Determination of cationic polar pesticides in cereals using improved cation-exchange separation technology combined with suppressed conductivity and tandem mass spectrometry

Significance of the Topic

Quaternary amine polar pesticides such as mepiquat, chlormequat, paraquat and diquat are widely used as plant growth regulators and harvest desiccants on cereal crops. Their charged ionic nature and strong interaction with sample matrices make accurate detection and quantification in food challenging. Reliable analytical methods are essential to ensure compliance with regulatory limits and to protect consumer health.

Objectives and Study Overview

This study aimed to develop and validate a robust analytical workflow for simultaneous determination of four quaternary amine pesticides in oat cereal matrices. Key goals included optimizing extraction protocols, improving chromatographic resolution on a cation-exchange column, and achieving high sensitivity and reproducibility using suppressed conductivity detection coupled with tandem mass spectrometry.

Methodology and Instrumentation

The extraction step followed the European Union Reference Laboratory Quick Polar Pesticide Extraction (QuPPE) version 12 method, using acidified methanol or HCl-methanol mixtures. Extracts were cleaned, diluted and injected onto a Thermo Scientific Dionex IonPac CS21-Fast-4 µm cation-exchange column. The chromatographic system featured a self-generating methanesulfonic acid gradient and an electrolytic trap suppressor for conductivity detection. A Thermo Scientific TSQ Altis Plus triple quadrupole mass spectrometer operated in SRM mode provided confirmatory detection. Chromeleon CDS controlled the IC-MS/MS workflow.

Key Results and Discussion

The method achieved baseline separation of target pesticides from matrix ions within a 15 min gradient and a total 34 min run time. Limits of determination were below 0.5 µg/kg in cereal samples, with limits of detection around 0.07–0.09 µg/L. Recovery experiments at 5 µg/L spiking levels yielded 85–117% recoveries across ground and toasted oat matrices. Naturally incurred residues in oat samples ranged from 0.4 to 1.7 µg/kg, well below EU maximum residue limits (0.02–15 mg/kg). An additional 15 min 1 mM MSA wash step successfully removed HCl-extraction matrix interferences.

Benefits and Practical Applications

• High sensitivity and specificity for quaternary amine pesticides in complex cereal matrices
• Efficient chromatographic resolution using dedicated cation-exchange columns
• Validated recoveries and reproducibility suitable for routine monitoring laboratories
• Compliance with EU regulatory requirements for polar pesticide residues

Future Trends and Potential Applications

Emerging trends include expanding the method to other food matrices, integrating high-resolution mass spectrometry for broader screening, and automating sample preparation for higher throughput. Miniaturized or on-site IC-MS/MS platforms may further enhance field testing capabilities for rapid food safety assessments.

Conclusion

The developed IC-MS/MS method offers a robust, sensitive, and reliable approach for the simultaneous quantification of quaternary amine polar pesticides in oat cereals. Its validated performance supports routine quality control and regulatory compliance in food safety laboratories.

References

1. Kolberg DI, Mack D, Anastassiades M, Hetmanski MT, Fussell RJ, Meijer T, Mol HG. Ion chromatography–tandem mass spectrometry for determination of anionic polar pesticides. Anal Bioanal Chem. 2012; DOI:10.1007/s00216-012-6340-9.
2. European Commission. Quick Polar Pesticide method QuPPe-PO, Version 12.0.
3. Madden JE, Saini C. Thermo Scientific Technical Note TN73990.
4. Christison T, Madden JE, Rohrer J. Thermo Scientific Application Note AN000607.