Determination of acidic herbicides in water using liquid chromatography-tandem quadrupole mass spectrometry with direct injection

Significance of the Topic

The monitoring of acidic herbicides in surface and drinking water is critical for environmental safety and public health. Regulatory bodies such as the EU Drinking Water Directive and the US Safe Drinking Water Act set stringent limits for individual pesticide residues, requiring reliable analytical methods capable of detecting compounds at sub‐microgram per liter levels. Rapid and sensitive approaches help water utilities and laboratories ensure compliance and protect ecosystems.

Objectives and Overview of the Study

This study aims to develop and validate a fast, direct‐injection LC–MS/MS method for quantifying 19 acidic herbicides in water. Key goals include:

• Achieving detection limits below regulatory thresholds (0.1 µg/L).
• Eliminating time‐consuming sample preparation steps such as SPE.
• Demonstrating linearity from 0.01 to 0.2 µg/L in drinking water matrices.

Methodology

Ten‐milliliter water samples were centrifuged and filtered through a 0.2 µm PVDF syringe filter. A 1.5 mL aliquot was acidified with formic acid and directly injected (250 µL) onto the LC column. A binary gradient of 0.02 % formic acid in water (mobile phase A) and methanol (mobile phase B) provided chromatographic separation at 40 °C. Mass spectrometric detection employed multiple reaction monitoring (MRM) with optimized source conditions and soft ionization for labile analytes.

Used Instrumentation

• LC System: Waters ACQUITY Premier UPLC I-Class FTN Plus (250 µL loop, 30 µL needle, 250 µL syringe).
• Column: ACQUITY Premier HSS T3, 1.8 µm, 2.1 × 100 mm, 40 °C.
• MS System: Xevo TQ Absolute triple quadrupole mass spectrometer with StepWave™ XS ion optics.
• Software: waters_connect™ with MS Quan module for data acquisition and quantitation.

Main Results and Discussion

Reducing the source block temperature to 120 °C and desolvation gas temperature to 300 °C, combined with soft ionization, minimized in‐source fragmentation of sensitive compounds (e.g., 2,4-DB, dicamba, MCPB, triclopyr) and boosted signal intensity. The method demonstrated excellent selectivity and sensitivity, with all analytes reliably quantified at 0.02 µg/L—well below the 0.1 µg/L regulatory limit. Chromatographic separation and dual MRM transitions facilitated clear identification and robust quantitation across the calibration range.

Benefits and Practical Applications

• Rapid analysis: direct injection avoids laborious extraction steps.
• High sensitivity: capable of detecting herbicides at trace levels.
• Cost‐effective: reduced consumables and preparation time.
• Scalable for routine QA/QC in water testing laboratories.

Future Trends and Possibilities for Use

Emerging developments may include integration of high‐resolution mass spectrometry for broader suspect screening, automated online sample preparation to further increase throughput, and adaptation to other environmental matrices. Advances in software algorithms and AI‐driven data processing will streamline method validation and regulatory reporting.

Conclusion

The direct large‐volume injection LC–MS/MS method on the Waters ACQUITY Premier and Xevo TQ Absolute platform delivers a fast, sensitive, and reliable solution for monitoring acidic herbicides in drinking water. By simplifying sample preparation and achieving sub‐regulatory detection limits, this approach meets the needs of modern environmental laboratories.

References

1. Shah D. Determination of acidic herbicides in water using liquid chromatography-tandem quadrupole mass spectrometry with direct injection. Waters Corporation; 2023.