Multiresidue method for the quantification of pesticides in fruits, vegetables, cereals and black tea using UPLC MS/MS

Importance of the Topic

As global demand for safe food grows, reliable testing of pesticide residues in fruits, vegetables, cereals and tea is essential to meet regulatory Maximum Residue Levels (MRLs) and protect public health. Multi-residue analysis methods must address diverse chemistries, complex food matrices and low detection limits.

Objectives and Study Overview

The study aimed to develop and validate a single UPLC-MS/MS protocol for quantifying 552 pesticides and relevant metabolites across five representative commodities: spinach, strawberry, soybean, wheat flour and black tea. Performance was assessed for 256 key analytes to confirm sensitivity, precision and robustness in accordance with EU guidelines.

Methodology and Instrumentation Used

Sample Preparation:

• Homogenization of samples and freezing prior to extraction
• QuEChERS extraction protocols from European Reference Laboratories for fruit, vegetables and cereals

Instrumentation:

• UPLC system: ACQUITY UPLC I-Class with FL Sample Manager
• Column: ACQUITY UPLC HSS T3, 1.8 µm, 2.1×100 mm
• Post-injector mixing kit: 50 µL extension loop to improve peak shape of polar analytes
• Mobile phases: 5 mM ammonium formate with 0.1% formic acid in water (A) and in 50:50 MeCN:MeOH (B)
• MS detector: Xevo TQ-XS operating in positive and negative electrospray ionization modes

Main Results and Discussion

• Sensitivity: For over 90% of the 256 tested compounds in spinach, strawberry and soybean, and above 79% in wheat flour and tea, limits of detection (S/N>10) reached 0.005 mg/kg.
• Linearity and Precision: Matrix-matched calibration curves showed R2>0.99; more than 85% of analytes exhibited peak area RSDs <10% at concentrations of 0.005, 0.01 and 0.05 mg/kg.
• Matrix Effects: All commodities displayed both suppression and enhancement (>20%) of analyte signals, underscoring the need for matrix-matched calibration or standard addition to ensure accurate quantitation.
• Peak Shape Improvement: The post-injector extension loop enabled injection of typical QuEChERS extracts with 25% organic content into high-aqueous mobile phase, yielding sharp peaks for early-eluting polar pesticides like methamidophos.

Benefits and Practical Applications

• Comprehensive Coverage: Single method for over 550 compounds simplifies laboratory workflows.
• Regulatory Compliance: Achieves EU default MRL detection levels, supporting routine monitoring.
• Efficiency: Rapid UPLC separations and automated MS/MS detection facilitate high sample throughput.
• Versatility: Applicable to diverse matrices encountered in QA/QC, food safety and research laboratories.

Future Trends and Potential Applications

• Expansion of Analyte Scope: Incorporation of emerging pesticides and transformation products.
• Enhanced Sample Preparation: Adoption of automated QuEChERS and online clean-up for throughput gains.
• High-Resolution MS Integration: Use of full-scan, accurate-mass instruments for untargeted screening.
• Data Analytics: Application of chemometric and machine-learning tools to interpret complex datasets and improve quantitation.

Conclusion

A robust UPLC-MS/MS multi-residue method was established for 552 pesticides, demonstrating high sensitivity, precision and adaptability across challenging food matrices. The approach meets regulatory requirements and offers a streamlined workflow for routine pesticide residue analysis.

Reference

D. Shah, J. Wood, G. Fujimoto, E. McCall, S. Hird, P. Hancock. "Multiresidue method for the quantification of pesticides in fruits, vegetables, cereals and black tea using UPLC-MS/MS." Waters Corporation, 2021.