Ultra-Trace Quantification of Per- and Polyfluoroalkyl Substances (PFAS) in Drinking Water

Significance of the Topic

Per- and polyfluoroalkyl substances PFAS are persistent environmental pollutants of growing concern due to their bioaccumulation and potential adverse health effects. Recent interim health advisory limits set by the US EPA require detection of PFOA at 0.004 ng/L and PFOS at 0.02 ng/L in drinking water. Ultra-trace quantification methods are essential for regulatory compliance, public health monitoring and baseline occurrence studies at part-per-quadrillion levels.

Aims and Study Overview

This study aimed to develop and verify an analytical workflow for the simultaneous quantification of PFOA PFOS PFBS and GenX in drinking water at concentrations matching or exceeding current US EPA and proposed EU limits. The approach combined optimized solid-phase extraction SPE protocols with LC/MS/MS analysis on an Agilent 1290 Infinity II LC coupled to a 6495C triple quadrupole mass spectrometer. Two liquid chromatography setups were evaluated to balance sensitivity peak shape and background contamination.

Methodology and Instrumentation

The sample preparation followed EPA method 533 with adjustments to minimize PFAS background. Unpreserved 250 mL water samples were spiked with isotopically labeled surrogates and extracted using Agilent Bond Elut PFAS WAX cartridges. After conditioning loading and elution the extracts were concentrated to 1 mL in PFAS-free polypropylene vials.

Two injection strategies were tested:

• Diol guard cartridge upstream of a C18 analytical column with a 100 µL injection for optimal chromatographic focusing.
• Sandwich injection onto a C18 column using 30 µL sample with water plugs before and after to improve peak shape and reduce matrix load.

The LC/MS/MS analysis employed an Agilent 1290 Infinity II system with a PFC-free delay column and a 6495C TQ with Jet Stream ESI in negative mode. Mobile phases A (2 mM ammonium acetate in water) and B (95:5 acetonitrile water) were delivered at 0.4 mL/min under a gradient. Dynamic multiple reaction monitoring dMRM transitions were sourced from the Agilent PFAS MRM database without further user optimization.

Main Results and Discussion

Calibration curves for all four analytes exhibited excellent linearity with R2 > 0.99 and average relative standard errors between 8 and 20% across 0.0004 to 0.04 ng/L equivalent concentrations. The Diol guard approach produced superior peak shapes but introduced a low-level PFOA background. The sandwich injection reduced background signals albeit with slightly broader peaks yet maintained required detection limits. Real water samples including ultrapure bottled laboratory water reagent water and two commercial bottled waters revealed PFOA levels above advisory limits in all cases and one sample exceeding 35 pg/L, highlighting method sensitivity and real-world applicability.

Benefits and Practical Applications

This method achieves parts-per-quadrillion sensitivity necessary for meeting ultra-low PFAS regulatory thresholds. It offers laboratories a robust validated workflow combining SPE consumables with high sensitivity LC/TQ instrumentation. The dual injection strategies provide flexibility to optimize for peak performance or matrix reduction as needed.

Future Trends and Potential Applications

Continued refinement may focus on broader PFAS panels automated sample preparation and higher throughput workflows. Advances in high-resolution mass spectrometry and miniaturized SPE formats could further lower detection limits and expand monitoring to additional environmental matrices such as soils biota and wastewater. Standardization across laboratories will support reliable global PFAS monitoring programs.

Conclusion

The developed Agilent-based SPE LC/TQ method delivers unparalleled ultra-trace PFAS quantification in drinking water. It meets stringent interim US EPA advisory limits for PFOA PFOS PFBS and GenX with excellent linearity precision and robustness. The two LC injection approaches provide tailored options for sensitivity and background control. Demonstrated success in real water samples confirms its suitability for routine regulatory and research applications.

Reference

• United States Environmental Protection Agency Per- and Polyfluoroalkyl Substances PFAS Updated January 5 2023
• European Union Proposal for a Directive of the European Parliament and of the Council Amending Directives 2000/60/EC 2006/118/EC and 2008/105/EC October 26 2022
• Per- and Polyfluoroalkyl Substances PFAS Analysis for Environmental Samples Agilent Technologies consumables ordering guide publication number 5994-2357EN 2022
• Hindle R Hunt K Anumol T EPA Method 533 for Analysis of PFAS in Drinking Water Using Agilent 6470 LC/MS/MS Agilent Technologies application note publication number 5994-1628EN 2020