METHOD VALIDATION OF THE ANALYSIS OF ORGANOCHLORINE PESTICIDES AND POLYCHLORINATED BIPHENYLS USING DILLME AND GC-MS/MS

Importance of the Topic

The persistence of organochlorine pesticides and polychlorinated biphenyls (PCBs) in aquatic environments poses significant ecological and human health risks due to bioaccumulation and toxicity. Regulatory limits for these compounds are set at extremely low concentrations, requiring highly sensitive analytical techniques that minimize sample and solvent usage while maintaining reliable quantification.

Objectives and Study Overview

This study aimed to validate an automated dispersive liquid–liquid microextraction (DiLLME) method, coupled with large volume injection (LVI) and GC–MS/MS, for the analysis of 18 organochlorine pesticides and PCBs in various water matrices. The goal was to achieve limits of quantitation (LOQs) below 10 ng/L, assess method precision and bias, and demonstrate compliance with regulatory requirements.

Methodology

• Six milliliters of sample were manually transferred into high-recovery vials.
• Automated spiking of internal standards and addition of isopropanol as dispersant and dichloromethane/pentane as extraction solvent using a dual-head robotic autosampler.
• Emulsion formation by vortex mixing, followed by centrifugation to separate extraction solvent.
• Large volume injection (10 µL) on a cooled injection system optimized via design of experiments to handle complex solvent mixtures.
• GC–MS/MS analysis using multiple reaction monitoring (MRM) over a calibration range of 0–200 ng/L.
• ANOVA was applied to determine LOQs (ten-fold within-batch standard deviation) and evaluate precision and bias across borehole, surface, tap, and laboratory water matrices.

Instrumentation

• GERSTEL MultiPurpose Sampler with dual-head robotics
• GERSTEL QuickMix vortexing module
• GERSTEL CIS 4C cooled injection system
• GERSTEL UPCPlus automated pipetting
• Anatune CF200 centrifuge
• Agilent 7890B gas chromatograph
• Agilent 7010 triple quadrupole mass spectrometer with high-efficiency source

Main Results and Discussion

• Calibration linearity for all analytes achieved R² ≥ 0.990, with individual compounds such as heptachlor endo-epoxide and dieldrin exhibiting R² of 0.997–0.998.
• LOQs ranged from 3.4 to 8.7 ng/L, all well below the 10 ng/L target and regulatory prescribed values.
• Signal-to-noise ratios for key transitions at 10 ng/L exceeded 50 for most compounds, ensuring clear detection.
• Recoveries at 20 ng/L spikes in tap water averaged within ±3%, complying with the 25% bias requirement.
• Precision at 20 ng/L was below 25% for all analytes except δ-HCH (28.5%), which can be improved by using a 13C-labelled internal standard.
• Sample volume reduction from 250 mL to 6 mL represented a forty-fold decrease in required water, dramatically lowering transport and waste disposal costs.

Benefits and Practical Applications

• Significant reduction in sample and solvent consumption
• Lower operating costs and environmental footprint
• High throughput enabled by full automation
• Improved analyst safety by minimizing manual handling
• Potential consolidation of multiple pollutant analyses into a single method

Future Trends and Potential Uses

Advances in automated microextraction and LVI are likely to expand multi-analyte workflows for trace contaminants in environmental, food, and biological matrices. Integration of design of experiments software can further streamline method development, while the adoption of isotopically labelled standards will enhance accuracy for challenging compounds. Coupling with high-resolution mass spectrometry may extend applicability to emerging pollutants.

Conclusion

This validation demonstrates that automated DiLLME coupled with LVI–GC–MS/MS meets stringent regulatory requirements for organochlorine pesticides and PCBs at low nanogram-per-liter levels using minimal sample volumes. The method offers robust performance, cost and time savings, and environmental benefits, making it an effective solution for routine water quality monitoring.

References

• Anatune Ltd. Application Note AS230. Cambridge, UK, 2019.
• Anatune Ltd. Application Note AS198. Cambridge, UK, 2019.