Thermal Degradation Studies of Electronic Cigarette Liquids Part 2: Development of a Model Reaction System Used to Study α-dicarbonyl Formation Melvin, M.S.; Avery, K.C.; Ballentine, R.M.; Gardner, W.P.; McKinney, W.J.; Smith, D.C.; Wagner, K.A. Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 1
Diacetyl (µg/g) Diacetyl Formation During Aerosol 2.0 Generation Liquid 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Aerosol A B C D E F G H Product Diacetyl levels elevated in aerosol relative to e-liquid suggesting diacetyl formation during aerosol generation Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST11 2
Observed Diacetyl Formation in Aerosol Glycerin Propylene Glycol??? Diacetyl Nicotine Attributed to thermal degradation processes Provide more detailed information on reaction pathway Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 3
Diacetyl Formation: Approach Develop equivalent model reactor - Equivalent = generate similar product yields as aerosol process Identify precursor compounds - 13 C-labeled propylene glycol and glycerin Propose reaction pathway Confirm proposed pathway - Identify key intermediates - Verify with synthetic organic chemistry Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 4
Microwave Optimization Reference formulation: - 50:50 propylene glycol:glycerin containing 2.5% nicotine and 15% water (on a weight basis) Sample size: - 500 mg of sample Screened range of times and temperatures - Fixed power of 200W - 1 to 15 minutes - 80 C to 220 C in 20 C increments Analyze samples using o-phenylenediamine method CEM Discovery SP Hybrid Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 5
Diacetyl (ng/g (ng/g of e-liquid) e-liquid) Reaction Screening Studies (N=3) 10000 900 9000 800 8000 700 7000 600 6000 500 5000 400 4000 3000 300 2000 1000 0 Diacetyl Diacetyl Yield Yield at Varying at Indicated Temperatures Temperatures 3 Min Over Reaction Time Time 160 C 180 C 0 80 2 100 4 120 6 140 8 160 10 180 12 200 14 220 16 Temperature Time (minutes) ( C) Diacetyl generation increased linearly with time Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 6
Diacetyl (ng/g of e-liquid) Reaction Screening Studies (N=3) 900 800 700 600 500 400 300 200 100 0 Diacetyl Yield at Varying Temperatures at 3 Min Reaction Time 80 100 120 140 160 180 200 220 Temperature ( C) Diacetyl generation increased linearly with time Yields increased with temperature Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 7
Microwave System Compared to Aerosol Microwave: - Standard conditions = 3 minutes at 180 C using 200 W power Aerosol collection: - Reference formulation (900 mg) - MarkTen XL cartridge - 50 puffs - 55 ml Puff Volume, 5 sec Puff Duration, 30 sec Puff Interval, Square Wave Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 8
Analyte Yield (ng/g) Microwave System Compared to Aerosol (55 ml Puff Volume, 5 sec Puff Duration, 30 sec Puff Interval, Square Wave, 50 puffs) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Liquid Microwave Aerosol Glyoxal MethylGlyoxal Diacetyl Acetyl Propionyl Equivalent results for diacetyl and acetyl propionyl Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 9
Analyte Yield (ng/g) Microwave System Compared to Aerosol (55 ml Puff Volume, 5 sec Puff Duration, 30 sec Puff Interval, Square Wave, 50 puffs) 35000 2000 1800 30000 1600 25000 1400 20000 1200 1000 15000 800 10000 600 400 5000 200 0 Liquid Microwave Aerosol Glyoxal MethylGlyoxal Diacetyl Acetyl Propionyl Equivalent results for diacetyl and acetyl propionyl Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 10
Analyte Yield (ng/g) Microwave System Compared to Aerosol (55 ml Puff Volume, 5 sec Puff Duration, 30 sec Puff Interval, Square Wave, 50 puffs) 2000 1800 1600 1400 1200 1000 800 600 400 200 0 Liquid Microwave Aerosol Glyoxal MethylGlyoxal Diacetyl Acetyl Propionyl Equivalent results for diacetyl and acetyl propionyl Elevated levels of glyoxal and methylglyoxal observed in aerosol relative to microwave system Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 11
