Natural Gas Analysis Using the Agilent 990 Micro GC Equipped with COX and 5CB Channels

Importance of Natural Gas Analysis

Natural gas is a widely used energy source whose commercial value and safety depend on accurate determination of its calorific value and composition. With evolving regulations and the emergence of hydrogen-enriched gas blends, reliable on-line monitoring of permanent gases and hydrocarbons from C1 to C8 is essential for industry, utilities, and quality control laboratories.

Objectives and Study Overview

This application note evaluates a cost-effective, two-channel configuration of the Agilent 990 Micro GC for rapid simultaneous analysis of H₂, O₂/N₂, CO, CO₂ and C1–C8 hydrocarbons within a single five-minute run. Key performance metrics include repeatability of component quantification and gross heating value (HV), as well as estimated detection limits.

Methodology and Instrumentation

The system employs two parallel columns: a 1 m COX module operated in backflush mode to separate permanent gases, and an 8 m 5CB column in straight configuration for C2–C8 alkanes. Argon serves as carrier gas on the COX channel, helium on the 5CB channel. Injection conditions include a 40 ms sample loop and column temperatures of 65 °C (COX) and 75 °C (5CB). Standard calibration gases spanning hydrogen, permanent gases and light to heavy hydrocarbons were used to assess chromatographic resolution, repeatability, and detection limits.

Key Results and Discussion

Chromatograms demonstrate baseline separation of H₂, O₂/N₂, CO, CO₂ and CH₄ within 1.2 minutes on the COX channel, and C2–C8 alkanes resolved on the 5CB column in under 1.5 minutes for C6 and under five minutes for C7–C8. Ten replicate injections of a simulated gas blend yielded retention time RSDs below 0.02% (CO₂ < 0.5%) and peak area RSDs under 0.5% (CO₂ < 1%). Calculated gross heating value repeatability was 0.021% RSD. Estimated lower detection limits are <200 ppm for permanent gases (H₂: 20 ppm) and ≤1 ppm for C2–C8 hydrocarbons.

Benefits and Practical Applications

The two-channel Agilent 990 Micro GC configuration offers:

• Rapid total analysis time under five minutes
• High repeatability for routine quality control (HV RSD < 0.025%)
• Low carrier gas consumption and minimal power requirements
• Compact footprint suitable for online or field deployment

This approach enables cost-efficient monitoring of natural gas pipelines, blending stations, and hydrogen enrichment processes.

Future Trends and Potential Applications

Advances may include integration with real-time data analytics and remote telemetry for predictive maintenance, expansion to trace impurity detection (H₂S, COS), and coupling with preconcentration modules to lower detection limits further. Portable, battery-powered Micro GC units will support decentralized energy infrastructure and hydrogen economy applications.

Conclusion

The presented two-channel Agilent 990 Micro GC configuration delivers reliable, rapid, and cost-effective natural gas analysis. By combining COX backflush and 5CB separation modules, it achieves simultaneous quantification of permanent gases and C1–C8 hydrocarbons with excellent repeatability and low detection limits, meeting current market benchmarks for heating value accuracy.

References

• Permanent Gases on a COX Module Using an Agilent 490 Micro GC. Agilent Technologies application note, 5990-7054EN, 2012.
• Hydrogen Detection with a TCD using Mixed Carrier Gas on the Agilent Micro GC. Agilent Technologies application note, 5991-3199EN, 2013.
• Fast Analysis of Natural Gas using the Agilent 990 Micro GC Natural Gas Analyzer. Agilent Technologies application note, 5994-1040EN, 2019.
• Biogas Analyzer Based on the Agilent 990 Micro GC. Agilent Technologies application note, 5994-1376EN, 2019.