TP8 Perfluorochemical Monitoring
Tuesday, 15 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(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