Analysis of US EPA TO-15 for Ambient Air Monitoring Using Cryogen- Free Thermal Desorption and Gas Chromatography Coupled to a Single Quadrupole Mass Spectrometer (GC/MSD)

Significance of the Topic

Monitoring volatile organic compounds (VOCs) in ambient air is critical to evaluate their environmental and health impacts and to comply with air quality regulations. US EPA Method TO-15 provides a standardized canister-based approach for trace-level analysis of air toxics, but it requires efficient preconcentration and water management to achieve low detection limits in humid conditions.

Objectives and Study Overview

This study assesses a cryogen-free thermal desorption and GC/MS system for US EPA TO-15 compliance, analyzing 65 target compounds (propene to naphthalene) in humidified canister samples at 50%, 75%, and 100% relative humidity (RH).

Methodology and Instrumentation

The workflow includes canister sampling, autosampler-based withdrawal (up to 400 mL), and storage up to 20 days. A Kori-xr device removes water vapor from the sample stream, followed by UNITY-xr thermal desorption. Separation is performed on an Agilent 7890B/8890 GC with a DB-624 column, and detection uses an Agilent 5977B single quadrupole MS in SCAN or SIM mode.

Key Results and Discussion

Chromatographic performance was consistent across humidity levels. Calibration linearities ranged from R2 = 0.9987 to 1.000 (0.22–25 ppbv). Method detection limits (MDLs) ranged from 4 to 95 pptv (mean 14 pptv), well below the ≤ 0.5 ppbv requirement. Relative response factor RSDs were below 30% as per TO-15 criteria. No analyte breakthrough was observed for the most volatile compounds. Real rural air sampling detected ethanol, acetone, carbon disulfide, and toluene at quantifiable levels.

Practical Benefits and Applications

• Cryogen-free operation simplifies maintenance and reduces costs.
• Efficient water removal preserves column and detector life.
• High sensitivity and reproducibility support routine ambient air monitoring, industrial emissions testing, and landfill gas analysis.

Future Trends and Potential Applications

• Integration with high-resolution mass spectrometry for enhanced identification.
• Development of portable, field-deployable TD-GC/MS systems.
• Expansion of target compound libraries and coupling with real-time monitoring.
• Implementation of automated data processing and AI-driven analytics.

Conclusion

The cryogen-free TD-GC/MS approach meets US EPA TO-15 requirements across a broad humidity range, delivering low pptv detection limits, excellent linearity, and robust, maintenance-friendly operation for ambient air toxic analysis.

References

1. US EPA. Compendium Method TO-15: Determination of Volatile Organic Compounds (VOCs) in Air Collected in Specially Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry. Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air, Second Edition, US Environmental Protection Agency, 1999.
2. US EPA. Definition and Procedure for the Determination of the Method Detection Limit, Revision 2. US Environmental Protection Agency, October 2009.