Abstract:

Perfluorinated compounds （PFCs） are widely used， persistent， and their presence in water is of significant concern. PFCs， particularly short-chain variants， are highly soluble and mobile in water， which enables their transport over long distances via river systems， potentially leading to extensive contamination. These compounds are resistant to degradation， which is challenging for conventional water-treatment methods that often remove PFCs ineffectively， leading to their prolonged presence in water bodies. This paper establishes a magnetic solid-phase extraction method for 11 PFCs in enriched water using magnetic polystyrene pyrrolidone （Fe₃O₄-PLS） as a magnetic adsorbent. Purified lipophilic PLS magnetic beads were used as the solid-phase extractant， and their surfaces were modified using phenyl and pyrrolidone groups to facilitate the adsorption of PFCs that contain hydrophilic functional groups and hydrophobic alkyl side chains. PFCs in water were determined accurately and sensitively by liquid chromatography-tandem mass spectrometry （LC-MS/MS）. The method involved accurately weighing 50 mg （±0.05 mg） of the Fe₃O₄-PLS into a 500-mL beaker， adding 2 mL of methanol （for activation）， placing the beaker on a magnet for 30 s， and discarding the methanol once the methanol and Fe₃O₄-PLS had been completely separated. A 200-mL aliquot of an aqueous mixed PFC solution was added to the beaker， sonicated for 15 min， and then placed on a strong magnet until the Fe₃O₄-PLS had completely separated at the bottom of the beaker. The upper liquid was discarded. A 4-mL acetonitrile containing 0.1% formic acid was added as the Fe₃O₄-PLS eluent， ultrasonicated for 30 s， after which the beaker was placed on the magnet and the eluate collected. The sample was taken to dryness under a stream of nitrogen， the residue was redissolved in 0.5 mL of acetonitrile， ultrasonicated for 10 s， and then membrane-filtered prior to analysis by LC-MS/MS. The 11 PFCs exhibited good linear relationships ranging from 1 to100 μg/L， with correlation coefficients （R²） ranging from 0.997 6 to 0.999 9. Limits of detection and quantification （LODs and LOQs， respectively） were determined to be 0.001–0.620 ng/L and 0.002–2.065 ng/L， respectively， indicative of high sensitivity. The 11 PFCs exhibited recoveries of 60.8%–120.0% at various concentrations （0.05， 1， 10， and 50 μg/L）. Relative standard deviations （RSDs） ranged from 1.0% to 20.0%， which meet the requirements for PFC analysis in water. The concentrations of the 11 PFCs at 15 sites in the Dongtiaoxi River， Hangzhou （near factories， reservoirs and residential areas） were analyzed using the developed method. A total of six PFCs， namely perfluorooctanoic acid （PFOA）， perfluorononanoic acid （PFNA）， perfluorooctane sulfonic acid （PFOS）， perfluoroheptanoic acid （PFHpS）， perfluorobutanesulfonate （PFBS） and perfluorodecanoic acid （PFDA）， were detected at mass concentrations of 11.4–30.7 ng/L. The highest mass concentration of PFOA was determined to be 25.5 ng/L. The PFCs in the Dongtiaoxi River were found to be mainly associated with precursor degradation and industrial wastewater discharge. A sudden rise in the pollution level was observed near the sampling point with the lowest detected concentration， which is possibly ascribable to the strong hydrodynamic difference between the hydraulic transport process near the river wharf and the highly turbulent flowing water. This difference results in the suspended particles in surface water mixing with re-suspended sediment particles such that PFCs are released back into the surface water. Pollution levels were observed to continuously decrease in the directions of the extended river and its estuary and tributaries. Risk assessments revealed that the PFC levels in the surface water of the Dongtiaoxi River basin are much lower than the official health reference value and have not reached levels that are expected to cause ecological harm and risk human health. The data are expected to support monitoring-system improvements by providing an in-depth understanding of occurrence characteristics， and help formulate a management plan for PFCs in the Dongtiaoxi River.

Key words: magnetic solid-phase extraction （MSPE）, ultra-high performance liquid chromatography-tandem mass spectrometry （UHPLC-MS/MS）, perfluorinated compounds （PFCs）, water