Fully automated analysis of 549 pesticides in oil with LCxGC and FOCUS auto sampler

Importance of the topic

Analysis of pesticide residues in edible oils is critical for food safety and regulatory compliance. Traditional methods require extensive manual cleanup to remove fats and oils, leading to high costs and long turnaround times. A fully automated workflow combining size exclusion cleanup with large-volume injection GC-MS promises to streamline multi-residue screening at trace levels.

Aims and study overview

This application note demonstrates a fully automated LC×GC approach for the simultaneous analysis of 549 pesticides spiked into sunflower oil at 10 ppb. The goal is to evaluate performance, recovery, and throughput using an online size exclusion cleanup step coupled with a programmable temperature vaporizing (PTV) GC-MS large-volume injection.

Methodology

• Sample preparation employs size exclusion chromatography (SEC) to separate high-molecular-weight oil constituents from pesticide analytes.
• A 100 µL aliquot of spiked oil is injected onto a mixed-bed SEC column using an ethyl acetate/hexane mobile phase (1 mL/min).
• The late-eluting SEC fraction containing pesticides is automatically transferred via side-port syringe to the PTV injector for large-volume injection.
• GC-MS analysis follows a temperature program from 50 °C (5 min) to 150 °C at 40 °C/min, then to 280 °C at 5 °C/min (hold 20 min).

Instrumentation

• SEC system: Shimadzu LC-20AD pump, FOCUS LC-valve, PL mixed E column.
• GC: Shimadzu 2010 GC-MS with OPTIC 3 PTV injector and TC-5 MS column (20 m×0.18 mm×0.18 µm).
• Autosampler: FOCUS Robotic Sample Processor with LC-GC interface kit.

Main results and discussion

Online SEC effectively separates oil matrix (early peaks) from pesticides (later fraction). The PTV-GC-MS total ion chromatogram of the collected fraction shows clear pesticide signals with negligible oil interference. At 10 ppb spiking level, the majority of 549 target compounds exhibit satisfactory recoveries and sharp peak shapes. Method speed and reproducibility are significantly improved compared to off-line cleanup.

Benefits and practical applications

• Fully automated sample cleanup and injection reduce labor and risk of contamination.
• Low detection limits at sub-ppb levels are achievable without manual SPE.
• High throughput screening for compliance testing in food quality control laboratories.
• Broad analyte scope supports multi-residue monitoring in edible oils.

Future trends and potential applications

Integration of tandem mass spectrometry (MS/MS) for enhanced selectivity, expansion to other high-fat matrices (e.g., dairy, meat), and development of advanced software for automated data processing will further improve throughput. Coupling with online solid-phase extraction could address coeluting small fatty acids, extending the method’s robustness.

Conclusion

The automated SEC-PTV-GC-MS workflow provides a rapid, reliable, and highly automated solution for screening hundreds of pesticides in oil matrices at low ppb levels. It reduces manual handling, accelerates analysis times, and maintains analytical performance, making it well suited for routine food safety testing.

Reference

No external references were cited in this application note.