Determination of Anionic Polar Pesticides in Wheat Flour Extracts Using UPLC-MS/MS with the Torus DEA Column

Significance of the Topic

The accurate determination of anionic polar pesticides in wheat flour is critical for food safety monitoring and regulatory compliance. Highly polar, ionic compounds present analytical challenges due to poor retention on conventional reversed-phase columns and significant matrix effects. Developing robust methods capable of achieving low detection limits (down to 0.01 mg/kg) in complex, high-starch/protein matrices is essential for reliable multi-residue analysis.

Objectives and Study Overview

This application note evaluates a modified QuPPe (Quick Polar Pesticides) extraction procedure combined with ultraperformance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). The aim was to assess chromatographic performance, sensitivity, and reproducibility for a suite of anionic polar pesticides and their metabolites in wheat flour, using a Torus DEA column on an ACQUITY UPLC H-Class Bio System coupled to a Xevo TQ-XS mass spectrometer.

Methodology and Instrumentation

Sample Preparation:

• 5 g wheat flour homogenized and extracted with water and formic acid–methanol.
• Freezing-out step at –4 °C for one hour prior to centrifugation.
• Filtration (0.2 µm PTFE) into autosampler vials.

UPLC Conditions:

• Column: Torus DEA, 2.1×100 mm, 1.7 µm.
• Mobile phases: A) 50 mM ammonium formate + 0.9% formic acid; B) acetonitrile + 0.9% formic acid.
• Gradient: 10→90% B over 4 min, hold, then re-equilibrate; 20 min total run time.
• Flow rate: 0.5 mL/min; column temp: 50 °C; injection: 10 µL.

MS/MS Conditions:

• Instrument: Xevo TQ-XS with ESI in negative ion mode.
• MRM transitions optimized via IntelliStart; soft ionization applied for ethephon.
• Desolvation: 600 °C, 1000 L/h; source: 150 °C; capillary: 2.5 kV.

Used Instrumentation

• ACQUITY UPLC H-Class Bio System with FTN Sample Manager.
• Torus DEA column (Waters).
• Xevo TQ-XS triple quadrupole MS.
• MassLynx v4.2 & TargetLynx XS software.

Results and Discussion

The method achieved baseline separation of isobaric pairs (e.g., AMPA/fosetyl-Al; fosetyl-Al/phosphonic acid) and demonstrated limits of quantification of 0.01 mg/kg for all analytes. Calibration curves (0.005–0.25 mg/kg) yielded r²>0.99 and residuals within ±20% except AMPA at the lowest level. Precision from 15 replicate injections at 0.1 mg/kg showed RSDs <5% (AMPA 9.6%, fosetyl-Al 5.4%). Endogenous phosphonic acid in the blank matrix was quantified at 0.002 mg/kg. Chromatographic retention times and ion ratios complied with SANTE guidelines.

Benefits and Practical Applications

• Single-run quantification of multiple anionic polar pesticides without derivatization.
• High sensitivity and selectivity suitable for MRL surveillance in wheat flour.
• Inert flow path minimizes metal-anion interactions, improving peak shape stability.
• Compatibility with established QuPPe extraction and ability to dilute high-level residues for compliance checks.

Future Trends and Applications

Emerging opportunities include:

• Adopting dedicated anionic polar pesticide columns for expanded compound scope.
• Integration with high-resolution mass spectrometry for non-target screening.
• Automated, miniaturized extraction workflows to increase throughput.
• Application of this approach to other challenging food matrices (e.g., cereals, pulses).
• Harmonization of global MRL standards and method inter‐laboratory validation.

Conclusion

The combination of a Torus DEA column on an ACQUITY UPLC H-Class Bio System with a Xevo TQ-XS MS provides a robust, sensitive platform for routine analysis of anionic polar pesticides in wheat flour. The method meets regulatory criteria for retention stability, linearity, precision, and detection limits. Laboratories should perform in-house validations to confirm fitness for purpose across diverse commodity matrices.

References

1. EURL Quick Polar Pesticides (QuPPe) method guidance. EURL-SRM.
2. Wuyts B. et al. Anionic Polar Pesticides in Spinach using Torus DEA Column. Waters application note 720006213EN, 2018.
3. European Union SANTE/11813/2017: Analytical Quality Control and Method Validation for Pesticide Residues.
4. Waters Torus DEA Column Startup Guide 720006156EN, 2017.