Identification and Characterization of Per- and Polyfluoroalkyl Substances Isomers in Bird Eggs by Liquid Chromatography-Ion Mobility-High-Resolution Mass Spectrometry

values for PFNA and PFNS isomers. The workflow was successfully applied to 41 great and blue tit egg samples collected near a contaminated industrial site in Belgium, where 20 linear and 34 branched PFAS isomer features were detected. Correlation analysis between the number of isomers detected for each PFAS in bird eggs revealed distinct co-occurrence patterns among branched PFAS isomers, with PFBS and PFDoDA showing unique behavior compared with other PFAS classes. A significant difference in PFOS isomer profiles was identified between the two species, which may be related to differences in foraging behavior and species-specific accumulation. The results demonstrate that LC-IM-HRMS is a useful tool for confidence-enhanced PFAS isomer identification in complex biological samples despite the limited availability of single-branched isomer standards and highlight the value of isomer-resolved analysis for environmental biomonitoring and exposure characterization.