Sulfonic acid-functionalized covalent organic frameworks as the coating for stir bar sorptive extraction of fluoroquinolones in milk samples

Sulfonic acid-functionalized covalent organic frameworks (COF-SO 3 ) as a coating of stir bar sorptive extraction (SBSE) for capturing three fluoroquinolones from milk have been developed. The COF-SO 3 material was characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. Milk without any typical treatments like protein precipitation and defatting was only diluted five times with water for test. Combined with high-performance liquid chromatography (HPLC), a SBSE-HPLC method was established for detecting fluoroquinolones in milk samples. The corresponding wide linear ranges (4.00–500.0 µg L −1 ), low detection limits (1.20–2.62 µg L −1 ), good test repeatability (RSD < 5.2%), and acceptable enrichment factors (56.2–61.5) were implemented for three fluoroquinolones. The analytical method was applied to determine trace targets and provided satisfactory results. Furthermore, the research displayed satisfied reproducibility for bar-to-bar (RSD < 6.5%) and batch-to-batch (RSD < 8.6%) tests. Graphical abstract