Determination of Pesticides in Aqueous Samples by On-Line Coupling Solid-Phase Extraction to Gas Chromatography with At-Column Concentrating Interface

Importance of the Topic

The presence of pesticides and herbicides in surface and drinking water poses significant environmental and public health challenges. Regulatory agencies worldwide have tightened limits on trace contaminants to safeguard human health and ecosystems. Reliable, sensitive, and fully automated methods are essential for routine monitoring of water quality and compliance with stringent regulations.

Objectives and Study Overview

This study aimed to integrate an automated on-line solid-phase extraction system with capillary gas chromatography mass spectrometry using an at-column concentrating large volume injection interface. The system was evaluated for its ability to detect and quantify thirty commonly regulated pesticide and herbicide compounds in aqueous samples with high sensitivity and reproducibility.

Methodology and Instrumentation

An on-line coupling was established between a Prospekt automated SPE instrument and an HP6890 GC equipped with an OPTIC 2-200 programmable-temperature vaporizer. A PLRP-S SPE cartridge captured analytes from a two milliliter water sample, followed by elution with acetone under controlled flow and purge conditions. The eluate was transferred through an inactive capillary to an at-column concentrating liner. Solvent vapour was vented while target analytes were focused at the head of a NB-5 analytical capillary column. The GC oven was ramped to desorb and separate the compounds, which were detected in selected ion monitoring mode on an HP5973 mass spectrometer.

Instrumentation

• Automated SPE system Prospekt with MIDAS autosampler and PLRP-S cartridge
• HPLC pump PU610 for controlled elution
• Gas chromatograph HP6890 with OPTIC 2-200 large volume injection liner
• Analytical column NB-5 30 meters by 0.25 millimeter inner diameter
• Mass spectrometer HP5973 in SIM mode

Main Results and Discussion

The method achieved recoveries above eighty percent for the majority of the thirty analytes and relative standard deviations below five percent over seven consecutive injections at one microgram per liter spiking levels. Heat-labile pesticides remained intact due to low injector temperatures during solvent venting. Chromatographic peak shapes were consistently sharp, demonstrating effective concentration at the column head and minimal matrix effects.

Benefits and Practical Applications

• Full automation reduces manual handling, operator error, and labor costs
• Large volume injection enhances sensitivity for trace-level analysis
• Wide applicability to regulatory monitoring of drinking and environmental waters
• Robust performance for a broad range of pesticide chemistries, including heat-sensitive compounds

Future Trends and Potential Applications

Advances in SPE sorbent materials and high-resolution mass spectrometry promise even greater sensitivity and selectivity. Emerging needs for rapid on-site testing could be met by miniaturized interfaces and portable GC/MS systems. Integration with data analytics and automated reporting will streamline environmental surveillance and support real-time water quality management.

Conclusion

The described on-line SPE–GC/MS method with at-column concentrating large volume injection offers a powerful tool for routine determination of pesticides in aqueous samples. It combines automation, sensitivity, and robustness to meet current regulatory requirements and paves the way for future enhancements in environmental analysis.