Determination of Hydrocarbon and Oxygenate Composition in Liquefied Petroleum Using the Agilent GC Gasifier and Agilent 8890 GC

Importance of the Topic

Liquefied petroleum gas (LPG) is widely used in industrial and domestic applications. Accurate measurement of its hydrocarbon and oxygenate content is essential for safety, quality control, and compliance with standards. Traditional LPG sampling often suffers from condensation, component discrimination, and adsorption losses, leading to poor repeatability and accuracy.

Objectives and Overview

This study evaluates the performance of the Agilent GC gasifier coupled to an Agilent 8890 GC for simultaneous determination of hydrocarbons and oxygenate impurities in LPG. It aims to address common sampling challenges by ensuring uniform vaporization, preventing condensation, and minimizing adsorption.

Methodology

An Agilent GC gasifier with a pressure-reducing regulator flash-vaporizes high-pressure LPG at the orifice, ensuring all components vaporize together. Heated and insulated components, plus deactivated flow-path tubing, prevent condensation and adsorption of polar oxygenates. The gasifier connects directly to the 8890 GC back inlet. Two gas sampling valves (0.25 mL loops at 150 °C), a split/splitless inlet, two flame ionization detectors (FIDs), and an oven program (90 °C to 168 °C at 6 °C/min) enable separation of C3–C5 hydrocarbons and common oxygenates (methanol, acetone, dimethyl ether, MTBE). Data acquisition was performed at 5–20 Hz with OpenLab 2.4 software.

Instrumentation Used

• Agilent 8890 GC
• Agilent GC gasifier with heated regulator and transfer line
• Two 6-port gas sampling valves (0.25 mL loops)
• Agilent HP-AL/M column (30 m × 0.53 mm, 15 µm)
• Agilent Lowox column (10 m × 0.53 mm, 10 µm)
• Agilent PLOT Al2O3 “M” column (30 m × 0.53 mm)
• Split/splitless inlet with deactivated liner
• Dual FIDs (H2, air, N2 makeup gases)
• OpenLab 2.4 software

Main Results and Discussion

Hydrocarbon analysis showed area repeatability (RSD) under 1% for C3–C5 components. Relative response factors (to n-butane) were determined with RSD <0.5%. Oxygenate calibration across typical concentration ranges yielded linearity coefficients (R²) better than 0.999. Ten-point repeatability tests (n=10) for dimethyl ether, MTBE, methanol, and acetone demonstrated area RSDs below 1%. Quantitative precision and accuracy met SH/T 0230-2019 standard criteria, with measured concentrations within 85–115% of certified values.

Benefits and Practical Applications

• Flash vaporization prevents component discrimination and condensation.
• Deactivated tubing eliminates adsorption losses of polar analytes.
• Compact design minimizes cold spots by placing the gasifier adjacent to the GC inlet.
• High repeatability and accuracy support routine QC in petrochemical and gas production facilities.

Future Trends and Applications

Advances may include integration with mass spectrometry for enhanced selectivity, automation for real-time online monitoring, miniaturized sampling modules for field analysis, and adaptation to other pressurized gas matrices such as synthetic natural gas or biogas.

Conclusion

The Agilent GC gasifier combined with the 8890 GC delivers reliable simultaneous analysis of hydrocarbons and oxygenates in LPG. Excellent repeatability, linearity, and compliance with industry standards demonstrate its suitability for precise, routine gas quality control.

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 LPG gases and propane/propene mixtures by gas chromatography.”