Analysis of Iminoctadine, Diquat and Paraquat in Tap Water

Importance of the Topic

Ensuring the safety of drinking water is a global priority. Monitoring trace levels of herbicides such as iminoctadine, diquat and paraquat helps protect public health and supports regulatory compliance. High-precision analytical methods are essential for detecting these polar compounds in complex water matrices.

Objectives and Study Overview

This study demonstrates a robust LC-MS/MS protocol using hydrophilic interaction chromatography (HILIC) to separate and quantify three quaternary ammonium herbicides in tap water. Key goals include achieving reliable retention, sensitivity at low µg/L levels and operational simplicity for routine quality control.

Methodology and Instrumentation

The analysis employs isocratic HILIC with a Shim-pack Velox HILIC column (100 mm × 2.1 mm I.D., 2.7 µm) and a Nexera X3 UHPLC system coupled to an LCMS-8050 triple quadrupole mass spectrometer. Mobile Phase A consists of 150 mmol/L ammonium formate buffer (pH 3.6), Phase B is acetonitrile at 50 % B constant. The flow rate is set to 0.40 mL/min, column temperature 30 °C and injection volume 5 µL. ESI in positive ion mode with MRM transitions monitors:

• Iminoctadine: m/z 178.90 → 69.10
• Diquat: m/z 183.10 → 157.10
• Paraquat: m/z 186.10 → 171.10

Detailed MS source conditions include probe voltage +0.5 kV, nebulizing gas 3.0 L/min, heating gas 15.0 L/min, drying gas 5.0 L/min, DL temperature 300 °C, heat block 500 °C, and interface 400 °C.

Main Results and Discussion

The method delivers sharp, well-resolved peaks for all three analytes with retention times optimized by HILIC selectivity. MRM detection provides high specificity, effectively discriminating target compounds from matrix interferences. The approach achieves limits of quantification suitable for regulatory monitoring (<1 µg/L). Calibration curves show linearity across the concentration range relevant for environmental surveillance.

Benefits and Practical Applications

• Rapid isocratic run for high sample throughput
• High sensitivity and selectivity via MRM detection
• Minimal sample preparation required for tap water
• Applicable to routine drinking water quality monitoring and compliance testing

Future Trends and Potential Applications

Expanding this approach to additional polar contaminants (e.g., ionic pesticides, veterinary drugs) can broaden environmental surveillance capabilities. Coupling HILIC-MS/MS with automated sample preparation or online SPE could further increase laboratory efficiency. Advances in high-resolution MS may enable simultaneous screening for unknown transformation products.

Conclusion

The presented HILIC-MS/MS protocol using Shim-pack Velox HILIC and LCMS-8050 offers a robust, sensitive solution for analyzing iminoctadine, diquat and paraquat in tap water. Its simplicity, speed and reliability make it well suited for routine water quality control laboratories.

Instrument Used

• Shim-pack Velox HILIC column, 100 mm × 2.1 mm, 2.7 µm (P/N: 227-32025-03)
• Nexera X3 UHPLC system
• LCMS-8050 triple quadrupole mass spectrometer

Reference

• Application News 01-00254. Shimadzu Corporation. 2024.