Isotope Labeling Studies Microwave conditions - 500 mg of sample reacted for 3 minutes at 180 C Test e-liquids - 50:50 propylene glycol: 13 C 3 -glycerin + 2.5% nicotine Method for determining % enrichment - Created single-ion recording MS method for all possible isotopes - Obtained relative isotopic abundances - Percentage of 13 C incorporation was then determined Natural isotope contribution and mass bias corrections applied according Paine et.al. 1 1) Paine, J. B., et al. (2007), J. Anal. Appl. Pyrolysis 80(2): 297-311. Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 12
Percent of Total Diacetyl Yield Diacetyl Isotopic Distribution 60 50 47.8 40 30 20 10 0 24.4 17.2 7.7 13C = 0 13C = 1 13C = 3 13C = 4 Number of 13 C Atoms Incorporated into Diacetyl Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 13
Isotope Labeling Analysis No 13 C labeled diacetyl: - Diacetyl can be generated from PG alone One 13 C labeled diacetyl: - Predominate pathway; GLY contributes one carbon-13 unit Three 13 C labeled diacetyl: - Minor pathway; GLY contributes three carbon-13 units Four 13 C labeled diacetyl: - GLY contributes four carbon-13 units to diacetyl formation Yield similar to diacetyl formation from propylene glycol alone Summary: Diacetyl formed from one carbon and three carbon precursors both of which can originate from both PG and GLY Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 14
Proposed Pathway: Acetol Formation Formation of acetol (hydroxyacetone) from propylene glycol or glycerin - Acetol yields similar to formaldehyde yields Acetol isomerization - Key step in proposed pathway Observed by NMR 2 2) Jensen, R. P., et al. (2017). Sci Rep 7: 42549. Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 15
Proposed Pathway: Acetol to Diacetyl Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 16
Verify with Synthetic Organic Chemistry Fortify reference solution with acetol and formaldehyde Perform aldol condensation using propylene glycol as reaction solvent Evaluate acid and base catalyzed aldol condensations Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 17
Diacetyl (ng/g of e-liquid) Acetol Effect on Diacetyl Yield 500 mg of reference formulation 3 minutes at 180 C 250 200 150 100 50 0 0 12.5 25 50 Amount of Added Acetol (ng) Diacetyl yield increases with increasing acetol concentration Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 18
Diacetyl (ng/g of e-liquid) Formaldehyde Effect on Diacetyl Yield 500 mg of reference formulation 3 minutes at 180 C 250 200 150 100 50 0 0 12.5 25 50 Amount of Added Formaldehyde (ng) Added Formaldehyde showed little effect Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 19
Diacetyl (ng/g e-liquid) Diacetyl (ng/g e-liquid) Diacetyl Yields from Aldol Reactions 500mg of propylene glycol + 100 µm Acetol + 100 µm Formaldehyde 3 minutes at 180 C Base Catalyzed: Nicotine 1200 1000 800 600 400 200 0 0 125 150 200 250 Amount Added Nicotine (ng) Acid Catalyzed: Acetic Acid Aldol reaction replicated in microwave model system - Base catalysis not as efficient as acid catalysis 8000 6000 4000 2000 0 0 10 25 50 100 Amount Added Acetic Acid (µl) Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 20
Conclusions a-dicarbonyl compounds are formed during the generation of aerosol for the device types tested Rapid heating via microwave technology can prove a useful tool as a model system for studying the formation of these compounds This tool was applied to the determination of pathways for diacetyl formation Diacetyl appears to be formed through the aldol condensation between acetol and formaldehyde Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 21
Acknowledgements George Karles, Yezdi Pithawalla, and Pete Lipowicz Thutrang Nguyen, Kathy Jerome, and Ha Nguyen CEM Corporation Altria Client Services Regulatory Sciences Matt S. Melvin October 9, 2017 2017 CORESTA - ST12 22
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