Innovative Cryogen-Free Ambient Air Monitoring in Compliance with US EPA Method TO-15

Significance of the Topic

Monitoring of volatile organic compounds (VOCs) in ambient air is critical for assessing human health risks, environmental impacts and compliance with regulatory standards. Traditional cryogen-cooled preconcentration systems face limitations in cost, logistics and water management at high humidity. A cryogen-free, autosampler-based approach offers the potential for robust, reliable analysis across a wide volatility range without the drawbacks of liquid cryogen.

Study Objectives and Overview

This application study demonstrates compliance with US EPA Method TO-15 for the analysis of 65 target air toxics in humidified canister samples (50 – 100 % relative humidity) using a fully automated, cryogen-free thermal desorption GC/MS system. The goals are to evaluate chromatographic performance, method detection limits, linearity and reproducibility under varied humidity conditions and to illustrate real-world sample analysis.

Methodology and Instrumentation

The analytical workflow integrates three key components:

• CIA Advantage canister autosampler: automated introduction of up to 27 pre-evacuated canisters via a 0.5 mL loop or mass flow controller.
• Kori-xr water condenser: Peltier-cooled trap at –30 °C for selective removal of moisture without affecting VOC trapping.
• UNITY-xr thermal desorber: electrically cooled focusing trap combining porous polymer, graphitized carbon and molecular sieve sorbents for comprehensive VOC retention and rapid backflush desorption.

Desorbed analytes are separated on a 60 m DB-624 column and detected with a quadrupole MS in scan or SIM mode. Standard method parameters (sample volumes up to 400 mL, helium carrier gas, temperature programming and post-sampling purges) were applied.

Key Results and Discussion

The system delivered consistent chromatographic peak shapes for all 65 compounds at 50 – 100 % RH. Method detection limits ranged from 4 pptv (dichlorotetrafluoroethane, tetrahydrofuran, 1 1 1-trichloroethane, 1 2 4-trichlorobenzene) to 95 pptv (propene), with 83 % of targets below 20 pptv. Linear responses (R2 > 0.998) were observed over 0.1 – 25 ppbv, with relative standard deviations below 10 % for most analytes. Real rural air analysis (250 mL) detected ethanol, acetone, carbon disulfide and toluene at sub-ppbv levels.

Benefits and Practical Applications

The cryogen-free configuration offers:

• Elimination of liquid nitrogen or dry ice supply and hazards.
• Automated, high-throughput analysis of varied humidity samples.
• Enhanced instrument uptime and reduced flow-path blockages from ice formation.
• Broad volatility coverage from light VVOCs to semi-volatiles.

This approach suits regulatory monitoring, industrial emissions testing and emergency response sampling.

Future Trends and Opportunities

Advancements may include integration with on-line sampling networks, coupling to high-resolution mass spectrometry for non-target screening, miniaturized portable units for field deployment and expanded multisorbent trap chemistries for emerging contaminants. Further automation of sample re-collection and data processing will drive rapid decision-making in air quality assessment.

Conclusion

The cryogen-free autosampler–Kori-xr–UNITY-xr system meets and exceeds US EPA TO-15 performance criteria for humid air canister analysis, achieving low pptv detection limits, robust linearity and reproducible results across a full range of VOC targets. This methodology simplifies operations, reduces costs and enhances reliability for ambient air toxics monitoring.

References

• US EPA Compendium Method TO-15 Determination of Volatile Organic Compounds in Ambient Air by GC/MS Second Edition 1999
• Markes International Technical Note UNITY-xr and Kori-xr Cryogen-Free Thermal Desorption Systems 2017
• US EPA Guidance on Canister Cleaning and Storage for TO-15 Analysis 1999
• US EPA Procedure for MDL Determination 40 CFR 136 Appendix B