Applying ‘MRM Spectrum Mode’ and Library Searching for Enhanced Reporting Confidence in Routine Pesticide Residue Analysis

Significance of Topic

In routine pesticide residue monitoring, false positive and false negative results present a major challenge to regulatory compliance and food safety. Enhancing specificity and confidence in compound identification is critical to meet stringent guidelines and reduce reporting errors.

Study Objectives and Overview

The study aimed to develop and evaluate a workflow using multiple reaction monitoring spectrum mode to monitor an increased number of fragment ion transitions per pesticide. The method targeted 193 pesticides, employing 1 291 MRM transitions in a 15 minute LC MS MS run. Objectives included assessing detection limits, linearity, repeatability, and the impact of additional transitions on data quality.

Methodology and Instrumentation

A QuEChERS extraction produced acetonitrile extracts from diverse food matrices including turmeric, plum, peppermint, parsnip, cherry, lime, pumpkin, tomato, and potato. A Nexera UHPLC system equipped with an HSS T3 column (100 × 2.1 mm, 1.7 μm) provided chromatographic separation. The LC was coupled to a triple quadrupole mass spectrometer operating in positive and negative electrospray ionisation with fast polarity switching. Instrument parameters included 3 ms dwell time per MRM and 5 ms polarity switching, delivering high data density across a 15 minute gradient.

Used Instrumentation

• Shimadzu Nexera UHPLC system with HSS T3 column
• Shimadzu LCMS-8060 triple quadrupole mass spectrometer
• Electrospray ionisation in positive and negative mode
• LabSolutions Insight software for data processing and library matching

Main Results and Discussion

• The MRM Spectrum mode acquired 1 291 transitions without compromising sensitivity, with limits of quantitation at 0.01 mg/kg and linearity up to 0.2 mg/kg (R2 > 0.999).
• Repeatability in avocado matrix (0.1 mg/kg) showed peak area RSD below 3.5% even when monitoring over 150 overlapping transitions in high density time windows.
• Peak areas measured with 1 291 transitions correlated strongly with a conventional 2 MRM per compound method (R2 = 0.9989), indicating equivalent quantitation performance.
• Library searchable MRM product ion spectra enabled reliable identification across complex matrices, achieving similarity scores above 98 for targets such as demeton-S-methyl sulphone and carbendazim.
• Coeluting isomers desmedipham and phenmedipham were distinguished by selective fragment ions in the MRM spectrum, preventing false positives.

Benefits and Practical Applications

• Enhanced confidence in pesticide identification by combining quantitation and library searchable product ion spectra in a single run.
• Compliance with EU SANTE/11945/2015 identification criteria using additional transitions beyond standard two ion ratio checks.
• High throughput analysis of over 190 pesticides in 15 minutes suitable for routine monitoring labs.
• Flexible method setup using a comprehensive pesticide MRM database to accelerate implementation.

Future Trends and Potential Applications

• Expansion of MRM spectrum libraries to include more environmental contaminants and metabolites.
• Integration with machine learning algorithms to further reduce false positives through automated spectral interpretation.
• Application to other complex food matrices and extension to confirmatory analysis in clinical and environmental laboratories.
• Development of unified workflows combining full scan, data independent acquisition, and MRM spectrum modes for comprehensive screening.

Conclusion

MRM Spectrum mode offers a robust approach for simultaneous quantitation and confident identification of a large number of pesticides. By monitoring up to ten fragment ions per compound, it meets regulatory requirements and significantly reduces false detect reporting without sacrificing throughput or data quality.

Reference

1. European Commission SANTE/11945/2015 Guidance document on analytical quality control and method validation procedures for pesticides residues analysis in food and feed
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