Analysis of Iminoctadine, Paraquat, and Diquat in Tap Water Using Triple Quadrupole LC/MS/MS [LCMS-8050]

Significance of the Topic

The accurate determination of trace levels of iminoctadine, paraquat and diquat in tap water is critical for ensuring public health and regulatory compliance. These compounds are widely used as an antimicrobial agent and non-selective herbicides, respectively. Their potential toxicity and persistence in drinking water necessitate sensitive, robust analytical methods.

Objectives and Study Overview

This study demonstrates the performance of a Japanese Ministry of Health, Labour and Welfare appendix method for simultaneous analysis of iminoctadine, paraquat and diquat in tap water using solid-phase extraction (SPE) coupled with triple quadrupole LC/MS/MS. A secondary objective was to evaluate a simplified sample pretreatment that omits the nitrogen blowdown concentration step.

Methodology and Instrumentation

Sample pretreatment follows a dechlorination step with sodium thiosulfate, SPE on a divinylbenzene–N-vinylpyrrolidone copolymer cartridge, elution with acetonitrile/formic acid, and final volume adjustment. The simplified approach skips the nitrogen evaporation and directly dilutes the SPE eluate.

Instrumentation

• LC/MS/MS system: Shimadzu LCMS-8050 triple quadrupole
• Analytical column: Inertsil WP300 SIL, 100 × 2.1 mm, 3 µm
• Mobile phase: 150 mmol/L ammonium formate in water : acetonitrile (40:60, v/v)
• Flow rate: 0.3 mL/min; column temperature: 30 °C; injection volume: 5 µL
• Ionization: ESI positive; probe voltage: 1 kV; interface: 400 °C; DL: 300 °C; block heater: 500 °C
• Gas flows: nebulizing 3 L/min; drying 5 L/min; heating 15 L/min
• MRM transitions: iminoctadine m/z 179→69; paraquat m/z 171→77; diquat m/z 183→157

Main Results and Discussion

Retention times for the standards were 1.5 min (iminoctadine), 4.9 min (paraquat) and 5.7 min (diquat). Calibration at 0.25 µg/L produced clear MRM peaks with minimal background interference. Spike-and-recovery tests at 0.05 and 0.25 µg/L in tap water yielded recoveries of 85–95%, meeting the 70–120% acceptance criteria. The simplified pretreatment without nitrogen evaporation provided equivalent recoveries, indicating no loss of sensitivity or accuracy.

Benefits and Practical Applications

• High sensitivity and selectivity for trace-level herbicides and antimicrobials.
• Robust workflow with SPE cleanup to minimize matrix effects.
• Simplified protocol reduces sample handling time and risk of analyte loss.
• Applicable for routine water quality monitoring in environmental and regulatory laboratories.

Future Trends and Applications

Advances in micro-extraction and on-line SPE integration may further streamline sample preparation. Emerging high-resolution mass spectrometry could allow simultaneous screening of broader pesticide panels. Automation and high-throughput workflows will support large-scale monitoring programs. Green chemistry approaches may reduce solvent consumption and waste.

Conclusion

The described LC/MS/MS method provides reliable, accurate quantitation of iminoctadine, paraquat and diquat in tap water. The simplified pretreatment approach maintains performance while improving throughput. This protocol supports regulatory water testing and routine environmental monitoring.

References

1. Ministry of Health, Labour and Welfare, Japan. Notification No. 3-6 (Appendix Method 21), March 2015.
2. Shimadzu Corporation. Application Note No. C129A: Analysis of Iminoctadine, Paraquat, and Diquat in Tap Water Using LCMS-8050, First Edition May 2016.