Method for the determination of 182 Residual Pesticides in Milk using LCMS-8045 and GCMS-TQ8040 NX

Importance of the Topic

Milk is a widely consumed food, especially by infants and children, and its safety is critical due to potential pesticide contamination from animal feed and water. Regulatory maximum residue limits for pesticides in milk are particularly stringent, necessitating sensitive and reliable analytical methods for routine monitoring in dairy products.

Objectives and Study Overview

The aim was to develop and validate a high-throughput, multi-residue workflow for the determination of 182 pesticides in milk using Shimadzu LCMS-8045 and GCMS-TQ8040 NX. The study covers method development, extraction optimization, calibration strategies, and validation against international guidelines.

Methodology

Sample preparation employed a modified QuEChERS protocol to achieve efficient matrix removal and analyte recovery:

• Deproteinization with acetonitrile followed by partitioning into two aliquots (A and B).
• Aliquot A split into A-I and A-II for LC-MS/MS and GC-MS/MS clean-up steps.
• C18 sorbent and MgSO₄ used for clean-up; solvent exchange into aqueous mobile phase for LC and ethyl acetate for GC analysis.
• Final extract volumes adjusted to avoid sample dilution.

Quantification was performed by external standard calibration with weighted linear regression (1/C²) using matrix-matched standards over 1–20 µg/L (extended to 40 µg/L for selected compounds). Method validation followed SANTE guidelines, assessing specificity, linearity, recovery, repeatability, and reproducibility.

Used Instrumentation

• LCMS-8045 tandem quadrupole mass spectrometer with Nexera X2 LC system.
• GCMS-TQ8040 NX triple quadrupole GC-MS system with AOC-20i+s auto-injector.
• Shim-pack XR-ODS II column (3.0 mm × 150 mm, 2.2 µm) for LC; SH-Rxi-5Sil MS capillary column (30 m × 0.25 mm, df = 0.25 µm) for GC.
• LabSolutions Insight data processing software with Shimadzu residue pesticide method packages.

Key Results and Discussion

• Linearity: Correlation coefficients (R²) exceeded 0.97 for all analytes within the calibration range.
• Limits of quantification: 5 µg/kg for 101 LC-amenable and 73 GC-amenable compounds; 10 µg/kg for the remaining 31 pesticides.
• Recoveries: 70–120% for the majority of analytes; 35–70% for 18 compounds; only one compound exceeded 120% recovery.
• Precision: Repeatability (RSDr) and reproducibility (RSDR) at LOQ levels were below 20% for all compounds, meeting SANTE criteria.

Benefits and Practical Applications

• Rapid analysis with total run times of 20 min for LC-MS/MS and 25 min for GC-MS/MS supports high sample throughput.
• Robust multi-residue capability simplifies routine monitoring of a broad pesticide spectrum in dairy laboratories.
• Modified QuEChERS extraction reduces matrix effects and improves sensitivity at low µg/kg levels.

Future Trends and Potential Uses

• Integration of high-resolution accurate mass spectrometry to expand screening capabilities.
• Automation of sample preparation for enhanced laboratory efficiency.
• Application of chemometric and machine-learning tools for data interpretation and pattern recognition.
• Extension of method to other complex food matrices and environmental samples.

Conclusion

The validated method delivers sensitive, accurate, and reproducible quantification of 182 pesticides in milk, aligning with international guidelines and supporting regulatory compliance. Its combination of ultra-fast LC-MS/MS and GC-MS/MS analysis with a streamlined QuEChERS workflow meets the demands of modern high-throughput testing laboratories.

References

1. GB 2763-2019 National Food Safety Standard—Maximum Residue Limits for Pesticides in Food.
2. Anastassiades M, Lehotay SJ, Štajnbaher D, Schenck FJ. Fast and Easy Multiresidue Method Employing Acetonitrile Extraction/Partitioning and “Dispersive Solid-Phase Extraction” for the Determination of Pesticide Residues in Produce. J AOAC Int. 2003;86:412–431.
3. European Commission. Guidance Document on Analytical Quality Control and Method Validation Procedures for Pesticide Residues and Analysis in Food and Feed. SANTE/12682/2019.