Improved Analysis of Environmental Samples Using Soft Ionization and Novel GCxGC-HR-TOFMS

Significance of the Topic

Comprehensive and accurate chemical analysis of environmental matrices is critical for monitoring pollutants and understanding environmental processes. Two-dimensional gas chromatography coupled with high-resolution mass spectrometry (GCxGC-HR-TOFMS) enhances separation power and selectivity. Integrating novel soft ionization techniques further improves analyte identification by generating prominent molecular ions and reducing spectral complexity.

Objectives and Study Overview

This work evaluates a new multimode ion source compatible with GCxGC-HRTOFMS, capable of electron impact (EI) and positive/negative chemical ionization (CI). The study focuses on performance metrics—dynamic range, sensitivity, peak shape—and applies the method to snow samples from Moscow, prepared via EPA Method 8270 extraction.

Methodology and Instrumentation

Gas chromatographic separation employed an Agilent 7890B GC with a LECO quad-jet liquid nitrogen-cooled thermal modulator. Columns: Rxi-5SilMS (30 m × 0.25 mm × 0.25 µm) primary, Rxi-17SilMS (1 m × 0.25 mm × 0.25 µm) secondary. Temperature program: 50 °C (2 min), ramp 5 °C/min to 300 °C (8 min hold). Modulation period 5 s, helium flow 1 mL/min. Detector: LECO Pegasus® GC-HRT+ with Folded Flight Path mass analyzer, Encoded Frequent Pushing at 200 spectra/s.

Main Results and Discussion

Preliminary data demonstrate:

• Enhanced dynamic range in all three ionization modes; EI and CI peaks ~0.08 s in 2D chromatography.
• Negative CI achieved low-femtogram detection limits (e.g., OFN), with up to 200× sensitivity increase for halogenated compounds such as PCBs.
• Positive CI improved alkane ionization, enabling clear chain-length identification (C15–C35).
• Consistent retention times across EI, positive CI, and negative CI using a single chromatographic method facilitates accurate multi-mode data alignment.
• Application to Moscow snow extract revealed thousands of analytes, with the greatest peak count in negative CI mode.

Benefits and Practical Applications

The multimode source streamlines environmental workflows by providing complementary information: EI for structural fragments, positive CI for hydrocarbons, negative CI for halogenated pollutants. This versatility reduces analysis time and simplifies method development in QA/QC and research laboratories.

Future Trends and Applications

Advancements may include integration with ambient sampling, automated data processing using formula-based algorithms, and extending soft ionization to novel GC formats. Emerging applications encompass real-time monitoring of atmospheric aerosols and forensic pollutant profiling.

Conclusion

The novel Folded Flight Path multimode ion source on GCxGC-HRTOFMS delivers improved dynamic range, sensitivity, and peak capacity across EI and CI modes. Its ability to maintain consistent retention times and provide complementary ionization makes it a powerful tool for comprehensive environmental analysis.

Reference

EPA Method 8270: Liquid-Liquid Extraction