Branched Perfluorooctane Sulfonate Isomer Quantification and Characterization in Blood Serum Samples by HPLC/ESI-MS(/MS)

Abstract

Perfluorooctane sulfonate (PFOS) is a global contaminant and is currently among the most prominent contaminants in human blood and wildlife samples. Although "total PFOS" (SigmaPFOS) analytical methods continue to be the most commonly used for quantification, recent analytical method developments have made it possible to resolve the various isomers of PFOS by HPLC-MS/MS. Characterized technical PFOS standards (i.e., containing a mixture of PFOS isomers) are now available that enable isomer specific quantification of PFOS, however the advantages of such an analysis have notyet been examined systematically. Herein, PFOS isomers have been individually quantified for the first time in real samples and the results are compared to a traditional SigmaPFOS method; the influence of analytical standards and isomer specific electrospray and MS/ MS behavior were also investigated. The two human serum standard reference materials chosen for analysis contained dramaticallydifferent PFOS isomer profiles (approximately 30-50% total branched isomers) emphasizing that isomer patterns should not be ignored and may provide useful information on exposure sources (i.e., direct exposure to PFOS vs indirect exposure from PFOS-precursors). Depending on the sample and the particular MS/MS transition chosen for SigmaPFOS analysis (i.e., 499-->80 or 499-->99), SigmaPFOS concentrations may be over- or underestimated compared to the isomer specific analysis. Differences in the extent of in-source fragmentation and MS/MS dissociation contributed to the systematic analytical bias. It was also shown that SigmaPFOS data are prone to interlaboratory variation due to various choices of PFOS standards and instrumental conditions used. In the future, for either SigmaPFOS or isomer specific PFOS analyses, we suggest that accuracy can be maximized and interlaboratory discrepancies minimized by using a common chemically pure technical PFOS standard characterized by 19F NMR.

Technical‐grade perfluorooctane sulfonate alters the expression of more transcripts in cultured chicken embryonic hepatocytes than linear perfluorooctane sulfonate

“…Research investigating effects of branched PFOS isomers in mammals should be prioritized, especially given that branched isomers appear to accumulate in human samples. Branched proportions as high as 50% [63] have recently been reported in human serum.…”

Inter-individual, inter-city, and temporal trends of per- and polyfluoroalkyl substances in human milk from Swedish mothers between 1972 and 2016

“…For PFOA, the m/z 413/169 ion was used for quantication because of an interference in m/z 413/369. For PFOS, concentrations are reported as the average of m/z 499/80 and 499/99 ions for both branched and linear isomers, as described in Riddell et al 35 Sum PFOS was then obtained by summing the concentrations of branched and linear PFOS.…”

Perfluorooctane sulfonate toxicity, isomer‐specific accumulation, and maternal transfer in zebrafish (Danio rerio) and rainbow trout (Oncorhynchus mykiss)

“…These observations suggest that there is more than one mechanism controlling the biological handling of PFOS isomers. For example, based on the elevated UFs of iso, and 1m-PFOS and their elution order on alkyl reversed-phase columns [49,50], it appears that hydrophobicity plays a role to some extent in mediating isomerspecific uptake/elimination. Furthermore, the observation of a highly variable UF for DM3 between zebrafish and trout suggests that some species-specific biological mechanism plays a role, perhaps binding to serum proteins [51] or renal transport proteins [52].…”