Abstract:

Per- and polyfluoroalkyl substances （PFASs） are widely utilized in various industrial applications. Their persistence in ecosystems raises significant global environmental health concerns. Numerous studies have confirmed the toxicity of PFASs to human endocrine and immune systems. The carcinogenic risks associated with PFASs exposure increasingly alarm public health authorities worldwide. As a result， regulatory policies have been implemented to restrict both the production and environmental release of PFASs. In China， the GB 5749-2022 standard establishes stringent limits for PFASs concentrations in drinking water， capping levels of perfluorooctane sulfonic acid （PFOS） at 40 ng/L and perfluorooctanoic acid （PFOA） at 80 ng/L. Effective monitoring of PFASs requires advanced analytical techniques that exhibit exceptional sensitivity. Ultra-high performance liquid chromatography-tandem mass spectrometry （UHPLC-MS/MS） has emerged as the preferred technique for detecting these substances due to its superior selectivity and low detection limits. However， complex environmental matrices necessitate optimized sample pretreatment strategies to enhance analysis accuracy. Efficient extraction methods must effectively address matrix interference while ensuring analyte enrichment. Dispersive membrane extraction （DME） presents distinct advantages for the pretreatment of PFASs； its operational simplicity is complemented by high enrichment capabilities and efficient mass transfer. The selection of extraction materials critically influences DME performance parameters. Metal-organic frameworks （MOFs） are porous materials composed of organic ligands and metal clusters， featuring tunable pores， high surface areas， and rapid mass transfer. These unique properties enable their current use in sample pretreatment for environmental analysis. This study integrates DME with UHPLC-MS/MS utilizing cationic MOF membranes， enabling simultaneous detection of eight different PFASs within seawater matrices. Optimized parameters ensure reliable quantification of trace-level contaminants throughout this process. The experimental design assessed various parameters， including types of organic solvents （methanol and acetonitrile）， ammonium acetate concentrations in the aqueous phase （0.1， 0.5， 1.0， 2.0， and 5.0 mmol/L）， as well as ion source voltages （-2 500， -3 500， and -4 500 V）， all of which influenced detection efficacy. Chromatographic separation was performed using an ACQUITY UPLC BEH C18 column （100 mm×2.1 mm， 1.7 μm）. Gradient elution combined 1 mmol/L ammonium acetate with acetonitrile for optimal results. Detection was conducted utilizing electrospray ionization （ESI） in negative ion scanning mode coupled with multiple reaction monitoring （MRM）. The results indicated that all eight PFASs could be effectively separated within a timeframe of 12 min， exhibiting favorable peak shapes and high response values. Under optimal conditions， the eight PFASs demonstrated strong linearity across their respective concentration ranges； the correlation coefficients （r²） were all not less than 0.990 7. Recoveries of PFASs at spiking levels of 10， 50， and 100 ng/L ranged from 50.4% to 116.4%， while intra-day and inter-day relative standard deviations （RSDs） varied from 1.0% to 19.2% and from 2.2% to 19.5%， respectively. The method’s limits of detection （LODs） ranged from approximately 0.07 ng/L to 0.49 ng/L， whereas the limits of quantification （LOQs） varied from around 0.22 ng/L to 1.63 ng/L. Jiaozhou Bay serves as a typical semi-enclosed bay along the Pacific coast where terrestrial runoff converges nutrients alongside diverse organic/inorganic pollutants that pose potential health risks for aquatic organisms inhabiting these waters. This method was utilized for the detection of the eight PFASs in the surface seawater of Jiaozhou Bay， and seven types were successfully identified. Among these， potassium 11-chloroeicosafluoro-3-oxaundecane-1-sulfonate （Minor F-53B） exhibited the highest detection concentration， with an average mass concentration of 17.11 ng/L. When compared to the 2018 detection results of PFASs in the surface seawater of Jiaozhou Bay， the average mass concentration of perfluorooctanoic acid （PFOA） has significantly decreased. Additionally， potassium 9-chlorohexadecafluoro-3-oxanonane-1-sulfonate （F-53B）， one of the newly emerging PFASs， was detected in the surface seawater of Jiaozhou Bay， which may be attributed to the recent shift in PFASs production. The widespread use of these new PFASs may introduce environmental risks. These risks resemble those of traditional PFASs and require urgent attention. In summary， this method is operationally straightforward， rapid， and highly sensitive； it is suitable for analyzing the eight PFASs in seawater. This approach can provide a valuable data foundation and scientific basis for research and analysis concerning PFASs in environmental water bodies.

Key words: per- and polyfluoroalkyl substances （PFASs）, dispersive membrane extraction （DME）, cationic metal-organic framework, ultra-high performance liquid chromatography-tandem mass spectrometry （UHPLC-MS/MS）