Amino-functionalized Fe3O4@SiO2-NH2@MIL-101(Fe)-NH2 for magnetic solid-phase extraction of PFOA and PFOS from water and milk.

Per- and polyfluoroalkyl substances, known as PFASs, are persistent organic pollutants. Perfluorooctanoic acid and perfluorooctane sulfonate, referred to as PFOA and PFOS, respectively, require selective sample preparation before trace-level LC-MS/MS analysis. Herein, an amino-functionalized magnetic MIL-101(Fe) composite, Fe3O4@SiO2-NH2@MIL-101(Fe)-NH2, was synthesized and applied as an MSPE sorbent for PFOA and PFOS in water and dairy matrices. The composite integrates magnetic Fe3O4@SiO2-NH2 nanoparticles with an amino-functionalized MIL-101(Fe) porous framework, enabling rapid magnetic separation and multiple adsorption interactions. Adsorption equilibrium was reached within 10 min, and the adsorption mechanism was dominated by electrostatic attraction, hydrogen-bonding, and hydrophobic interactions. Under optimized conditions, the method exhibited satisfactory linearity within the ranges of 0.05-50 ng mL-1 and 0.5-50 ng mL-1 for PFOA and PFOS, respectively. The limits of detection were 0.25 ng L-1 for PFOA and 2.5 ng L-1 for PFOS in water, and 0.005 ng g-1 for PFOA and 0.020 ng g-1 for PFOS in dairy samples. Recoveries ranged from 73.86% to 118.30% with RSDs no more than 15%. The sorbent remained stable over five consecutive cycles and was successfully applied to spiked water, milk, and milk powder samples. This work provides a practical strategy for designing amino-functionalized magnetic MOF composites for rapid and sensitive enrichment of PFOA and PFOS in complex environmental and food matrices.