Conventional PFAS monitoring approaches are focused on the detection of a few known PFAS chemicals, which usually underestimates the overall contamination of the environment. The numerous PFAS precursors found in industrial products and in the environment can, over time, degrade into the persistent perfluoroalkyl acids (PFAAs). The TOP assay was created to address this analytical gap by oxidizing the precursors of PFAS to stable end-products and, therefore, enabling a more precise estimate of total PFAS pollution and risk in the long term.
Principle of the TOP Assay
The principle of the TOP assay relies on the chemical oxidation, which is normally carried out by hydroxyl radicals produced by the action of persulfate in the presence of an alkaline solution in heated conditions. These powerful oxidants transform the PFAS precursors into terminal perfluoroalkyl carboxylic acids (PFCAs), followed by the measurement of this using standard PFAS analytical methods. When the concentration of PFCA increases after it is oxidized, this is a sign that precursor PFAS is present and in abundance.
Procedure Overview
The test is performed by keeping environmental samples (e.g., water, soil extracts, leachates) mixed with an oxidizing agent at specific temperature and pH conditions. The samples are neutralized after oxidation, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Before and after oxidation results are compared to identify contributions to precursors.
Applications of the TOP Assay
The TOP assay is popular in the field of environmental monitoring, assessment of contaminated sites, drinking water, and regulatory studies. It can be especially useful in evaluating locations affected by aqueous film-forming foams (AFFF), industrial discharges, landfills, and wastewater treatment facilities, where PFAS precursor materials are typically present.
