Two dimensional chromatography: LC-GC online coupling of an Agilent 1260 Infinity LC and an Agilent 7890A GC

Importance of the Topic

Coupling liquid chromatography (LC) and gas chromatography (GC) online streamlines the analysis of complex mixtures by uniting LC’s sample cleanup and fractionation capabilities with GC’s high resolution and selective detection. This integrated approach reduces manual intervention, minimizes sample loss and contamination, and delivers faster, more reliable results, making it essential for fields such as food analysis, lipidomics, and quality control.

Objectives and Study Overview

This study demonstrates an automated online interface between an Agilent 1260 Infinity LC and an Agilent 7890A GC using an Agilent 1200 Series 2-position/6-port switching valve. The system employs the multimode inlet (MMI) in solvent vent mode for efficient solvent removal, and evaluates performance using a standard mixture of cholesteryl fatty acid esters.

Used Methodology and Instrumentation

Methodology:

• LC Conditions: 2 µL injection, n-hexane/tert-butyl methyl ether (96:4, v/v), Eurospher-100Si column (250 mm×2 mm, 5 µm), 0.200 mL/min, 205 nm detection.
• GC Transfer: 200 µL loop on 2-position/6-port valve; pressure-controlled gas line via PCM-C module.
• MMI Settings: Solvent vent mode, initial 50 °C, vent flow 1000 mL/min at 4 psi, purge flow 2.5 mL/min, rapid ramp to 350 °C (900 °C/min).
• GC Conditions: Restek Rtx-200MS column (30 m×250 µm, 0.1 µm), H₂ carrier, multistep temperature and pressure program, FID at 360 °C.

Instrumentation:

• Agilent 1260 Infinity LC
• Agilent 1200 Series 2-position/6-port switching valve with 200 µL loop
• PCM-C pressure control module
• Agilent 7890A GC with Multimode Inlet (PTV)
• Restek Rtx-200MS capillary column
• Flame ionization detector (FID)

Main Results and Discussion

Optimized vent and purge flows ensured complete removal of up to 200 µL organic solvent without sample loss. Chromatograms of cholesteryl esters obtained via online LC-GC closely matched those from direct GC injection, confirming negligible band broadening or degradation. Precise control of transfer timing and inlet parameters proved critical: slight deviations altered sensitivity and peak shape. Among tested liners, the Agilent 5183-4647 delivered the best reproducibility and analyte response.

Benefits and Practical Applications

The online LC-GC system offers:

• Automated sample cleanup and fractionation in a closed setup
• Reduced solvent consumption and analysis time
• Enhanced repeatability and sensitivity
• Applicability to complex matrices such as vegetable oils, margarines, and functional foods for steryl ester profiling

Future Trends and Applications

Advances are expected in coupling LC-GC with mass spectrometry for comprehensive lipidomics, development of greener solvent systems, and integration into high-throughput platforms for real-time process monitoring. Emerging interfaces may further enhance sensitivity and broaden analyte scope across food science, pharmaceuticals, and environmental analysis.

Conclusion

The described online coupling of Agilent 1260 Infinity LC and 7890A GC via a solvent vent MMI interface provides a robust, high-throughput solution for analyzing cholesteryl fatty acid esters. Its demonstrated performance suggests wide potential for routine and research applications requiring precise fractionation and high-resolution separation.

References

• Grob K., Lanfranchi M., Mariani C., “Evaluation of olive oils through the fatty alcohols, the sterols and their esters by coupled LC-GC,” J Am Oil Chem Soc, 1990, 67(10):626–634.
• Kamm W., Dionisi F., Fay L.B., Hischenhuber C., Schmarr H.G., Engel K.H., “Analysis of steryl esters in cocoa butter by on-line liquid chromatography-gas chromatography,” J Chromatogr A, 2001, 918(2):341–349.
• Miller A., Frenzel T., Schmarr H.G., Engel K.H., “Coupled liquid chromatography-gas chromatography for the rapid analysis of γ-oryzanol in rice lipids,” J Chromatogr A, 2003, 985(1–2):403–410.
• Dugo P., Dugo G., Mondello L., “On-line coupled LC-GC: theory and applications,” LC-GC Eur, 2003, 16(12a):35–43.
• Hyoetylaeinen T., Riekkola M.L., “On-line coupled liquid chromatography-gas chromatography,” J Chromatogr A, 2003, 1000(1–2):357–384.
• Hyoetylaeinen T., Riekkola M.L., “Perspectives of on-line coupled liquid chromatography-gas chromatography,” Anal Bioanal Chem, 2004, 378(8):1936–1938.