Determination of perfluorooctane sulfonate and perfluorooctanoic acid in human plasma by large volume injection capillary column switching liquid chromatography coupled to electrospray ionization mass spectrometry

Abstract

Rapid, selective, and sensitive methodology for the quantification of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in human plasma using packed capillary liquid chromatography coupled to electrospray ionization ion-trap mass spectrometry has been developed. Plasma proteins were precipitated using acetonitrile and the resulting supernatant was diluted 1 + 1 with water containing 10 mM ammonium acetate (NH₄Ac) prior to injection. Sample volumes of 250 μL were loaded onto a 30 mm×0.32 mm ID 10 μm Kromasil C₁₈ precolumn by a carrier solution consisting of 10 mM NH₄Ac in ACN/H₂O (5/95, v/v) at a flow rate of 100 μL/min, providing on-line analyte enrichment and sample clean-up. Backflushed elution onto a 100 mm×0.32 mm ID 3.5 μm Kromasil C₁₈ analytical column was conducted using an ACN/H₂O solvent gradient containing 10 mM NH₄Ac. In order to improve the robustness and performance of the method, perfluoroheptanoic acid (PFHA) was used as internal standard. Separation and detection of PFOA, PFHA, and PFOS were achieved within 10 minutes. Ionization was performed in the negative mode in the m/z range 250–550. The method was validated over the concentration range 1–200 ng/mL for PFOA and over the range 5–200 ng/mL untreated plasma for PFOS, yielding correlation coefficients of 0.997 (PFOA) and 0.996 (PFOS), respectively. The within-assay (n = 6) and between-assay (n = 6) precisions were in the range 2.1–9.2 and 5.6–12%, respectively. The concentration limits of detection (cLOD) of PFOA was 0.5 ng/mL while the cLOD of PFOS was estimated to be 0.2 ng/mL in untreated plasma.