FindPFΔS: Non-Target Screening for PFAS─Comprehensive Data Mining for MS² Fragment Mass Differences

Abstract

The limited availability of analytical reference standards makes non-target screening approaches based on high-resolution mass spectrometry increasingly important for the efficient identification of unknown PFAS (per- and polyfluoroalkyl substances) and their TPs. We developed and optimized a vendor-independent open-source Python-based algorithm (FindPFΔS = FindPolyFluoroDeltas) to search for distinct fragment mass differences in MS/MS raw data (.ms2-files). Optimization with PFAS standards, two pre-characterized paper and soil samples (iterative data-dependent acquisition), revealed Δ­(CF2) n , ΔHF, ΔC n H3F2n–3, ΔC n H2F2n–4, ΔC n HF2n–5, ΔC n F2n SO3, ΔCF3, and ΔCF2O as relevant and selective fragment differences depending on applied collision energies. In a PFAS standard mix, 94% (36 of 38 compounds from 10 compound classes) could be found by FindPFΔS. The use of fragment differences was applicable to a wide range of PFAS classes and appears as a promising new approach for PFAS identification. The influence of mass tolerance and intensity threshold on the identification efficiency and on the detection of false positives was systematically evaluated with the use of selected HR-MS2-spectra (20,998) from MassBank. To this end, with the use of FindPFΔS, we could identify different unknown PFAS homologues in the paper extracts. FindPFΔS is freely available as both Python source code on GitHub () and as an executable windows application () with a graphical user interface on Zenodo.

PhotoTOP: PFAS Precursor Characterization by UV/TiO2 Photocatalysis

“…To evaluate the suitability of the PhotoTOP with real samples, it was applied to two previously characterized PFAS-coated papers (P1 & P2), , two technical PFAS mixtures [Zonyl RP (monomeric) and Cartafluor CFI (polymeric)], and one unknown water-repellent fabric (canvas).…”

“…Furthermore, selected volatile precursors (e.g., fluorotelomer alcohols (FTOHs) and FT-thiols) were detected by coupling an Agilent 7890B gas-chromatograph (GC) via an APCI interface with the QTOF-MS (method details in section S2; Table S5). For each homologous series one reference standard was used for validation, except for fluorotelomer mercapto alkyl phosphate (FTMAP) sulfoxide/sulfone homologues, which were previously identified, and newly tentatively identified PFAS (four further FTMAP-related compounds and fluorotelomer aldehydes (FTALs); for details on identification see section S4 and Figures S17–S21) in the paper extracts (for several precursors no reference standard was available). Each measurement sequence included a solvent and extraction blank (for sample extracts) and quality controls to monitor instrument performance similar as described above for target analysis.…”

“…In case of PFCAs, the molar mass-based peak areas of the predominant insource fragment ions [M-CO 2 ] − were also added. Furthermore, a more in-depth non-target screening (NTS) via FindPFΔS and Kendrick mass defect analysis (MS 1 , peak picking with the Agilent FindByMolecularFeature algorithm) was performed to search for unknown PFAS precursors in selected sample extracts (more details on identification level and identity in section S4, further details on NTS described elsewhere). , For raw data evaluation, the Agilent Mass Hunter Qualitative Analysis 10.0 and Quantitative Analysis 10.1 were used.…”

“…Besides high-resolution mass spectrometry (HRMS), which considerably helped to increase knowledge about distinct identities of numerous new PFAS, − there are also sum-parameter approaches that are necessary due to the fact that many PFAS are not readily ionizable or extractable from their matrix . While parameters such as total fluorine (TF) and absorbable and extractable organic fluorine (AOF, EOF) , have their individual advantages they also go along with the loss of information on identity of individual PFAS, their properties, fate, and toxicity (e.g., chain length, bioaccumulation) …”

“…To evaluate the effect of matrix (dissolved organic carbon; DOC) on the PhotoTOP oxidation we oxidized 8:2 fluorotelomer sulfonic acid (FTSA)­with four different matrix dilutions. To this end, we applied the UV/TiO 2 oxidation to two precharacterized (regarding the occurrence of precursors) , PFAS-coated paper samples and a technical grease-repellent PFAS standard as well as an acrylic PFAS copolymer and an unknown water-repellent fabric sample. We discuss the ability of the PhotoTOP to unravel the chain-length distribution of precursors in oxidized samples (already known precursors and in this study via non-target screening newly identified precursors) by the generated perfluoroalkyl carboxylic acids (PFCAs).…”