Determination of Hydrocarbon Composition in Liquefied Petroleum Gas Using the Agilent GC Gasifier and the Agilent 990 Micro GC

Significance of the topic

Precise determination of hydrocarbon composition in liquefied petroleum gas (LPG) is vital for quality control, commercial trading, and regulatory compliance. Variations during sampling and vaporization can lead to component discrimination and poor repeatability, affecting downstream processes and customer specifications.

Objectives and study overview

This work demonstrates a rapid, reliable approach for analyzing C2–C8 hydrocarbons in LPG using the Agilent GC gasifier coupled to the Agilent 990 Micro GC. The goal is to minimize condensation and discrimination effects, achieve high precision and accuracy, and comply with industry standards.

Methodology and instrumentation

The method employs:

• An Agilent G3535A GC gasifier with heated, deactivated flow path and pressure-reducing regulator to instantly vaporize high-pressure liquid samples.
• An Agilent 990 Micro GC system fitted with an 8 m J&W CP-Sil 5 CB backflush column, helium carrier gas, and automated injection at 110 °C.
• Operating parameters: gasifier at 150 °C, transfer line at 100 °C, sample inlet pressure up to 1,000 psi, output fixed at ~12 psi, injection time 40 ms.

Main results and discussion

Repeatability and precision:

• Fifty consecutive runs of calibration standard achieved area relative standard deviations (RSD) <1% and retention time RSD <0.2% across C2–C8.
• Carryover evaluated via alternating blank runs yielded <0.4% residual signal for heavier components.
• Calibration against n-butane internal standard delivered relative response factors with experimental concentrations deviating <10% from nominal values.

Accuracy and compliance:

• Quantitative results for LPG standard 2 matched nominal concentrations within ±10%.
• Two-run repeatability met SH/T 0230-2019 and ASTM D2163-14 criteria for all components (r < difference between runs).

The total analysis time per C2–C6 sample is under two minutes, offering high throughput for industrial labs.

Benefits and practical use of the method

Key advantages:

• Simultaneous vaporization of all analytes avoids fractionation.
• Heated, inert flow path prevents condensation and adsorption.
• High precision and accuracy suitable for QA/QC and trade compliance.
• Fast cycle times enhance laboratory productivity.

Future trends and possibilities

Advancements may include integration with online sampling systems for real-time monitoring, further miniaturization of micro GC modules, automated data processing with AI-based interpretation, and expanded analyte panels for trace impurities.

Conclusion

The Agilent GC gasifier coupled to the 990 Micro GC provides a robust, fast, and precise solution for LPG hydrocarbon analysis. Its performance meets industry standards, ensuring reliable composition results for commercial and regulatory applications.

References

1. SH/T 0230-2019. Determination of composition in liquefied petroleum gases by gas chromatography.
2. ASTM D2163-14. Standard test method for determination of hydrocarbons in liquefied petroleum gases and propane/propene mixtures by gas chromatography.