Quantitative Determination of Diquat and Paraquat in Drinking Water via EPA Method 549.2

Importance of the Topic

Diquat and paraquat are globally used non-selective herbicides known for rapid control of invasive plants but pose significant health risks due to acute toxicity upon human exposure. Their extensive agricultural use and potential to contaminate drinking water sources drive the need for sensitive, reliable analytical methods to ensure compliance with regulatory guidelines such as EPA Method 549.2.

Objectives and Study Overview

This study demonstrates an automated solid-phase extraction (SPE) workflow coupled with high-performance liquid chromatography with diode array detection (HPLC-DAD) for quantitative determination of diquat and paraquat in reagent water according to EPA Method 549.2. Key goals include verifying low system background, demonstrating method capability (IDC), and establishing method detection limits (MDL).

Methodology and Instrumentation

The extraction was performed on a Biotage Horizon 5000 automated SPE system using ISOLUTE C8(EC) 500 mg/6 mL cartridges. The procedure involved:

• Conditioning cartridges with reagent water, methanol, and EPA-specified buffer solutions
• Loading 250 mL samples (1 L for blanks) at pH 7–9
• Washing with methanol to remove matrix interferences
• Eluting analytes with disk elution solution and adding ion-pair reagent, yielding a final 5 mL extract

The HPLC-DAD analysis used an Agilent 1260 Infinity II system with a YMC AQ12S03 column (4.6×150 mm) at 35 °C, 2.0 mL/min flow, and detection wavelengths of 257 nm (paraquat) and 308 nm (diquat).

Used Instrumentation

• Biotage Horizon 5000 SPE system
• ISOLUTE C8(EC) SPE cartridges
• Agilent 1260 Infinity II HPLC with Diode Array Detector
• YMC AQ12S03 analytical column

Main Results and Discussion

• Lab reagent blanks exhibited non-detectable levels for both analytes, confirming low background.
• IDC on four fortified blanks at 100 µg/L achieved mean recoveries of 94.94% (RSD 1.54%) for paraquat and 91.68% (RSD 2.03%) for diquat, within ±30% accuracy and <30% precision criteria.
• MDL study with five replicates at 0.80 µg/L produced MDLs of 0.298 µg/L for paraquat and 0.237 µg/L for diquat, satisfying EPA requirements.

Benefits and Practical Applications

The validated method provides:

• Automated, high-throughput sample preparation for routine water quality monitoring
• Sensitive quantification of ultra-trace herbicides in compliance with regulatory standards
• Robust performance suitable for environmental and regulatory laboratories

Future Trends and Potential Applications

Potential developments include coupling SPE with mass spectrometry for enhanced sensitivity, miniaturizing SPE cartridges to reduce solvent use, and deploying portable SPE systems for on-site testing. Integration with automated data management and cloud analytics could further optimize monitoring workflows.

Conclusion

The automated SPE-HPLC-DAD approach meets all EPA Method 549.2 quality control criteria, delivering accurate, precise, and sensitive determination of diquat and paraquat in drinking water. Its automation and robustness make it ideal for regulatory compliance and environmental surveillance.

References

• Munch J.W., Bashe W.J. Method 549.2—Determination of Diquat and Paraquat in Drinking Water by Liquid-Solid Extraction and High Performance Liquid Chromatography with Ultraviolet Detection. National Exposure Research Laboratory, U.S. EPA; 1997.