Facile construction of hydrophilic core-shell structured magnetic covalent organic framework for efficient magnetic solid-phase extraction of five glucocorticoids from milk sample

Glucocorticoids play a key role in a variety of physiological processes, but their extensive use in the environment has brought potential health hazards. Herein, it is of great necessity to develop a rapid and efficient method for the detection of glucocorticoids. In this work, a hydrophilic core-shell structured magnetic covalent organic framework (HMCOF) was fabricated via a post-modification strategy for the efficient magnetic solid-phase extraction (MSPE) of five glucocorticoids from tap water and milk samples. The HMCOF featured a Fe₃O₄@SiO₂ magnetic core encapsulated by a porous COF shell modified with polyethylene glycol, endowing it with a hydrophilic outer layer, porous structure and sufficient paramagnetism. The adsorption studies showed that HMCOF exhibited high adsorption capacities (50.77–80.25 mg g −1 ) for glucocorticoids. Notably, HMCOF retained 80 % of its adsorption capacity after 5 cycles, confirming its reusability. Under the optimal conditions of MSPE, the HMCOF-based MSPE-UPLC method was developed to test five glucocorticoids, which demonstrated good linearity (5–150 ng mL −1 , R 2  ≥ 0.9991), low detection limits (0.2–1.4 ng mL −1 ) and satisfactory spiked recovery rates (89.5–114.2 %) with intra-day variability below 4.3 % and inter-day precision within 6.3 %. The method underscores the potential of HMCOF serving as an adsorbent for MSPE, providing a promising approach for the analysis of glucocorticoids within food products.