Quaternary amine polar pesticides using improved cation-exchange separation technology combined with tandem mass spectrometry detection

Significance of the Topic

Quaternary amine polar pesticides such as chlormequat, mepiquat, paraquat, and diquat are widely employed as plant growth regulators and desiccants. Their persistent residues in cereal products pose food safety challenges. Owing to their ionic characteristics, these compounds require specialized separation and detection strategies to ensure accurate quantification and regulatory compliance.

Objectives and Study Overview

This study demonstrates a robust analytical workflow for determining four quaternary amine polar pesticides in oat cereal matrices. By integrating the European QuPPe version 12 extraction protocol with improved cation-exchange chromatography and tandem mass spectrometry, the method aims to achieve baseline resolution, low detection limits, and reliable recoveries.

Methodology

Sample Preparation and Extraction
Ground oatmeal and toasted oat cereals were extracted via the EURL Quick Polar Pesticide (QuPPe v.12) approach. Formic acid–methanol was applied for mepiquat and chlormequat, while HCl–methanol was used for paraquat and diquat. Extracts were shaken at 80 °C, centrifuged, filtered, and diluted prior to analysis.
Chromatographic Conditions
A Thermo Scientific Dionex IonPac CG21-Fast guard column coupled to a CS21-Fast analytical column provided cation-exchange separation. A methanesulfonic acid gradient (3 mM to 25 mM) at 0.30 mL/min and a 10 µL injection volume yielded baseline separation of analytes and matrix ions within 15 min, followed by a 15 min, 1 mM wash to remove residual matrix.

Instrumentation

• Thermo Scientific Dionex ICS-6000 HPIC system
• Dionex AS-AP autosampler
• Thermo Scientific TSQ Altis Plus triple quadrupole mass spectrometer (SRM mode)
• Thermo Scientific ISQ EC single quadrupole mass spectrometer (SIM mode)
• Thermo Chromeleon CDS version 7.3

Results and Discussion

The optimized IC-MS/MS method provided clear separation of the four quaternary amine pesticides and common matrix cations within a 15 min window. MS calibration curves were quadratic over 1–100 µg/L, with limits of detection of 0.07–0.09 µg/L and quantitation down to ~0.1 µg/L. Recovery experiments at 5 µg/L and 25 µg/L spikes yielded 85–117% and 86–118%, respectively. Unspiked cereal samples contained 0.4–1.7 µg/kg of residual pesticides, well below MRLs of 0.02–15 mg/kg. Single-quadrupole SIM analysis achieved LODs in the low µg/L range but with lower sensitivity compared to SRM.

Practical Benefits and Applications

• Enables accurate monitoring of quaternary amine pesticides in food safety and QA/QC laboratories
• High sensitivity and selectivity ensure detection below regulated maximum residue levels
• Effective matrix removal reduces analytical interferences
• Suitable for high-throughput routine screening of cereal and grain products

Future Trends and Opportunities

Further enhancements may include novel cation-exchange stationary phases for faster separations, coupling with high-resolution mass spectrometry for comprehensive screening, microflow IC to reduce solvent consumption, and fully automated QuPPe workflows. The methodological framework can be extended to other polar pesticide classes and complex matrices such as fruits, vegetables, and environmental samples.

Conclusion

The cation-exchange IC-MS/MS approach delivers a sensitive, reliable, and reproducible platform for quantifying quaternary amine polar pesticides in oat-based products. The method meets stringent regulatory requirements and supports efficient food safety testing.

References

1. Kolberg DIS, Mack D, Anastassiades M, Hetmanski MT, Fussell RJ, Meijer T, Mol HG. Determination of anionic polar pesticides by IC-MS. Anal Bioanal Chem. DOI: 10.1007/s00216-012-6340-9.
2. European Commission. Quick Polar Pesticide (QuPPe-PO) Method, Version 12.
3. Christison T, Madden JE, Rohrer J. Thermo Scientific Technical Note TN73990 and Application Notes AN000607, AN001166.