Direct Determination of Paraquat, Diquat, Mepiquat, Morpholine, and Chlormequat Pesticides Using Ion Chromatography and High Resolution Accurate Mass Spectrometry

Significance of the topic

Cationic quaternary amine pesticides such as paraquat, diquat, mepiquat, chloromequat and morpholine pose significant health risks due to acute and chronic toxicity. Reliable and rapid analytical methods are essential for regulatory monitoring and ensuring food safety. Ion chromatography coupled with high resolution accurate mass spectrometry (IC-HRAMS) offers a promising platform for direct detection of these polar compounds in complex matrices.

Objectives and overview of the study

This study aimed to develop and validate a fast and sensitive method for direct determination of six cationic pesticides in homogenized fruit and vegetable samples. The workflow combined QuPPe multiresidue extraction with cation-exchange chromatography and serial detection using suppressed conductivity and parallel reaction monitoring (PRM) on a high resolution Orbitrap mass spectrometer.

Methodology and instrumentation

Sample extraction followed the European QuPPe protocol using cold methanol and dilution prior to analysis.
Chromatographic separation employed a Thermo Scientific Dionex IonPac CS17 cation-exchange column with an electrolytically generated methanesulfonic acid gradient at 0.4 mL/min over 10 min.
Serial detection included:

• Suppressed conductivity with a Dionex CERS 500e suppressor to monitor ionic conductivity.
• High resolution accurate mass detection in full scan and PRM modes on a Q Exactive Hybrid Quadrupole-Orbitrap instrument.

Used instrumentation

• Dionex Integrion HPIC compact system with reagent-free IC and CD detector.
• Thermo Scientific Dionex IonPac CS17 cation-exchange column (2 × 250 mm) and a prototype JM006 column.
• Dionex AS-AP autosampler.
• Thermo Scientific Q Exactive Focus Hybrid Quadrupole-Orbitrap mass spectrometer with HESI II source.

Main results and discussion

All six pesticides exhibited good chromatographic performance with peak asymmetries of 1.0–1.1 and elution within 10 min. Mepiquat and chloromequat achieved resolution factors above 2, while diquat and paraquat coeluted chromatographically but were resolved by PRM due to distinct accurate masses. Mass accuracy was maintained below 4 ppm. Recovery experiments in spiked extracts yielded 80–120% and limits of detection were in the single to low double-digit µg/L range. No native pesticide residues were detected in tested fruit and vegetable samples.

Benefits and practical applications

The method provides a rapid, robust approach for routine monitoring of polar quaternary amine pesticides in food matrices. Direct IC-HRAMS analysis eliminates the need for ion-pair reagents and achieves both chromatographic separation and high specificity by accurate mass MS/MS, facilitating compliance with regulatory requirements.

Future trends and opportunities

Further column development, such as optimization of prototype cation-exchange phases, could improve chromatographic separation of structurally similar quaternary amines. Integration of automated sample preparation and high-throughput workflows will support large-scale screening. Expansion to additional polar pesticide classes via IC-HRAMS will strengthen comprehensive contaminant surveillance.

Conclusion

This study demonstrates a fast, sensitive IC-HRAMS method for six quaternary amine pesticides in fruits and vegetables, combining QuPPe extraction, CEX separation, suppressed conductivity and accurate mass PRM detection. The approach meets regulatory mass accuracy limits and offers practical advantages for food safety laboratories.

Reference

1. European Commission. Quick Polar Pesticides (QuPPe) Method, 2018.
2. Adams S. Analysis of Polar Pesticides by Ion-Exchange Chromatography Tandem Mass Spectrometry. NACRW 2016.
3. Thermo Scientific. Application Note 661: Fast Routine Analysis of Polar Pesticides.
4. Thermo Scientific. Application Note 666: Routine Analysis of Polar Pesticides.
5. Rajski et al. Coupling Ion Chromatography to Q-Orbitrap for Fast Analysis of Anionic Pesticides, J. AOAC Int., 101(2), 2018.
6. SANTE/11813/2017. European Commission Directorate General for Health and Food Safety, Pesticides and Biocides.