<p>Per- and polyfluoroalkyl substances (PFAS) comprise a diverse group of thousands of compounds, for which only a limited number of analytical reference standards are available. This presents significant challenges for the identification and quantification of PFAS in environmental samples. The PhotoTOP assay addresses this issue by photocatalytic oxidation of PFAS precursors into quantifiable perfluoroalkyl carboxylic acids. In this study, the PhotoTOP was applied for the first time to both aqueous film-forming foam (AFFF)–related PFAS standards and AFFF-contaminated soil. Precursors, intermediates, and final oxidation products were identified using target analysis and non-target screening (NTS). Numerous novel PhotoTOP intermediates were detected, such as perfluoroalkyl sulfonamide–based and fluorotelomer sulfonamide–based compounds, dimers, fluorotelomer betaines, and unsaturated perfluoroalkyl sulfonic acids. Mass balance analysis based on semiquantitative NTS (qNTS) data revealed near-complete conversion of PFAS precursors in both standards and contaminated soil. Additionally, transformation kinetics were investigated, providing insight into the behavior and persistence of PFAS precursors during PhotoTOP treatment and their potential fate in the environment.</p> Graphical abstract <p></p>