Total oxidizable precursors assay for PFAS in human serum

Per-and polyfluoroalkyl substances (PFAS) are a class of chemicals including over 4700 substances. As a limited number of PFAS is routinely analyzed in human serum, complementary analytical methods are required to characterize the overlooked fraction. A promising tool is the total oxidizable precursors (TOP) assay to look for precursors by oxidation to perfluoroalkyl acids (PFAA). The TOP assay was originally developed for large vol-umes of water and had to be adapted for 250 mu L of human serum. Optimization of the method was performed on serum samples spiked with model precursors. Oxidative conditions similar to previous TOP assay methods were not sufficient for complete oxidation of model precursors. Prolonged heating time (24 h) and higher oxidant amount (95 mg of Na2S2O8 per 225 mu L of serum) were needed for complete conversion of the model precursors and accomplishing PFAA yields of 35-100 %. As some precursors are not fully converted to PFAA, the TOP assay can only provide semi-quantitative estimates of oxidizable precursors in human serum. However, the TOP assay can be used to give indications about the identity of unknown precursors by evaluating the oxidation products, including perfluoroalkyl sulfonic acids (PFSA) and perfluoroalkyl ether carboxylic acids (PFECA). The optimized TOP assay for human serum opens the possibility for high-throughput screening of human serum for undetected PFAA precursors.

Automated summary

This article introduces a method for analyzing overlooked oxidizable precursors in human serum. The method involves the oxidation of precursors to perfluoroalkyl acids (PFAA) to assess undetected PFAS precursors in human serum. After optimization, the method can provide indications for high-throughput screening of undetected PFAA precursors in human serum.