Hot Spring Gas Analysis for Earthquake Surveillance Using the Agilent 990 Micro GC

Significance of the Topic

The composition of gases emitted from hot springs is linked to subsurface geochemical changes preceding earthquakes. Monitoring trace constituents such as helium, neon, hydrogen and hydrogen sulfide within a carbon dioxide–rich matrix provides valuable indicators for seismic surveillance.

Objectives and Study Overview

This study evaluates the Agilent 990 Micro GC for rapid and precise analysis of hot spring gas. Key objectives include:

• Quantification of permanent gases and hydrogen sulfide in a CO₂-dominated sample matrix.
• Achievement of high retention time and peak area repeatability for low-ppm analytes.
• Optimization of chromatographic conditions to support real-time earthquake monitoring.

Methodology and Instrumentation

The analytical setup comprised two channels on the Agilent 990 Micro GC:

• Channel 1: Agilent J&W CP-Molsieve 5Å (3 m precolumn + 20 m analytical column) with argon carrier gas and backflush to remove CO₂.
• Channel 2: Agilent J&W PoraPLOT U (10 m straight column) with helium carrier gas for methane, CO₂ and H₂S separation.

The following parameters were applied:

• Injector and column temperatures set between 50 °C and 60 °C.
• Injection times of 150 ms for trace permanent gases and 100 ms for H₂S to optimize sensitivity.
• Backflush time of ~31 s to prevent CO₂ carryover and maintain column efficiency.

Results and Discussion

The system demonstrated excellent analytical performance:

• Retention time RSDs below 0.05% across ten replicate injections.
• Peak area RSDs under 5% for helium, neon, hydrogen and hydrogen sulfide.
• Detection limits ranging from 0.17 ppm (methane) to 13.8 ppm (nitrogen).
• Clear chromatographic resolution of six permanent gases on channel 1 and three species (CH₄, CO₂, H₂S) on channel 2.

Backflush optimization was critical to preserve baseline stability in the CO₂ matrix and ensure reproducible separations.

Benefits and Practical Applications

The rapid (sub-7 min) and reliable analysis enables:

• On-site or near-field monitoring of spring gas composition as a seismic proxy.
• Early detection of geochemical shifts that may precede seismic events.
• High-throughput screening in remote locations with minimal sample preparation.

Future Trends and Potential Applications

Emerging developments may include:

• Integration with automated sampling systems and real-time data networks for continuous surveillance.
• Adaptation to other volcanic and tectonic gas monitoring scenarios.
• Coupling with mass spectrometric or isotopic detectors for expanded geochemical insights.

Conclusion

The Agilent 990 Micro GC offers a field-deployable, high-precision platform for hot spring gas analysis, delivering fast turnaround, low detection limits and robust repeatability. This capability enhances geochemical surveillance and supports earthquake early warning strategies.

Reference

1. Zhang J. Biogas Analyzer Based on the Agilent 990 Micro GC. Agilent Technologies Application Note 5994-1376EN, 2019.
2. Padrón E. et al. Continuous Monitoring of Diffuse H₂ Degassing at the Summit Cone of Teide Volcano, Tenerife. Geophysical Research Abstracts 20, EGU2018-19250-2, 2018.