Improved Performance And Dynamic Range For EPA Method TO-15 using the Entech 7200 and Thermo Scientific ISQ QD GCMS

Importance of the Topic

Canister-based sampling and GC-MS analysis under EPA Method TO-15 are critical for monitoring volatile organic compounds (VOCs) in environmental and industrial settings. Achieving low part-per-billion (ppb) to part-per-trillion (ppt) detection limits while maintaining a wide dynamic range is essential for applications ranging from ambient air monitoring to vapor intrusion studies. Advances in preconcentration and sample handling directly impact data quality, laboratory throughput, and method robustness.

Objectives and Overview of the Study

This application note evaluates a new analyzer combining the Entech 7200 preconcentrator with the Thermo Scientific ISQ QD GC-MS to:

• Enhance sensitivity and lower detection limits for TO-15 target compounds
• Extend linear calibration range by 100- to 2000-fold
• Minimize water and CO₂ interference during preconcentration
• Reduce carryover and maintenance downtime

Methodology and Instrumentation

The system employs a three-stage Extended Cold Trap Dehydration process:

• Stage 1: Silonite-D treated trap cooled to –40 °C for direct water freeze-out
• Stage 2: Tenax trap at –40 °C to capture VOCs with high adsorption strength
• Stage 3: Ultra-low volume focusing trap for sharp injection peaks

Additional innovations include:

• Electronic Volume Control (EVC) for precise volumetric sampling independent of matrix changes
• Digital Rotary Valve Control to eliminate cross-sample contamination by isolating ports between operations
• Silonite-D coated transfer lines for ultra-inert sample pathways and near-100 % compound recovery

Instrumentation Used

• Entech 7200 Preconcentrator with Accu-Sample™ Technology
• Thermo Scientific ISQ QD GC-MS
• Entech 7650 Robotic Autosampler
• SUMMA or Silonite canisters for air sampling
• Dynamic dilution system for calibration standard preparation

Results and Discussion

Calibration over three orders of magnitude (0.04 to 40 ppbv) produced linear responses with most compounds showing relative standard deviations (RSDs) below 15 %, well under the 30 % requirement of TO-15. Method detection limits (MDLs) as low as 0.02 ppbv were achieved using 125 mL injections. Chromatograms for light (e.g., propene), polar (e.g., acrolein, formaldehyde) and heavy (e.g., naphthalene) VOCs exhibited sharp peak shapes, minimal tailing, and no carryover, validating the efficacy of sub-ambient trapping and inert coatings.

Benefits and Practical Applications

• Improved sensitivity and reproducibility at low sample volumes
• Extended dynamic range reduces the need for multiple dilutions
• Minimal carryover enables rapid recovery from high-concentration samples
• Automated valve control and robotics enhance throughput and sample isolation
• Suitability for ambient air, field canister, QA/QC and vapor intrusion analyses

Future Trends and Applications

Ongoing developments may include deeper sub-ambient cooling, integration with real-time data analytics, and expansion to emerging VOCs and alternative matrices (e.g., process gases). Enhanced automation, AI-driven method optimization, and further improvements in inert materials promise even higher performance for regulatory and research laboratories.

Conclusion

The combination of the Entech 7200 preconcentrator and Thermo Scientific ISQ QD GC-MS significantly surpasses EPA TO-15 requirements by delivering ultra-low detection limits, broad dynamic range, and robust performance. Innovations in cold trapping, inert flow paths, and precise sample handling translate into reliable, high-throughput analyses suitable for demanding environmental and industrial applications.

References

No specific literature references were provided in the original material.