vapers (Oakville, CT), the AeroTank Clearomizer from My Vapor Store (Panama City, FL), and the e-go V v2 variable voltage battery from Vivid Smoke (Irvine, CA). Nicotine, methamphetamine, methadone, nicotine-d4, methamphetamine-d11, and methadone-d9 reference standards were all purchased from Cerilliant Corporations (Round Rock, TX). The methanol and 20 mL scintillation vials were purchased from Fisher Scientific (Pittsburgh, PA). The Micro-Orifice Uniform Deposit Impactor (MOUDI) was purchased by MSP Corporation (Shoreview, MN). The flow meter was purchased from Dwyer (Michigan City, IN).
Particle size experiments
An AeroTank Clearomizer with a KangerTech pre-assembled atomizer was used in conjunction with an eGo-V2 variable voltage battery to develop a model for research, to easily control variables, and generate the condensation aerosol. This specific device was used due to its popularity in the United States at the time of purchase, and the atomizer was easy to adapt with typical user modifications, such as coil configurations.
Nicotine e-liquid formulations were prepared at 12 mg/mL in 50:50 PG:VG 100% PG, or 100% VG solution in order to measure the impact of PG and VG formulation on particle size. Coil resistance was set at 1.5, 1.8, or 2.2 Ω at 4.3 V. Common battery output voltages were set at 3.9, 4.3, or 4.7 V at 1.8 Ω, the most common resistance for this device. Methamphetamine and methadone e-liquid formulations were prepared at 60 mg/mL in 50:50 PG:VG solution to evaluate the impact of different drugs on particle size and generated with a device operated at the most common battery and resistance settings of 3.9, 4.3, or 4.7 V at 1.8 Ω. E-liquids were stored in a cabinet at room temperature until the experiments were started. The AeroTank clearomizers were filled at half capacity with e-liquid formulation at the day of the experiment and were vortexed prior to aerosol generation. The battery was charged the night prior to the experiments.
A 10-stage micro-orifice uniform deposit impactor (MOUDI), draws the sample through a cascading sequence of nozzles that deposit the aerosol onto plates, was used for particle size analysis8,9,10. Aluminum disks were placed on the plates for stages 1–9 of the MOUDI with filter paper placed on the final stage (stage 10). The mass of the AeroTank Clearomizer containing the e-liquid, each aluminum disk, and the filter were recorded pre- and post aerosolization. The 10-stage MOUDI was operated at a flow rate of 30 L/min. The e-cigarette mouthpiece was positioned flush with the USP induction port (simulated throat) which was connected to the inlet of the impactor to allow sampling of the e-cigarette aerosol. The e-liquids were undiluted. An aerosol was generated 6 times, 10 seconds each, for a single MOUDI collection and performed in triplicate. The particle size distribution data generated by the MOUDI was time-averaged data. Following each experiment, the aluminum disks and the filter were weighed and then were each placed into 20 mL scintillation vials and washed with 1 mL methanol. The USP induction port was washed with 1 mL methanol.
Particle size distributions of the glycols was determined gravimetrically. The change in weight of each aluminum disk and filter was used to determine the total mass of e-liquid collected in the MOUDI. The percent mass recovered on each MOUDI stage was determined for each trial (n = 3) and averaged.
Analysis of nicotine particle size samples by LC-MS/MS
A previously validated method was used to analyze nicotine concentrations on each stage of the MOUDI using a Quattro micro MS with a Shimadzu LC system (Shimadzu, Kyoto, Japan). Chromatographic separation was achieved on an Agilent Polaris 5-Si A 50 × 3 mm, 5 μm column (Agilent Technologies, Santa Clara, CA). The injection volume was 10 μL with a flow rate of 0.4 mL/min. The total run time for this method was 4.5 minutes and the instrument was operated in multiple reaction monitoring mode (MRM) for the following m/z transitions: Nicotine, 163 > 130 and 163 > 117; and nicotine-d4, 167 > 134. A seven-point calibration curve ranging 10–1000 ng/mL of nicotine, along with a blank, double blank control, and nicotine controls were analyzed. Controls were prepared as a limit of quantitation quality control (10 ng/mL), low quality control (30 ng/mL), mid quality control (300 ng/mL), and high quality control (900 ng/mL). The internal standard (100 ng/mL nicotine-d4) was added to each calibrator, blank, control, and samples. Dilutions of the samples were prepared to assure that all samples were bracketed within the calibration range.
Analysis of methamphetamine and methadone particle size samples by GC/MS
An Agilent 6890 N Gas Chromatograph with a 5973 Mass Selective Detector (MSD) was used for chromatographic separation and detection using a HP-5MS 30 m × 0.25 mm id × 0.25 μm column (Agilent Technologies, Santa Clara, CA) and helium carrier gas.
For methamphetamine, the GC/MS was operated in split mode at 6:1 ratio and a 1 μL injection volume. The helium carrier gas had a flow rate of 35 cm/s and the inlet temperature was set to 275 °C. The GC oven had an initial temperature of 120 °C with a ramp rate of 10 °C/min until 200 °C before undergoing a second temperature ramp of 30 °C/min until 280 °C. The total run time was 10.67 minutes. The MSD was operated in select ion monitoring (SIM) mode with 58, 64, 91, 96, and 134 m/z as the selected ions and the quantitation was performed using 58 and 64 m/z as the quantitative ions for methamphetamine and methamphetamine-d11 respectively. A six-point calibration curve ranging from 100–2000 ng/mL of methamphetamine, along with a blank, double blank control, and methamphetamine controls were analyzed. Controls were prepared with a limit of quantitation quality control (100 ng/mL), low quality control (150 ng/mL), mid quality control (600 ng/mL), and high quality control (1500 ng/mL). The internal standard (500 ng/mL methamphetamine-d11) was added to each calibrator, blank, control, and samples. Dilutions of the samples were prepared to ensure all samples were bracketed within the calibration range.
For methadone, the GC/MS was operated in split mode at 20:1 ratio and a 1 μL injection volume. The helium carrier gas had a flow rate of 39 cm/s and the inlet temperature was set to 275 °C. The GC oven had an initial temperature of 225 °C with a temperature ramp of 15 °C/min until 285 °C for a total run time of 4 minutes. The MSD was run in SIM mode with the following ions monitored: 72, 223, 294, and 309 m/z for methadone and 78, 226, 303, and 318 m/z for methadone-d9 and quantitation was performed using 72 and 78 m/z as the quantitative ions for methadone and methadone-d9, respectively. A seven-point calibration curve ranging from 100–5000 ng/mL of methadone, along with a blank, double blank control, and methadone controls were analyzed. Controls were prepared with a limit of quantitation quality control (100 ng/mL), a low quality control (150 ng/L), a mid quality control (1000 ng/mL) and a high quality control (4500 ng/mL). The internal standard (500 ng/mL methadone-d9) was added to each calibrator, blank, control, and samples. Dilutions of the samples were prepared to ensure all samples were bracketed within the calibration range.
The geometric mean diameter (GMD), geometric standard deviation (GSD), and mass median diameter (MMAD) were calculated using the methods detailed by Ramachandran and Cooper22. Precision was evaluated by calculating each relative standard deviation for each replicate measurement. The threshold for statistical difference was set at a P-value of 0.05 (n = 3).