Less is more: a methodological assessment of extraction techniques for per- and polyfluoroalkyl substances (PFAS) analysis in mammalian tissues

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants. Studying the bioaccumulation in mammalian tissues requires a considerable effort for the PFAS extraction from complex biological matrices. The aim of the current work was to select and optimize the most efficient among common extraction strategies for eleven perfluoroalkyl acids (PFAA). Primary extractions from wild boar tissues (liver, kidney, and lung) were performed with methanol at neutral, acidic, or alkaline conditions, or with methyl-tert-butyl ether (MTBE) after ion-pairing with tetrabutylammonium (TBA) ions. A second purification step was chosen after comparing different solid-phase extraction (SPE) cartridges (Oasis WAX, ENVI-Carb, HybridSPE Phospholipid) and various combinations thereof or dispersive SPE with C18 and ENVI-Carb material. The best extraction efficiencies of the liquid PFAA extraction from tissue homogenates were achieved with methanol alone (recoveries from liver 86.6-114.4%). Further purification of the methanolic extracts using dispersive SPE or Oasis WAX columns decreased recoveries of most PFAA, whereas using pairs of two SPE columns connected in series proved to be more efficient albeit laborious. Highest recoveries for ten out of eleven PFAA were achieved using ENVI-Carb columns (80.3-110.6%). In summary, the simplest extraction methods using methanol and ENVI-Carb columns were also the most efficient. The technique was validated and applied in a proof of principle analysis in human tissue samples.