The application of LC-UFMSMS to the analysis of pesticide residues in negative ion ESI

Significance of the Topic

The reliable detection of pesticide residues such as glyphosate and its metabolite AMPA in food and environmental samples is critical for health, regulatory compliance and environmental monitoring. The development of highly sensitive, robust and rapid analytical workflows supports better risk assessment and ensures consumer safety in agriculture and water resources.

Objectives and Study Overview

This study evaluates the performance of FMOC derivatization combined with reversed-phase ultrafast liquid chromatography and tandem mass spectrometry (LC-UFMSMS) in negative ion electrospray ionization (ESI). The primary goal is to achieve sub-picogram detection limits for glyphosate and AMPA while expanding the approach to a broader range of phenoxy and carboxylate herbicides.

Methodology and Instrumentation

Sample Preparation and Derivatization

• Food matrices (grains and fruits) spiked at concentrations from 0.001 to 1 ppm were extracted using a QuEChERS protocol.
• Extracts were derivatized with FMOC reagent to convert polar herbicides into hydrophobic derivatives amenable to reversed-phase separation.

Chromatography and Mass Spectrometry

• Instruments: Shimadzu Nexera LC-30 UHPLC coupled to LCMS-8030 and LCMS-8040 systems equipped with UFSweeperTM in-line filter.
• Column: Shimpack XR-ODS III (75 mm×2.1 mm, 1.7 µm) at 0.4 mL/min.
• Mobile phase: gradient of 10 mM ammonium acetate (aqueous) and 10 mM ammonium acetate in methanol.
• Injection volumes ranged from 1 to 10 µL, corresponding to 1–1000 pg on column.
• MRM transitions were optimized automatically for protonated FMOC derivatives, with collision gas (argon) at 230 kPa.

Main Results and Discussion

The LCMS-8040 enabled detection of 1 pg FMOC-glyphosate and 2.5 pg FMOC-AMPA on column with signal-to-noise ratios above 5:1 and 6:1 respectively. Linearity was demonstrated over three orders of magnitude (1–1000 pg on column) with correlation coefficients (R2) of 0.9999. The UFSweeper filter effectively suppressed matrix interferences from QuEChERS extracts, stabilizing baseline noise. Method sensitivity exceeded current regulatory requirements and extended to a panel of 14 herbicides, all showing detection limits below 2 pg and robust negative ion MRM responses.

Benefits and Practical Applications

The FMOC derivatization strategy allows the use of standard reversed-phase LC, improving chromatographic robustness and ease of method transfer. High sensitivity and selectivity support trace-level quantitation in complex food matrices, facilitating routine compliance testing in QA/QC laboratories. The miniaturized sample injection and potential for automated derivatization enhance throughput for high-volume screening.

Future Trends and Potential Applications

Further integration of high-resolution mass spectrometry could expand analyte coverage and confirmatory capabilities. On-line derivatization and microfluidic sample handling may drive fully automated workflows with reduced solvent consumption. The methodology could be adapted to environmental monitoring of water and soil, and to emerging contaminants beyond herbicides.

Conclusion

The combined FMOC derivatization and LC-UFMSMS approach delivers exceptional sensitivity, linearity and robustness for negative ion analysis of glyphosate, AMPA and a suite of herbicides. The method is well suited for regulatory and research laboratories requiring high-throughput, trace-level quantitation in complex matrices.

Reference

• Grieves N, Mulders J, Peebles B, et al. The application of LC-UFMSMS to the analysis of pesticide residues in negative ion ESI. Shimadzu Australasia; Metabolomics Australia; Murdoch University.