Consolidating LC×LC-HRMS/MS Technique for the Non-targeted Analysis of Poly- And Perfluorinated Substances: a Trial on Aqueous-Film Forming Foams.

To date, poly- and perfluoroalkyl substances (PFASs) represent a real threat for both their environmental persistence, wide physicochemical variability, and their potential toxicity. Thus far a large portion of these chemicals remain structurally unknown. These chemicals, therefore, require the implementation of complex non-targeted analysis workflows using high resolution mass spectrometry coupled with liquid chromatography (LC-HRMS) for their comprehensive detection and monitoring. This approach, even though comprehensive, does not always provide the much needed analytical resolution for the analysis of complex PFAS mixtures such as fire-fighting aqueous-film forming foams (AFFFs). This study consolidates the advantages of LC×LC technique hyphenated with high-resolution tandem mass spectrometry (HRMS/MS) for the identification of PFASs in AFFF mixtures. A total of 57 PFAS homologue series (HSs) were identified in 3M and Orchidee AFFF mixtures thanks to the (i) high chromatographic peak capacity (n’2D,c~300) and the (i) increased mass domain resolution provided by the “remainder of Kendrick Mass” (RKM) analysis on the HRMS data. Then, we attempted to annotate PFASs of each HSs exploiting the available reference standards and the FluoroMatch workflow in combination with the RKM defect by different fluorine repeating units, such as CF2, CF2O, and C2F4O. This approach resulted in 12 identified PFAS HSs, including compounds belonging to the HSs of PFACAs, PFASAs, SF5-PFASAs, N-SPAmP-FASA, and N-CMAmP-FASA. The annotated categories of perfluoroalkyl aldehydes, and chlorinated PFASAs represent a first record of PFAS HSs in the investigated AFFF samples.