Determination of Pesticides in Tomato by GCxGC-TOFMS

Importance of the topic

The presence of pesticide residues in tomatoes and their processed products poses significant risks to consumer health and is tightly regulated by food safety authorities worldwide. Global tomato production exceeds 130 million tonnes, with key producers including China, the EU, India, the USA, and Turkey. Reliable detection and quantitation of a broad spectrum of pesticides at trace levels are essential for regulatory compliance, quality assurance, and public health protection.

Study objectives and overview

This application note describes the development of a comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) workflow for simultaneous qualitative and quantitative analysis of 164 targeted pesticide residues in peeled tomato matrix. The approach addresses extensive matrix interferences encountered even after standard QuEChERS extraction and cleanup, leveraging enhanced chromatographic resolution and mass spectral deconvolution to achieve low-level detection limits.

Methodology and used instrumentation

Sample preparation involved QuEChERS extraction compliant with EN 15662, followed by dSPE cleanup on a 10 g peeled tomato sample. Blank extracts confirmed absence of contaminants before matrix-matched calibration. A 164-pesticide standard mix spiked blank matrix at levels of 2.5, 5, 10, 25, and 50 ng/g.

GCxGC-TOFMS conditions:

• Instrumentation: Pegasus BT 4D with QuadJet™ thermal modulator and Gerstel CIS4 cold splitless inlet.
• Columns: 1D HP-5MS UI (30 m × 0.25 mm × 0.25 µm), 2D Rxi-17Silms (1.5 m × 0.15 mm × 0.15 µm).
• Oven program: 75 °C (2.05 min) ramped to 320 °C at 5 °C/min, secondary oven +5 °C, modulator +15 °C.
• Modulation: 4 s for the first 862 s, then 5 s to end to optimize resolution and prevent wrap-around.
• Mass spectrometry: m/z 40–600, acquisition rate 200 spectra/s, ion source at 250 °C.

Main results and discussion

Two-dimensional contour plots of extracts spiked at 50 ng/g demonstrated separation of 164 targets and identification of over 2 100 non-target peaks (similarity >80%). Key observations:

• Enhanced peak resolution in the second dimension separated coeluting analytes such as δ-Lindane, Paraoxon methyl, and Disulfoton, which would coelute in 1D GC.
• Automatic spectral deconvolution resolved overlapping compounds like Pirimicarb and Pentachloroaniline.
• Calibration curves for Chlorothalonil and Fenitrothion showed excellent linearity (R2 ≥ 0.99) using matrix-matched external standards and hexachlorobenzene as internal standard.
• Ion ratio stability across calibration levels (±30%) confirmed quantitative reliability for regulated compounds (e.g., Cyanazine, Dicofol).
• Non-target screening simultaneously identified aroma-active volatiles—5-Hepten-2-one, 6-methyl-; methyl salicylate; β-Ionone—with high similarity scores (>850) and clear 2D separation from matrix interferences.

Method benefits and practical applications

The described GCxGC-TOFMS workflow provides:

• Superior separation of complex tomato matrix components, reducing false positives and improving quantitation accuracy.
• Sensitivity to achieve quantitation at low parts-per-billion levels (2.5 ng/g) with potential to reach 0.5–1 ng/g by adjusting injection volume.
• Concurrent target and non-target screening capabilities, enabling retrospective analysis for new or emerging contaminants and profiling of flavor compounds.
• Compliance with SANTE/11813/2017 guidelines for pesticide residue analysis in food matrices.

Future trends and potential applications

Advancements may include expanding compound libraries for broader non-target screening, integration of machine learning algorithms for automated peak annotation, and application to other food matrices (fruits, vegetables, processed foods). Enhanced ionization techniques and column chemistries could further lower detection limits and improve throughput for high-throughput regulatory monitoring.

Conclusion

A robust GCxGC-TOFMS method using the Pegasus BT 4D system was established for comprehensive pesticide residue analysis in peeled tomatoes. The approach meets regulatory requirements for sensitivity and specificity, while offering the flexibility to conduct non-target screening within the same dataset. This makes it a valuable tool for food safety laboratories seeking reliable, high-resolution analysis of complex samples.

Reference

SANTE/11813/2017 guidelines for unit mass resolution TOFMS pesticide analysis.