Selective Detection and Identification of Perfluorinated Alkyl Substances Using Low-Resolution Precursor Ion Mass Spectrometry

Using a low-resolution triple quadrupole mass spectrometer, a nontargeted approach for detecting and identifying perfluorinated alkyl substances (PFAS) has been developed and applied. Because many PFAS will fragment to C2F5− at m/z 119, we used precursor ion scanning mode to detect multiple classes of PFAS in a sample without the need for target ions as required by purely selective methods such as multiple reaction monitoring (MRM). Precursor ion scanning offers a relatively simple way to detect and identify nontargeted PFAS that is potentially accessible to more laboratories than approaches using high-resolution mass spectrometry. Specifically, we have used the method to measure traditional classes of PFAS-like perfluorinated carboxylic acids, sulfonates and sulfonamides, as well as recently developed PFAS-like hexafluoropropylene oxide – dimer acid (HFPO-DA, GenX), and other recently discovered classes like hydrogenated perfluorocarboxylic acids (HPFCAs) and unsaturated PFAS (UPFAS). Using a triple quadrupole mass spectrometer with a single common fragment results in a smaller fraction of PFAS that will be detected compared to the high throughput techniques, and the low-resolution mass spectrometry limits the selectivity somewhat. In addition to PFAS, precursor ion scanning of m/z 119 also detected alkylbenzene sulfonates, a class of very common surfactants that also fragment to a product ion at the same nominal mass. The method detection limits were ∼30 ng/L for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), including a 10,000 × concentration by solid phase extraction. We demonstrated the effectiveness of this approach to identify several classes of recently discovered PFAS compounds in well water samples from French Island, WI, which had been previously identified as having significant PFAS contamination.