Simultaneous Determination of 48 Legacy and Emerging Per- and Polyfluoroalkyl Substances in Milk by Cold-Induced Liquid-Liquid Extraction Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

ObjectiveTo establish a rapid and comprehensive method for the simultaneous determination of 48 per- and polyfluoroalkyl substances （PFAS） in milk by liquid-liquid extraction coupled with ultra-performance liquid chromatography tandem-mass spectrometry （UPLC-MS/MS）.MethodsMilk samples were measured， extracted with 10% methanol-acetonitrile （1∶9，V/V） solution. The mixture was shaken， frozen at -20 ℃ for 30 min and centrifuged at 4 ℃. The combined liquid was evaporated under nitrogen and resuspended for injection and analysis. Chromatographic separation was performed using a gradient elution with a mobile phase of 2 mM ammonium acetate aqueous solution and acetonitrile. The analysis was carried out on an C18 column （3.0 mm×100 mm， 2.7 µm）. Detection was carried out using negative ion electrospray ionization （ESI-） in multiple reaction monitoring （MRM） mode， and quantification was achieved by the internal standard method.ResultsThe correlation coefficients （R） for all 48 PFAS were greater than 0.998 6 within the concentration range of 0.01-20 µg/L. The method detection limits ranged from 0.3 to 4.5 ng/L， and the quantification limits ranged from 1.0 to 15.2 ng/L. Recovery rates for three different spiked concentrations （0.01， 0.05， and 0.20 µg/L） ranged from 60.1% to 119%， with intra-day and inter-day relative standard deviation （RSD） smaller than 15.2%. When applied to 15 milk samples from local supermarkets in Guangzhou City， only 17 PFASs were detected， of which 6：2 FTS （66.7%）， PFOA （53.3%）， PFHxDA （53.3%）， PFBA （46.7%）， PFNA （33.3%）， and HFPO-DA （33.3%） had higher detection rates， and the mean concentrations were 1.17， 0.46， 0.57， 1.27， 0.32， and 1.65 ng/L， respectively. Some emerging PFAS， such as 3，6-OPFHpA， PFOPA， Cl-PFOPA， 6：2PAP and N-MeFOSE were also detected at trace levels.ConclusionThis method exhibits excellent sensitivity， accuracy， precision， and ease of use， making it suitable for the simultaneous detection for 48 PFAS in milk samples.