Determination of anionic polar pesticides by ion chromatography with serial detection by suppressed conductivity and mass spectrometry

Importance of the Topic

Public concern over residual polar pesticides in food has grown alongside regulatory scrutiny of widely used herbicides such as glyphosate and its metabolites. Polar pesticides include ionic herbicides, fungicides, and growth regulators that often remain in low µg/kg levels in crops. Accurate, sensitive, and high-throughput methods are essential for routine monitoring of these contaminants in a variety of food matrices.

Objectives and Study Overview

This application note demonstrates a rapid method for simultaneous determination of ten anionic polar pesticides and three disinfection byproducts in food extracts. Ion chromatography (IC) with serial detection by suppressed conductivity and single quadrupole mass spectrometry (IC-MS) is evaluated for linearity, detection limits, reproducibility, and recovery in homogenized pear and pea samples.

Methodology and Instrumentation

The method employs a Thermo Scientific Dionex ICS-6000 HPIC system with an EGC 500 KOH eluent generator, CR-ATC 600 trap, and ASRS 300 suppressor. Separation uses an IonPac AG19 guard column and AS19 analytical column (2 × 250 mm) with a stepped KOH gradient (15–75 mM) at 0.375 mL/min, 40 °C. A diverter valve directs eluent to suppressed conductivity detection or to the Thermo Scientific ISQ EC single quadrupole MS operating in negative ESI mode (full scan and SIM). Sample preparation follows a simplified QuPPe extraction with cold methanol, centrifugation, filtration, and 2- or 5-fold dilution.

• Instrumental setup
  • Dionex ICS-6000 RFIC with dual pumps and high-pressure degasser
  • Dionex EGC 500 KOH cartridge and CR-ATC 600 trap column
  • Dionex IonPac AG19 and AS19 4 µm columns
  • Dionex ASRS 300 suppressor in recycle mode for conductivity detection
  • ISQ EC single quadrupole MS with HESI II probe and nitrogen generator
  • Chromeleon 7.2 CDS with instrument method triggers for emergency diverter control
• Chromatographic conditions
  • Gradient from 15 to 75 mM KOH over 14 min
  • Partial-loop injection: 2 µL of a 5 µL loop
  • Suppressed conductivity followed by negative ESI-MS detection
  • SIM windows for each analyte

Main Results and Discussion

All analytes eluted within 14 minutes. Conductivity detection provided a global chromatogram while SIM traces enabled selective confirmation. Calibration was linear (r2 > 0.99) for glyphosate, AMPA, glufosinate, 3-MPPA, and bialaphos over 0.05–10 mg/L and quadratic for bromate, bromide, chlorite, cyanuric acid, and fosetyl down to 0.01 mg/L. Method detection limits ranged from 1.5 to 136 µg/L, with glyphosate at the highest MDL due to ionization characteristics. Retention time RSDs were <0.5% and peak area RSDs <3%. Recovery experiments at 100 µg/L spike in 2- and 5-fold diluted pear and pea extracts yielded 80–120% except AMPA in pears (70–76%). The dual detection approach and automated emergency valve triggers protect the MS during suppressor failures.

Benefits and Practical Applications

• Fast screening of multiple anionic pesticides and disinfection byproducts in under 15 min per run
• Simultaneous suppressed conductivity and ESI-MS detection for robust quantitation and confirmation
• Single quadrupole MS provides cost-effective selectivity suitable for routine QA/QC environments
• Simple QuPPe-based sample prep compatible with diverse fruit and vegetable matrices

Future Trends and Potential Uses

Integration of ion chromatography with triple quadrupole MS (IC-MS/MS) or high-resolution accurate mass spectrometers (IC-HRAM-MS) will further lower detection limits and increase selectivity. Automated sample preparation platforms and expanded analyte libraries will support broader monitoring of cationic and zwitterionic polar pesticides. Advances in eluent generation and suppressor technologies will improve peak shapes and method robustness.

Conclusion

The presented IC-MS method on a Dionex ICS-6000 and ISQ EC single quadrupole MS offers a rapid, sensitive, and reproducible approach for determination of anionic polar pesticides and related disinfection byproducts in food extracts. With MDLs in the low µg/L range, good recoveries, and minimal instrument downtime through automated safety triggers, the method is well suited for routine screening in food-testing laboratories.

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