Detection of Basic and Acidic Pesticides and Herbicides at Trace Levels by Online SPE LC/MS in Drinking Water

Importance of the Topic

Monitoring trace levels of pesticides and herbicides in drinking water is essential to meet stringent regulatory limits and protect public health and the environment. Sensitive, streamlined analytical methods enable laboratories to detect contaminants at sub–parts-per-trillion levels, ensuring safe water supplies.

Objectives and Study Overview

This work presents an online solid-phase extraction (SPE) coupled to liquid chromatography/triple quadrupole mass spectrometry (LC/MS) method for simultaneous quantification of basic and acidic pesticides and herbicides in drinking water. The method employs the Agilent 1200 Infinity Series Online SPE solution with Agilent 6460 Triple Quadrupole MS, using a commercial pesticide application kit as a starting point. Performance metrics such as linearity, limits of detection (LOD) and quantification (LOQ), precision, recoveries, and carryover were evaluated.

Methodology and Instrumentation

The analytical workflow combines large-volume injections (up to 1,800 µL) on interchangeable SPE trapping cartridges and direct on-column injection for flexible sample processing. Key components include:

• Agilent 1200 Infinity Series Online SPE Solution with two 2-position/10-port valves and interchangeable PLRP-S cartridges
• Agilent 6460 Triple Quadrupole LC/MS with Jet Stream thermal gradient focusing
• ZORBAX Eclipse Plus C18 analytical column (2.1 × 150 mm, 3.5 µm)
• Agilent MassHunter software suite for data acquisition, optimization, qualitative, and quantitative analysis

Chromatographic separation employed water/ammonium formate/formic acid and acetonitrile gradients at 0.4 mL/min and 40 °C. Positive and negative electrospray ionization modes were optimized for each analyte via MRM transitions determined by the MassHunter optimizer.

Main Results and Discussion

Basic pesticides and herbicides:

• Linearity: R² > 0.999 for 14 compounds over 0.1–100 ppt calibration range
• LOQs: predominantly sub-ppt levels; LODs down to tens of ppt or lower
• Precision: retention time RSD < 0.05 %; peak area RSD < 10 %
• Recoveries: 67–98 % from SPE cartridges
• Carryover: ≤ 0.005 % for all compounds

Acidic pesticides and herbicides:

• Linearity: R² > 0.995 for six compounds over 10–2,000 ppt range
• LOQs: single-digit ppt for most; exception hexaflumuron at 100 ppt due to adsorption
• Precision: retention time RSD < 0.03 %; peak area RSD < 6 %
• Recoveries: 96–194 %, influenced by analyte affinity differences between cartridges and C18 column
• Carryover: ≤ 0.003 %

Benefits and Practical Applications

The described online SPE LC/MS approach delivers high throughput, minimal sample preparation, and ultra-trace sensitivity for multi-residue pesticide/herbicide monitoring. It supports regulatory compliance, environmental surveillance, and quality control in municipal and industrial water testing laboratories.

Future Trends and Opportunities

Advancements may include expanded SPE sorbent chemistries to improve retention of challenging analytes, higher-throughput valve configurations, integration with high-resolution MS for broader analyte coverage, and full automation toward continuous monitoring systems.

Conclusion

An automated online SPE LC/MS method using Agilent Infinity Series instruments and triple quadrupole detection achieves reliable, sensitive quantitation of both basic and acidic pesticides/herbicides at trace levels in drinking water. The protocol offers excellent performance for routine environmental analysis.

Used Instrumentation

• Agilent 1200 Infinity Series Online SPE Solution (binary pump, autosampler with 900 µL head, Flexible Cube with two Quick-Change valve heads)
• Agilent 6460 Triple Quadrupole LC/MS with Jet Stream technology
• Analytical column: Agilent ZORBAX Eclipse Plus C18, 2.1 × 150 mm, 3.5 µm
• Trapping columns: PLRP-S cartridges, 2.1 × 12.5 mm, 15–20 µm
• Software: Agilent MassHunter Acquisition, Optimizer, Qualitative, Quantitative

References

1. European Union Drinking Water Directive 98/83/EC, European Commission.
2. Naegele E., "Quantification of trace-level herbicides in drinking water by online enrichment with the Agilent 1200 Infinity Series Online-SPE Solution and Triple Quadrupole MS Detection," Agilent Application Note, 2013, Publication 5991-1738EN.
3. Naegele E., "Comparison of Direct Injection and Online SPE for Quantification by LC/MS of Trace-Level Herbicides in Water," Agilent Technical Note, 2013, Publication 5991-2140EN.