EPA TO-15 Analysis Using Hydrogen Carrier Gas and the Agilent HydroInert Source

Significance of the Topic

Ambient air monitoring of volatile organic compounds (VOCs) is critical for assessing environmental pollution, human health impacts, and regulatory compliance. Helium shortages have spurred interest in hydrogen as an alternative GC carrier gas, yet hydrogen can induce undesired reactions in conventional MS sources. Combining cryogen-free thermal desorption, advanced water management, hydrogen carrier gas, and the Agilent HydroInert source offers a robust strategy for high-humidity EPA Method TO-15 analyses.

Objectives and Overview

This study demonstrates the viability of using hydrogen carrier gas with the HydroInert EI source to analyze 65 target air toxics (from propene to naphthalene) at 100% relative humidity. Key objectives included achieving EPA TO-15 criteria for sensitivity, linearity, reproducibility, and detection limits, while reducing cycle time and eliminating cryogen use.

Methodology and Instrumentation

• Sampling: CIA Advantage-xr canister autosampler, up to 400 mL drawn from evacuated canisters.
• Water Removal: Kori-xr device to selectively remove moisture before trapping.
• Preconcentration: UNITY-xr thermal desorber with Peltier cooling and multisorbent focusing trap.
• GC/MS Setup: Agilent 8890B GC (DB-624 column, 60 m × 0.25 mm × 1.40 µm) with 2.0 mL/min hydrogen flow; Agilent 5977B MSD with HydroInert source (70 eV, 300 °C).
• Standards: 65-compound mix diluted to 10 ppbv at 100 % RH; calibration range 0.5–10 ppbv; MDLs determined at 0.1 ppbv.

Main Results and Discussion

• Chromatography: Hydrogen reduced GC cycle time by 40% (27 min vs. 45 min) while preserving excellent peak shape, notably for light VOCs at 100% RH.
• Spectral Fidelity: The HydroInert source prevented hydrogenation and dechlorination, achieving library match scores >90% versus NIST20 for all analytes.
• Linearity and Sensitivity: Mean R2 of 0.999 across 0.5–10 ppbv; MDLs ranged from 11 ppt (4-ethyltoluene) to 53 ppt (carbon disulfide), vastly below the TO-15 limit of 500 ppt.
• Reproducibility: Response factor RSDs averaged 7.5% (<30% requirement); retention time RSD 0.09% (<1% criterion); area RSD 1.22% for ten replicates at 10 ppbv.
• Real Sample Analysis: Analysis of 400 mL rural air identified and quantified seven TO-15 VOCs (e.g., acetone, toluene, chlorobenzene) at sub-ppbv levels.

Benefits and Practical Applications

• Elimination of liquid cryogen reduces operational cost and complexity via electrical trap cooling.
• Hydrogen carrier gas accelerates analysis and provides a sustainable helium alternative.
• Compatibility with existing helium-based libraries and quantitative methods ensures seamless method transfer.
• Effective water management supports reliable VOC quantitation in high-humidity ambient, industrial, and indoor air monitoring.

Future Trends and Opportunities

• Broader adoption of hydrogen with inert-source technologies for challenging matrices and high-throughput laboratories.
• Advancements in automated online sampling and real-time VOC monitoring exploiting hydrogen’s benefits.
• Expansion of spectral libraries and software adaptation for optimized hydrogen-based workflows.
• Coupling with multidimensional separations and complementary detectors to address emerging air contaminants.

Conclusion

The integration of hydrogen carrier gas with the Agilent HydroInert source and cryogen-free thermal desorption meets and exceeds EPA TO-15 performance criteria for humid air VOC analysis. This approach delivers superior sensitivity, spectral integrity, reproducibility, and faster throughput, offering a reliable, cost-effective alternative to helium-based methods for ambient air toxics monitoring.

References

• Compendium Method TO-15: Determination of Volatile Organic Compounds (VOCs) in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS), US EPA, Second Edition, 1999.
• Ambient Air Determination of Volatile Organic Compounds Tank Sampling/Gas Chromatography-Mass Spectrometry, Ministry of Ecology and Environment of the People’s Republic of China.