Offline Automated Extraction of Non-Polar Pesticides in Water with Analysis by GC/MS

Significance of the Topic

This application note addresses the challenge of monitoring non-polar pesticides in environmental and drinking waters. These compounds are highly hydrophobic, prone to bioaccumulation, and toxic at low concentrations. Automated small-scale extraction offers a more efficient, reproducible, and safer alternative to manual liquid–liquid methods, reducing solvent use, hands-on time, and analyst exposure while maintaining sensitivity and accuracy.

Study Objectives and Overview

The aim of the study was to demonstrate a proof-of-principle method for automated offline extraction of 45 non-polar pesticides from water using the GERSTEL MPS2 system, followed by analysis on an Agilent 7890 GC with a triple-quadrupole MS. The study evaluated linearity, accuracy, and detection capability over three days in collaboration with ALS Wakefield.

Methodology

• Preparation of Standards: Two sets of spiked water standards (Set A for calibration, Set B for QC) at 20, 50, 80, 120, and 150 ng/L in 200 mL volumes.
• Automated Extraction: Triplicate 15 mL aliquots were placed into 20 mL headspace vials. The MPS2 added ethyl acetate co-solvent and 1 mL hexane extraction solvent. Samples were agitated at 500 rpm for 10 min.
• Transfer and Analysis: The organic layer was transferred to GC vials. A 25 µL injection was made on a GC/QQQ. MS/MS MRM transitions were used for each pesticide, supported by internal standards.

Instrumentation Used

• GERSTEL MPS 2 XL-xt with agitator
• Maestro control software (v1.4.18.25/3.5)
• Agilent 7890 GC with 7000B triple-quadrupole MS

Results and Discussion

The method produced clear extracted-MRM chromatograms at 150 ng/L (Figure 1) and distinct overlays at all five levels for representative compounds (e.g., pp-DDT at 20–150 ng/L, Figure 2). Calibration curves for 45 analytes achieved R² ≥ 0.99 with linear or quadratic fits. At 20 ng/L, 35 pesticides met accuracy within ±20% of nominal; all were within ±30%. Estimated detection limits could be below 1 ng/L based on signal-to-noise, though untested. Automated small-scale extraction reduced solvent use to 1 mL per sample and allowed overlapping sample preparation and analysis (Figure 3), improving throughput and minimizing analyst idle time.

Benefits and Practical Applications

• Reduced solvent consumption and exposure (orders of magnitude lower than 10–100 mL classical extractions).
• High reproducibility, accuracy, and linearity across environmental concentration ranges.
• Scalable throughput via pre-prepare-ahead function in Maestro software.
• Potential integration into routine QA/QC and environmental monitoring workflows.

Future Trends and Applications

Further development could include full integration of MPS2 with the GC inlet, use of larger volume injections (e.g., via GERSTEL CIS) or higher-sensitivity QQQ instruments (e.g., Agilent 7010) to lower detection limits to regulatory levels (≈0.1 ng/L). Optimization of sample-to-solvent ratios and equilibration times would refine extraction efficiency. A comprehensive validation in diverse water matrices is recommended to establish robustness, limits of detection/quantification, and recovery under real-world conditions.

Conclusion

This study confirms that automated offline liquid–liquid extraction using the GERSTEL MPS2 combined with GC–MS/MS analysis is a viable approach for non-polar pesticide monitoring. The method delivers rapid preparation, reduced solvent use, high reproducibility, and sufficient sensitivity for environmental surveillance. Implementation of proposed enhancements will further improve sensitivity, lower quantitation limits, and support high-throughput regulatory and research applications.

References

• O’Connor S. Offline Automated Extraction of Non-Polar Pesticides in Water with Analysis by GC/MS. Anatune Ltd Technical Note AS144; 2015.