Screening and Quantitation of 240 Pesticides in Difficult Food Matrixes Using the Agilent 6545 Q-TOF LC/MS System

Importance of the Topic

Comprehensive monitoring of pesticide residues in food is critical for consumer safety and regulatory compliance. With over 1,000 pesticides and metabolites regulated by global authorities, sensitive and accurate analytical methods are essential to detect contaminants at levels below maximum residue limits (MRLs). Advanced high-resolution liquid chromatography–mass spectrometry (LC-MS) techniques enable broad screening and reliable quantitation in complex food matrices, supporting food quality control and public health initiatives.

Objectives and Study Overview

This study develops and evaluates an ultra-high performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) method capable of screening and quantifying 240 pesticides and metabolites in challenging food matrices. Two representative matrices were chosen: black tea, characterized by complex polyphenols, and avocado, rich in lipids. The method aims to demonstrate detection below European Commission MRLs and to showcase improvements in sensitivity and throughput compared to previous instrument generations.

Methodology and Instrumentation

The analytical workflow comprises sample extraction, chromatographic separation, accurate mass screening, and targeted MS/MS confirmation.

• Sample Preparation: A citrate-buffered QuEChERS protocol was applied. Tea samples were pre-wetted before extraction; avocado extracts underwent lipid removal by dispersive SPE.
• Chromatography: Agilent 1290 Infinity UHPLC with ZORBAX Eclipse Plus C18 column at 45 °C, gradient elution over 22 min, 0.4 mL/min flow, 3 µL injection.
• Mass Spectrometry: Agilent 6545 Q-TOF MS with Jet Stream ESI source, operated in positive mode. Key innovations include a high-voltage power supply, enhanced detector gain, and Particle Swarm Optimization (SWARM) tuning to maximize ion transmission for fragile small molecules in the 50–250 m/z range.
• Data Processing: MassHunter Qualitative and Quantitative Analysis software with a Personal Compound Database Library (PCDL) for Find by Formula screening, and targeted MS/MS or Auto MS/MS for structural confirmation.

Main Results and Discussion

The new SWARM tune combined with hardware upgrades yielded up to 4-fold sensitivity improvement over previous Q-TOF models. In black tea at 2 ppb spike level, over 80% of pesticides showed signal enhancement above 3x. In avocado at 10 ppb, similar gains were observed.

• Screening: Find by Formula matching scores exceeded 97/100 for most compounds, even in the presence of heavy matrix interference.
• Quantitation: Over 70% of analytes were detected below 1 ng/g in tea, and nearly all pesticides in avocado at 10 ng/g. Calibration curves demonstrated linearity (R2 > 0.99) using targeted MS/MS.
• Confirmation: Targeted and Auto MS/MS approaches provided fragment ion spectra matching the library, ensuring reliable compound identification.

Benefits and Practical Applications

This UHPLC-Q-TOF/MS method offers:

• Broad scope: Simultaneous screening of hundreds of pesticides with a single run.
• High sensitivity: MRL compliance across diverse and difficult matrices.
• Flexible tuning: Customized optimization for small molecule transmission.
• Efficient workflow: Reduced tune time and retrospective Auto MS/MS capabilities for expanding target lists.

Future Trends and Opportunities

Emerging trends include integration of real-time data processing with machine learning for automated compound discovery, expansion of high-resolution screening to non-targeted contaminants, and coupling to orthogonal separations (ion mobility) for enhanced selectivity. Further miniaturization and automation of sample preparation will improve laboratory throughput and reduce solvent consumption.

Conclusion

The Agilent 6545 Q-TOF LC/MS System, paired with advanced UHPLC, achieves reliable screening and quantitation of 240 pesticides in complex food matrices at sub-MRL levels. Its enhanced sensitivity and flexible tuning capabilities support high-confidence analysis, making it a valuable tool for food safety laboratories and regulatory compliance.

References

• European Commission Regulation (EC) No 396/2005 on pesticide MRLs.
• EU Guidance SANCO/12571/2013 for method validation in pesticide analysis.
• US CFR 40 Part 180 Tolerance Information for Pesticide Chemicals.
• Application Note: Analysis of Pesticide Residues in Spinach Using QuEChERS and LC/MS/MS, Agilent, 2012.
• Application Note: Exact Mass Library for Pesticide Screening in Produce, Agilent, 2013.