Dissolved Gas Determination Using the D-19 ASTM Method

Importance of Topic

The rise in hydraulic fracturing has elevated concerns about dissolved gas contamination in water sources. Reliable analysis of gases such as methane, ethane, ethylene, and propane is critical for environmental monitoring and public health.

Objectives and Study Overview

This study evaluates the formal ASTM D-19 method for dissolved gas analysis, addressing variability in the common RSK-175 procedure by standardizing the calibration within an aqueous matrix. It also demonstrates the integration of an automated headspace sampling system to enhance consistency and remove manual Henry's constant calculations.

Methodology and Instrumentation

The procedure replicates standard headspace sampling with automated calibration preparing saturated gas solutions at 20°C followed by serial dilutions. Key steps include sample equilibration and headspace analysis, with calibration curves generated directly from aqueous standards.

Instrumental Setup

• Autosampler: EST Analytical LGX50 with 1 mL headspace loop, 60°C sample temperature, 10 min equilibration.
• Gas Chromatograph: Agilent 7890 GC with Restek RT Q-bond column (30 m×0.53 mm, 20 µm), 45°C initial hold, ramp to 180°C.
• Detector: Flame Ionization Detector at 250°C.

Main Results and Discussion

• Calibration linearity: R² ≥0.997 across 0.006–11.6 ppm ranges.
• Method Detection Limits (MDLs): 1.08–2.68 µg/L for the four gases.
• Precision and Accuracy: Mid-point recoveries >89% with %RSD <8%.
• Surrogate performance: Average recovery 100% with 5.7% RSD over 20 blanks.

Benefits and Practical Applications

Automating headspace sampling enhances sample integrity by avoiding manual handling, ensures reproducible surrogate additions, and simplifies analysis by eliminating Henry's constant calculations. This method supports environmental labs in consistent monitoring of water contamination.

Future Trends and Opportunities

Further development may include on-site field deployable units, expanded analyte lists, real-time data integration, and coupling with advanced detectors or portable GC systems for rapid decision-making.

Conclusion

The ASTM D-19 method, combined with the LGX50 autosampler, delivers precise and accurate dissolved gas measurements. The approach meets formal method requirements and streamlines laboratory workflows.