Dispersive liquid-liquid micro-extraction for the automated sample preparation of PFAS in drinking water

Significance of the Topic

The persistence and toxicity of per- and polyfluoroalkyl substances (PFAS) have made their monitoring in drinking water a global priority. Dispersive liquid–liquid microextraction (DLLME) delivers a miniaturized, solvent-efficient alternative for preconcentrating trace-level PFAS, enhancing detection while aligning with green chemistry principles.

Objectives and Overview

This work demonstrates an automated DLLME protocol on the Thermo Scientific TriPlus RSH SMART liquid handling station for the efficient extraction and preconcentration of 56 PFAS in drinking water. The method aims to meet stringent regulatory limits and can be interfaced with both LC-MS and GC-MS platforms.

Instrumentation Used

The automated workflow employs the TriPlus RSH SMART autosampler equipped with syringe tools, vortexer, centrifuge, and solvent stations. Analytical separation and detection are performed using a Thermo Scientific Vanquish Flex HPLC system coupled to an Orbitrap Exploris 240 mass spectrometer. Chromeleon 7.3.2 software controls both sample preparation and data acquisition.

Methodology

Fifteen milliliters of acidified water are spiked with 22 isotopically labeled internal standards. DLLME is executed in two steps: first with a low-density dispersant/extractant mixture, then with a high-density extractant. Each step is followed by vortex mixing and centrifugation. The resulting ~30 µL organic extract is injected (10 µL) onto a C18 column with gradient elution (water/methanol with ammonium acetate and acetic acid) and analyzed by full-scan, SIM, and AIF HRAM MS.

Key Results and Discussion

Calibration was linear over 0.1–100 ng/L (R² > 0.99) for all 56 PFAS. Limits of quantification ranged from 0.1 to 5 ng/L. Intra- and inter-day precision and accuracy for spiked tap and bottled water (5 and 75 ng/L) met acceptance criteria of ±30% and <30% RSD. Stability tests confirmed sample integrity up to 12 hours pre-extraction and 24 hours post-extraction. Cross-contamination remained below 20% of LOQ signal.

Benefits and Practical Applications

• High enrichment factors (up to 500) enhance sensitivity for trace PFAS analysis.
• Minimal solvent use and elimination of SPE cartridges reduce cost and environmental impact.
• Automated processing of 54 samples in ~9 minutes each improves throughput and reproducibility.
• Modular design allows seamless integration with LC-MS and potential adaptation to GC-MS workflows.

Future Trends and Potential Applications

Expanding DLLME to complex environmental and biological matrices, exploring novel green dispersant/extractant systems, and integrating on-line automated platforms with high-resolution MS will further streamline PFAS analysis. Development of tailored isotopic standards for emerging PFAS will enhance quantitation accuracy.

Conclusion

The automated DLLME method on the TriPlus RSH SMART platform offers a robust, rapid, and eco-friendly solution for ultra-trace PFAS determination in drinking water, meeting regulatory requirements while reducing labor, time, and solvent consumption.

References

• Thermo Fisher Scientific Application Note 002902. Direct injection of drinking water for analysis of 54 PFAS compounds by LC-MS/MS aligned with current and evolving global regulations.
• Thermo Fisher Scientific Application Note 73883. Determination of per- and polyfluorinated alkyl substances (PFAS) in drinking water using automated solid-phase extraction and LC-MS/MS for U.S. EPA Method 533.
• Thermo Fisher Scientific Application Note 73346. Determination of per- and polyfluorinated alkyl substances (PFAS) in drinking water using automated solid-phase extraction and LC-MS/MS.
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