Improved Total Oxidizable Precursor Assay for Quantifying Polyfluorinated Compounds Amenable to Oxidative Conversion to Perfluoroalkyl Carboxylic Acids

Despite the fact that thousands of perfluoroalkyl andpolyfluoroalkylsubstances (PFASs) are in widespread commercial use, analytical methodscapable of quantifying them in environmental samples are availablefor less than 100 compounds. The total oxidizable precursor (TOP)assay provides a means of quantifying unknown PFASs by oxidizing PFASsinto perfluoroalkyl carboxylates (PFCAs), which are readily measuredby liquid chromatography-tandem mass spectrometry. To improvethe reproducibility of the TOP assay, [C-13(8)]perfluorooctane sulfonamide was added to samples prior to oxidationas an efficiency indicator and its conversion to [C-13(8)] perfluorooctanoic acid was quantified. The recovery of precursorswas also improved by including the analysis of ultrashort PFCAs, namelytrifluoroacetic acid and perfluoropropyl carboxylic acid, which revealedthe presence of ultrashort precursors. A method for distinguishingbetween branched and linear PFCAs was also integrated into the assayto enhance its ability to differentiate between PFASs produced byelectrochemical fluorination and those produced by fluorotelomerization.In addition to its potential application in forensic studies, theimproved TOP assay reduces uncertainties associated with incompleteoxidation of precursors or formation of ultrashort PFCAs that arenot detected by standard analysis methods. An enhanced TOP assay to ensure complete oxidation in environmentalsamples and improve concentration estimation for oxidizable short-chainpolyfluoroalkyl substances.

Automated summary

Despite the widespread use of thousands of PFASs, there are only analytical methods available for quantifying them in environmental samples. The TOP assay quantifies unknown PFASs by oxidizing them into PFCAs, which are easily measured. The improved TOP assay includes the use of an efficiency indicator and the analysis of ultrashort PFCAs to enhance its reproducibility and accuracy.