Using Hydrogen as Carrier Gas for GC/MS Analysis: GCxGC-HR-TOFMS with Multi-Mode Ion Source

Significance of the Topic

Global helium shortages and rising costs motivate exploration of hydrogen as an alternative carrier gas for gas chromatography–mass spectrometry (GC/MS). Hydrogen offers higher diffusivity, faster separations, reduced operating costs, and a reactive environment that may benefit certain analyses, but it can also alter ionization behaviour and spectral appearance.

Objectives and Study Overview

This study benchmarks the performance of comprehensive two-dimensional gas chromatography coupled to high-resolution time-of-flight mass spectrometry with a Multi-Mode Ion Source (GCxGC-HR-TOFMS with MMS) using hydrogen vs helium carrier gas. Key aims include:

• Assess electron ionization (EI), positive chemical ionization (PCI), and electron capture negative ionization (ECNI) modes with H2 and He
• Compare library matching scores, peak shapes, and background signals
• Demonstrate non-target screening capability on an SVOC MegaMix standard

Methodology

Two LECO Pegasus GC-HRT+ 4D instruments coupled to Agilent 7890B GCs with QuadJet™ thermal modulators were employed. Columns used were Rxi-5ms (30 m × 0.25 mm × 0.25 µm) and Rxi-17SilMS (1.4 m × 0.25 mm × 0.25 µm). Carrier gas flow rates were set to 1.0 mL/min for He and 1.2 mL/min for H2 (> 99.99999% purity). A 76-component EPA Method 8270 MegaMix and a 6-component internal standard mix were analyzed under:

• Ionization: EI at 250 °C; PCI/ECNI with CH4 reagent gas
• Mass range: EI 10–1000 m/z, PCI 50–1000 m/z, ECNI 30–1000 m/z
• Resolution ≥ 25,000; mass accuracy ≤ 1 ppm; acquisition rates 12 spectra/s (1D) and 200 spectra/s (2D)

Applied Instrumentation

• LECO Pegasus GC-HRT+ 4D mass spectrometer
• Agilent 7890B gas chromatograph with QuadJet™ modulator
• Rxi-5ms and Rxi-17SilMS columns
• COSMOS MF.H2 hydrogen generator

Main Results and Discussion

Electron ionization with H2 largely maintained high spectral library match scores, with only minor deviations for some compounds. Positive chemical ionization produced consistent [M + H]+ and alkyl adduct patterns under both carrier gases. ECNI mode generated expected negative ion fragments. Comprehensive 2D separations delivered high peak capacity and minimal tailing. Representative analytes including phenol, 2-nitrophenol, and diethyl phthalate exhibited comparable retention times, signal intensities, and matching scores across both gases.

Benefits and Practical Applications

• Helium-free operation reduces dependency on scarce resources and operational costs
• Faster separations due to higher diffusivity of hydrogen
• Flexible ionization modes enhance identification confidence in non-target screening
• High resolution and mass accuracy support trace-level analysis in environmental, industrial, and QA/QC laboratories

Future Trends and Potential Applications

Further work will extend evaluation to complex real-world matrices and broaden non-target analysis workflows. Expanding spectral libraries with hydrogen-specific templates and optimizing chemical ionization conditions will enhance identification reliability. Integration with advanced data processing and artificial intelligence can accelerate high-throughput screening.

Conclusion

This evaluation demonstrates that hydrogen is a viable alternative carrier gas for GCxGC-HR-TOFMS with a Multi-Mode Ion Source, offering comparable spectral quality, robust separation, and multi-ionization flexibility. Continued optimization and library development will solidify hydrogen’s role in future GC/MS applications.

References

1 Mazur DM, et al. GC-HRMS with Complementary Ionization Techniques for Target and Non-target Screening for Chemical Exposure: Expanding the Insights of the Air Pollution Markers in Moscow Snow. Science of Total Environment. 2021;761:144506.