DEVELOPING A ROBUST LC-MS/MS METHOD FOR THE DETERMINATION OF ANIONIC POLAR PESTICIDES IN A RANGE OF FOODSTUFFS WITHOUT DERIVATIZATION

Significance of the Topic

In recent years, concerns over glyphosate safety and other polar anionic pesticides have driven the demand for robust analytical surveillance in food matrices. Existing reversed-phase methods fail to retain these low molecular weight analytes, necessitating innovative chromatographic strategies to ensure sensitive and reliable detection.

Objectives and Study Overview

This study aimed to develop and validate a single LC-MS/MS workflow for direct analysis of a broad panel of anionic polar pesticides in diverse foodstuffs without derivatization. Key goals included:

• Extending analyte scope beyond glyphosate, glufosinate, and AMPA to multiple anionic pesticides and metabolites
• Achieving sufficient chromatographic retention and baseline separation to prevent interferences
• Ensuring method robustness against matrix complexity for routine operation

Methodology and Instrumentation

Samples from retail outlets were homogenized and extracted using the acidified methanol Quick Polar Pesticides (QuPPe) protocol. An alternate aqueous extraction was also evaluated. Chromatographic separation employed a dedicated anionic polar pesticide column (Waters 186009287) on a UPLC-MS/MS platform. Two mobile phase methods were optimized:

• Method A: Buffered formic acid mobile phase enabling inclusion of chlorate and perchlorate
• Method B: Formic acid–only eluent for enhanced sensitivity in low ppb range

Results and Discussion

Retention and Separation

• All analytes eluted well beyond the column void volume, with AMPA retention at over 3.5× t₀
• Baseline resolution was achieved for critical isobaric pairs such as n-acetyl AMPA/AMPA and phosphonic acid/fosetyl aluminum

Matrix Effects and Stability

• RADAR full-scan monitoring highlighted the complex ion suppression profile of crude QuPPe extracts
• Retention times remained stable within ±0.1 min across tomato, cucumber, and wheat flour matrices

Sensitivity and Precision

• Method B yielded accuracies of 70–120% and %RSD < 5% at spike levels of 0.01 mg/kg, 2×, and 5× in representative commodities
• Limits of detection surpassed regulatory minimum residue limits (MRLs) by a wide margin

Practical Benefits and Applications

• Single-run analysis of at least 13 anionic polar pesticides without derivatization simplifies laboratory workflows
• Robust performance across diverse matrices supports routine QA/QC and regulatory surveillance
• High sensitivity and reproducibility enable confident enforcement of compound-specific and summed MRL definitions

Future Trends and Potential Applications

• Integration of high-resolution MS data (e.g., RADAR scans) offers opportunities for retrospective screening of emerging polar contaminants
• Further expansion of analyte scope to include novel metabolites and degradation products
• Automation of extraction and data processing to enhance throughput in high-volume testing laboratories

Conclusion

A robust, derivatization-free LC-MS/MS method has been established for anionic polar pesticides in food matrices. By addressing retention, separation, matrix complexity, and detection limits, the method delivers reliable, sensitive, and high-throughput analysis that exceeds current regulatory requirements.

References

• European Union (2017) SANTE 11813/2017. Guidance Document on Analytical Quality Control and Method Validation Procedures for Pesticide Residues Analysis in Food and Feed.
• European Commission (2019) QuPPe Method. http://www.eurl-pesticides.eu/userfiles/file/EurlSRM/meth_QuPPe-PO_EurlSRM.pdf
• Chamkasem N., Harmon T. (2016) Analytical and Bioanalytical Chemistry, 408(18), 4995–5004.