Abstract: Per- and polyfluoroalkyl substances (PFASs) are typical synthetic persistent organic pollutants characterized by extreme resistance to degradation, marked bioaccumulation, and potential toxic risks. They can contaminate milk and milk powder through environmental transport, food packaging contact, and contaminated feed and water, posing health risks especially to sensitive groups such as infants and young children. Given the widespread consumption of dairy products, PFASs contamination in this food category has become a global food safety concern. Because these matrices are rich in endogenous interfering substances such as proteins, phospholipids, and fats, conventional weak-anion-exchange solid-phase extraction (WAX) pretreatment is cumbersome, prone to background contamination from laboratory materials and solvents, and time-consuming, which hampers the rapid screening of large sample batches. Pass-through solid-phase extraction (SPE), featuring one-step purification without conditioning, washing, and elution, offers a simpler and cleaner alternative. Accordingly, referring to the World Health Organization (WHO) priority monitoring list of food PFASs and prioritizing high-risk compounds and routine monitoring needs, we established a novel method for the simultaneous determination of 17 PFASs in milk and milk powder using pass-through SPE combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS).===The samples were extracted with acetonitrile to precipitate proteins. The extract was then purified by a pass-through solid-phase extraction column specifically designed for phospholipid removal. Sodium chloride was added to promote phase separation. The residue was obtained after nitrogen evaporation and redissolved in a methanol-water mixture (1:1, V/V). Chromatographic separation was performed on a BEH C18 column (100 mm×2.1 mm, 1.7 μm) with a gradient elution using methanol and 2 mmol/L ammonium acetate aqueous solution. Target analytes were detected via negative electrospray ionization in multiple reaction monitoring mode and quantified by internal standard method. All 17 PFASs showed good linearity in the range of 0.1‒10 ng/mL, with all correlation coefficients (r) greater than 0.999. The limits of detection (LODs) and limits of quantification (LOQs) were in the ranges of 0.02‒0.04 μg/kg and 0.07‒0.11 μg/kg, respectively. Three levels of standard addition recovery tests (0.1, 1.0 and 10.0 μg/kg) were conducted to verify method performance. The average recoveries of all target pollutants ranged from 74.4% to 114%, and all relative standard deviations ranged from 0.90% to 19.4% (n=6), confirming that the established method has excellent accuracy and precision.===The practical applicability of the optimized method was verified through the detection of 10 commercially available dairy products, covering 5 liquid milk and 5 milk powder samples. Perfluoropentanoic acid (PFPeA) was only detected in one milk powder sample at a concentration of 1.70 μg/kg. The proposed method is accurate, reliable, highly sensitive and reproducible. It enables simultaneous screening and quantification of 17 PFASs, and is applicable to the rapid detection of large batches of milk and milk powder samples. Moreover, it offers reliable technical support for routine monitoring of per- and polyfluoroalkyl pollutants in dairy products as well as dietary risk assessment.

Key words: per- and polyfluoroalkyl substances (PFASs), pass-through solid-phase extraction, liquid chromatography-tandem mass spectrometry (LC-MS/MS), milk, milk powder