Alternative Methods to RSK 175 Using Purge and Trap Concentration and Automated Headspace for the Analysis of Dissolved Gases in Drinking Water

Importance of the Topic

Rapid and accurate measurement of dissolved hydrocarbons in drinking water is critical to assess environmental impacts of hydraulic fracturing. Reliable detection of methane and related gases ensures water safety and regulatory compliance.

Objectives and Study Overview

This study compares alternative approaches to the conventional RSK 175 method by evaluating purge and trap concentration versus automated headspace GC/FID techniques for quantifying methane, ethane, ethene, and propane in water samples. Calibration linearity, detection limits, precision, and carryover are assessed to determine method performance.

Methodology and Instrumentation

The analysis utilized two automated systems:

• Purge and Trap: Stratum Purge and Trap Concentrator paired with AQUATek 100 Autosampler, employing a proprietary trap and recirculating chiller at <10°C, with 5 mL purge volume.
• Headspace: Teledyne Tekmar HT3 and Versa analyzers using 10 mL sample vials and loop sampling under fixed temperature and pressure conditions.

Chromatographic separation was achieved on a Restek Rt-U-BOND 15 m × 0.53 mm × 20 μm column with a 35→190°C oven program. Detection was performed by FID at 190°C with constant makeup flow.

Main Results and Discussion

• Both methods displayed excellent linearity (r2 > 0.995) across ppb to ppm ranges for all analytes.
• Purge and Trap achieved MDLs of 0.4 ppb for methane and 18–31 ppb for C2–C3 gases, with carryover below 0.04%.
• Headspace MDLs ranged from 2 ppb to 25 ppb, with precision (%RSD) within 2–11%.
• Overlay chromatograms confirmed comparable responses between HT3 and Versa systems.

Benefits and Practical Applications of the Method

• Full automation reduces manual handling and potential error, enhancing sample throughput.
• Purge and trap allows direct liquid analysis without additional sample preparation.
• Automated headspace offers consistent equilibration and solvent-free analysis.
• Both approaches align with RSK 175 and BOL6019 protocols, facilitating implementation in environmental laboratories.

Future Trends and Applications

• Development of multi-analyte platforms for comprehensive water quality monitoring.
• Portable field-deployable instruments for on-site gas detection.
• Method extension to emerging contaminants from fracking fluids.
• Integration with digital analytics and remote reporting for real-time compliance.

Conclusion

Purge and trap and automated headspace GC/FID methods offer robust, sensitive, and precise measurement of dissolved C1–C3 gases in water. Automation significantly improves laboratory efficiency while meeting regulatory standards, supporting effective environmental monitoring amid expanding fracking activities.

References

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2. Pennsylvania Department of Environmental Protection. C1 to C3 Dissolved Gases via Headspace and GC/FID, Revision 5, 2011.
3. Energy Information Administration. Annual Energy Outlook 2009.
4. Tip of the Mitt Watershed Council. Natural Gas Drilling and Water.
5. Ohio Department of Natural Resources. The Facts about Hydraulic Fracturing.
6. United States Environmental Protection Agency. Hydraulic Fracturing.
7. Energy Information Administration. Review of Emerging Resources: U.S. Shale Gas and Shale Oil Plays.