Zr-functionalized hydrogen-bonded organic framework for magnetic solid-phase extraction and LC-MS/MS determination of fluoroquinolones in milk.

Fluoroquinolone antibiotics (FQs) are frequently detected at trace levels in milk, complicating accurate quantification due to matrix interference and stringent regulatory limits. This study developed a zirconium-functionalized magnetic hydrogen-bonded organic framework (Zr@MHOF101) for selective magnetic solid-phase extraction (MSPE) of six FQs prior to LC-MS/MS analysis. Three π-conjugated carboxylic acid-based HOFs were synthesized and compared. Magnetic functionalization enabled rapid phase separation and altered adsorption behavior, while Zr post-modification increased adsorption selectivity toward FQs in milk matrices. Optimized MSPE enabled rapid enrichment (2 min) using 3 mg adsorbent and 1 g milk, achieving LODs of 0.1-0.2 μg/kg, LOQs of 0.2-0.5 μg/kg, and recoveries of 77.17%-105.49%. Compared to MOF/COF sorbents, Zr@MHOF101 reduced resource use and improved FQs selectivity over other antibiotics, providing a practical tool for monitoring residues in complex food matrices.