Background Perfluoroalkyl substances (PFAS) are a novel type of persistent organic pollutants with potential human health effects. To establish a method for determination of PFAS in biological samples is of great significance for both exposure and health risk assessments.

Objective This methodological study aims to establish an ultra-high performance liquid chromatography-quadrupole/orbitrap high resolution mass spectrometry (UPLC-Q-Orbitrap HRMS) method for simultaneous determination of 6 perfluorinated carboxylic acids (perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, and perfluorododecanoic acid), 5 perfluorosulfonic acids (perfluorobutane sulfonate, perfluorohexane sulfonate, perfluoroheptane sulfonate, perfluorooctane sulfonate, and perfluorodecane sulfonate), and 1 perfluoralkyl sulfonicacid (perfluorooctane sulfonamide) in human serum.

Methods Three solid phase extraction (SPE) columns, namely ProElut PLS, Oasis HLB, and Supelclean ENVI-18, were compared for their retention of PFAS. To obtain a better extraction recovery rate, methanol wash solutions with four different fractions and three eluents (acetonitrile, methanol, and isopropanol) were tested. Ammonium acetate buffer salt was added to improve the peak shape. A pre-separation column was used to reduce background noise. PFAS were quantified by isotopic internal standard method. The limits of quantification were determined at 10 times signal-to-noise ratio. The accuracy and precision were evaluated by recovery rate and intraand inter-day relative standard deviations. The established method was applied to 20 umbilical cord serum samples.

Results An optimal recovery rate (39%-103%) was achieved by using Oasis HLB column, washing with 30% methanol (v/v) and eluting with isopropanol. Good peak shape and mass response were obtained by using H₂O-methanol (containing 5 mmol·L^-1 ammonium acetate) as mobile phase and C₁₈ column as separation column. The linearity ranges of calibration curves of 12 analytes were from 0.01 to 10.00 μg·L^-1 (perfluoroheptanoic acid and perfluorooctane sulfonate: 0.10-10.00 μg·L^-1; perfluorodecane sulfonate and perfluorooctane sulfonamide: 0.05-10.00 μg·L^-1), with a limit of quantification between 0.01 and 0.10 μg·L^-1. The average recoveries of the analytes in spiked serum samples ranged from 81.0% to 123.7%. The relative standard deviations of the intra- and inter-day precision were from 1.2% to 14.8% and from 0.4% to 16.1%, respectively. PFAS were detected in all the 20 serum samples, and 9 kinds of PFAS were 100% detectable.

Conclusion The established method is featured with good linearity and a low limit of detection. Various methodological indicators show that the method can be applied to the simultaneous determination of multiple PFAS in serum samples accurately and rapidly.