Monitoring for Metaldehyde in Raw, Process and Potable Waters using Direct Aqueous Injection on the Agilent 6490 LC/MS/MS

Importance of the Topic

Metaldehyde is a widely used molluscicide for slug and snail control in agriculture and horticulture. It is resistant to removal by granular activated carbon and is not degraded by conventional oxidation processes, making its presence in water sources a significant challenge. Compliance with strict regulatory limits such as the 0.1 microgram per liter threshold set by the European Drinking Water Directive demands highly sensitive and reliable analytical methods for trace level monitoring.

Objectives and Study Overview

The primary goal was to establish a robust, high throughput method for determining metaldehyde levels in raw, process and potable waters using direct aqueous injection on an Agilent 6490 LC/MS/MS. A secondary aim was to incorporate simultaneous screening of an analytical suite of 20 pesticide compounds in a single 10 minute chromatographic run.

Methodology and Instrumentation

• Sample Preparation: Direct injection of water samples (100 microliter volume) with online addition of internal standard metaldehyde-D16 dispenses with time consuming extraction steps.
• Chromatography: Agilent 1260 HPLC with a Poroshell 120 EC-C18 column (2.1 x 75 mm, 2.7 micrometer) and guard column at 60 degree Celsius.
• Mobile Phase: Gradient of 0.1 percent acetic acid in water and acetonitrile at a flow rate of 0.45 mL per minute over a 10 minute run time.
• Detection: Agilent 6490 Triple Quadrupole LC/MS/MS with Jet Stream interface employing positive and negative ionisation switching to analyse 17 compounds in positive mode and 3 in negative mode.

Main Results and Discussion

The method demonstrated excellent linearity from 0 to 0.3 microgram per liter, extendable to 2 microgram per liter with additional calibration standards. The limit of detection for metaldehyde was 0.009 microgram per liter. Recoveries for a 0.1 microgram per liter spike ranged from 96 to 98 percent across clean hard, clean soft, and raw water matrices with relative standard deviations below 6 percent. All 20 targeted pesticides were resolved within 10 minutes, with metaldehyde eluting at 2.34 minutes in positive mode.

Benefits and Practical Applications

• Rapid analysis with minimal sample preparation increases laboratory throughput and reduces labor costs.
• Low detection limits ensure compliance with stringent drinking water regulations.
• Simultaneous multi residue capability allows comprehensive monitoring in a single run.
• Enhanced reproducibility by avoiding extraction variability.

Future Trends and Potential Applications

Advances may include further expansion of analyte panels, integration of online sample preparation automation, and adaptation to other persistent micropollutants. Emerging high resolution mass spectrometry could enhance selectivity for complex matrices. Continuous in situ monitoring platforms may leverage this methodology for real time water quality surveillance.

Conclusion

A validated direct aqueous injection LC/MS/MS approach offers a sensitive, reliable and high throughput solution for trace level determination of metaldehyde and related pesticides in diverse water types. With excellent recovery, linearity and low detection limits, the method supports regulatory compliance and routine environmental monitoring needs.

Reference

• Official Journal of the European Communities Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption
• Cheeseman RV, Wilson AL and Gardner MJ 1989 A Manual on Analytical Quality Control for the Water Industry WRc report NS30