Direct Analysis of Iminoctadine, Diquat and Paraquat in Tap Water Using a Triple Quadrupole Mass Spectrometer

Significance of the Topic

Pesticides such as iminoctadine, diquat and paraquat pose environmental and health risks even at low concentrations. Accurate monitoring of these compounds in drinking water is vital for compliance with regulatory targets. Direct analysis by LC-MS/MS without solid-phase extraction can greatly streamline routine water quality testing.

Objectives and Study Overview

This study evaluates a direct injection method using a triple quadrupole mass spectrometer for quantitative analysis of iminoctadine, diquat and paraquat in tap water. The method aims to achieve detection limits down to one-hundredth of the Japanese water quality targets while eliminating time-consuming sample pretreatment.

Methodology and Instrumentation

• Chromatography performed on a Shim-pack Velox HILIC column, isocratic with 50% acetonitrile and 150 mmol/L ammonium formate buffer at pH 3.6; flowrate 0.4 mL/min; column temperature 30 °C; injection volume 5 µL.
• Mass spectrometry on LCMS-8050 in positive ESI mode with MRM transitions 178.9>69.1 for iminoctadine, 183.1>157.1 for diquat and 186.1>171.1 for paraquat; source settings optimized for sensitivity.
• Calibration standards prepared in a water:acetonitrile:formic acid mixture at concentrations from 0.02 to 2.5 µg/L.
• Tap water samples dechlorinated with sodium thiosulfate and spiked at 0.05 and 0.5 µg/L, corresponding to one-hundredth and one-tenth of target values.

Main Results and Discussion

Calibration curves demonstrated excellent linearity across 0.02–2.5 µg/L with R²>0.998 for all analytes at the LLOQ of 0.02 µg/L. Spike and recovery tests showed no matrix interference, with accuracies between 94.7 % and 106.5 % and repeatabilities below 6.1 % RSD. Chromatograms confirmed clear separation and sensitive detection of each compound without solid-phase extraction.

Benefits and Practical Applications

• Elimination of solid-phase extraction reduces analysis time, labor requirements and variability due to operator technique.
• High sensitivity enables monitoring of pesticides well below regulatory limits.
• Method is suitable for routine water quality control laboratories and environmental monitoring programs.

Future Trends and Applications

Future developments may extend direct injection protocols to a broader range of polar and ionizable contaminants. Automation with on-line sample preparation and high-throughput LC-MS platforms could further enhance efficiency and data quality. Integration with multi-residue screening workflows and field-deployable mass spectrometers offers promising directions.

Conclusion

The direct LC-MS/MS method on the LCMS-8050 platform provides robust, sensitive and reproducible quantitation of iminoctadine, diquat and paraquat in tap water at levels one-hundredth of regulatory targets without solid-phase extraction. This streamlined approach supports efficient routine water quality monitoring and regulatory compliance.

References

1. Notice from Ministry of Health Labour and Welfare Enactment of the Ministerial Ordinance on Water Quality Standards and Partial Amendment to the Enforcement Regulations of the Water Supply Act October 10 2003 last revision March 26 2021 Appendix 2 Targeted pesticides list Complementary Items to Set the Targets for Water Quality Management No 15
2. Notice from Ministry of Health Labour and Welfare Appendix 4 Inspection Methods for Complementary Items to Set the Targets for Water Quality Management October 10 2003 last revision March 26 2021