Analysis of ultra-short-chain and short-chain PFAS in environmental samples: A review

Ultra-short-chain (USC) and short-chain (SC) per- and polyfluoroalkyl substances (PFAS) are increasingly reported in environmental samples, but their quantitative analysis remains challenging. The measurement process often suffers from poor chromatographic retention, elevated background contamination, and matrix interferences. Environmental monitoring of USC PFAS has also been limited to a few perfluoroalkyl acids, such as trifluoroacetic acid (TFA), perfluoropropanoic acid (PFPrA), and C1-C3 perfluoroalkane sulfonates, while neglecting a plethora of USC precursors originating from aqueous film-forming foams, fluorinated ionic liquids (e.g., bistriflimide), and other applications. In this study, we reviewed findings from about 200 articles reporting USC and SC PFAS, with a specific focus on analytical methods and challenges. Key sample preparation steps reported for effective quantification of USC and SC PFAS included, but were not limited to, the use of PFAS-free labware, proper sample storage, isotope dilution, mild sample acidification before solid-phase extraction (off-line or on-line SPE), and specific cleanup procedures to eliminate matrix interferences. Approximately one-third of the reviewed studies employed reversed-phase liquid chromatography (RPLC), often resulting in poor sensitivity and inadequate retention of TFA. Preferred chromatographic modes for USC PFAS were hydrophilic interaction liquid chromatography (HILIC) and mixed-mode anion exchange liquid chromatography (AEX). Analytical figures of merit, including contamination and filtration artifacts, extraction efficiency, and limits of detection, are critically discussed. A list of ultra-short-chain PFAS relevant to environmental screening is also provided.