[Magnetic fluorinated covalent triazine frameworks for efficient extraction of perfluorinated compounds].

Abstract

Perfluorinated compounds （PFCs） are a new type of persistent organic pollutants. When consumers consume soft drinks contaminated with PFCs， it can cause severe systemic diseases. Increasing concern regarding the presence of PFCs in soft drinks has resulted in the need for reliable analytical methods for the monitoring of PFCs. However， the content of PFCs in soft drinks is extremely low and the matrix is complex， making it difficult to directly determine their content using high performance liquid chromatography-tandem mass spectrometry （HPLC-MS/MS）. Therefore， the necessary sample pretreatment is required before instrumental analysis. Magnetic solid-phase extraction （MSPE） is a simple， rapid， and efficient solid-liquid separation technique， and its extraction efficiency depends on the characteristics of the magnetic adsorbent. Covalent triazine frameworks （CTFs） are porous organic polymers connected by triazine bonds. They have the characteristics of large specific surface area， rich pore structure， adjustable functionality， good chemical stability and thermal stability， making them widely used in sample pretreatment. In this study， a magnetic fluorinated covalent triazine framework material （Fe₂O₃/CTF-F） was prepared by a one-pot method and characterized in detail. The X-ray photoelectron spectra （XPS）， Fourier-transform infrared （FT-IR） spectrum， and X-ray diffraction （XRD） pattern demonstrated the successful synthesis of Fe₂O₃/CTF-F with a high fluorine content （17.50%）， which was formed through tetrafluoroterephthalonitrile polymerization and hydrated ferric chloride decomposition. The highly fluorinated material can provide a specific and strong affinity for PFCs through fluorous-fluorous （F-F） interactions. The experimental results of nitrogen adsorption-desorption and magnetic properties showed that the Fe₂O₃/CTF-F has a high specific surface area （1 452.3 m²/g） and porosity （0.82 cm³/g）， as well as a strong magnetic responsivity （7.1 emu/g）. It indicates that the Fe₂O₃/CTF-F possesses a large number of accessible adsorption sites and a rapid magnetic separation capability， providing a guarantee for efficient extraction of PFCs. Subsequently， the Fe₂O₃/CTF-F was used as an adsorbent for MSPE technology for the efficient extraction of seven PFCs. Because of its many accessible adsorption sites and strong fluorine-fluorine interactions， the Fe₂O₃/CTF-F showed excellent extraction ability for PFCs. Finally， by combining the MSPE method with HPLC-MS/MS technology， a new analytical method was established for the analysis of PFCs in soft drinks. To achieve the best performance， single-factor experiments were conducted to optimize the dosage of the adsorbent， the extraction time， the elution solvent and elution time in the MSPE process. Under the optimal conditions， the established analytical method has the advantages of wide linear ranges （0.008-250.0 pg/mL）， high linear correlations （R≥0.999 2）， low LODs （0.002-0.005 pg/mL）， and good repeatability （RSDs≤8.2%， n=5）. The established analytical method was then used to analyze five kinds of soft drink samples， and ultra-trace amounts of PFCs were detected in all samples， with contents ranging from 3.5 to 54.6 pg/mL. Among them， the highest content of perfluorooctanoic acid （PFOA） measured was 54.6 pg/mL， and its content did not exceed the limit stipulated in the national standard GB 5749-2022 （80 pg/mL）. Besides， the established analytical method was also compared comprehensively with other reported methods. The established method only requires a small amount of adsorbent （5.0 mg）， and can achieve a low detection limit （0.002 pg/mL） after a short pretreatment time （20 min）. The comparison results indicate that the established method has the advantages of being rapid， sensitive， and accurate， and can be used for the monitoring of PFCs in soft drinks. Meanwhile， the preparation method of the Fe₂O₃/CTF-F in this study is very simple and convenient， which is conducive to the transformation and application of this method. In conclusion， the Fe₂O₃/CTF-F is a highly potential adsorbent for the efficient extraction of PFCs， and the established analytical method is also suitable for the high-sensitivity detection of PFCs in soft drinks.