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

Significance of the Topic

Liquid chromatography–gas chromatography coupling combines the cleanup, fractionation and preconcentration capabilities of LC with the high separation efficiency and sensitivity of GC. This integrated approach is essential for reliable analysis of complex lipid matrices such as cholesteryl fatty acid esters, minimizing sample loss and contamination while improving throughput and reproducibility.

Study Objectives and Overview

This technical overview presents the online integration of an Agilent 1260 Infinity LC with an Agilent 7890A GC via an Agilent 1200 Series 2-position/6-port switching valve and the solvent vent mode of a multimode inlet. The primary goal was to assess system performance by comparing GC traces of a cholesteryl fatty acid ester mixture acquired through LC-GC coupling against a conventional split injection GC analysis.

Methodology and Instrumentation

• LC Conditions: 2 µL injection of n-hexane/tert-butyl methyl ether (96:4 v/v) at 0.200 mL/min on a 250 mm × 2 mm id, 5 µm Eurospher-100Si column; UV detection at 205 nm.
• Transfer Interface: Agilent 1200 Series 2-position/6-port valve with 200 µL loop; carrier gas line routed to a multimode inlet with pressure control via PCM-C module.
• GC Conditions: Solvent vent mode at 50 °C with 1000 mL/min vent flow at 4 psi until 0.5 min, then purge to split vent at 2.5 mL/min; inlet heated to 350 °C at 900 °C/min; Restek Rtx-200MS column (30 m × 250 µm, 0.1 µm df); oven program from 40 °C (2 min) to 310 °C then 340 °C; FID at 360 °C.

Instrumentation Used

• Agilent 1260 Infinity LC system
• Agilent 1200 Series 2-position/6-port switching valve
• Agilent 7890A GC with multimode inlet (MMI)
• Flame ionization detector
• PCM-C pressure control module

Main Results and Discussion

The online LC-GC setup produced chromatograms of cholesteryl esters (C12–C22) closely matching those from a standalone GC with split injection. Optimization of solvent vent and purge flows was critical: excessive flows reduced sensitivity, while insufficient flows led to incomplete solvent removal. The Agilent 5183-4647 liner delivered the best reproducibility and sensitivity compared to alternative liners tested.

Benefits and Practical Applications of the Method

• Automated sample cleanup and fractionation in a closed system
• Reduced solvent effects and minimal manual handling
• High reproducibility and sensitivity for complex lipid analyses
• Suitable for routine determination of steryl esters in fats, oils and functional foods

Future Trends and Potential Applications

The approach can be extended to other complex lipid classes and biogenic compounds. Integration with mass spectrometry and advanced detectors, further automation and application in quality control and lipidomics represent promising future directions.

Conclusion

Online coupling of an Agilent 1260 Infinity LC and 7890A GC via a multimode inlet in solvent vent mode is a robust and sensitive method for cholesteryl fatty acid ester analysis, effectively combining LC fractionation with GC separation efficiency.

Reference

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