A Direct Aqueous Injection Method for Polar Pesticides in Drinking and Nonpotable Water

Significance of the topic

The widespread use of phosphonate herbicides such as glyphosate and its metabolites poses a significant environmental and public health concern. Their high polarity and tendency to chelate metal surfaces make conventional extraction and analysis challenging. Developing a sensitive, rapid, and robust method for routine monitoring of these polar pesticides at sub-ppb levels in drinking, surface, and groundwater is essential for regulatory compliance and water quality assurance.

Study objectives and overview

This application aimed to establish and validate a direct aqueous injection liquid chromatography–triple quadrupole mass spectrometry (LC/TQ) method for quantifying glyphosate, aminomethylphosphonic acid (AMPA), glufosinate, and related metabolites. Emphasis was placed on simplifying sample preparation, accelerating analysis, and achieving reliable performance across diverse water matrices.

Methodology

• Sample preparation involved collecting river, bore-hole, and drinking water, spiking with calibration standards, and adding sodium thiosulfate to quench residual chlorine. 1 mL aliquots were directly injected without further cleanup.
• Calibration curves were generated in matrix-matched and ultrapure water across six levels up to 0.5 µg/L. Quality control samples were prepared at blank, low, and high spike levels.
• Data acquisition employed dynamic multiple reaction monitoring (dMRM) to accommodate primary and confirmatory transitions for each analyte.

Instrumentation used

• Agilent 1290 Infinity II liquid chromatograph with high-speed pump, autosampler, and multicolumn thermostat
• Metrohm A Supp 5 (4 × 150 mm) column at 40 °C, 0.7 mL/min flow, 100 µL injection, 18.2 min gradient
• Agilent 6495D triple quadrupole MS with Jet Stream electrospray source in fast polarity-switching dMRM mode
• Agilent MassHunter software for tuning, data acquisition, and quantitative processing

Main results and discussion

• Linearity: All targets showed R2 ≥ 0.995 across 0.01–0.5 µg/L.
• Sensitivity: Instrument LOD < 0.01 µg/L, LOQ < 0.03 µg/L.
• Precision and accuracy: RSD ≤ 12.5% at 0.03 and 0.10 µg/L; recoveries between 75% and 125%.
• Matrix effects: Moderate signal suppression in real waters mitigated by matrix-matched calibration and isotope-labeled internal standards.
• Chromatography: Sharp, well-resolved peaks for glyphosate, AMPA, and glufosinate within 18.2 min.
• Stability: Retention times and response remained consistent over 200 injections; negligible spray shield fouling due to waste diversion outside analyte window.

Benefits and practical applications

• Fast direct injection workflow eliminates derivatization and solid-phase extraction steps, increasing sample throughput.
• High sensitivity and reproducibility support regulatory monitoring and research studies at trace levels.
• Flexibility to expand the analyte panel by adding dMRM transitions for emerging polar pesticides and metabolites.

Future trends and opportunities

• Integration of online sample enrichment or miniaturized LC formats to further reduce limits of detection.
• Expansion to high-resolution mass spectrometry for non-target screening of emerging contaminants.
• Automation of sample handling and data processing to support large-scale environmental surveillance networks.
• Development of portable MS-based platforms for in-field testing of polar pesticides.

Conclusion

The direct aqueous injection LC/TQ method developed on the Agilent 1290 Infinity II and 6495D system delivers rapid, sensitive, and reliable quantitation of highly polar pesticides in various water matrices. Its robustness, minimal sample preparation, and capacity to accommodate additional analytes make it well suited for routine environmental and drinking water testing.

References

• Day Powell; Agilent Technologies, Inc. A Direct Aqueous Injection Method for Polar Pesticides in Drinking and Nonpotable Water. Application Note, Agilent Technologies, February 2025.