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

Determination of cationic polar pesticides in cereals is critical for ensuring food safety and regulatory compliance. Quaternary amine pesticides such as mepiquat, chlormequat, paraquat, and diquat pose unique analytical challenges due to their highly charged nature and structural similarity. Robust methods enable accurate monitoring of trace residues to protect consumer health and adhere to maximum residue limits (MRLs).

Objectives and study overview

This study aimed to develop and demonstrate a rapid, sensitive, and reliable ion chromatography–tandem mass spectrometry (IC-MS/MS) method for the quantitation of four quaternary amine polar pesticides in oat cereal matrices. Key goals included baseline chromatographic resolution of target analytes, effective removal of interfering matrix components, and quantitation at sub-μg/kg levels within the regulatory MRL range.

Methodology and instrumentation

Sample preparation followed the European QuPPE version 12 Quick Polar Pesticide extraction protocol using 1:1 methanol/acid (100 mM formic acid for mepiquat and chlormequat, 100 mM HCl for paraquat and diquat). Extracts were centrifuged, filtered, diluted, and analyzed by IC-MS/MS. A post-run wash step with 1 mM methanesulfonic acid (MSA) ensured complete matrix removal.

Used instrumentation

• Thermo Scientific Dionex ICS-6000 HPIC system with Chromeleon™ CDS v7 control
• Thermo Scientific Dionex IonPac CG21-Fast-4µm guard and CS21-Fast-4µm analytical columns (2 mm i.d.)
• Eluent: MSA gradient from 3 to 25 mM over 15 min, flow rate 0.30 mL/min, column at 40 °C
• Suppressor: Dionex CDRS 600, suppressed conductivity detection
• Thermo Scientific TSQ Altis™ Plus triple quadrupole mass spectrometer with HESI-II source in positive SRM mode
• Nitrogen sheath, auxiliary, and sweep gases; vaporizer at 300 °C, ion transfer tube at 350 °C

Main results and discussion

Calibration curves were quadratic over 1–100 µg/L, with limits of detection (LODs) of 0.07–0.09 µg/L (3× S/N). Recoveries in ground and toasted oat cereals ranged from 85% to 117% at 5 µg/L spike levels. Residual pesticide levels in commercial oats fell between 0.4 and 1.7 µg/kg, well below EU MRLs (0.02–15 mg/kg). A 15 min 1 mM MSA wash effectively eliminated matrix interferences after HCl extraction.

Benefits and practical applications

This IC-MS/MS approach delivers high selectivity and sensitivity for quaternary amine pesticides, enabling sub-µg/kg quantitation in complex cereal matrices. Fast chromatographic separation (<34 min) and robust matrix removal make it suitable for routine quality control in food safety laboratories, regulatory testing, and agricultural monitoring.

Future trends and potential applications

Advances may include coupling to high-resolution mass spectrometry for non-target screening, expanded multi-class pesticide panels, and miniaturized chromatography formats for higher throughput. Automation of sample preparation and integration with laboratory information management systems (LIMS) will further enhance efficiency and data traceability.

Conclusion

An IC-MS/MS method using cation-exchange separation and SRM detection provides accurate, sensitive, and reliable analysis of quaternary amine pesticides in cereals. The protocol meets regulatory requirements, offers rapid turnaround, and supports comprehensive food safety testing.

References

• Kolberg D.I.S., Mack D., Anastassiades M., Hetmanski M.T., Fussell R.J., Meijer T., Mol H.G. Validation of polar pesticide residues by ion chromatography–MS. Anal Bioanal Chem. DOI:10.1007/s00216-012-6340-9.
• European Commission. Quick Polar Pesticide (QuPPE) method version 12. EU Reference Laboratories.
• Madden J.E., Saini C. Thermo Scientific Technical Note TN73990: IC-MS/MS determination of quaternary amine pesticides.
• Christison T., Madden J.E., Rohrer J. Thermo Scientific Application Note AN0006074: Polar pesticide analysis in cereals.