Bringing Cationic and Zwitterionic PFAS into Focus: Chemical Diversity, Environmental Occurrence and Current Analysis Methods

Per- and polyfluoroalkyl substances (PFAS) are contaminants whose vast chemical diversity poses substantial challenges to environmental monitoring. Among them, cationic and zwitterionic PFAS have largely remained under the radar, with limited information available on their environmental fate and effects. One of the primary challenges in analyzing these precursors is the limited availability of native reference standards and surrogate internal standards, precluding accurate quantification. Some methods originally developed for anionic PFAS underperformed at extracting cationic and zwitterionic PFAS, and these precursors can also transform during sample processing, further confounding the analysis. This paper provides a critical overview of the chemical diversity, origins, environmental occurrence, and analytical methods for cationic and zwitterionic PFAS. The individual steps of the analytical process, including sample collection and pre-treatment strategies, extraction techniques, chromatographic separation, and mass spectrometry detection, are reviewed, with particular attention to method limitations and pitfalls. We also summarize the analytical figures of merit attained in the literature, including limits of detection, extraction efficiency, and matrix effects. This review should be useful to end-users wishing to expand existing PFAS workflows to cationic and zwitterionic compounds.