Faster Yet Sensitive Determination of N-Methylcarbamates in Rice, Potato, and Corn by HPLC

Significance of the Topic

The N-methylcarbamate pesticides and their oxime derivatives are widely applied in agriculture due to their broad-spectrum activity. However, their potential neurotoxic effects and strict regulatory limits demand analytical methods that are both rapid and highly sensitive for residue monitoring in food crops.

Study Objectives and Overview

This work presents a streamlined sample preparation and HPLC method for simultaneous determination of eleven EPA Method 531.2 carbamates in rice, potato, and corn. The approach aims to reduce analysis time while maintaining low detection limits and robust quantitation.

Methodology and Instrumentation

Sample preparation combines a salting-out extraction and a dispersive solid-phase cleanup:

• Salting-out extraction with acetonitrile, sodium chloride, and magnesium sulfate to partition carbamates into the organic phase.
• Dispersive SPE (dSPE) using 50 mg primary secondary amine (PSA) to remove pigments, sugars, lipids, and organic acids.

Chromatographic separation and detection:

• Dionex UltiMate 3000 HPLC: HPG-3400A pump, WPS-3000 autosampler, TCC-3000 column compartment, FLD-3400RS fluorescence detector.
• Acclaim Carbamate guard (3.0×10 mm) and analytical (3.0×150 mm, 3 µm) columns at 50 °C.
• Gradient mobile phase of methanol–water (14→70% methanol) at 0.9 mL/min.
• Postcolumn derivatization: first reaction coil with 0.2% NaOH at 100 °C, second coil with o-phthalaldehyde (OPA) reagent at ambient temperature, 0.3 mL/min reagent flow.

Main Results and Discussion

Optimization studies showed:

• PSA effectively removed coextractives without significant loss of target analytes, unlike activated carbon which retained some carbamates and the surrogate standard.
• Complete water removal by MgSO₄ improved PSA performance.
• Calibration was linear (r²≥0.9965) over 0.25–8 µg/L; method detection limits ranged from 0.04 to 0.11 µg/L in solution (0.4–1.1 µg/kg in samples).
• Reproducibility: retention time RSD ≤0.07%, peak area RSD ≤3.0% (standards) and ≤7.0% (spiked crops).
• Spike recoveries in rice, potato, and corn averaged 84–103% for all carbamates.
• Detection of native residues in fresh corn was confirmed by LC-MS.

Benefits and Practical Applications

This method offers rapid turnaround and high sensitivity, making it well suited for routine pesticide monitoring in food safety laboratories. Its compatibility with EPA guidelines and minimal solvent usage support compliance and operational efficiency.

Future Trends and Opportunities

Emerging directions include:

• Integration of automated and miniaturized sample prep platforms to increase throughput.
• Coupling with LC-MS/MS for expanded multi-residue screening and confirmation.
• Green extraction techniques to reduce solvent consumption and waste.
• Method extension to new or regulated carbamate derivatives as pesticide approvals evolve.

Conclusion

The described salting-out and dSPE cleanup combined with HPLC-FLD and postcolumn OPA derivatization delivers a fast, sensitive, and reproducible protocol for quantifying N-methylcarbamates in rice, potato, and corn, meeting regulatory requirements for food safety analysis.

Reference

1. U.S. EPA Method 531.2, Revision 1.0. Measurement of N-methylcarbamoyloximes and N-methylcarbamates in Water. EPA, 2001.
2. Dionex Corp. Determination of N-Methylcarbamates by Reversed-Phase HPLC. Application Note 96, 2007.
3. Dionex Corp. Determination of N-Methylcarbamates Using Acclaim Carbamate and FLD-3400RS. Application Brief 115, 2010.
4. Dionex Corp. Determination of N-Methylcarbamates in Drinking Water by HPLC. App. Update 177, 2010.
5. Basheer C. et al. Micro-SPE and HPLC for Carbamate Pesticides. J. Chromatogr. A 2009, 1216, 211.
6. Liu C.W. et al. Multiresidue Carbamate Insecticides by SPE and HPLC. Chin. J. Chromatogr. 2003, 21, 255.
7. Okihashi M. et al. Carbamates in Foods by ASE with Mini-Column Cleanup. Analyst 1998, 123, 711.
8. Dionex Corp. Accelerated Solvent Extraction of Pesticide Residues in Food. App. Note 332, 2004.
9. Ding T. et al. Carbamate Residues in Rice by HPLC-MS with Post-Column Derivatization. Chin. J. Anal. Lab. 2007, 26(9), 77.
10. Zhou Z.M. et al. Carbamates in Corn by CPE and HPLC–Vis. J. Agric. Food Chem. 2009, 57, 8722.
11. AOAC Official Method 2007.01. Pesticide Residues in Foods by ACN Extraction and MgSO₄ Partitioning.
12. EN 15662, 2008. Pesticide Residues in Plant Foods by GC-MS and/or LC-MS/MS with ACN Extraction and dSPE Cleanup.
13. Liu M. et al. Carbamate and OP Pesticides in Fruits by LC–MS with dSPE. Chin. J. Anal. Chem. 2006, 34, 941.
14. Wang L. et al. LC-MS for Direct Determination of N-Methyl Carbamates in Water. LPN 2386-01, 2010.
15. EPA. Agreement to Terminate Aldicarb Uses. Factsheet, 2010.