Method for the determination of 346 Residual Pesticides in Milk using LCMS-8045 and GCMS-TQ8040 NX

Significance of the Topic

Milk is a dietary staple, especially for infants and children, and its safety is critically linked to public health. Pesticide residues in milk pose a unique analytical challenge due to the complexity of the dairy matrix and stringent maximum residue limits. A reliable multi-residue method enables regulatory compliance and protects consumers from potential toxic effects.

Objectives and Overview

This study aims to establish a rapid, sensitive and high-throughput workflow for the simultaneous quantification of 346 pesticide residues in milk. By combining modified QuEChERS extraction with state-of-the-art LC-MS/MS and GC-MS/MS technologies, the method covers compounds regulated under major international standards, including FSSAI, EU, CODEX and APEDA.

Methodology and Used Instrumentation

Milk samples from the local market were spiked to prepare matrix-matched calibration standards spanning 2.5 to 40 µg per liter. Fortified samples at 5 and 10 µg per kilogram (and double levels for certain dual-analysis analytes) were prepared in six replicates. Validation followed SANTE guidelines for specificity, linearity, recovery and precision.

• Sample preparation employed a modified QuEChERS protocol. After deproteinization with acetonitrile, samples were split for LC and GC analysis. Cleanup utilized C18 sorbent, magnesium sulfate, and solvent exchanges to isolate analytes and minimize matrix effects.
• LC-MS/MS conditions included a Shimadzu LCMS-8045 with Nexera X2, using a C18 reversed-phase column and a water/methanol ammonium formate gradient. Ionization was by ESI, with optimized gas flows and temperatures for fast cycle times.
• GC-MS/MS analysis was performed on Shimadzu GCMS-TQ8040NX with an AOC-20i autosampler and SH-Rxi-5Sil MS column. Splitless injection and a programmed oven ramp enabled separation of volatile and semi-volatile pesticides.
• Data acquisition used multiple reaction monitoring transitions (one target and two references for most analytes). Instrumental methods were optimized via Shimadzu’s Method Package and Smart Pesticides Database. LabSolutions Insight software facilitated seamless data processing and validation.

Main Results and Discussion

The method achieved a limit of quantitation of 5 µg/kg for 165 compounds by LC-MS/MS and 118 compounds by GC-MS/MS. The remaining analytes met a 10 µg/kg LOQ. Linearity across the calibration range showed correlation coefficients greater than 0.99. Mean recoveries for 294 compounds fell between 70 and 120 percent, with only three exceeding 120 percent. Precision expressed as RSD for repeatability and reproducibility remained below 20 percent for all analytes. Representative calibration curves and chromatograms confirmed robust performance at LOQ levels for both platforms.

Benefits and Practical Applications

• Short analysis times (21 minutes for LC-MS/MS, 25 minutes for GC-MS/MS) support high laboratory throughput.
• Reduced injection volumes and flow rates extend column lifetime and enhance assay stability over prolonged use.
• Comprehensive coverage of 346 pesticides aligns with multiple regulatory requirements, simplifying compliance efforts.
• The unified extraction procedure streamlines sample handling and reduces labor and solvent consumption.
• Sensitive and reproducible quantification at low µg/kg levels enables reliable monitoring of milk safety.

Future Trends and Possibilities

Advances in high-resolution mass spectrometry, automated sample preparation, and miniaturized extraction systems will further enhance sensitivity and ease of use. Expanded spectral libraries and artificial intelligence-driven data analysis can accelerate method development and strengthen non-target screening. Integration with digital quality management systems and online monitoring platforms may enable real-time compliance and risk assessment in dairy processing.

Conclusion

A simple, sensitive and rapid multi-residue method has been validated for the determination of 346 pesticides in milk using combined LC-MS/MS and GC-MS/MS techniques. The approach demonstrates excellent linearity, recovery and precision at regulatory trace levels. Its high throughput and broad coverage make it well suited for routine testing laboratories in the dairy industry.

References

1. GB2763-2019 National Food Safety Standard Maximum Residue Limits for Pesticides in Food
2. M Anastassiades et al Fast and Easy Multiresidue Method Employing Acetonitrile Extraction Partitioning and Dispersive Solid-Phase Extraction for the Determination of Pesticide Residues in Produce Journal of AOAC International 86 412–431 2003
3. European Commission Guidance Document on Analytical Quality Control and Method Validation Procedures for Pesticide Residues Analysis in Food and Feed SANTE 12682 2019