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

Significance of the Topic

Environmental monitoring increasingly relies on sensitive, reliable analytical techniques to detect trace contaminants. Coupling liquid chromatography (LC) with capillary gas chromatography (CGC) enhances selectivity and resolution for complex mixtures. A fully automated on‐line LC‐CGC system reduces manual sample handling, minimizes errors, and accelerates high‐throughput screening in environmental analysis.

Objectives and Study Overview

This study presents the development and evaluation of a robust, fully automated interface for on‐line LC‐CGC coupling. The goals were to integrate standard LC and GC hardware via a flow cell and large‐volume sampler (LVS) with programmed temperature vaporization (PTV) injection, to demonstrate seamless operation under single‐PC control, and to validate performance through the analysis of phenylurea pesticides in tobacco leaf extracts.

Methodology and Instrumentation

The system comprises:

• LC: Hewlett‐Packard 1100 series with quaternary pump, degasser, autosampler, column thermostat, and UV/diode‐array detector.
• GC: Hewlett‐Packard 6890 equipped with a PTV injector (solvent‐venting mode) and FID or MS (HP 5973 MSD) detector.
• Interface: Gerstel large‐volume sampler modified as a flow cell with septumless head, synchronized syringe and LC flow via dedicated controller and software.

Heart‐cuts are defined by LC retention times and capillary dimensions. At target window, the syringe draws up to 2 mL of LC eluate; solvent is vented at low PTV temperature and split flow. Subsequent splitless transfer at elevated temperature injects analytes into the capillary GC column (30 m×0.25 mm i.d., 0.25 μm HP-5MS).

Main Results and Discussion

System performance was validated with:

• Dibenzothiophene markers from crude oil fractions (normal phase LC on aminopropyl silica): six‐run RSDs ≈2% on peak area.
• Phenylurea pesticides in tobacco leaves: size-exclusion LC (30 cm×7.5 mm i.d., 5 μm, acetone–cyclohexane 2:1, 1 mL/min, UV at 245 nm). Heart‐cut fraction (8.2–9.2 min) transferred to CGC–MS.

The total ion chromatogram remains complex but extracted‐ion monitoring at m/z 61 enables clear detection of monolinuron and metobromuron at 16.16 min and 17.24 min. Library matching confirmed identities. Limits of detection reached ≈1 ppb with RSDs <10%, well below regulatory maxima.

Benefits and Practical Applications

The on‐line LC‐CGC system:

• Eliminates extensive off‐line clean‐up (e.g., florisil, silica columns).
• Reduces solvent consumption and manual labor.
• Offers high reproducibility and sensitivity for trace analysis.
• Provides flexible fraction transfer (normal phase, reversed phase, size exclusion).

This workflow is well suited for environmental laboratories, quality control, and research requiring robust multidimensional separations.

Future Trends and Applications

Potential developments include:

• Expansion to additional analyte classes (pesticides, pharmaceuticals, petrochemicals).
• Integration with high‐resolution MS and alternative detectors (ECD, NPD, FPD).
• Automated method optimization via software and AI‐driven protocols.
• Miniaturized and multiplexed interfaces for ultra‐high throughput.

Conclusion

The fully automated LC‐CGC interface combining a flow cell, large‐volume sampler, and PTV injector offers a versatile, user‐friendly platform for environmental analysis. It streamlines sample processing, enhances analytical performance, and operates under centralized software control, demonstrating reproducible sensitivity at sub‐ppb levels.

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