Soil Gas Analysis: The Solution for Extending the Hydrocarbon Range of TO-17

Significance of the Topic

Soil gas analysis is critical for assessing volatile and semi-volatile hydrocarbon contamination in subsurface environments and for preventing toxic vapors from migrating into occupied structures. Accurate soil vapor measurements support regulatory compliance, protect human health, and guide remediation strategies at contaminated sites.

Objectives and Study Overview

This work describes the design of a novel thermal desorption sorbent tube for soil gas sampling under EPA Method TO-17. The main objectives were:

• Extend analyte range beyond naphthalene into diesel-range hydrocarbons
• Retain highly volatile compounds such as vinyl chloride during sampling
• Avoid sorbent-induced artifacts that could cause false positives
• Enable rapid tube cleanup and reuse to reduce operational costs
• Maintain effective water management using hydrophobic adsorbents
• Support increased sampling volumes to meet stringent detection limits

Methodology

Soil gas samples and standards were collected on PerkinElmer SVI sorbent tubes and analyzed using a TurboMatrix 650 thermal desorber interfaced to a Clarus 690 GC and Clarus SQ 8 MS. The protocol included automated leak and impedance checks, surrogate or internal standard spiking, and a dry purge to remove moisture. An electronic Peltier-cooled concentrator trap (10 °C) with hydrophobic packing focused analytes prior to rapid thermal desorption into the GC column. Split, splitless, and re-collection injection modes provided analytical flexibility.

Instrumentation Used

• PerkinElmer TurboMatrix 650 Thermal Desorber
• PerkinElmer Clarus 690 Gas Chromatograph
• PerkinElmer Clarus SQ 8 Mass Spectrometer
• High temperature volatile-capable GC column
• Peltier-cooled low-dead-volume trap

Main Results and Discussion

Breakthrough testing with 10 L of humidified nitrogen showed minimal loss, with dichlorodifluoromethane at 1 % breakthrough and no detectable breakthrough for vinyl chloride, meeting EPA criteria. Recovery studies demonstrated >99 % recovery for most PAHs and diesel-range compounds (pyrene recovery improved from 90 % at 325 °C to 99 % at 360 °C). Dynamic range spanned four orders of magnitude (0.05 to 250 μg/m3) with linearity coefficients (R2) above 0.999 for all analyte classes. Instrument precision at 0.5 ng on column yielded relative standard deviations below 8 %, and signal-to-noise ratios exceeded 500:1 at reporting limits of 0.05 μg/m3. Automated water management effectively reduced moisture to background levels, preserving chromatographic performance.

Benefits and Practical Applications

• Compact sorbent tubes simplify field logistics and reduce shipping costs
• Thermal desorption regenerates tubes, enabling immediate reuse
• Automated moisture removal prevents analyte quenching and maintains sensitivity
• Integrated spiking and system checks ensure data quality and traceability
• Flexible injection and re-collection options support trace-level analysis and legal sample preservation

Future Trends and Potential Applications

Anticipated developments include on-site real-time soil gas monitoring platforms, expanded sorbent materials for emerging contaminants, integration with advanced data analytics and machine learning for source apportionment, and deployment of compact automated samplers for remote or distributed networks.

Conclusion

The PerkinElmer SVI thermal desorption tubes used in conjunction with EPA Method TO-17 offer a robust, cost-effective approach to soil gas analysis. They provide extended hydrocarbon coverage, high analyte recoveries, low detection limits, efficient water management, and streamlined workflows that meet or exceed regulatory requirements.