Sensitive and Rapid Determination of Paraquat and Diquat in Tap and Environmental Waters

Importance of the Topic

Paraquat and diquat are potent quaternary ammonium herbicides used globally to control terrestrial and aquatic weeds. Their persistence and high toxicity pose serious health risks if present in drinking or environmental waters. Rapid, sensitive analysis is essential to ensure compliance with regulatory limits and to protect public health.

Objectives and Overview of the Study

This work presents the development of a fully automated high-performance liquid chromatography (HPLC) method employing on-line solid phase extraction (SPE) and ultraviolet detection for rapid quantification of paraquat and diquat in tap and pond water. The method aims to achieve method detection limits (MDLs) equal to or better than those specified by U.S. EPA Method 549.2 and EU Directive 98/83/EC.

Methodology and Instrumentation

The analytical system comprises a Thermo Scientific UltiMate 3000 x2 Dual RSLC controlled by Chromeleon 7.1 software, coupled with an Orion 2-Star pH meter. Samples are filtered and injected (1 mL) onto an Acclaim Trinity P1 3×10 mm guard cartridge for on-line SPE. Elution and separation occur on an Acclaim Trinity Q1 3×50 mm analytical column using a binary mobile phase:

• On-line SPE loading (0–2 min): 100 mM ammonium acetate (pH 5.0)/acetonitrile/water (10/5/85, v/v/v), flow 0.7 mL/min
• Gradient elution (2.1–4.5 min): 55% buffer/45% acetonitrile; reequilibration to 10% buffer/5% acetonitrile (4.6–10 min)
• Analytical separation: 35% buffer/65% acetonitrile, flow 0.5 mL/min, column temperature 30 °C
• Detection wavelengths: 260 nm for paraquat, 310 nm for diquat

Main Results and Discussion

Baseline separation of both analytes is achieved in under 7 min with peak widths <1 min and asymmetry factors near unity. Precision (n=5) yields retention time RSD <0.2% and peak area RSD ≈5%. Calibration curves are linear from 1 to 1000 µg/L (r2 ≥0.997). Calculated MDLs are 0.09 µg/L (paraquat) and 0.10 µg/L (diquat), meeting EPA and EU requirements. Recoveries in spiked tap and pond water range 104–108%.

Benefits and Practical Applications

The automated on-line SPE-HPLC approach reduces manual sample handling, lowers contamination risk, and increases laboratory throughput. Its sensitivity, robustness, and compliance with regulatory standards make it well suited for routine monitoring of herbicide residues in drinking and environmental waters.

Future Trends and Potential Applications

Future enhancements may include coupling on-line SPE with mass spectrometry for broader multi-residue analyses and deeper detection limits. Development of field-portable LC systems, advanced mixed-mode stationary phases, and integrated data processing will further facilitate in-field screening and method transfer across laboratories.

Conclusion

A rapid, sensitive, and fully automated on-line SPE-HPLC UV method has been established for paraquat and diquat determination in water matrices. It delivers sub-µg/L detection limits, excellent precision, and high recoveries, aligning with EPA 549.2 and EU 98/83/EC guidelines and streamlining routine water quality analysis.

References

1. U.S. EPA Method 549.2: Determination of Diquat and Paraquat in Drinking Water by HPLC-UV.
2. EU Directive 98/83/EC: Quality of Water Intended for Human Consumption.
3. Thermo Scientific application notes on Acclaim Trinity mixed-mode columns.