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

Význam tématu

Hydraulic fracturing has become widespread for natural gas extraction, raising concerns about methane and light hydrocarbon contamination in drinking water. Fast, accurate quantification of dissolved gases is critical for environmental monitoring and ensuring water safety.

Cíle a přehled studie

This study assesses two alternative approaches to the EPA’s RSK 175 method for analyzing dissolved methane, ethane, ethene, and propane in water: a purge-and-trap concentrator and automated headspace sampling. Calibration performance, detection limits, carryover, and system comparability are evaluated.

Použitá metodika a instrumentace

The purge-and-trap method used a Stratum PTC with an AQUATek 100 autosampler and proprietary trap, interfaced to a GC/FID (Restek Rt-U-BOND column). A chiller bath maintained samples below 10 °C and a 5 mL purge volume was applied. Headspace analysis employed Teledyne Tekmar HT3 and Versa instruments with loop sampling on 10 mL volumes, also coupled to GC/FID. Key parameters included oven temperature programs, carrier and makeup gas flows, and timed purge and desorb cycles.

Hlavní výsledky a diskuse

Both methods achieved strong linearity (r2 ≥ 0.9958) over wide concentration ranges from ppb to ppm levels. Purge-and-trap detection limits spanned 0.4 ppb for methane to 31 ppb for ethene; headspace MDLs ranged from 2 ppb to 25 ppb. Percent relative standard deviations were generally below 15%, and carryover was under 0.04% for all analytes. Chromatograms showed consistent retention and response between headspace systems and purge-and-trap.

Přínosy a praktické využití metody

• Complete automation improves sample throughput and reproducibility.
• Elimination of manual handling reduces human error and contamination risk.
• Compatibility with existing GC/FID setups facilitates adoption in environmental laboratories.

Budoucí trendy a možnosti využití

Future work may extend these automated methods to additional dissolved gases, refine low-level detection, and integrate on-site sampling for real-time monitoring. Standardization across regulatory bodies will enhance data comparability and support expanded environmental surveillance.

Závěr

The proposed purge-and-trap and automated headspace techniques meet or exceed RSK 175 and BOL6019 performance criteria for dissolved gas analysis in water. Their automation, robust detection limits, and minimal carryover make them efficient, reliable tools for monitoring the environmental impact of hydraulic fracturing.

Reference

1. Don H. Kampbell and Steve A. Vandegrift. Analysis of Dissolved Methane Ethane and Ethylene in Ground Water by a Standard Gas Chromatographic Technique. Journal of Chromatographic Science, Vol. 36, pp. 253-256, May 1998.
2. Pennsylvania Department of Environmental Protection. C1 to C3 Dissolved Gases via Headspace and GC/FID. Revision 5, February 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: US Shale Gas and Shale Oil Plays.