Development and optimization of PFAS extraction in soil's headspace followed by multidimensional gas chromatography...

Per- and polyfluoroalkyl substances (PFAS) are a large class of synthetic "forever chemicals" due to their exceptional stability resulting from the strong carbon-fluorine bond, which makes them persistent, bioaccumulative, and associated with health and ecological risks. Despite their relatively high molecular weights, many PFAS exhibit sufficient volatility to be analyzed by gas chromatography coupled with mass spectrometry (GC-MS). In this study, a novel analytical workflow was developed for extracting and analyzing (semi-)volatile PFAS in soil samples, combining dynamic headspace extraction (DHS) using thermal desorption (TD) tubes with both one-dimensional gas chromatography (1D-GC) and comprehensive two-dimensional gas chromatography (GC×GC), each coupled with time-of-flight mass spectrometry (TOFMS). Nine target PFAS compounds were selected, comprising fluorotelomer alcohols (FTOHs), fluorotelomer acrylates (FTAc), and sulfonamide-based derivatives (N-MeFOSA, N-EtFOSA, N-MeFOSE, and N-EtFOSE). Building on a prior aqueous-sample study, Tenax TA was identified as the optimal sorbent based on recovery and reproducibility. Extraction volumes of 1 L, 2 L, and 5 L were evaluated, with 1 L providing the best recovery-reproducibility balance. Three different conditions (no solvent, pure water, and 1:1 (v/v) water-methanol mixture) were tested to evaluate solvent effects. The water-methanol mixture yielded the highest recovery, ensuring consistent reproducibility. Detection limits as low as 7.02 pg g⁻¹ were achieved, demonstrating excellent sensitivity. In a soil case study, the use of GC×GC-TOFMS enabled the identification of 106 additional environmentally relevant compounds. Overall, the DHS-TD-GC×GC-TOFMS approach offers a sensitive, robust platform for quantifying (semi-)volatile PFAS and screening other trace contaminants, supporting comprehensive environmental monitoring.