Preparation of MIL-68@Fe₃O₄@PVDF composites via the spray phase inversion method and their magnetic solid-phase extraction of parabens and bisphenol A

In this study, the spray phase inversion method was employed for the first time to prepare MIL-68@Fe₃O₄@PVDF. The preparation process involved dispersing Fe₃O₄ in a PVDF/DMF solution; when the Fe₃O₄-loaded PVDF solution was atomized and sprayed into ethanol containing dispersed MIL-68, PVDF underwent phase inversion to form magnetic solid microspheres, with MIL-68 simultaneously immobilized on their surface. The procedure is facile, convenient, and suitable for the synthesis of various magnetic composites. The MIL-68@Fe₃O₄@PVDF composite exhibited favorable adsorption performance toward methylene blue (MB). The adsorption kinetics and isotherm data were well fitted to the pseudo-second-order kinetic model and the Langmuir isotherm model, respectively, indicating monolayer chemisorption on homogeneous adsorption sites. Based on this, a magnetic solid-phase extraction (MSPE) method coupled with high-performance liquid chromatography (HPLC) was established using MIL-68@Fe₃O₄@PVDF as the adsorbent for the determination of five parabens and bisphenol A (BPA) in water samples. After optimizing the MSPE conditions, the established method showed a good linear relationship for parabens and BPA in the concentration range of 1.5-400.0 ng mL^-1 (r > 0.9996). It also achieved low limits of detection (LODs, 0.4-1.0 ng mL^-1) and limits of quantitation (LOQs, 1.3-4.0 ng mL^-1), along with high spiked recoveries (80.0-107.3%) and acceptable precision (RSD ≤ 8.81%). In conclusion, the spray phase inversion method provides a simple and efficient strategy for fabricating magnetic composites. Furthermore, it offers a novel approach to improve the application efficiency of nano-adsorbents in MSPE, laying a foundation for their broader use in the trace analysis of complex samples.