High-Pressure Liquid Injection Device for the Agilent 7890A and 6890 Series Gas Chromatographs

Significance of the topic

The analysis of highly volatile, pressurized hydrocarbon samples such as liquefied natural gas and light olefins presents significant challenges in gas chromatography due to phase changes, analyte discrimination and potential carryover. A robust injection approach that maintains sample integrity and accuracy across a wide boiling range is essential for reliable quantitative results in petrochemical and environmental laboratories.

Study objectives and overview

The primary objective was to design and evaluate a high-pressure liquid injection (HPLI) device compatible with the Agilent 7890A and 6890 series gas chromatographs. The study aimed to demonstrate representative sampling of pressurized hydrocarbon matrices, minimize analyte discrimination, achieve excellent repeatability and extend quantitative analysis from C1 to C40 compounds.

Instrumentation used

• Agilent 7890A gas chromatograph equipped with split/splitless inlet
• 4-port high-pressure rotary valve (0.06 µL loop)
• Siltek deactivated removable needle interface
• Auxiliary EPC (electronic pneumatic control) module or pneumatic control module (PCM)
• Restrictor metering valve and particle filter for sample line protection
• Flame ionization detector (FID) with hydrogen and air flows

Methodology

The HPLI device is mounted directly above the GC inlet and operates via pneumatic actuation. Sample loading occurs at port S under pressures up to 5,000 psig, followed by a brief (2–3 s) inject cycle into the heated split/splitless inlet. Auxiliary helium flow (50–200 mL/min) ensures proper vaporization and improves peak shape. A wide range of pressurized samples were evaluated: liquefied natural gas, ethylene, propylene, propane/n-butane blends, 1,3-butadiene, glycols and nC5-nC40 boiling point standards diluted in carbon disulfide.

Results and discussion

• Repeatability: RSD values typically below 1% for quantitative analyses of volatile hydrocarbons.
• Carryover: less than 0.01% for heavy components (nC10+), demonstrating minimal sample memory effects.
• Limit of detection: impurity detection limits for ethylene (0.27–1.61 ppm) were nearly ten-fold lower than ASTM D6159.
• Quantitative accuracy: propane/n-butane blends showed deviations within 1% of certified values; response factors stable across C5–C18.
• Wide boiling range: successful analysis of C5–C40 hydrocarbons with negligible discrimination and consistent peak widths.

Benefits and practical applications

• Enables representative sampling of pressurized and condensable hydrocarbon streams.
• Improves quantitative accuracy and precision in petrochemical quality control, LNG characterization and olefin impurity analysis.
• Reduces maintenance by minimizing carryover and needle fouling.
• Compatible with existing GC systems for streamlined integration into analytical workflows.

Future trends and possibilities

Anticipated developments include extending the approach to unstable condensate matrices, integrating automated high-pressure sampling with advanced autosamplers, exploring coupling with mass spectrometry for trace analysis, and applying data analytics for real-time process monitoring in petrochemical plants.

Conclusion

The novel HPLI device effectively combines a deactivated needle interface and high-pressure rotary valve to provide accurate, reproducible injections of volatile hydrocarbon samples up to C40 at pressures of 1,200–5,000 psig. Its simple installation, ease of operation and superior analytical performance make it a valuable tool for laboratories performing challenging gas chromatographic analyses.

References

• C. J. Cowper and A. J. DeRose, The Analysis of Gases by Chromatography, Pergamon Press, 1983.
• K. J. Rygle, G. P. Feulmer, R. F. Scheideman, J. Chromatogr. Sci. 22 (1984) 514–519.
• J. Luong, R. Gras, R. Tymko, J. Chromatogr. Sci. 41 (2003) 550–555.