Preliminary Evaluation of ATEX-PTV-GC-QTOF-MS for Determination of Pesticides in QuEChERS Extracts of Samples Containing High Concentrations of Chlorophyll

Importance of the Topic

The analysis of pesticide residues in green commodities poses significant challenges due to non-volatile chlorophyll and other matrix components contaminating the GC inlet. An efficient method enabling direct injection of QuEChERS extracts would streamline routine testing in food safety laboratories and reduce sample preparation time.

Objectives and Overview of the Study

This work evaluates an automated ATEX-PTV-GC-QTOF-MS system for direct analysis of crude QuEChERS extracts from herb samples containing high chlorophyll levels. The primary aim is to assess detection limits, recovery, precision, and compound coverage with minimal clean-up.

Methodology and Instrumentation

The study employed the GC-QTOF-MS MultiFlex system (Anatune) comprising a Gerstel Multi-Purpose Sampler with automated tube exchange (ATEX), a Programmable Thermal Vaporisation (PTV) inlet (CIS 4), and an Agilent 7200 GC-QTOF-MS.

• Sample preparation: QuEChERS citrate extraction with d-SPE clean-up (PSA, C18, carbon).
• Injection: 5 µL of raw extract into a disposable microvial within the PTV liner.
• PTV protocol: solvent venting followed by temperature ramp to volatilise analytes, cold trapping at −50 °C, then injection into HP-5 MS column (30 m × 0.25 mm, 0.25 µm film).
• GC-QTOF parameters: He at 1 mL/min, EI 70 eV, full-scan at 8 000 resolution.

Main Results and Discussion

Fresh coriander extracts were spiked with 132 target pesticides. Key findings:

• Lowest calibrated levels for many analytes fell below 10 ng/g.
• 35 compounds achieved recoveries between 70–120% with CVs <20% at 10 ng/g.
• ~40 analytes were marginally outside these criteria, notably early-eluting organophosphates and some polar compounds.
• Thermal degradation affected captan and dicofol under the current PTV conditions.
• ~30 late-eluters (e.g., pyrethroids such as cyfluthrin, permethrin) showed insufficient signal at 10 ng/g.

Benefits and Practical Applications

The ATEX-PTV system permits direct injection of minimally cleaned extracts, reducing labor and solvent usage. Automated liner exchange prevents carry-over and inlet fouling, enhancing throughput in routine pesticide monitoring.

Future Trends and Applications

Further optimization of PTV temperature programs, internal standard selection, and MS acquisition settings could expand compound coverage and improve recoveries. Adaptation for other challenging matrices (e.g., fatty or pigmented samples) and coupling with high-throughput robotics may advance regulatory compliance workflows.

Conclusion

This preliminary evaluation demonstrates promising performance for direct pesticide screening in chlorophyll-rich extracts using ATEX-PTV-GC-QTOF-MS. While some compounds require method refinement, the approach offers a viable path to faster, contamination-free analysis.

Reference

1. Katan Patel, R.J. Fussell, D.M. Goodall, B.J. Keely. Analysis of pesticide residues in lettuce by large volume-difficult matrix introduction-GC-TOF-MS. The Analyst, 2003, 128, 1228–1231.