Rapid Determination of TO-15 Volatile Organic Compounds (VOCs) in Air

Significance of the Topic

The rapid and reliable analysis of volatile organic compounds (VOCs) in air is critical for environmental monitoring, regulatory compliance, and public health protection. EPA Method TO-15 provides performance-based guidelines for whole-air canister sampling and GC-MS analysis of 65 target VOCs. Improving sample throughput and maintaining method compliance are key drivers for analytical laboratories.

Study Objectives and Overview

This study assessed the performance of Nutech’s 8900DS preconcentrator combined with an Agilent 6890 GC and 5973 MS detector using a Restek Rxi-5Sil MS column (30 m × 0.32 mm × 1.00 µm). Five EPA TO-15 criteria were evaluated: canister blank levels, calibration precision, method detection limits, replicate precision, and audit accuracy. The goal was to determine if a shorter 30 m column could meet TO-15 requirements while reducing analysis time compared to standard 60 m columns.

Methodology and Instrumentation

• Canister Preparation: Six SilcoCan® canisters cleaned via automated TO-Clean cycles (three evacuations to 500 mTorr at 100 °C followed by humidified nitrogen pressurization) to achieve blank VOC levels < 0.2 ppbv.
• Preconcentration: 400 mL whole‐air samples spiked with 100 mL TO-14A internal standard mix, focused through three cryogenically cooled traps (glass beads, Tenax®, proprietary trap) in the Nutech 8900DS.
• Chromatography: Rxi-5Sil MS column temperature program from 32 °C to 230 °C, helium carrier at 1.5 mL/min, 16.5 min run time.
• Detection: Agilent 5973 MS in full scan (35–250 amu) and SIM modes, tune type BFB, electron ionization at 69.9 eV.
• Calibration and Validation: Five-point calibration (1.0–10.0 ppbv), MDLs determined per 40 CFR 136 Appendix B, replicate precision via dual-canister and seven-replicate tests, audit accuracy from 10 ppbv standard.

Results and Discussion

• Canister Blanks: All target VOCs < 0.2 ppbv (ethanol at 160 pptv), meeting TO-15 blank criteria.
• Calibration Precision: Average RSD of relative response factors was 9.31% (method requirement < 30% with ≤2 exceptions).
• Detection Limits: Average scan MDL of 0.06 ppbv and SIM MDL of 35.9 pptv, below TO-15 limit of 0.5 ppbv.
• Precision: Average replicate difference of 4.29% and seven-replicate RSD of 6.86%, exceeding the requirement of ±25%.
• Accuracy: Mean audit accuracy of –2.82% for 65 VOCs, within the ±30% tolerance.
• Column Performance: The 30 m column provided comparable separation of 65 VOCs in 16.5 min, with narrower peaks and increased sensitivity. Total throughput including preconcentration and GC cycle was ~22 min, doubling sample capacity versus 60 m columns.

Benefits and Practical Applications of the Method

• Increased throughput reduces per-sample cost and instrument idle time.
• Shorter GC run times enhance laboratory productivity for routine environmental monitoring.
• Performance-based flexibility allows adaptation of stationary phases for challenging VOC mixtures.

Future Trends and Applications

Advances in column chemistries (e.g., Rtx-VMS) and faster preconcentration modules will further improve separation of polar or coeluting analytes. Integration with automated calibration verification and remote monitoring can streamline QA/QC. Emerging ambient air sensors and AI-driven data analysis may complement GC-MS for high-frequency VOC surveillance.

Conclusion

The Nutech 8900DS preconcentrator, coupled with an Agilent 6890/5973 GC-MS and a 30 m Rxi-5Sil MS column, meets all EPA TO-15 performance criteria while reducing analysis time from ~30 min to ~16.5 min per run. Enhanced sample throughput and maintained analytical integrity make this approach advantageous for environmental laboratories.

References

• U.S. Environmental Protection Agency. Compendium Method TO-15, Determination of Volatile Organic Compounds in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry; 1999.