Automated determination of EU Water Framework Directive priority contaminants in surface water at pg/L detection limits using Stir Bar Sorptive Extraction (SBSE) GC/MS/MS

Importance of the Topic

European legislation under the Water Framework Directive requires monitoring of priority contaminants at trace levels in surface and coastal waters. Achieving low detection limits in the picogram per liter range is critical to assess chemical status, protect aquatic ecosystems and ensure safe water use. Automated sample preparation and highly sensitive analysis methods are needed to comply with stringent environmental quality standards.

Objectives and Study Overview

This study aimed to develop and validate a single-run analytical workflow for the simultaneous determination of approximately 100 priority pollutants at low double-digit to low triple-digit pg/L levels in 100 mL surface water samples. The target list comprised EU-WFD priority substances, additional regulated pesticides, PAHs, PCBs and PBDEs. Special emphasis was placed on extracting both dissolved and particle-adsorbed compounds and meeting EU regulatory performance criteria for limit of quantification (LOQ), precision and trueness.

Methodology and Instrumentation

A sequential stir bar sorptive extraction (SBSE) approach was used for analyte enrichment. Two PDMS-coated GERSTEL Twister® bars extracted analytes under different conditions (aqueous and organic modifier) from 100 mL samples. Thermal desorption in a GERSTEL Thermal Desorption Unit (TDU) transferred analytes to the GC, with a cooled injection system (CIS) refocusing compounds before separation on an Agilent HP-5ms capillary column. Detection employed an Agilent 7010 triple quadrupole mass spectrometer in multiple reaction monitoring (MRM) mode. Calibration was performed over concentration ranges tailored to each LOQ, using carbon-13 and deuterated internal standards to correct matrix effects.

Used Instrumentation

• GERSTEL MultiPurpose Sampler (MPS) robotic autosampler
• GERSTEL Thermal Desorption Unit (TDU 2)
• GERSTEL Cooled Injection System (CIS 4)
• Agilent 7890 GC with HP-5ms Ultra Inert capillary column
• Agilent 7010 Triple Quadrupole MS with High Efficiency Source

Main Results and Discussion

LOQs met or exceeded EU-WFD requirements for nearly all analytes, ranging from sub-ng/L to low ng/L levels. Only cypermethrin, heptachlor and heptachlorepoxide failed to reach the most stringent inland water LOQs. Precision (n=6) at LOQ was excellent, with relative standard deviations of 1–15% (average 6.9%), and trueness ranged between 90 and 110%. Calibration functions were linear or gently quadratic with excellent correlation coefficients. Particle-adsorbed compounds (e.g. PAHs) were accurately quantified using certified sediment spiking experiments. Application to real river, groundwater, tap and effluent samples confirmed method robustness, absence of significant interferences and reliable quantitation of both dissolved and bound fractions.

Benefits and Practical Applications

• Minimal sample volume (100 mL) reduces field logistics
• Automated SBSE-TDU-GC-MS/MS ensures high throughput and reproducibility
• Comprehensive single-run analysis of diverse contaminant classes
• Accurate determination of particle-adsorbed pollutants fulfills EU-WFD total concentration requirement
• Extensible to routine monitoring in environmental, industrial and compliance laboratories

Future Trends and Opportunities

Adoption of negative chemical ionization (NCI) could improve sensitivity for halogenated pesticides like cypermethrin and heptachlor. Integration with LC-MS/MS would expand coverage to polar priority substances. Further miniaturization and field-deployable SBSE devices may enable near-real-time water quality surveillance. Data-driven optimization of extraction parameters and MRM transitions will enhance confidence in emerging contaminant monitoring.

Conclusion

The sequential SBSE-TDU-GC-MS/MS method provides a robust, sensitive and automated solution for EU-WFD priority contaminant analysis at pg/L levels in minimal sample volumes. Validation demonstrated compliance with regulatory performance criteria, and successful application to real samples highlights its utility for comprehensive water quality assessment.

Reference

• Directive 2000/60/EC: Establishing a framework for Community action in the field of water policy
• Directive 2008/105/EC: Environmental quality standards in the field of water policy
• Directive 2013/39/EU: Amending Directives 2000/60/EC and 2008/105/EC on priority substances
• Commission Directive 2009/90/EC: Technical specifications for chemical analysis and monitoring of water status
• Commission Implementing Decision (EU) 2015/495: Union-wide monitoring watch list
• OGewV July 2011: German surface water ordinance
• Ochiai N, Sasamoto K, Kanda H. Sequential SBSE for uniform enrichment of organic pollutants. GERSTEL AppNote 12/2008
• DIN 32645:2008-11: Chemical analysis – detection and quantification limits under repeatability conditions
• Koch M. Freeware for uncertainty calculation. Institute for Urban Water Management, University of Stuttgart, 2015