A Single-Method Approach for the Analysis of Volatile and Semivolatile Organic Compounds in Air Using Thermal Desorption Coupled with GC–MS

Significance of the Topic

Monitoring both volatile organic compounds (VOCs) and semivolatile organic compounds (SVOCs) in ambient air is critical for assessing human health risks, understanding emission sources, and ensuring compliance with environmental regulations. Historically, separate EPA methods (TO-15 for VOCs and TO-13A for SVOCs) were required, increasing sample complexity, cost, and laboratory workload. A unified approach can streamline sampling, reduce environmental impact, and improve analytical efficiency.

Study Objectives and Overview

This study evaluates a single-tube, thermal desorption (TD) method based on EPA TO-17 for simultaneous analysis of VOCs (C4–C12) and SVOCs (C12–C40) in air. The goals were:

• Develop a multi-layer sorbent TD tube capable of trapping analytes from C4 to C40.
• Validate method performance: breakthrough volume, linearity, detection limits, precision, recovery, and carryover.
• Compare field results at a former manufactured gas plant site using combined TO-15/TO-13A vs. single TO-17.

Methodology and Instrumentation

Sampling and desorption:

• A proprietary TD tube (XRO-40 Extended Range Organics) with sequential weak, strong, and strongest charcoal sorbents was used to collect 45 L of ambient air at ~10 mL/min.
• Dry purge (2 min) removed residual moisture; no cryogens required.
• Two-stage thermal desorption (380 °C primary tube, then 5 °C to 380 °C trap) concentrates analytes before GC injection.

Separation and detection:

• TurboMatrix 650 ATD system automates TD onto a Clarus 680 GC equipped with a high-temperature column, interfaced to a Clarus SQ8 mass spectrometer (electron ionization, scan 35–300 amu).

Main Results and Discussion

Breakthrough and loading tests:

• No detectable breakthrough for 16 VOCs and 16 PAHs after 10 L humidified air challenge.
• Tube loading up to 205 mg total analyte without breakthrough confirms capacity far above expected field loads.

Calibration, detection limits, and precision:

• Linearity established over 0.2–50 ng for all compounds; R² > 0.995 (most > 0.999).
• Detection limits (45 L sample) ranged from 0.0044 to 0.011 µg/m³ for VOCs and 0.0044 to 0.0092 µg/m³ for SVOCs, outperforming TO-15 and comparable to TO-13A.
• Repeatability RSD < 6% for all analytes (n = 6), well within EPA TO-17 criteria (≤ 30%).

Recovery and carryover:

• Full desorption observed; no target analytes detected in blank or reinjection sequences, indicating negligible carryover.

Field evaluation at a former manufactured gas plant:

• Four sampling events at three perimeter sites compared TO-17 vs. TO-15 (VOCs) and TO-13A (SVOCs).
• TO-17 results closely matched or slightly exceeded combined methods, demonstrating practical equivalence.
• Hydrophobic sorbents allowed consistent sampling without filter pre-treatment; filtered vs. unfiltered tubes showed no bias.

Benefits and Practical Applications

• Single-tube TO-17 approach reduces sampling complexity, shipping costs, and laboratory preparation time (no solvent extraction or canister cleaning).
• Lower detection limits achieved by larger sample volumes and efficient desorption.
• Safer operation (no high-voltage canister evacuation or solvent handling), more environmentally friendly (no organic solvents).
• Applicable to fence-line monitoring, remediation sites, industrial emission assessment, and regulatory compliance.

Future Trends and Opportunities

• Expansion to additional emerging contaminants expected to be added to EPA lists; performance-based flexibility of TO-17 will accommodate new targets.
• Integration with portable or on-site TD–GC–MS systems for real-time air monitoring.
• Advanced sorbent materials and multi-dimensional GC techniques to enhance resolution and selectivity.
• Machine learning–based data analysis workflows to accelerate interpretation and QA/QC.

Conclusion

The study demonstrates that a single TD–GC–MS method based on EPA TO-17 can reliably quantify both VOCs and SVOCs in ambient air, with performance equal to or better than the dual-method TO-15/TO-13A approach. By simplifying sampling, reducing costs, and improving safety and environmental impact, this unified method offers a robust solution for air quality laboratories and field applications.

Reference

1. U.S. EPA Method TO-15. Determination of Volatile Organic Compounds in Air Collected in Specially Prepared Canisters and Analyzed by GC/MS. 1999.
2. U.S. EPA Method TO-17. Determination of VOCs in Ambient Air Using Active Sampling on Sorbent Tubes. 1999.
3. U.S. EPA Method TO-13A. Determination of PAHs in Ambient Air by GC/MS. 1999.
4. Provost, R.L.; Marotta, L.D. Single Tube Sampling and Analysis of Volatile and Semi-Volatile Organics in Air — The Cost Effective Green Solution. 2014.