Fast routine analysis of polar pesticides in foods by suppressed ion chromatography and mass spectrometry

Significance of the Topic

Polar ionic pesticides such as glyphosate, AMPA, glufosinate and their metabolites are widely used in agriculture and often appear as residues in food and drinking water. Their highly polar nature makes conventional reversed‐phase HPLC unsuitable without derivatization or specialized columns. Regulatory bodies set maximum residue levels (MRLs) as low as 10–100 µg/kg in foods and 100 ng/L in water, driving the need for robust analytical methods that can meet these stringent requirements in routine high‐throughput laboratories.

Objectives and Study Overview

This work aimed to develop and validate a direct ion chromatography–tandem mass spectrometry (IC-MS/MS) method that:

• Quantifies multiple polar ionic pesticides and metabolites simultaneously in food matrices.
• Meets or exceeds current regulatory MRLs without derivatization steps.
• Demonstrates high throughput, robustness and reproducibility under routine conditions.

Methodology and Used Instrumentation

Sample preparation consisted of:

• Homogenizing 10–15 g of sample (lettuce, orange or wheat flour).
• Sequential extraction with water and chilled methanol, followed by centrifugation and 0.45 µm filtration in plastic vials to avoid analyte adsorption.
• Injection of the clear extract into the IC-MS/MS system.

The chromatographic system included:

• Dionex Integrion HPIC with in‐situ KOH eluent generation (EluGen KOH cartridge).
• Dionex IonPac AS24 analytical column (2 × 250 mm) with AG24 guard column.
• Dionex AERS 500 suppressor operating in external water regeneration mode.

Mass spectrometric detection was performed on a TSQ Endura triple quadrupole in negative heated‐ESI SRM mode. Calibration employed matrix‐matched standards over 0–600 µg/kg, and instrument tuning used an extended mass range calibration solution for improved low‐m/z accuracy.

Main Results and Discussion

• Matrix effects were significant in all food types, necessitating matrix‐matched calibration.
• Linearity: correlation coefficients ≥ 0.985 for all analytes from 0 to 600 µg/kg.
• Limits of quantification (LOQs) ranged from 1–20 µg/kg depending on compound and matrix; limits of detection (LODs) were 1–10 µg/kg.
• Recoveries: 70–120% across three spike levels (50, 200, 500 µg/kg) in lettuce and orange; wheat flour showed lower recoveries for glyphosate and AMPA and non‐detectable ethephon, suggesting the need for internal standards or modified extraction for that matrix.
• Precision: intra‐day and inter‐day RSDs were typically below 20%.
• Proficiency testing (FAPAS red grape purée) yielded 553 µg/kg ethephon (assigned 629 ± 216 µg/kg), in acceptable range.

Benefits and Practical Application of the Method

This IC-MS/MS approach offers:

• Direct analysis of underivatized polar pesticides, reducing sample handling and potential artifacts.
• High specificity and low detection limits via SRM on a triple quadrupole.
• Robustness suitable for routine QA/QC and regulatory monitoring without extensive column maintenance.
• Flexibility to accommodate diverse food matrices with minimal method changes.

Future Trends and Potential Applications

Advancements may include:

• Use of isotopically labeled internal standards to improve accuracy in challenging matrices.
• Automation of sample preparation and online dilution for ultra-high throughput.
• Expansion of analyte panels to emerging polar contaminants and metabolites.
• Integration with high-resolution MS for non‐target screening in food and environmental samples.

Conclusion

The validated IC-MS/MS method provides a streamlined, reliable workflow for quantifying multiple polar ionic pesticides and their metabolites in food at levels complying with current MRLs. Its simplicity, speed and specificity make it a strong candidate for routine food safety laboratories.

Reference

• European Commission SANTE/11945/2015. Guidance on analytical quality control and method validation for pesticide residues in food and feed.
• Regulation (EC) No 396/2005 on maximum residue levels of pesticides in or on food and feed of plant and animal origin.
• Hanke I, Singer H, Hollender J. Ultratrace determination of glyphosate, AMPA and glufosinate in water by SPE–LC–MS/MS. Anal Bioanal Chem. 2008;391(6):2265–2276.
• QuPPe Method (EU Reference Laboratory for Pesticide Residues). QuPPe database; 2016.
• IARC Q&A on Glyphosate. International Agency for Research on Cancer; 2016.
• EFSA. EFSA explains the carcinogenicity assessment of glyphosate. EFSA Journal; 2016.