A Fully Automated and Robust LC-CGC Combination for Application in Environmental Analysis

Importance of the Topic

Liquid chromatography–capillary gas chromatography (LC–CGC) coupling delivers a powerful solution for separating and analyzing complex environmental samples. Automated hyphenation of LC and GC enhances sensitivity, selectivity, and throughput while reducing manual sample handling and potential contamination.

Objectives and Study Overview

This work aims to present a fully automated, robust interface for on-line LC–CGC coupling, leveraging a flow cell and large-volume programmable temperature vaporisation (PTV) injector. The system integrates control of both chromatographs on a single PC and is demonstrated through the analysis of phenylurea pesticides in tobacco leaf extracts.

Methodology and Instrumentation

The configuration combines an HP 1100 LC with an HP 6890 GC, both controlled via ChemStation software. Key components:

• A T-shaped flow cell with septumless head placed at the LC detector outlet.
• A Gerstel Multipurpose Sampler for heartcut fraction collection (up to 2 mL) synchronized to LC flow.
• A PTV injector operated in solvent-venting mode to transfer collected fractions into a capillary GC column.
• Detection options: FID, MS (HP 5973 MSD in full scan and selected ion monitoring), ECD, NPD, or FPD.

Main Results and Discussion

Analysis of standard mixtures and environmental samples demonstrated:

• Effective transfer of LC fractions with RSDs around 2 % for dibenzothiophene markers.
• Size exclusion LC separated phenylurea pesticides eluting between 8.2–9.2 min.
• Monolinuron and metobromuron detected at retention times of 16.16 min and 17.24 min using MS ion m/z 61.
• Sensitivity achieved down to ~1 ppb with RSDs below 10 %, well below regulatory limits.

Benefits and Practical Applications

• Full automation reduces manual steps: only extraction, filtration, concentration and direct LC–CGC analysis.
• Improved compound identification through combined LC and GC selectivities.
• Applicability to various LC modes (normal phase, reversed phase, size exclusion) and diverse analyte classes.
• Single-PC control streamlines data acquisition and processing.

Future Trends and Opportunities

• Extension to additional pollutant classes, metabolites, and complex matrices.
• Integration with high-resolution MS and automated library matching for comprehensive screening.
• Development of multidimensional chromatography workflows (LC×GC×GC).
• Adoption in environmental monitoring, food safety, pharmaceutical QA/QC, and metabolomics.
• Miniaturization and microfluidic implementations for high-throughput labs.

Conclusion

The described LC–CGC interface offers a versatile, robust platform for automated heartcutting and large-volume injection. It enhances analytical performance in environmental applications, delivering high sensitivity, reproducibility, and streamlined workflows.

References

• P. Sandra, F. David, A. Kot and E. Sippola, Int. Environm. Tech., 4(2), 1994.
• R.E. Majors, J. Chromatogr. Sci., 18, 571, 1980.
• I.L. Davies et al., Anal. Chem., 60, 683, 1988.
• M.-L. Riekkola, J. Chromatogr., 473, 315, 1989.
• F. Munari and K. Grob, J. Chromatogr. Sci., 28, 61, 1990.
• H.J. Cortes, Multidimensional Chromatography, Marcel Dekker, 1990.
• K. Grob, On-Line Coupled LC-GC, Hüthig Verlag, 1990.
• F. David et al., Labor Praxis, 21-5, 1997.
• F. Berthou, Y. Dreano and P. Sandra, J. High Resolut. Chromatogr., 7, 679, 1984.
• F. David et al., presented at the 20th Int. Symp. on Capillary Chromatography, 1998.