Accurate Collection of Low Level TO-15 Compounds using Low Flow, 1 Week Time Integrated Sampling into Silonite Coated Canisters

Significance of the Topic

The accurate collection of volatile organic compounds (VOCs) at trace levels over extended sampling periods is critical for environmental monitoring, industrial hygiene, and regulatory compliance. Conventional short‐term sampling often misses low‐level or polar compounds, whereas passive tube methods fail to capture the full spectrum of TO-15 targets. Extended low‐flow sampling into inert canisters offers a comprehensive solution for multi‐day, part‐per‐trillion VOC analysis.

Objectives and Overview of the Study

This study aimed to validate the performance of Entech’s CS1200E5 low‐flow controllers and Silonite-coated canisters for collecting EPA Method TO-15 analytes at sub-ppb levels over 1–7 days. Specific goals included demonstrating consistent sampling rates below 1 cc/min, evaluating analyte recoveries across a broad compound range—including polar species—and verifying flow stability for time‐integrated sampling.

Methodology and Used Instrumentation

An Entech Model 4700 Precision Dilution System prepared a 0.5 ppb TO-15 challenge mixture in a 15 L Silonite cylinder. A custom manifold delivered the standard at 10 cc/min to five CS1200E5 samplers (three Silonite‐coated, two uncoated) each connected to 1.4 L or 6 L Silonite canisters. The samplers and manifold were pre-cleaned in an Entech 3100D Canister Cleaning System. Flow controllers were calibrated by timing the pressure drop from 20" to 10" Hg to set 0.8 cc/min for 24 h or 0.5 cc/min for 1 week sampling. Samples were analyzed with an Entech 7200 Preconcentrator coupled to an Agilent 6890/5973 GC-MS under full‐scan conditions.

Main Results and Discussion

• Short-term (24 h) sampling of the TO-15 mix into 1.4 L canisters at 0.8 cc/min achieved recoveries within ±10% for nearly all 60+ compounds, meeting EPA Method TO-15 accuracy.
• One-week sampling into 6 L canisters at 0.5 cc/min produced final pressures of 2–2.5” Hg across five samplers, confirming stable flow control and true time integration.
• Recoveries remained within ±20%, with minor positive bias for acetone attributable to background levels and significantly lower acetone blanks observed in Silonite-coated compared to uncoated controllers.
• The inert Silonite coating on stainless steel surfaces minimized adsorption of halogenated and polar VOCs, improving recoveries and precision over uncoated samplers.

Benefits and Practical Applications

• Enables comprehensive VOC profiling—including polar and low‐boiling species—over multi‐day deployments, reducing the number of samples required for long-term monitoring.
• Low-flow, extended sampling yields sufficient sample volume for ppt‐level detection while maintaining high precision and accuracy.
• Simplifies field operation with tool-free quick-connect valves, robust flow control, and inert internal surfaces.

Future Trends and Potential Applications

Advances in surface passivation and flow controller design may extend unattended sampling to two weeks or longer, facilitating continuous ambient air monitoring for health risk assessment. Integration with remote telemetry, automated canister retrieval, and real-time GC-MS interfaces could further enhance site surveillance in industrial, urban, and indoor air quality studies.

Conclusion

The modified CS1200E5 flow controller paired with Silonite-coated canisters reliably meets EPA Method TO-15 requirements for 1-week trace VOC sampling. The system delivers stable low‐flow operation, high analyte recoveries across a broad compound set, and reduced background for critical polar species, providing a robust platform for comprehensive extended‐duration air monitoring.

Reference

Cardin D, Robinson T, Casteel C, Markle D. Accurate Collection of Low Level TO-15 Compounds using Low Flow, 1 Week Time Integrated Sampling into Silonite Coated Canisters. Entech Instruments Application Note A-3736-05, 2014.