PFAS Screening in Soil by Combustion Gas Analysis with Fourier Transform Infrared Spectroscopy.

Although several methods have been developed for the detection of total per- and polyfluoroalkyl substances (PFAS), most of them are not applicable for rapid site characterization. We report a combustion-gas analytical approach for PFAS, offering a simple, robust, and field-deployable method for PFAS screening in soil. We demonstrate that PFAS with varying functional groups and structures are combusted to SiF4 and HF, whereas inorganic fluorine forms only HF. This distinction overcomes a major challenge of inorganic fluorine interference in total PFAS analysis, as SiF4 can be selectively quantified by FTIR. We then applied the method to PFAS measurement in soil samples. Soil was extracted with basic methanol, which further minimized interference from inorganic fluorine and enabled semiquantitative detection, and the extracts were combusted for analysis. The method detection limits ranged from 13 to 16 μgPFAS/gsoil for three PFAS, with relative standard deviations of 34-47% at concentrations near the detection limit, indicating the current applicability of the method as a screening tool rather than quantitation, pending further process development. The developed screening method and tool has the capability to directly screen for PFAS at contaminated sites, which often have total PFAS concentrations between 10 and >100 μg/g.