A clean-up method to remove taurine conjugated bile acid isomers interference for perfluorooctane sulfonate (PFOS) analysis in biotic matrices by isotope dilution LC-MS/MS and investigation of other MRMs interference.

This paper presents a clean-up method to remove the Multiple Reaction Monitoring (MRM) isobaric interference from taurine conjugated bile acid isomers to the primary transition ion m/z = 499 > 80 for PFOS analysis in biological samples. Upon the identification of taurodeoxycholate (TDCA) isomers interference, the sample was evaporated to dryness under nitrogen, reconstituted with 1% formic acid in acetonitrile, then passed through an Agilent EMR-lip Solid-Phase-Extraction (SPE) cartridge. The eluent was concentrated and re-analysed. The method has been successfully applied in PFOS analysis of serum, liver, egg, shrimp, and fish samples with comparable values between two transition ions m/z = 499 > 80 & 99 and spike recoveries from 70% to 125%. Another interference to m/z = 499 > 80 in shrimp samples was investigated and tentatively speculated as taurine conjugate with unsaturated fatty acid. In addition, the method could remove the steroid sulfates interference to PFHxS transitions m/z = 399 > 80 and m/z = 399 > 99 in human serum samples. The Perfluoro-1-methylheptanesulfonate (P1MHpS), a branched PFOS isomer (br-PFOS), was identified to interfere with PFOS quantification in serum samples, causing either over- or under-estimation of PFOS values due to its response factors being 250% for the m/z = 499 > 99 transition and 5% for 499 > 80 transition. A calculation formula was proposed for quantification of P1MHpS and total PFOS values. About 20% of serum samples contained significant P1MHpS at 12-27% of total PFOS, indicating its high accumulation behaviour in human serum.