Discovery of Pesticide Protomers Using Routine Ion Mobility Screening

Significance of the topic

This study addresses the critical need for high-confidence screening of more than 500 regulated pesticides in food and environmental matrices under stringent global regulations. By integrating ion mobility spectrometry with high-resolution mass spectrometry, the approach enhances specificity and reduces false positives and negatives in multi-residue pesticide analysis.

Objectives and Study Overview

The primary objective was to implement routine ion mobility screening to identify and characterize pesticide protomers—ions differing only by protonation site—improving assay selectivity and reproducibility. The method was validated using standard solutions, spiked mandarin matrices, and a European proficiency test sample (FV-13).

Methodology and Instrumentation

Sample Preparation:

• Extract 10 g homogenized sample with 60 mL 20 mM ammonium acetate in methanol using Ultra-Turrax.
• Filter and dilute to 100 mL with 5 mM ammonium acetate in water.

Chromatography and Ion Mobility:

• Waters ACQUITY UPLC I-Class with BEH C18 (2.1×100 mm, 1.7 µm) at 45 °C, flow rate 0.45 mL/min; gradient of 0.1% formic acid in water (A) and acetonitrile (B).
• Waters SYNAPT G2-S HDMS, ESI+ mode, mass range 50–1200 Da, drift gas N2, IMS wave height 40 V, velocity 650 m/s, duty cycle 10.8 ms.
• Data acquired with MassLynx and UNIFI; leucine enkephalin (m/z 556.2766) as lock mass.

Key Results and Discussion

Ion mobility differentiation successfully separated protomers of indoxacarb and fenpyroximate, each exhibiting two distinct collision cross section values (indoxacarb: 136.49 Å2 and 147.94 Å2; fenpyroximate: 147.15 Å2 and 158.33 Å2). Mobility-resolved fragmentation spectra revealed unique and common fragment ions for each protomer, demonstrating the influence of protonation site on fragmentation behaviour. Conventional MRM-based methods may be biased if protomer distributions fluctuate, while IMS-MS full-spectrum acquisition ensures comprehensive data for more robust assay development.

Benefits and Practical Applications

• Enhanced screening specificity by combining retention time, accurate mass, and CCS values.
• Improved reproducibility and selectivity of fragment ion selection for confirmatory analysis.
• Structural elucidation and spectral cleanup in complex matrices through mobility separation.
• Retrospective data mining capability for both mass and mobility dimensions, supporting future method refinements.

Future Trends and Opportunities

Investigate how experimental parameters (flow rate, voltages, matrix composition) influence protomer formation. Expand CCS libraries to cover a broader range of pesticides. Integrate IMS-MS into routine regulatory multi-residue workflows. Leverage non-targeted acquisition strategies and machine learning for automated protomer discovery and annotation.

Conclusion

Integrating ion mobility and CCS measurements into pesticide residue screening significantly enhances method specificity and robustness by revealing protomer-specific fragmentation patterns. IMS-HRMS offers a comprehensive, non-targeted approach that supports regulatory compliance, retrospective analysis, and advanced assay development.

References

1. European Commission SANCO/12571/2013 Method Validation & Quality Control Procedures for Pesticide Residues Analysis in Food & Feed.
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