Direct Quantification of Acidic Herbicides in Drinking Water Samples Using Ultra-Sensitive UPLC/MS/MS Analysis

Significance of the topic

Phenoxyacetic acid herbicides account for a large share of weed-control agents used in agriculture and forestry. Their widespread application and potential for environmental persistence raise concerns over drinking water safety. Sensitive, rapid analytical methods are essential to ensure compliance with regulatory limits and to assess human and ecological exposure.

Objectives and study overview

This work presents a direct-injection UPLC/MS/MS protocol for the simultaneous quantification of a range of acidic herbicides in drinking water at trace levels (low ng/L). The aim is to bypass time-consuming enrichment steps, achieve sub-5 ng/L detection limits, and maintain high throughput and robustness.

Methodology and instrumentation used

A Waters ACQUITY UPLC I-Class System equipped with a 2.1×100 mm BEH C18 column (1.7 µm) was operated at 60 °C. A 5-minute linear gradient from 5% to 95% acetonitrile (both solvents containing 0.5% formic acid) was run at 0.5 mL/min. A 100 µL direct injection was performed for each 8-minute cycle.

• Mass spectrometry: Xevo TQ-S triple quadrupole with StepWave ion optics.
• Ionization: ESI in negative mode, capillary voltage 2 kV, desolvation at 550 °C.
• Data acquisition: MRM transitions optimized via Quanpedia database and IntelliStart™, with RADAR™ mode for concurrent full-scan monitoring.
• Internal standard: deuterated 2,4-D.

Main results and discussion

Calibration for most analytes was linear from 5 to 1000 ng/L (r² > 0.995), while triclopyr showed linearity from 25 ng/L upward. Limits of detection reached 2.5 ng/L for all compounds except triclopyr (5 ng/L). Recovery of a 100 ng/L spike in natural spring water ranged from 107% to 117%, with coefficients of variation below 5%.
RADAR data revealed a matrix interference zone near the end of the gradient (4.2–5.2 min), but all target analytes eluted at least 30 seconds earlier, minimizing co-elution risk. Column lifetime testing over 500 injections demonstrated stable peak shape and minimal backpressure increase (<200 psi), confirming method robustness.

Benefits and practical applications of the method

• Eliminates sample enrichment and cleanup, reducing labor and turnaround time.
• Delivers ultra-low detection limits that meet or exceed EPA and EU drinking water standards.
• Enables high-throughput monitoring for regulatory compliance and environmental surveillance.
• Supports routine QA/QC workflows in analytical laboratories.

Future trends and applications

Continued expansion of direct-injection approaches for other classes of ionic contaminants is anticipated. Integration with automated sample handling and real-time data-processing tools, including AI-driven anomaly detection, will enhance laboratory efficiency. Further adoption of full-scan modes like RADAR™ may support retrospective data mining and non-target screening.

Conclusion

This study demonstrates a fast, sensitive, and robust direct-injection UPLC/MS/MS workflow for acidic herbicides in drinking water. The method achieves low ng/L detection, reliable quantitation, and high throughput without extensive sample preparation, offering significant advantages for environmental monitoring and regulatory testing.

References

• Kellogg RL, Nehring R, Grube A, Goss DW, Plotkin S. Environmental Indicators of Pesticide Leaching and Runoff from Farm Fields. USDA Forest Service, Pesticide Background Statements, Vol. I Herbicides; 2000.
• U.S. EPA. Re-registration Eligibility Decision for 2,4-D. Federal Register; 2005.
• European Commission. List of Authorized Pesticides: 2,4-D. Document 7599/VI/97-Final; 2001.
• Chiras DD. Environmental Science. 8th ed. Jones & Bartlett; 2010.
• Schecter A, Birnbaum L, Ryan JJ, Constable JD. Dioxins: An Overview. Environ Res. 2006;101(3):419–428.
• EU Council Directive 98/83/EC on drinking water quality. Official Journal L330/32; 1998.