Techniques to characterize PFAS burden in biological samples: Recent insights and remaining challenges

Per/polyfluoroalkyl substances (PFASs) are a class of ubiquitous environmental contaminants associated with several adverse health effects in humans and animals. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) has traditionally been used to provide targeted quantitation of PFASs in biological samples. The analyte lists covered by targeted LC-MS/MS methods have grown rapidly as more PFASs have been discovered, though not all organofluorine is amenable to this technique. Integrative techniques measuring total organofluorine (TOF) coupled with LC-MS/MS analysis demonstrate that a significant fraction of TOF in biological samples is not captured by LC-MS/MS. This missing organofluorine may be contributed by PFASs that are not amenable to typical PFAS analytical conditions. Here, we review recent progress in quantifying total PFAS burden and identifying the compounds that comprise the unidentified organofluorine fraction (UOF), with a focus on human biological samples. While LC coupled to high-resolution mass spectrometry (LC-HRMS) has identified several novel PFASs in biological samples, these efforts do not appear to fully explain UOF content. Closing the UOF gap will necessitate the development of additional analytical approaches to broaden the chemical space captured by PFAS analysis. We highlight the use of additional chromatographic methods, advanced separation approaches such as ion mobility spectrometry (IMS), and continued improvement of HRMS semi-quantitation methods as promising paths forward to close the UOF gap.