HILIC Method for the Separation of Diquat and Paraquat

Importance of the Topic

Paraquat and diquat are widely used non-selective herbicides with high polarity and water solubility, presenting challenges for conventional reversed-phase chromatography and requiring reliable monitoring due to their toxicity.

Objectives and Study Overview

This study aims to develop a rapid, robust HILIC method for the separation and quantification of quaternary ammonium herbicides paraquat and diquat using a Syncronis HILIC stationary phase.

Methodology

The method employs hydrophilic interaction liquid chromatography (HILIC) with a zwitterionic stationary phase and an organic-rich mobile phase (20:80 water/acetonitrile with 0.1% TFA). Standards of paraquat (1400 µg/mL) and diquat (1800 µg/mL) were prepared in the mobile phase and mixed 1:1 for analysis.

Used Instrumentation

• HPLC system: Thermo Scientific Accela HPLC/UHPLC
• Column: Syncronis HILIC, 5 µm, 100 x 2.1 mm
• Column temperature: 45 °C
• Injection volume: 1 µL
• Flow rate: 0.3 mL/min
• Detection: UV at 254 nm for paraquat and 308 nm for diquat

Main Results and Discussion

The developed isocratic method achieved separation of paraquat (tR 1.30 min) and diquat (tR 1.47 min) with high reproducibility (RSD ≤0.5% for retention times and ≤1.4% for peak areas) and a resolution of 1.61. The Syncronis HILIC column provided sharp peaks and a stable baseline.

Benefits and Practical Applications

This HILIC approach offers a fast, reliable analysis of highly polar quaternary ammonium compounds without derivatization, suitable for environmental and food safety monitoring and QA/QC laboratories.

Future Trends and Potential Applications

Advancements in HILIC column chemistries and integration with mass spectrometry are expected to further enhance the analysis of polar pesticides and emerging contaminants. Method transferability to complex matrices and automation will expand its utility.

Conclusion

The Syncronis HILIC method enables rapid, precise separation of paraquat and diquat, demonstrating its applicability for routine monitoring of these hazardous herbicides.

References

1. U.S. EPA Method 549.2 (1997). Determination of diquat and paraquat in drinking water by Liquid-Solid Extraction and HPLC-UV.
2. World Health Organization. WHO classification of pesticides by hazard (accessed online).