Monitoring VOCs in Ambient Air: A New EPA Method and a Complete Solution

Importance of the Topic

Monitoring volatile organic compounds in ambient air is critical for assessing air quality, meeting regulatory standards, and protecting public health. Traditional canister sampling can be expensive, cumbersome, and prone to moisture interference. The development of an efficient sorbent tube and thermal desorption approach offers a practical alternative for environmental monitoring programs.

Objectives and Overview

This summary covers the US EPA Method TO-17, which describes active sampling of VOCs onto multisorbent tubes followed by thermal desorption and gas chromatography analysis. The goal is to present a complete workflow from sample collection through data generation, highlighting the method design, quality control measures, and instrument configuration.

Methodology and Instrumentation

A dual-tube sampling manifold collects air simultaneously onto two sorbent tubes at a 1:4 flow ratio for integrity checks. Key features include:

• Sorbent tubes packed with multisorbent beds (e g Tenax GR with Carbopack B or Carbopack C with Carboxen 1000) to trap a broad range of VOCs with minimal moisture effects
• Flow rates between 10 and 200 mL/min yielding nominal volumes of 1 and 4 liters per tube
• Two-stage thermal desorption units offering preconcentration, dry purge, and analyte refocusing prior to gas chromatography
• Gas chromatograph fitted with a 60 m VOCOL capillary column (0 25 mm ID, 1 5 µm film) coupled to FID or mass spectrometry detection

Main Results and Discussion

Breakthrough volume experiments demonstrated that over thirty EPA TO-14 target analytes exhibited volumes in excess of 5 liters at 25 °C and 65% relative humidity on the selected tube configurations. Chromatographic performance on the VOCOL column provided baseline separation of chlorinated ethenes, aromatic compounds, and light hydrocarbons within a 50-minute run. Dual-tube sampling confirmed consistency of analyte capture and alerted to potential sample loss under variable conditions.

Benefits and Practical Applications

The TO-17 workflow delivers several advantages:

• Cost-effective and portable sampling compared to large canisters
• Enhanced analyte coverage from light gases to semi-volatiles via multisorbent beds
• Integrated quality control through paired-tube collection
• Reduced moisture interference during humid sampling
• Compatibility with existing thermal desorption and GC systems for routine air monitoring

Future Trends and Opportunities

Emerging developments may include field-deployable thermal desorbers, expanded sorbent chemistries for polar compounds, real-time coupling of desorption with mass spectrometry, and automation of sampling schedules. Integration with data analytics and remote monitoring networks will enhance responsiveness to environmental events.

Conclusion

EPA Method TO-17 provides a robust, streamlined approach for VOC monitoring in ambient air. The combination of multisorbent tubes, controlled thermal desorption, and established GC separations ensures reliable data generation. This solution supports regulatory compliance and research applications by delivering high sensitivity, broad analyte range, and built-in quality assurance.

References

US EPA Method TO-17, Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling onto Sorbent Tubes, Office of Research and Development, EPA Cincinnati OH 1999
Supelco Reporter Volume 16, No. 2, 1997