Preparation, characterization, and application of chitosan–kaolin-based nanocomposite in magnetic solid-phase extraction of tetracycline in aqueous samples

A magnetic adsorbent based on chitosan–kaolin (Cs-k-Fe₃O₄) nanocomposite was synthesized by a one-pot co-precipitation method. The nanocomposite was used as an adsorbent in magnetic solid-phase extraction of tetracycline (TC) in wastewater and surface water. The Cs-k-Fe₃O₄ nanocomposite was characterized by the Fourier transform infrared spectrometer, X-ray powder diffractometer, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), and transmission electron microscope. The performance of Cs-k-Fe₃O₄ for extraction and pre-concentration of TC in wastewater was evaluated by investigating the effect of sample pH, extraction time, the mass of adsorbent, sample, and eluent volumes using a central composite design. The optimized extraction conditions were; 7, 60 mg, 30 mL, 15 min, and 2259 µL for sample pH, mass of adsorbent, sample volume, extraction time, and eluent volume, respectively. A pre-concentrated TC was further analyzed using high-performance liquid chromatography coupled with a diode array detector (HPLC–DAD). Under optimal conditions, the analytical method yielded good linearity for TC with a coefficient of determination (R²) of 0.9928 and the limits of detection and quantitation of 0.21 and 0.63 µg L⁻¹, respectively. The method was validated using spike recovery experiments, and the percentage recoveries ranged from 89 to 103%, with intraday and interday relative standard deviations ranging between 0.6–2.7 and 1.0–2.0, respectively. The application of the analytical method in environmental analysis of TC resulted in the detection of the analyte in wastewater influent with a concentration of 2.92 µg L⁻¹, while the effluent levels were below the quantitation limit. Overall, the proposed analytical method proved to be efficient for the monitoring of TC in water.