Two Headspace Solutions for the Analysis of Dissolved Gases in Water by Method RSKSOP-175

Importance of the Topic

Dissolved gas analysis in water is a key technique for assessing environmental quality and safety, particularly in regions impacted by subsurface hydrocarbon exploitation. Headspace equilibration based on US EPA method RSKSOP-175 provides a standardized procedure for quantifying gases such as methane, ethene, ethane, and propane in groundwater. Recent growth in shale gas recovery and concerns about groundwater contamination have driven demand for robust and automated headspace methods.

Objectives and Study Overview

The primary aim of this application note is to evaluate the performance of two automated headspace analyzers, HT3 and Versa, from Teledyne Tekmar for dissolved gas analysis in groundwater. Specific goals include assessing calibration linearity, precision, method detection limits, and comparing results between the two instruments under identical analytical conditions.

Methodology and Analytical Approach

Sample preparation followed the foundation of RSKSOP-175 by displacing 10% of the vial volume with helium to form a headspace, then equilibrating the sample via controlled shaking. Standard calibration solutions were generated by saturating chilled water with individual gases and diluting to defined concentrations in 22 mL headspace vials. Both analyzers operated with identical heat, pressurization, equilibration, and injection protocols to ensure comparability. Gas separation and detection were performed on an Agilent 6890 gas chromatograph equipped with a flame ionization detector and a Restek Rt-U-Bond column under a temperature program optimized for light hydrocarbons.

Used Instrumentation

• Teledyne Tekmar HT3 Automated Headspace Analyzer
• Teledyne Tekmar Versa Automated Headspace Analyzer
• Agilent 6890 GC with flame ionization detector
• Restek Rt-U-Bond column, 15 m x 0.53 mm ID, 20 µm film thickness

Main Results and Discussion

Both analyzers demonstrated excellent calibration linearity across the tested concentration ranges, with correlation coefficients exceeding 0.996 for all gases. Precision studies at the lowest calibration level yielded %RSD values below 6% for HT3 and below 4% for Versa. Method detection limits ranged from 0.002 mg/L for methane to 0.025 mg/L for ethene. Comparative chromatograms showed similar peak shapes and retention times, confirming that automation did not compromise analytical performance.

Benefits and Practical Applications

• High throughput analysis with reduced manual labor
• Improved reproducibility and quality control compliance
• Applicable in environmental monitoring, remediation assessment, and regulatory laboratories
• Facilitates rapid screening for dissolved light hydrocarbons in groundwater

Future Trends and Applications

Ultrafast headspace techniques, integration with mass spectrometric detection, and on-site portable automation units are emerging developments. Advanced software algorithms for dynamic headspace modeling and coupling with other detectors could further expand applicability in environmental and industrial contexts.

Conclusion

Automated headspace analysis using the HT3 and Versa systems effectively implements the principles of US EPA RSKSOP-175, delivering reliable quantification of dissolved hydrocarbons in groundwater. The combination of robust performance, ease of use, and adherence to regulatory standards positions these analyzers as valuable tools for environmental and industrial laboratories.

References

• Hudson F RSKSOP-175 Rev 2 May 2004 Sample Preparation and Calculation for Dissolved Gas Analysis in Water Samples Using GC Headspace Equilibration Technique