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

Importance of the Topic

Accurate and representative sampling of high-pressure volatile hydrocarbons is essential in petrochemical quality control, gas processing, and environmental monitoring. A dedicated injection device reduces sample loss, ensures consistent peak shape, and enhances analytical reliability.

Objectives and Study Overview

This white paper presents the design, installation, and performance evaluation of a high-pressure liquid injection (HPLI) accessory for Agilent 7890A and 6890 gas chromatographs. The goal is to enable precise quantitation of light petroleum fractions from methane to C40 under pressures up to 3000 psig, while maintaining ease of operation and compatibility with existing GC inlets.

Methodology

The HPLI employs a deactivated removable needle interfaced to a four-port Valco liquid rotary valve mounted directly above a split/splitless inlet. Sample loading and injection are controlled via an auxiliary EPC or PCM module, delivering 50–200 mL/min of carrier gas to optimize peak shape. Rotor volume is 0.06 µL. Pressurized liquid samples are introduced without needle withdrawal, minimizing pressure drop and dead volume.

Instrumentation

• Gas chromatograph: Agilent 7890A or 6890 series
• Injection device: High-pressure liquid injector (HPLI) with Valco 4-port valve and inert needle
• Flow control: Agilent Aux EPC (G3470A/G1570A) or PCM (G3471A/G2317A)
• Detector: Flame ionization detector at 250 °C (350 °C for C5–C40)
• Carrier gas: Helium; FID gases: H2 (35 mL/min), Air (400 mL/min)
• Accessories: Inline filter, restrictor valve PN 101-0355

Main Results and Discussion

Chromatograms for pressurized propylene and 1,3-butadiene studies demonstrated clear resolution of C1–C6 hydrocarbons and olefins. Peak identification under ASTM D6159 conditions showed excellent repeatability with relative standard deviations below 1%. Automated injection provided consistent performance and reduced discrimination across analytes.

Benefits and Practical Applications

• Enhanced inertness and low analyte discrimination up to C16
• Rapid installation (<10 minutes) and seamless integration with existing GC inlets
• Improved quantitation of polar and nonpolar hydrocarbons
• Ideal for trace impurity analysis in liquefied gas standards and process streams

Future Trends and Opportunities

Integration of the HPLI with automated sampling systems and on-line process monitoring promises greater throughput and data quality. Coupling with mass spectrometry or advanced detectors could expand capabilities to complex matrices and trace-level compliance testing. Ongoing miniaturization and remote control will further enhance field deployment and real-time analysis.

Conclusion

The Agilent HPLI accessory offers a robust, high-precision solution for sampling pressurized liquid hydrocarbons. Its innovative design, ease of use, and compatibility with standard GC inlets deliver reliable, repeatable analyses essential for modern analytical laboratories.