Do selected CF3-containing pharmaceuticals oxidize to trifluoroacetic acid (TFA)? – Analysis of ultra-short perfluoroalkyl acids (PFAAs) and their analytical challenges following oxidation

Sammanfattning: Total oxidizable precursor assay (TOPA) has been used to understand the contribution of unknown precursors to the extractable organofluorine (EOF) compounds. The investigation of compounds containing a CF3 moiety especially connected to an aromatic ring is important because any compounds with such a moiety (pharmaceuticals) may oxidize to form trifluoroacetic acid (TFA). This information may help to increase the understanding of the sources of TFA in the environment. TOPA has been used for this purpose, however, this method has a weakness as the conditions during oxidation results in samples containing high concentrations of sulfates. The sulfates might compete with C2-C3 perfluoroalkyl acids (PFAAs) for binding sites in the solid-phase extraction (SPE), which in turn decreases the recovery of these compounds substantially. This study aimed to optimize the extraction following the TOP assay to increase the recovery of C2-C3 PFAAs, and to apply the improved method to determine whether selected pharmaceuticals (fluoxetine, seproxetine and celecoxib) may oxidize to form TFA. The main parameters affecting the recoveries of C2-C3 PFAAs were found to be pH as well as sorbent volume of the SPE cartridge. The optimized method included adjusting samples to pH 2.0 using formic acid prior to solid phase extraction (SPE), as well as using 500 mg sorbent cartridges for SPE. By optimizing the extraction, it was possible to increase the recovery of TFA from 2% to 54%. All three pharmaceuticals were oxidized into TFA to various extent (molar ratio of TFA from fluoxetine: 35%, seproxetine: 63% and celecoxib: 35%). This knowledge could be used as an indication of potential precursors in a sample and can help understand the contribution of CF3-containing pharmaceuticals to the EOF.