Determination of Trace Level Herbicide Metabolites with a Customized Agilent 1200 Infinity Series Online SPE System in Combination with the Agilent 6490 Triple Quadrupole MS

Importance of the Topic

The release of herbicide degradation products into water sources presents a growing regulatory and environmental concern. Nonregulated metabolites can indicate contamination pathways and potential health impacts. European drinking water directives require detection limits of 25 ng/L for pesticides, while guidelines for certain metabolites lie even lower. Achieving reliable ultra trace quantitation is therefore crucial for environmental monitoring and public health protection.

Objectives and Study Overview

This work evaluates a customized online solid phase extraction SPE configuration integrated with high pressure UHPLC and tandem mass spectrometry to measure nonregulated herbicide metabolites in water. The study compares online SPE enrichment against direct injection under UHPLC conditions. Three representative metabolites of metolachlor, metazachlor, and dimethachlor are examined to assess sensitivity, linearity, and quantitative performance.

Methodology and Instrumentation

Analytical system design:

• Dual operational modes: online SPE and direct injection under UHPLC conditions
• Custom modules: Agilent 1200 Infinity series online SPE solution and Agilent 1290 Infinity Flexible Cube with piston pump and selection valves
• Chromatography: Two ZORBAX Eclipse Plus C18 columns (2.1 x 150 mm, 3.5 µm) and PLRP-S trapping cartridges for enrichment
• Mass spectrometry: Agilent 6490 triple quadrupole MS with Jet Stream technology operating in positive ion mode and optimized multiple reaction monitoring
• Injection parameters: Sample volumes of 100 µL for SPE and 10 µL for direct injection, gradient elution with 10 mM ammonium acetate in water and acetonitrile at 0.4 mL/min

Method development included flow injection optimization of collision energies and source parameters using MassHunter software suites. Calibration schemes covered wide concentration ranges to define limits of quantitation LOQ and detection LOD.

Results and Discussion

Calibration curves for direct injection yielded LOQs from 3.9 to 15.6 ng/L with linearity coefficients above 0.999. Online SPE achieved tenfold better sensitivity, with LOQs between 0.1 and 1.9 ng/L and similar linearity. Limits of detection reached subnanograms per liter. Chromatographic peaks after SPE were sharper, enhancing signal to noise. The enrichment step improved quantitation for less abundant metabolites and demonstrated robust recovery above 90 percent for nonpolar analytes. Polar metabolites required optimization of loading and wash conditions to minimize losses.

Benefits and Practical Applications

• Enhanced sensitivity allowing detection at subppt levels
• Seamless switch between SPE and direct injection within a single platform
• Automated enrichment reduces manual sample preparation
• High throughput analysis for environmental water testing
• Compliance with stringent regulatory requirements for water quality

Future Trends and Applications

Advancements may include integration with high throughput autosamplers, expansion to a wider range of polar and ionic metabolites, and coupling with high resolution mass analyzers for non targeted screening. Miniaturization of SPE cartridges and further automation of sample cleanup will support field deployable systems. Data driven workflows leveraging machine learning for rapid method optimisation and contaminant identification are anticipated.

Conclusion

The customized Agilent online SPE UHPLC MS system effectively quantifies trace herbicide metabolites at subnanogram per liter levels, surpassing direct injection sensitivity by an order of magnitude. This configuration provides environmental laboratories with a versatile and sensitive tool for regulatory compliance and water quality surveillance.

References

1. European Union Drinking Water Directive 98/83/EC
2. Agilent Application Note 5991-1738EN
3. Agilent Application Note 5991-2140EN