ROOM-TEMPERATURE AQUEOUS CO-PRECIPITATION SYNTHESIS OF MAGNETIC FE₃O₄@ZIF-8 CORE-SHELL NANOCOMPOSITE FOR MAGNETIC SOLID-PHASE EXTRACTION AND COLORIMETRIC DETERMINATION OF FLUOROQUINOLONE POLLUTANTS IN WATER SAMPLES

Abstract

Fluoroquinolone residues in aquatic environments require analytical methods that combine efficient extraction with simple and sensitive detection. In this study, an aqueous Fe₃O₄@ZIF-8 core-shell-type magnetic nanocomposite was prepared for magnetic solid-phase extraction (MSPE) and colorimetric detection of the ciprofloxacin (CIP), levofloxacin (LEV), and ofloxacin (OFX) in water samples at room temperature. The Fe₃O₄ magnetic nanoparticles were initially synthesized by aqueous precipitation and then coated with a ZIF-8 shell at room temperature. FTIR, XRD, SEM and TEM characterization confirmed the formation of the composite and its core-shell structure. The optimization of the MSPE conditions was conducted in terms of pH, adsorbent dose, extraction time, initial concentration, ionic strength and desorption volume. For maximum extraction performance, the pH of the solution was optimized at 6–7 and the contact time was optimized at 20–30 min, with about 20–30 mg of adsorbent. Initial adsorption was fast and reached nearly to the equilibrium after a while and the kinetic and equilibrium studies showed pseudo-second-order adsorption and saturation-type adsorption. The linear calibration response (R2) for the integrated analytical procedure was 0.9987, 0.9984, and 0.9986 for CIP, LEV and OFX, respectively. Mean extraction recoveries reached 95.1%, 94.3%, and 94.7%, with mean RSD values of 2.18%, 2.31%, and 2.24%. A sample of 50 mL was taken, and 5 mL of elution was used, which gave a nine-fold enrichment. Recoveries were generally over 90% for both spiked tap and surface waters, which indicated a low matrix influence. The composite also showed good extractability in repeated extractions. The developed Fe₃O₄@ZIF-8-MSPE/colorimetric method was thus an integrated magnetic separation method for the determination of CIP, LEV and OFX in aqueous samples. The integration made sample handling much easier.