Wide-spectrum target and total oxidizable precursor PFAS quantification with online enrichment and LC-HRMS:
Steven J Chow1, Eva-Maria Braxmaier2, Frédéric Haffter2
1Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, Dübendorf 8600, Switzerland.
Abstract:
Monitoring chemically diverse per- and polyfluoroalkyl substances (PFASs) in complex environmental matrices requires robust, streamlined analytical workflows. This study developed a high-throughput peak-focusing online solid-phase extraction (SPE) liquid chromatography high-resolution mass spectrometry (LC-HRMS) workflow to quantify 63 PFASs (nCF = 1-17, excluding trifluoroacetic acid) in wastewater, sludge, and total oxidizable precursor (TOP) assay samples. Underreported analytical challenges including HRMS isobars and precursor leaching from micropipette tips were investigated. Co-extracted matrix constituents, tentatively identified as linear alkylbenzene sulfonates and long-chain fatty acids, induced Orbitrap-specific ion competition that hindered quantification of long-chain PFASs in influent and sludge. Splitting the MS scan into two time- and mass-dependent ranges mitigated these effects and restored analyte sensitivity while maintaining full-scan capabilities. Validation using contemporary samples from two wastewater treatment plants (WWTPs) and legacy NIST SRM 2781 sludge demonstrated high reproducibility (intra-batch precision 8-17% for 95% of analytes). Median matrix limits of quantification were 2.5 ng/L (influent), 1 ng/L (effluent), and 1 ng/g (sludge). WWTP measurements revealed zwitterionic 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) as a dominant precursor in wastewater (max 405 ng/L) and sludge (max 60 ng/g), exceeding concentrations of ubiquitous perfluorocarboxylic acids (PFCAs), perfluorooctane sulfonic acid (PFOS), and other legacy PFASs. TOP assay results revealed substantial unknown precursor gaps, particularly in sludges where > 90% of oxidizable PFAS mass could not be explained by target precursors. To fill such PFAS mass gaps, this scalable full-scan analytical approach can readily accommodate new target analytes and provide valuable HRMS data for retrospective screening.
