The Analysis of Light Hydrocarbons Using the Agilent 6820 Gas Chromatograph with "M" Deactivated Alumina PLOT Column

Significance of the Topic

Accurate measurement of light hydrocarbons in refinery gas, liquefied petroleum gas (LPG) and natural gas streams is essential for process optimization, quality control and precise market valuation. The distribution and concentration of C1–C6 components affect combustion efficiency, safety and pricing. Advanced chromatographic methods that deliver high resolution, low bleed and wide dynamic range are therefore critical for routine and research laboratories in the energy and petrochemical sectors.

Objectives and Overview

This study presents a practical configuration of the Agilent 6820 Gas Chromatograph for simultaneous analysis of C1–C6 hydrocarbons. The aims are to demonstrate baseline separation of key isomers, illustrate system versatility for different sample matrices and highlight operational simplicity by interfacing a 6-port gas sampling valve directly to a split/splitless inlet.

Methodology and Instrumentation

An Agilent 6820 GC equipped with a split/splitless capillary inlet, flame ionization detector (FID) and a 6-port gas sampling valve set at 80 °C was used. Helium served as the carrier gas at 5 mL/min. Separation employed an Agilent HP-PLOT AL2O3 "M" deactivated column (50 m × 0.53 mm). Typical operating parameters included:

• Inlet temperature: 175 °C, split ratio 30:1
• Sample loop: 0.05–0.1 mL
• Oven program: 40 °C (2 min) to 140 °C (5 min) at 4 °C/min
• FID: 300 °C, H2 at 35 mL/min, air at 350 mL/min, make-up at 26 mL/min

For broader applications, a thermal conductivity detector (TCD) channel or a 10-port backflush valve can be integrated to handle permanent gases or heavier hydrocarbons (>C8).

Main Results and Discussion

Baseline resolution of all C4 isomers and pentanes was achieved within a single 25-minute run. The FID provided a wide linear dynamic range for trace to percent-level concentrations. Chromatograms of refinery gas standards showed clear identification of 12 components, including methane through n-pentane. A more complex standard yielded baseline separation of 21 hydrocarbons and isomers, highlighting the column's deactivation performance and low bleed characteristics.

Benefits and Practical Applications

The presented configuration offers:

• High isomer separation power, especially for C4 and C5 compounds
• Low column bleed, extending column lifetime and reducing background noise
• Direct valve-to-inlet interfacing, simplifying setup and improving sample transfer accuracy
• Wide dynamic range suitable for trace impurity detection and bulk composition analysis

This approach is well suited for routine QC in refineries, LPG blending, natural gas monitoring and dedicated C4 stream analysis.

Future Trends and Opportunities

Advancements may include further optimization of column deactivation chemistries to extend analyte range, integration of multiplexed sampling valves for high-throughput screening and coupling with mass spectrometric or photoionization detectors for enhanced speciation. Real-time on-site GC systems and AI-driven data analysis platforms will broaden the applicability in remote and field environments.

Conclusion

The Agilent 6820 GC with a 6-port sampling valve and HP-PLOT AL2O3 "M" column delivers robust, high-resolution analysis of light hydrocarbons. Its simple configuration and excellent performance make it a reliable choice for petrochemical laboratories requiring fast, accurate compositional data.

References

1. Firor R. Packed Column Refinery Gas Configuration for the HP 5890 Series II Gas Chromatograph. Agilent Technologies, Publication 228-126.
2. Firor R. Capillary Gas Chromatography Systems for the Analysis of Permanent Gases and Light Hydrocarbons. Agilent Technologies, Publication 228-125.