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TP8 Perfluorochemical Monitoring
(ARS-1117-544387) Separation and Fluorine Nuclear Magnetic Resonance Spectroscopy Analysis of the Individual Branched Isomers Present in Technical PFOS.
Arsenault, G1, Chittim, B1, McAlees, A1, McCrindle, R2, 1 Wellington Laboratories, Guelph, Ontario, Canada2 University of Guelph, Guelph, Ontario, Canada
ABSTRACT- The production of perfluoroalkylsulfonate derivatives via electrochemical fluorination is not a clean process but rather gives a complex mixture. The presence of C8 isomers in commercial perfluorooctanesulfonate (PFOS) is evidenced by their partial separation by liquid chromatography (LC), resulting into two broad peaks. In other studies, PFOS appears as a broad signal. Indeed, commercial perfluorooctanesulfonyl fluoride (PFOF), and derived products, were found to be mixtures of 70% linear and 30% branched isomers as determined by 19F NMR spectroscopy. This study allowed quantification of the individual normal chain, isopropyl branched, alpha branched, t-butyl branched and internal gem-dimethyl branched isomers. Apparently, in this study, it was not possible to quantify the individual internal CF3 branched isomers, presumably due to overlap of their NMR spectra. The objective of this work was to isolate individual isomers present in a mixture prepared from technical PFOF and characterize their structures by 19F NMR. A commercial sample of PFOF was converted to secondary sulfonamides (PFOSamide) using benzylamine and the resulting mixture separated by a combination of crystallisation and semi-preparative-scale HPLC. A set of six fractions was obtained, each containing a different isomer as the major component accompanied by smaller amounts of up to four further isomers. The normal chain sulphonamide was purified to better than 99%. The 19F-NMR spectra of these PFOSamide isomers were run on a 400 MHz Bruker instrument using d4-methanol as solvent and hexafluorobenzene as an internal standard (set at -169.00 ppm). As a result, the quantification of the individual internal CF3 branched isomers present in technical PFOS proved possible.
Key words: separation, branched, perfluorooctanesulfonate, isomers
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