Up in Vape: What is in my E-Juice Other than Nicotine, Propylene Glycol, and Glycerin

Importance of the Topic

As e-cigarette and vaping use expands worldwide, understanding the full chemical composition of e-liquids is crucial for assessing potential health risks. Beyond the primary components—nicotine, propylene glycol and glycerin—flavoring agents and trace contaminants may form harmful by-products during vaporization. A reliable analytical workflow enables laboratories to detect both major and minor constituents, ensuring product safety and regulatory compliance.

Objectives and Study Overview

This study presents an optimized gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) approach to screen e-liquids for harmful and potentially harmful constituents (HPHCs) and a wide range of flavoring compounds. Key goals included building a multiple reaction monitoring (MRM) transition database from scan data, improving detection limits for trace analytes, and demonstrating rapid compound identification across diverse flavor profiles.

Methodology and Instrumentation

Samples of commercially available e-liquids representing fruity, dessert and traditional tobacco flavors were diluted 2:1 in acetone to reduce viscosity. A 1 µL aliquot was injected into a split/splitless inlet at 240 °C with a 25:1 split using a low-pressure drop liner. Separation was achieved on a 30 m×0.25 mm×0.25 µm DB-Wax UI column with helium carrier gas at 1.2 mL/min. The column effluent entered an Agilent 7000D triple quadrupole MS with electron-impact ionization (ion source at 300 °C, quadrupole temperatures at 150 °C). Full-scan data were acquired before applying chromatographic deconvolution to extract clean spectra for library searching. A streamlined workflow in MassHunter Optimizer software generated and refined precursor-product ion pairs and collision energies to automate MRM transition creation.

Used Instrumentation

• Agilent 7890B GC with split/splitless inlet and UI low-pressure drop liner
• DB-Wax UI capillary column (30 m×0.25 mm×0.25 µm)
• Helium carrier gas, constant flow 1.2 mL/min
• Agilent 7000D Triple Quadrupole MS (EI source, 300 °C)
• Agilent MassHunter Data Analysis and MRM Optimizer software

Main Results and Discussion

Deconvolution of full-scan data against the NIST17 library yielded >70% tentative identifications across flavor categories. A custom MRM database targeting FDA HPHCs—aldehydes, nitrosamines, aromatic hydrocarbons—and key flavor markers enabled low-level quantitation with a 200× dilution factor. Notably, diacetyl, associated with bronchiolitis obliterans, was detected in one sample; trace coumarin was found in another despite its food ban. Common flavor compounds such as vanillin, ethyl vanillin and propylene glycol acetals were successfully distinguished. MRM screening chromatograms provided rapid confirmation of nicotine presence even in unlabeled products.

Benefits and Practical Applications of the Method

• High sensitivity for trace HPHCs at elevated sample dilutions minimizes matrix effects.
• Automated MRM generation accelerates method development for new compounds.
• Library-driven identification supports regulatory screening and product consistency testing.
• Comprehensive profiling of flavor chemicals aids formulation control and safety assessment.

Future Trends and Opportunities for Use

Advances in spectral deconvolution and machine learning will further enhance compound identification in complex matrices. Expansion of shared MRM databases and vendor-agnostic libraries may streamline method transfers between laboratories. Coupling real-time vapor phase sampling with high-resolution MS and hyphenated techniques could offer on-demand quality control at manufacturing lines. Integration of data analytics platforms will support large-scale surveillance of emerging vaping products.

Conclusion

The developed GC-MS/MS workflow combining deconvolution, spectral library matching and automated MRM optimization provides a robust platform for comprehensive e-liquid analysis. It enables simultaneous screening of major components, flavoring agents and trace toxicants, supporting both research and quality assurance in the rapidly evolving vaping industry.

References

• Agilent Technologies Application Note MP189, 2019.
• NIST17 Mass Spectral Library.
• FDA Harmful and Potentially Harmful Constituents (HPHCs) list for tobacco products.