Determination of glyphosate and AMPA in oat flour using ion chromatography-mass spectrometry

Significance of the Topic

Glyphosate is a global herbicide with potential health risks and widespread use in cereals. Its main metabolite, AMPA, also poses toxicological concerns. Monitoring these residues in food products such as oat flour is critical for consumer safety and regulatory compliance.

Study Objectives and Overview

The aim of this work was to establish a reliable and rapid method for simultaneous quantification of glyphosate and AMPA in oat flour by coupling ion chromatography with single quadrupole mass spectrometry (IC-MS). The study evaluates method performance using three distinct oat flour samples processed by a modified Quick Polar Pesticides Extraction (QuPPE) protocol.

Methodology and Instrumentation Used

• Sample Preparation: Extraction of 5 g oat flour with water and methanol, freeze at -20 °C, centrifugation, 10-fold dilution, cleanup via OnGuard II RP SPE and 0.2 µm filtration.
• Chromatography: Dionex IC system with electrolytic KOH eluent generation, Dionex IonPac AG19-4 µm guard and AS19-4 µm analytical columns, 30 min gradient, 0.35 mL/min flow, 30 °C.
• Detection: Suppressed conductivity detection (Dionex ADRS 600 suppressor) and electrospray ionization mass spectrometry in negative SIM mode on Thermo ISQ EC single quadrupole.
• Data Analysis: Chromeleon 7.2 software for chromatographic control, signal integration and quantification.

Main Results and Discussion

• Chromatographic Separation: Effective resolution of common inorganic anions, AMPA and glyphosate within 30 min on the AS19 column, as confirmed by conductivity and MS profiles.
• Detection Limits: LOD and LOQ estimated at 0.0725 µg/L (2.9 ng/g) and 0.242 µg/L (9.66 ng/g) for AMPA; 0.284 µg/L (11.4 ng/g) and 0.947 µg/L (37.9 ng/g) for glyphosate, based on S/N ratios of 3 and 10.
• Sample Analysis: AMPA was below detection in all three oat flour samples, while glyphosate concentrations ranged from 33.4 to 181 ng/g, demonstrating method sensitivity for regulatory levels well below the US EPA tolerance (30 mg/kg).

Benefits and Practical Applications

• Direct Analysis: Eliminates derivatization steps, reducing sample preparation time and reagent use.
• High Sensitivity and Selectivity: SIM mode on single quadrupole MS provides reliable quantification in complex matrices.
• Operational Efficiency: Integrated eluent generation and automated suppression enhance reproducibility and ease of use in routine testing.

Future Trends and Opportunities

• MS/MS Integration: Adoption of tandem MS for improved selectivity and lower detection limits in multi-residue screening.
• High-Throughput Workflows: Automation and miniaturization of sample preparation for large-scale monitoring.
• Regulatory Impact: Anticipated tightening of glyphosate limits may drive demand for more robust analytical protocols in the cereal industry.

Conclusion

A streamlined IC-MS method was demonstrated for quantifying glyphosate and AMPA in oat flour with minimal cleanup and high analytical performance. The approach meets stringent detection requirements and offers practical advantages for quality control laboratories and regulatory testing.

References

1. Electronic Code of Federal Regulations. eCFR — Code of Federal Regulations (2019).
2. Thermo Scientific Application Note 000282: Determination of glyphosate and AMPA in oat flour by IC-MS.