Determination of glyphosate and AMPA in oat flour by IC-MS

Significance of the topic

The widespread use of glyphosate, the active ingredient in many herbicides, has raised concerns about its residues in food products and potential health risks. Oat flour, a common dietary component, can accumulate trace levels of glyphosate and its main metabolite AMPA (aminomethylphosphonic acid).

Reliable, sensitive, and direct analytical methods are vital for routine monitoring of these ionic compounds at low concentrations without complex sample derivatization steps. Coupling ion chromatography (IC) with single quadrupole mass spectrometry (MS) offers a streamlined approach for high-throughput screening in food safety and regulatory compliance laboratories.

Objectives and study overview

This work aimed to develop and validate an IC-MS method for the direct simultaneous determination of glyphosate and AMPA in oat flour extracts.

The specific objectives were:

• Optimize chromatographic separation of glyphosate and AMPA from common anions using a hydroxide-selective anion-exchange column.
• Integrate a reagent-free IC system with a single quadrupole MS operated in selected ion monitoring (SIM) mode.
• Evaluate method performance: sensitivity, precision, accuracy, calibration linearity, and limits of detection/quantification in the oat flour matrix.

Methodology and instrumentation used

Sample preparation employed a modified Quick Polar Pesticides Extraction (QuPPE) protocol:

• Weighed oat flour (5 g), added water for hydration and methanol for extraction.
• Samples were frozen and centrifuged, then diluted tenfold with deionized water.
• Cleanup was achieved by passing extracts through an OnGuard II RP cartridge and 0.2 µm filtration.
• Isotopically labeled internal standards (13C/15N-labeled AMPA and glyphosate) were spiked at 10 µg/L for each 1 mL of final extract.

Chromatographic separation:

• System: Thermo Scientific Dionex Integrion RFIC with eluent generator.
• Column: Dionex IonPac AS19-4 µm guard (2×50 mm) and analytical (2×250 mm).
• Eluent: Gradient of KOH (14 mM to 60 mM) generated in-line by an EGC 500 cartridge and CR-ATC trap.
• Flow rate: 0.35 mL/min; column temperature: 30 °C; run time: 30 min.

Mass spectrometry:

• Instrument: Thermo Scientific ISQ EC single quadrupole MS with HESI-II probe.
• Mode: Negative electrospray ionization; SIM at m/z 168 (glyphosate), 110 (AMPA) and appropriate internal standard channels.
• Diverter valve positioned to waste most of the matrix and direct target peaks to MS from 8 to 25 min.
• Suppressor: ADRS 600 in external water mode to remove KOH before MS.

Main results and discussion

Calibration and linearity:

• Calibration range: 0.5–50 µg/L for glyphosate and 1–50 µg/L for AMPA.
• Internal standard calibration yielded r² > 0.9999 for both analytes.

Detection limits:

• Glyphosate LOD = 0.0725 µg/L (2.9 ng/g); LOQ = 0.242 µg/L (9.66 ng/g).
• AMPA LOD = 0.284 µg/L (11.4 ng/g); LOQ = 0.947 µg/L (37.9 ng/g).

Precision and accuracy:

• Peak area RSD ≤ 1.22% and retention time RSD ≤ 0.39% (n=9) confirmed excellent repeatability.
• Recoveries in oat flour matrix spiked at 1, 2, and 10 µg/L ranged from 96% to 101% for both analytes.

Sample analysis:

• Three oat flour samples were analyzed in duplicate.
• AMPA was not detected in any sample (below LOQ).
• Glyphosate was detected at 33.4 to 181 ng/g, well below the EPA limit of 30 mg/kg for oats.

Benefits and practical applications of the method

This IC-MS approach provides:

• Direct analysis without derivatization, reducing sample preparation time and complexity.
• High selectivity and sensitivity for polar ionic pesticides in complex food matrices.
• Cost-effective screening using a single quadrupole MS rather than tandem MS instruments.
• Reagent-free operation with in-line eluent generation and suppressor regeneration.

This workflow is well suited for routine monitoring of glyphosate and related polar contaminants by food safety, QA/QC, and environmental laboratories.

Future trends and potential applications

Further developments may include:

• Extension to other ionic pesticides and metabolites to create comprehensive polar pesticide screening panels.
• Automation of sample preparation using online SPE to improve throughput.
• Adaptation to high-resolution mass spectrometry for non-targeted and confirmatory analyses.
• Application in regulatory compliance monitoring of diverse food commodities beyond cereals.

Conclusion

The developed IC-MS method enables reliable, sensitive, and direct determination of glyphosate and AMPA in oat flour with minimal sample cleanup. The approach achieves low ng/g detection limits, excellent accuracy, and precision, while leveraging reagent-free IC and a single quadrupole MS for cost-effective routine analysis.

Reference

• 1. IARC. Q&A about Glyphosate. Lyon, France, 2016.
• 2. Grandcoin A, Piel S, Baurès E. AminoMethylPhosphonic acid in natural waters. Water Res. 2017;117:187–197.
• 3. eCFR Title 40. Part 180 Tolerances and exemptions for pesticide chemicals in or on raw agricultural commodities. 2019.
• 4. EWG. Roundup for Breakfast, Part 2: Glyphosate in cereals. 2018.
• 5. Adams S, Guest J, Dickinson M, et al. J Agric Food Chem. 2017;65(34):7294–7304.
• 6. Thermo Fisher Scientific. Integrion HPIC Installation & Operator’s Manual. 2020.
• 7. Thermo Fisher Scientific. ADRS Suppressor Manual. 2019.
• 8. Thermo Fisher Scientific. ISQ EC MS Operating Manual. 2018.
• 9. Thermo Fisher Scientific. Technical Note 72611: IC-MS Configuration. 2020.
• 10. Thermo Fisher Scientific. Anionic Pesticides Explorer Guide. 2021.
• 11. Thermo Fisher Scientific. IonPac AS19-4 µm Column Product Manual. 2019.
• 12. ICH Q2B. Validation of Analytical Procedures, Methodology. 1996.