Large-scale screening and quantitation of pesticide residues in milk using GC-(EI)-MS/MS

Importance of the topic

Milk and dairy products are essential dietary components but can accumulate pesticide residues through feed and environmental exposure. Accurate detection of trace-level contaminants supports regulatory compliance and protects public health by ensuring pesticide levels remain below maximum residue limits set by authorities. Reliable screening enhances consumer confidence and streamlines laboratory workflows.

Objectives and study overview

The study aimed to develop and validate a comprehensive analytical workflow for simultaneous screening and quantification of 155 pesticide residues in milk. It focused on method optimization according to SANTE guidelines and assessment of compliance with Indian FSSAI and European Commission MRL standards.

Methodology and instrumentation

• Sample preparation: Citrate-buffered QuEChERS extraction with acetonitrile, followed by cleanup using PSA and C18 sorbents to remove proteins and fats.
• Chromatography: Thermo Scientific TRACE 1310 GC with TriPlus RSH autosampler and TG-5SIL MS column; splitless injection at 280 °C.
• Mass spectrometry: Thermo Scientific TSQ 9000 triple quadrupole MS with ExtractaBrite EI source and Vacuum Probe Interlock for fast source exchange; data acquired in timed-SRM mode.
• Data processing: TraceFinder software with automatic SRM scheduling and dwell time optimization; identification based on retention time, ion ratio, and linearity filters.

Main results and discussion

• Linearity: Correlation coefficients > 0.99 from 0.001 to 0.10 mg/kg; signal-to-noise ratios ≥ 15 at the lowest levels.
• LOQ: 134 compounds quantified at 0.001 mg/kg, 17 at 0.0025 mg/kg, and 4 at 0.005 mg/kg; default reporting limit set at 0.01 mg/kg.
• Recovery and precision: Average recoveries of 72–117% with RSD < 15% across spiking levels (0.005, 0.010, 0.025 mg/kg).
• Matrix effects: Significant enhancement observed, requiring matrix-matched calibration.
• Repeatability: Area and retention time variations < 8% and < 0.1 min respectively over 88 injections, demonstrating high robustness.
• Isomer resolution: Baseline separation and reliable quantification of pesticide isomers, e.g., tetramethrin, with ion ratio criteria within ±30%.

Benefits and practical applications

The method delivers high throughput (≥ 40 injections/day), minimal downtime with NeverVent technology, and rapid SRM method setup. It meets international validation requirements, enabling routine pesticide monitoring in commercial laboratories with enhanced accuracy and efficiency.

Future trends and possibilities

Integration of high-resolution MS, expansion to other matrices, automation of sample handling, and adoption of green extraction techniques can further improve sensitivity, selectivity, and sustainability in pesticide residue analysis.

Conclusion

A robust QuEChERS-GC-EI-MS/MS workflow for 155 pesticide residues in milk was validated per SANTE guidelines. The approach achieves low LOQs, reliable recoveries, and throughput compatible with regulatory requirements, supporting stringent food safety monitoring.

References

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5. Insecticides/Pesticides Registered under Section 9(3) of the Insecticides Act, Government of India, 2019.
6. EN 15662:2008 QuEChERS Method, 2008.
7. SANTE/11813/2017 Validation Guidelines, EU, 2017.
8. FSSAI Manual for Food Safety, 17th Edition, 2017.
9. EU Pesticide MRL Database, 2019.