Losses of poly- and perfluoroalkyl substances to syringe filter materials

Abstract

Syringe filters are used to separate solids from liquids prior to analysis of poly- and perfluoroalkyl substances (PFASs). This is a critical step in sample preparation, as losses of PFASs to the filter material can be significant and lead to underestimation. This study evaluated losses of 21 PFASs in three different matrices (methanol, MilliQ water, and water containing 10 mg L^-1 dissolved organic carbon (DOC)) to six different types of syringe filter (0.45 and 0.22 μm). Regarding sample matrix, the lowest average ∑₂₁PFAS losses were observed in methanol (13%), followed by DOC water (19%) and MilliQ water (26%). Regarding syringe filter material, the lowest average losses of ∑₂₁PFAS in DOC water and MilliQ water were observed for a recycled cellulose filter (average losses 16% and 21%, respectively), while a polypropylene filter had the lowest ∑₂₁PFAS losses in methanol (9%). A smaller polyethersulfone (PES) filter (0.22 μm, 17 mm Ø) showed significantly (p < 0.05) lower ∑₂₁PFAS losses in DOC water (on average 7.3%) than a larger PES filter (0.45 μm, 37 mm Ø) (23%). In DOC water, losses to the filter increased by 3.8%, 5.1%, and 8.4% per CF₂-moiety for C₃-C₁₁ perfluoroalkyl carboxylates (PFCAs), perfluoroalkyl sulfonates (PFSAs), and fluorotelomer sulfonic acids (FTSAs), respectively. Comparing different functional groups of PFASs, losses increased as follows: PFCAs < PFSAs < FTSAs < perfluorooctanesulfonamides (FOSAs). Thus, care is needed when including filtration in PFAS analysis, since losses can be significant (up to 100%) depending on the type of syringe filter, target PFAS, and matrix.

Keywords: Analysis; Extraction; Filter; Method development; Per- and polyfluoroalkyl substances.