Analysis of Nicotine and Impurities in Electronic Cigarette Solutions and Vapor

Importance of the Topic

Electronic cigarettes have become widely adopted as alternatives to conventional smoking, yet the chemical composition of their aerosols remains poorly understood. Assessing nicotine levels alongside impurity and volatile compound profiles in both e-liquid and vapor is essential for consumer safety evaluations, regulatory decision-making, and laboratory quality control applications.

Objectives and Study Overview

The study aimed to develop an integrated analytical workflow for rapid quantification of nicotine in e-liquids, identification of liquid impurities, and comprehensive profiling of volatile and semi-volatile organic compounds in e-cigarette vapor. Key goals included: testing multiple carrier gases for gas chromatography, establishing robust calibration procedures, and designing a simple sampling device for vapor collection without specialized smoking machines.

Methodology

• Nicotine determination via fast GC-FID methods using helium or hydrogen carrier gas with a 30 m Rtx-VMS column, achieving run times under 5 minutes and linear calibration from 0.016 to 1.00 mg/mL.
• Impurity screening in e-liquids using GC-MS in scan mode on the same Rtx-VMS column with an Agilent 7890B/5977A system; qualitative identification via NIST spectral matching.
• Vapor sampling by drawing single 40 mL puffs—plus ten-puff sequences—through thermal desorption tubes packed with Tenax TA, Carbograph TD, and Carboxen 1003, followed by TD-GC-MS analysis on a Markes UNITY™ system paired with Agilent GC-MS.
• Blank and background assessments to account for laboratory air contributions and in-system pyrolysis of propylene glycol or glycerin.

Used Instrumentation

• Agilent 7890A/7890B GC systems with FID and 5977A MSD detectors.
• 30 m × 0.25 mm ID, 1.40 µm Rtx-VMS capillary column.
• Markes UNITY™ thermal desorption system and stainless steel TD tubes.
• Gas-tight syringe sampling device and calibrated balance for density measurements.

Main Results and Discussion

• Measured e-liquid nicotine concentrations exceeded labeled values by 4–28% after density-based conversions, consistent across four commercial brands.
• GC-MS screening of e-juices revealed 64 distinct compounds beyond listed ingredients, including flavor-related pyrazines and tobacco alkaloids, with over half remaining unidentified.
• A single 40 mL vapor puff yielded 82 volatile and semi-volatile compounds, uncovering toxic carbonyls (formaldehyde, acetaldehyde, acrolein) and siloxanes not present in the liquids, indicating thermal formation during vaporization.
• Acrolein levels per puff (0.003–0.015 µg/mL) paralleled those in conventional cigarettes and exceeded NIOSH short-term exposure limits; laboratory air and system pyrolysis accounted for up to 23% of measured carbonyls.
• Ten-puff sampling overloaded humectant peaks, demonstrating the benefit of single-puff analysis for maintaining sensitivity and avoiding carryover.

Benefits and Practical Applications

The integrated approach enables rapid quality control of e-liquids and accessible vapor testing without specialized smoking machines. Utilizing a single GC system and column for multiple analyses reduces resource demands and supports routine contract‐lab workflows. Single-puff thermal desorption sampling maximizes detectability while minimizing sample preparation time.

Future Trends and Applications

Advancements should target thermal desorption parameter optimization to minimize in-system pyrolysis, standardized puffing protocols for reproducible exposure assessments, and expansion to next-generation e-cigarette designs. Regulatory bodies may leverage these methods to establish product standards and inhalation risk limits.

Conclusion

This study demonstrates that e-cigarette vapor contains a complex mixture of harmful compounds not present in the original liquid. Rapid GC-FID, GC-MS, and thermal desorption methods provide a comprehensive, efficient toolkit for evaluating nicotine content and impurity profiles in both e-liquids and aerosols. Widespread adoption of these protocols will deepen understanding of user exposures and inform regulatory decisions.

Reference

1. Trtchounian A., Williams M., Talbot P. Conventional and electronic cigarettes (e-cigarettes) have different smoking characteristics. Nicotine Tob Res. 2010;12:905.
2. Brown C.J., Cheng J.M. Electronic cigarettes: product characterisation and design considerations. Tob Control. 2014;23(Suppl 2):ii4.
3. Pepper J.K., Eissenberg T. Waterpipes and electronic cigarettes: increasing prevalence and expanding science. Chem Res Toxicol. 2014;27:1336.
4. Farsalinos K.E. et al. Evaluating nicotine levels selection and patterns of electronic cigarette use in vapers who had achieved complete substitution of smoking. Subst Abuse. 2013;7:139.
5. Bullen C. et al. Electronic cigarettes for smoking cessation: a randomised controlled trial. Lancet. 2013;382:1629.
6. Caponnetto P. et al. Efficiency and safety of an electronic cigarette (ECLAT) as tobacco cigarettes substitute: a 12-month randomized control design study. PLoS One. 2013;8:e66317.
7. Goniewicz M.L. et al. Levels of selected carcinogens and toxicants in vapour from electronic cigarettes. Tob Control. 2014;23:133.
8. Schober W. et al. Use of electronic cigarettes impairs indoor air quality and increases FeNO levels of e-cigarette consumers. Int J Hyg Environ Health. 2014;217:628.
9. Kosmider L. et al. Carbonyl compounds in electronic cigarette vapors: effects of nicotine solvent and battery output voltage. Nicotine Tob Res. 2014;16:1319.
10. E-Cig Reviews on the Best E-Cigarettes of 2014. Ecigarette Reviewed. 2014.
11. Farsalinos K.E., Polosa R. Safety evaluation and risk assessment of electronic cigarettes as tobacco cigarette substitutes: a systematic review. Ther Adv Drug Saf. 2014;5:67.
12. Farsalinos K.E. et al. Evaluation of electronic cigarette use topography and estimation of liquid consumption: implications for protocol standards. Int J Environ Res Public Health. 2013;10:2500.
13. Ochiai N. et al. Stabilities of 58 volatile organic compounds in canisters under various humidified conditions. J Environ Monit. 2002;4:879.
14. NIST Mass Spectrometry Data Center. U.S. Department of Commerce. 2014.
15. Rodgman A., Perfetti T.A. The Chemical Components of Tobacco and Tobacco Smoke. CRC Press; 2nd ed. 2013.
16. Cogliano V.J. et al. Summary of IARC monographs on formaldehyde, 2-butoxyethanol, and 1-tert-butoxy-2-propanol. Environ Health Perspect. 2005;113:1205.
17. IARC Working Group. Alcohol drinking. IARC Monogr Eval Carcinog Risks Hum. 1988;44:1.
18. Stein Y.S., Antal M.J., Jones M. A study of the gas-phase pyrolysis of glycerol. Appl Pyrolysis. 1983;4:283.
19. ATSDR. Toxicological Profile for Acrolein. U.S. Department of Health and Human Services. 2007.
20. U.S. Food and Drug Administration. Electronic Cigarettes (e-Cigarettes). 2014.