Comparison of Different Sample Introduction Techniques for the Analysis and Characterisation of e-Liquids Using GC-MS

Significance of the Topic

Electronic cigarettes have become a widely adopted alternative to conventional smoking, driving the need for comprehensive quality control and regulatory compliance. The European Tobacco Products Directive (TPD) imposes stringent requirements on e-liquid composition, including quantification of glycols, carbonyls, metals, flavors, and nicotine. Reliable analytical methods are essential to address the complex matrix of propylene glycol (PG), vegetable glycerin (VG), water, flavorings, and nicotine in e-liquids, and to ensure reproducible, contamination-free results.

Study Objectives and Overview

This study aims to identify the most effective sample introduction technique for the GC-MS analysis and characterization of e-liquids under TPD guidance. Five approaches—standard split/splitless injection (SSL), Automated Tube Exchange (ATEX), Dynamic Headspace (DHS) as a Fully Evaporative Technique (FET), Twister Headspace, and Twister Liquid—were evaluated across a range of PG/VG ratios (10/90 to 80/20). Key performance metrics include chromatographic cleanliness, peak detection, and reproducibility.

Methodology and Instrumentation Used

A Gerstel MultiPurpose Sampler (MPS) 2 XL Dual Head equipped with a Thermal Desorption Unit (TDU), Cool Injection System (CIS 4), ATEX, Twister stir bars, and DHS modules facilitated automated sample handling. The analysis employed an Agilent 7890B GC coupled to a 7010 Triple Quadrupole MS operating in EI mode. Sample preparation varied by technique:

• SSL and ATEX: 1 µL neat e-liquid
• Twister Headspace: 1 mL e-liquid in 10 mL vial, 2 h at 40 °C
• Twister Liquid: 1 mL diluted in water, stirred 2 h at room temperature
• DHS FET: Headspace trapping on Tenax in the TDU liner

Main Results and Discussion

Comparative total ion chromatograms revealed that ATEX closely matched SSL performance while eliminating inlet contamination, improving system robustness. DHS FET offered cleaner baselines by reducing PG/VG background, with negligible loss of target analytes. Twister techniques provided enhanced selectivity: Headspace Twister captured volatile components, whereas Liquid Twister extracted less volatile, flavor-related compounds. Both formats improved detection of nicotine and trace flavor constituents previously masked by matrix noise.

Benefits and Practical Applications

• ATEX prevents cross-contamination, ensuring consistent data over extended runs
• DHS FET reduces matrix interference, enhancing baseline stability
• Twister extraction enables targeted profiling of volatile and semi-volatile compounds
• Automated workflows support high throughput and regulatory compliance

Future Trends and Opportunities

Emerging advances may include novel sorptive phases for broader analyte coverage, integration of high-resolution MS for improved structural characterization, and fully automated end-to-end platforms combining e-liquid and emission analysis. Data-driven optimization and miniaturized devices could further streamline routine QC in regulatory and industrial settings.

Conclusion

Selection of an appropriate sample introduction technique is critical for reliable GC-MS analysis of e-liquids. ATEX and DHS FET offer robust, low-contamination options, while Twister methods provide enhanced selectivity for volatile and nonvolatile components. These approaches support comprehensive e-liquid characterization in line with TPD requirements.

Reference

• Anatune Ltd. Technical note no. AS162, 2016. Comparison of Different Sample Introduction Techniques for the Analysis and Characterisation of e-Liquids Using GC-MS.