US EPA Method TO-17 for Monitoring Air Toxics in Ambient Air Using Sorbent Tubes and Automated, Cryogen-free Thermal Desorption

Importance of the Topic

Ambient air monitoring of volatile organic compounds classified as air toxics or hazardous air pollutants is essential for regulatory compliance, public health protection and source attribution. US EPA Method TO-17 prescribes active sampling onto sorbent tubes followed by thermal desorption–gas chromatography/mass spectrometry analysis.

Study Objectives and Overview

This application note evaluates a cryogen-free, automated thermal desorption system (Markes International Series 2 ULTRA-UNITY) coupled to GC/MS for TO-17 compliant determination of 62 volatile compounds ranging from methyl chloride to hexachloro-1,3-butadiene. Key aims include optimization of sorbent combinations, assessment of detection limits, linearity, reproducibility, carryover and real-air performance.

Used Instrumentation

• Markes Series 2 ULTRA-UNITY TD with Tenax, Carbopack X and Carboxen 1003 focusing trap
• Agilent GC/MS with J&W DB-624 column (60 m×0.32 mm, 1.8 µm)
• Air Toxic Analyzer and Universal stainless steel sorbent tubes
• Valco six-port valve and 1 mL standard gas loop for sample introduction

Methodology

One-liter air samples were drawn at 50 mL/min onto optimized sorbent tubes. Primary desorption at 320 °C transferred analytes onto a focusing trap held at 25 °C. Rapid trap heating (40 °C/s to 320 °C) delivered concentrated vapor to the GC column. The GC run used helium carrier gas under constant pressure, ramping from 35 °C to 230 °C. MS detection in full scan (35–300 amu) was used, with SIM mode available for enhanced sensitivity.

Results and Discussion

• All 62 target compounds were recovered quantitatively with detection limits below 0.1 ppb for a 1 L sample in both splitless and 10:1 split modes.
• Linearity was excellent (R2≥0.99) over 1–10 ppb for representative analytes such as Freon 113, chloroform and hexachloro-1,3-butadiene.
• Reproducibility tests showed relative standard deviations under 6% across a range of volatilities and polarities.
• Carryover remained below 0.5% after 10 ppb injections, ensuring reliable blank conditions.
• SecureTD recollection enabled repeat injections without significant loss, supporting method validation.
• Real-air sampling in office, laboratory and semirural environments identified common VOCs including alcohols, aldehydes, terpenes and aromatics.

Benefits and Practical Applications

This automated, cryogen-free TD-GC/MS platform offers high sensitivity, minimal carryover, full automation and the flexibility to reanalyze samples. It meets TO-17 compliance and is suited for regulatory monitoring, industrial hygiene assessments, environmental research and quality-control laboratories.

Future Trends and Possibilities

Advances may include enhanced sensitivity via SIM or high-resolution MS, expanded sorbent chemistries for ultra-volatiles, integration with real-time data analytics and portable TD units for field deployments. Coupling with advanced MS could further enable speciation of emerging air pollutants and complex mixtures.

Conclusion

The Markes Series 2 ULTRA-UNITY TD–GC/MS system demonstrates robust performance for US EPA Method TO-17 air toxics determination. The method achieves sub-ppb detection, excellent linearity, strong reproducibility, low carryover and the ability to perform repeat analyses, making it a powerful tool for ambient air quality monitoring.

References

1. E Hunter Daughtrey K D Oliver J R Adams K G Kronmiller W A Lonneman W A McClenny A comparison of sampling and analysis methods for low-ppbC levels of volatile organic compounds in ambient air J Environ Monit 2001 3 166-174