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

Significance of the Topic

Monitoring volatile organic compounds (VOCs) in ambient air is essential for assessing environmental quality and compliance with regulatory standards. The established EPA TO-15 method relies on helium carrier gas and cryogenic preconcentration, but global helium shortages have spurred adoption of hydrogen as an alternative. Efficient removal of humidity and preservation of mass spectral fidelity are critical for reliable quantitation at trace levels.

Study Objectives and Overview

This study evaluates a cryogen-free thermal desorption and GC/MS workflow using hydrogen carrier gas and the Agilent HydroInert source to analyze 65 target compounds ranging from propene to naphthalene at 100% relative humidity. The goal is to demonstrate method performance in accordance with EPA TO-15 criteria, including detection limits, linearity, and reproducibility, while addressing challenges posed by high humidity and alternative carrier gases.

Methodology

A 6 L canister was cleaned, evacuated, and filled with a 65-component VOC standard diluted to 0.5–10 ppbv at 100% RH. Samples (up to 400 mL) passed through a Kori-xr water removal module and were trapped on a UNITY-xr TD system before desorption into an Agilent 8890 GC with a DB-624 column. Hydrogen was used at a constant flow of 2 mL/min. The Agilent 5977B MSD equipped with a HydroInert source (electron ionization, 70 eV) scanned m/z 30–300. Linearity, method detection limits (MDLs), and reproducibility were assessed, and a real air sample was analyzed under the same conditions.

Instrumentation

• Canister autosampler: Markes CIA Advantage-xr
• Water removal: Markes Kori-xr
• Thermal desorber: Markes UNITY-xr
• Gas chromatograph: Agilent 8890
• Column: Agilent J&W DB-624 (60 m × 0.25 mm, 1.4 μm)
• Mass spectrometer: Agilent 5977B MSD with HydroInert EI source

Results and Discussion

Hydrogen carrier gas reduced the GC cycle time by 40% without altering elution order, improving sample throughput. Water removal at 100% RH preserved peak shapes across light and heavy VOCs. Library match scores exceeded 90% for all compounds, confirming spectral fidelity. Linearity (0.5–10 ppbv) was excellent (mean R2 ≈ 0.999), and MDLs ranged from 11 to 53 pptv, well below the 0.5 ppbv requirement. Reproducibility tests showed retention time RSD of 0.09% and peak area RSDs under 2% at 10 ppbv. Analysis of real air detected seven VOCs at quantifiable levels.

Benefits and Practical Applications

• Eliminates dependence on helium and liquid cryogen
• Maintains established spectral libraries and quantitative methods
• Supports robust operation under high humidity without source reactions
• Increases throughput through faster chromatographic cycles

Future Trends and Potential Applications

Expanding hydrogen-based GC/MS workflows to broader VOC panels and higher humidity levels will benefit ambient air and industrial monitoring. Advances in automated, portable thermal desorption systems and integration with high-resolution mass spectrometry could enable real-time field measurements and enhanced source apportionment in environmental studies.

Conclusion

The combination of cryogen-free preconcentration, hydrogen carrier gas, and the Agilent HydroInert source delivers EPA TO-15 compliant performance in humid air matrices. This approach offers reliable VOC detection at the low pptv level, improved throughput, and resilience to helium supply constraints.

References

• US EPA. Compendium Method TO-15: Determination of Volatile Organic Compounds in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry. Second Edition. US EPA, 1999.
• Ministry of Ecology and Environment of the People’s Republic of China. Ambient Air Determination of Volatile Organic Compounds by Tank Sampling and Gas Chromatography/Mass Spectrometry. MEE, 2015.