Why you should triple-check fluoride data in PFAS destruction and environmental fluorine balance.

Accurate quantification of inorganic fluoride (F^-) release is an essential metric for evaluating the efficacy of poly- and perfluoroalkyl substance (PFAS) degradation processes. However, current analytical methods for F^- measurement, including ion chromatography (IC), the use of ion selective electrodes (ISEs), and combustion ion chromatography (CIC), possess inherent limitations and susceptibility to interferences within complex environmental matrices. This perspective critically examines these under-recognized analytical pitfalls, such as the co-elution of inorganic fluoride with short-chain organic acids in IC, the inherent sensitivity limitations and stability issues of ISEs at trace concentrations, and the variable recovery of ultra-short-chain or volatile fluorinated species in combustion-based sum parameter analyses. We explain how these analytical discrepancies can lead to mischaracterization of defluorination efficiency and potentially result in overestimation of technological performance, misinformed risk assessments, and regulatory ambiguity. We propose a series of methodological recommendations, emphasizing the routine application of hyphenated techniques such as IC-mass spectrometry (IC-MS) for enhanced F^- validation, and the strategic utilization of fluorine-19 nuclear magnetic resonance (¹⁹F NMR) spectroscopy for comprehensive tracking of diverse organofluorine species. Emphasizing analytical cross-validation and holistic fluorine mass balance approaches is paramount for enabling reliable advancements in PFAS remediation.