Parameters setting of HPLC-MS/MS. 1

Parameters setting of HPLC-MS/MS. 10 µL of the eluent was injected into an Agilent 1290 HPLC equipped with an Agilent ZORBAX Eclipse Plus C18 column (100 mm × 3.0 mm, 3.5μm particle size). The column temperature was set at 40°C. The flow rate was maintained at 0.3 mL/min; the mobile phase consisted of eluent A (10 mM ammonium acetate in ultrapure water) and B (acetonitrile). The eluent gradient started with 70% A for 1 min, then 10% A for 13 min and followed by another 14 min, ultimately back to 70% A for 15 min. The mass spectrometer was equipped with an electrospray ionization (ESI) source, operating in the negative ion mode with a capillary voltage of 4000 eV, 45 psi N2 nebulizer gas at a flow of 6 L min-1, N2 collision gas, a temperature of 325C and a nozzle voltage of 500 V. Multiple reaction monitoring (MRM) mode was used to maximize the instrument performance. The parent ion, daughter ion, and collision energy (eV) for PFCAs determination were: PFOA (413 > 369, 5), perfluoroheptanoic acid (PFHpA, 363 > 319, 5), perfluorohexanoic acid (PFHxA, 313 > 269, 3), perfluoropentanoic acid (PFPeA, 263 > 219, 2), and perfluorobutanoic acid (PFBA, 213 > 169, 2), respectively.