Determination of Herbicide Degradates in Drinking Water on the Agilent 500 Ion Trap LC/MS (EPA 535)

Significance of the Topic

Monitoring trace levels of herbicide degradates in drinking water is crucial for ensuring compliance with regulatory standards and protecting public health. Degradates of chloroacetanilide herbicides are highly polar and can persist in water sources, making sensitive and accurate analysis essential for water utilities and environmental laboratories.

Objectives and Study Overview

This application study evaluates the performance of the Agilent 500 Ion Trap LC MS for quantifying ethane sulfonic acid and oxanilic acid degradates under EPA Method 535. The goals include establishing calibration linearity, assessing quantitative accuracy in reagent, tap, and surface water matrices, and demonstrating method robustness in complex samples.

Methodology and Instrumentation

The study employs solid phase extraction with carbon sorbents to concentrate 250 mL water samples, followed by LC separation on a C18 column using a fast ammonium acetate–methanol gradient. The Agilent 500 Ion Trap LC MS with electrospray ionization captures negative ions of surrogate standard Dimethachlor ESA and internal standard Butachlor ESA. Key instrumentation includes the Agilent 500 Ion Trap LC MS, ProStar 210 binary pump, ProStar 420 autosampler, and a VacElut SPE manifold for sample concentration.

Main Results and Discussion

Calibration for Dimethachlor ESA delivered excellent linearity across 0.01 to 3 ppm with an r2 of 0.9999. Surrogate recovery in reagent, tap, and surface water extracts ranged from 70 to 130 percent, meeting EPA acceptance criteria despite high organic content in surface water. The Enhanced Charge Capacity feature enabled faster gradients and shorter run times without compromising sensitivity or selectivity.

Benefits and Practical Applications

• Reliable quantitation of polar degradates in diverse water matrices
• Rapid analysis throughput through optimized gradient conditions
• Robust performance in samples with high organic loads
• Compliance with EPA Method 535 for unregulated contaminant monitoring

Future Trends and Opportunities

Further work may involve full validation with additional target analytes, expanded screening for related pesticide metabolites, and application of ion trap technology to other environmental monitoring challenges. Ongoing improvements in ion capacity and data processing will enhance laboratory productivity and data quality.

Conclusion

The Agilent 500 Ion Trap LC MS demonstrates reliable, accurate, and sensitive quantitation of herbicide degradates under EPA Method 535. Its robust performance in complex water matrices and efficient analysis time make it a valuable tool for environmental and drinking water laboratories.

References

1. 40 CFR Part 141 Unregulated Contaminant Monitoring Regulation UCMR Proposed Rule
2. J A Shoemaker and M V Bassett Method 535 Measurement of Chloroacetanilide Herbicide Degradates in Drinking Water by Solid Phase Extraction and LC MS MS Version 1.1 April 2005
3. United States Geological Survey National maps of herbicide use