Analysis of perfluoroalkyl and polyfluoroalkyl substances in serum and plasma by solvent precipitation-isotope dilution-direct injection-LC/MS/MS

Abstract

A validated liquid chromatography tandem mass spectrometry (LC/MS/MS) method is presented for the analysis of per- and polyfluoroalkyl substances (PFAS) in serum and plasma. The method employs stable-isotope labeled internal standard (IS) and surrogate recover standard (SRS) spiked serum or plasma samples that are mixed and precipitated with acetonitrile. Quantitation is performed with stable-isotope IS solvent (50 : 50 acetonitrile : water) calibration using one direct injection (DI) chromatographic analysis of precipitated sample supernate. The analytical method includes fifteen stable isotope labeled ISs, four SRSs ([1,2,3,4-¹³C₄]PFOA, [1,2-¹³C₂]PFUnA, [1,2,3,4-¹³C₄]PFOS, [2,3,4-¹³C₃]PFBA), and sixteen target analytes perfluoroalkyl carboxylic acids (PFCAs) (C4–C12), perfluoroalkyl sulfonic acids (PFSAs) (C4, C6, C8), N-ethyl perfluorooctane sulfonamido acetate (EtFOSAA), N-methyl perfluorooctane sulfonamido acetate (MeFOSAA), perfluorooctane sulfonamide (FOSA), and perfluorobutane sulfonamide (FBSA). Mean recoveries of control human plasma fortified with method target analytes over the range 2.5–175 ng mL⁻¹ (10–700 ng mL⁻¹ PFOS) are 83.7–103% with relative standard deviations (RSDs) of ≤14% (PFBA = 19%). Mean recoveries and RSDs of control human plasma fortified with mixed branched and linear isomer PFOA and PFHS (2.5 & 10.0 ng mL⁻¹), and PFOS (10 & 40 ng mL⁻¹) were 83.2% (RSD ± 7.7%), 101% (RSD ± 4.9%), and 101% (RSD ± 6.5%) respectively. Mean recoveries of control bovine serum fortified with the method target analytes over the lower concentration range 0.250–175 ng mL⁻¹ (1–700 ng mL⁻¹ PFOS) are 82.8–103% with RSDs ≤15% (MeFOSAA = 16%, EtFOSAA = 17%). Mean recoveries and RSDs for 736 American Red Cross (ARC) study plasma samples fortified with SRSs at 1 ng mL⁻¹ were 89.0% (±7.3% RSD) for [1,2,3,4-¹³C₄]PFOA, 91.8% (±10% RSD) for [1,2-¹³C₂]PFUnA, and 89.4% (±7.9% RSD) for [1,2,3,4-¹³C₄]PFOS.