Quantitative Determination of Residual Glufosinate, Glyphosate and AMPA in Rice Matrix by Direct LC-MS/MS Method

Significance of the Topic

This summary presents a robust analytical approach for sensitive and accurate quantification of polar herbicides glufosinate, glyphosate and its metabolite AMPA in rice. These compounds are widely used in agriculture and regulated by strict maximum residue limits (MRLs) in food matrices. Reliable monitoring supports food safety, regulatory compliance and public health protection.

Objectives and Study Overview

The study aimed to establish a direct liquid chromatography–tandem mass spectrometry (LC-MS/MS) method employing a QuPPe-based sample preparation to determine residual levels of glufosinate, glyphosate and AMPA in rice using the Shimadzu LCMS-8060NX system. Key goals included achieving a limit of quantitation (LOQ) of 0.1 mg/kg for glyphosate, matching EU regulatory requirements, and demonstrating acceptable linearity, accuracy, precision, matrix effects and recovery in a rice matrix.

Methodology and Used Instrumentation

Sample Preparation (QuPPe protocol):

• Grind 1 g rice; hydrate with 9 mL water (15 min).
• Spike with standard; add 9.9 mL MeOH/1% formic acid and 100 µL formic acid; shake (1 min).
• Add 1 mL 10% EDTA solution; shake (15 min); centrifuge at –9 °C, 11 000 rpm (10 min).
• Filter supernatant (0.22 µm nylon); dilute 2 mL extract with 2 mL acetonitrile; ultrafiltrate (3 kDa cutoff).
• Transfer to polypropylene vial for LC-MS/MS analysis.

LC-MS/MS Conditions:

• Column: Acclaim Trinity Q1 hybrid mode (3 × 100 mm, 3 µm).
• Mobile phase A: water + 50 mM ammonium formate + 1% formic acid (pH 2.8); B: acetonitrile; gradient in 10 min at 0.5 mL/min.
• Column oven: 40 °C; injection: 30 µL.
• Interface: HESI ESI (1 kV), interface temp 400 °C, DL 300 °C, heat block 400 °C.
• Gas flows: nebulizing 3 L/min, drying 15 L/min, heating 20 L/min.
• Mode: negative MRM with optimized transitions and collision energies for each analyte.

Main Results and Discussion

Calibration and Sensitivity:

• Linear range: 0.5–100 ng/mL; r² > 0.997 for all analytes.
• LOD and LOQ in rice: 1 ng/mL and 2.5 ng/mL, corresponding to 0.04 and 0.1 mg/kg.

Accuracy and Precision:

• Accuracy across calibration levels: 95–115% for all compounds.
• Intra- and inter-day RSD: <12% at the low level and <7% at higher levels.

Matrix Effect and Recovery:

• Matrix effects ranged from 85% to 105%.
• Recovery rates: 77–103%, with process efficiency 75–105%.

These performance metrics demonstrate the method’s suitability for routine compliance testing.

Benefits and Practical Applications of the Method

• Direct analysis without derivatization simplifies workflow.
• QuPPe sample prep effectively handles highly polar analytes.
• Meets EU MRL for glyphosate in rice (0.1 mg/kg).
• Applicable to QA/QC laboratories for high-throughput pesticide residue monitoring.

Future Trends and Potential Applications

• Integration of stable isotope-labeled internal standards to improve quantitation.
• Automation and miniaturization of sample preparation for increased throughput.
• Extension to other food matrices and environmental samples.
• Adoption of high-resolution mass spectrometry for broader pesticide screening.

Conclusion

The developed direct LC-MS/MS method on the Shimadzu LCMS-8060NX with QuPPe preparation offers sensitive, accurate and precise quantification of glufosinate, glyphosate and AMPA in rice. It achieves regulatory LOQs, demonstrates robust performance in a complex matrix and supports routine residue analysis in food safety laboratories.

Reference

1. N. Chamkasem, T. Harmon; Anal Bioanal Chem (2016) 408:4995–5004.
2. EURL-SRM; QuPPe PO Method, Version 12, July 2021.
3. M. Kawashima; Shimadzu Application News C181 (2018).
4. M. Kawashima, K. Ishioka, M. Kobayashi, J. Masuda; ThP104-ASMS-2020-Poster (2020).
5. D. Toinon; Shimadzu Application News C220 (2020).