Determination of Acidic Herbicides in Water Using Liquid Chromatography-Tandem Quadrupole Mass Spectrometry

Importance of the Topic

Monitoring acidic herbicides in drinking and surface waters is critical for protecting human health and aquatic ecosystems. These compounds, derived from benzoic, acetic, propanoic, butanoic and other acids, are widely applied in agriculture and recreational areas. Regulatory frameworks such as the EU Drinking Water Directive (0.1 µg/L per residue) and the Water Framework Directive drive the demand for robust multi-residue methods.

Objectives and Study Overview

The aim was to develop a rapid, targeted method to quantify 20 acidic herbicides at sub-µg/L levels using large-volume direct injection on a UPLC-MS/MS platform. The approach minimizes sample preparation while ensuring compliance with European and international water quality standards.

Used Instrumentation

• Waters ACQUITY UPLC I-Class System with FTN Sample Manager
• Waters Xevo TQ-XS Tandem Quadrupole Mass Spectrometer
• MassLynx MS Software v.4.2 and TargetLynx XS Application Manager

Methodology

Surface or drinking water samples (10 mL) were centrifuged and filtered (0.2 µm PVDF). A 1.5 mL aliquot was acidified with formic acid and analyzed directly (250 µL injection). Chromatography employed an HSS T3 column (2.1 × 150 mm, 1.8 µm) at 40 °C with a 15-minute gradient of 0.02% formic acid in water and methanol (0.4 mL/min). MS detection used ESI in positive and negative modes, with a soft ionization option for labile analytes. MRM transitions were optimized by IntelliStart.

Main Results and Discussion

Soft ionization reduced in-source fragmentation for dicamba, MCPB, 2,4-DB and triclopyr, enhancing sensitivity. Limits of quantification reached 0.01 µg/L. Calibration over 0.01–1.0 µg/L showed linearity (r2 > 0.99, residuals < 20%). Recovery in spiked drinking and surface waters ranged from 88% to 120%, with precision (RSD) ≤7% at 0.1 µg/L and ≤20% at 0.02 µg/L. Ion ratios and retention times met identification criteria within ±30% and ±0.1 min.

Benefits and Practical Applications

This streamlined method eliminates extensive extraction steps, reduces solvent use and analysis time, and supports routine monitoring in environmental and regulatory laboratories. It enables simultaneous quantification of multiple herbicide classes with high confidence.

Future Trends and Potential Applications

• Automation of sample handling and data processing
• On-site and portable LC-MS/MS systems for rapid field screening
• Integration of high-resolution mass spectrometry for non-target screening
• Development of lab-on-chip devices for decentralized testing
• Advanced data analytics and cloud connectivity for real-time compliance monitoring

Conclusion

The large-volume direct injection UPLC-MS/MS method on the ACQUITY UPLC I-Class and Xevo TQ-XS platform delivers rapid, sensitive and accurate multi-residue analysis of acidic herbicides in water, meeting stringent regulatory requirements and offering substantial gains in efficiency and throughput.

Reference

• World Health Organization. Guidelines for Drinking-Water Quality: 4th edition incorporating the first addendum. Geneva: WHO; 2017.
• European Commission. Council Directive 98/83/EC on the quality of water intended for human consumption. Off J Eur Communities. 1998.
• European Commission. Directive 2000/60/EC establishing a framework for community action in the field of water policy. Off J Eur Communities. 2000.
• Johnson I. Comparative Study of Pressures and Measures in the Major River Basin Management Plans – Task 2c. WRc plc; 2012.
• US Environmental Protection Agency. Safe Drinking Water Act. EPA; accessed April 2018.
• US Environmental Protection Agency. Summary of the Clean Water Act. EPA; accessed April 2018.