Semi-automated method for in-line removal of matrix components from food for the analysis of residual pesticides by LC-MS/MS

Importance of Topic

Liquid chromatography–tandem mass spectrometry (LC-MS/MS) is a gold standard for pesticide residue analysis in food commodities. However, complex food matrices often introduce interferences that compromise sensitivity, instrument robustness, and data quality. The semi-automated in-line sample preparation (ILSP) method offers a targeted cleanup approach that removes co-extracted matrix components prior to chromatographic separation, reducing contamination, simplifying workflows, and enhancing reproducibility across diverse food types.

Objectives and Study Overview

This work evaluates ILSP as a standalone or QuEChERS-compatible cleanup for the analysis of 61 pesticides in six challenging commodities: spinach, soybean meal, avocado, whole orange, black tea, and hibiscus tea. Key goals include optimizing valve switch times, establishing wash protocols, and demonstrating consistent recoveries at low (10 ng/g) and high (200 ng/g) concentration levels.

Methodology and Instrumentation

A binary HPLC system with an auxiliary pump delivers mobile phases (2 mM ammonium formate + 0.2% formic acid in water and methanol) to an ILSP cartridge via a 6-port high-pressure switching valve. The analytical column is replaced by a union during cleanup steps. Sample extracts (5–15 g homogenate in acetonitrile + 0.1% acetic acid) are injected directly onto the ILSP cartridge. Valve switching removes matrix pigments to waste, then directs analytes to the LC-MS/MS detector. Method development involved:

• Determining the last analyte elution time on ILSP for valve switch timing.
• Replacing mobile phase B with wash solvents to flush residual matrix.
• Monitoring total ion chromatograms to confirm baseline return.

Key Results and Discussion

Recoveries for all 61 pesticides met acceptance criteria (87–100% at low and high levels) across diverse matrices. Spinach and soybean meal showed >94% of analytes within range, while avocado and orange exhibited minimal matrix effects with timely valve switching. Difficult matrices like black tea and hibiscus tea delivered >92% of compounds within specifications. ILSP reduced instrument contamination and maintained stable MS response over extended runs.

Benefits and Practical Applications

• Automated cleanup lowers manual labor and error.
• Reduced matrix load extends column and source lifetime.
• Compatibility with existing QuEChERS protocols enables flexible implementation.
• High throughput supports routine QA/QC and regulatory testing.

Future Trends and Potential Applications

Advancements may include full automation of valve timing, expansion to other analyte classes (e.g., veterinary drugs, mycotoxins), integration with online data evaluation, and miniaturized cartridges for green analytical chemistry. Real-time matrix monitoring could further optimize wash cycles and reduce solvent usage.

Conclusion

Semi-automated ILSP provides a robust, reproducible in-line cleanup solution for pesticide residue analysis by LC-MS/MS. By minimizing matrix interferences and streamlining workflows, ILSP enhances data quality, instrument performance, and laboratory efficiency across a broad range of food matrices.

References

1. Lupo S.A., Romesberg R.L., Lu X. Automated inline pigment removal for the analysis of pesticide residues in spinach by liquid chromatography tandem mass spectrometry. J. Chromatogr. A. 1629 (2020) 461–477.