The retention time (tr) of each PFAS was measured using an LC system (1260 Infinity II) equipped with a single quadrupole mass selective detector (MSD) from Agilent Technologies (Santa Clara, USA). Nitrogen gas generated by an AT-10NP-CS nitrogen generator (Airtech Corporation, Yokohama, Japan) was used to spray the sample solution into the ionization chamber. The fragmentor voltage was 25 V, which was relatively low to minimize fragmentation of unstable PFAS. A mass chromatogram was obtained by using the negative selected ion monitoring (SIM) mode. The monitored ions are shown in Table . Most compounds were measured with an m/z value that corresponds to the deprotonated form of the acids ([M -H] -). Fragment ions were monitored for C6-C14 PFCAs, NFDHA, and HFPO-DA.