Application of magnetite nanoparticles for selective magnetic solid-phase extraction of tetracycline residues from honey prior to their HPLC-MS/MS determination.

Magnetite nanoparticles are proposed as a selective magnetic sorbent for the extraction of tetracyclines from both aqueous and organic media, with the sorption behavior systematically investigated as a function of contact time, sorbent mass, solution volume, and sorbate concentration. Under the optimized conditions, 20 mg of nanoparticles effectively isolated 94-100% of the analytes from 10 mL of aqueous, acetonitrile, ethyl acetate, or methanol solutions. It was demonstrated that a 0.1 M aqueous tetramethylammonium hydroxide solution can be used as an eluent compatible with mass spectrometric detection for the desorption of tetracyclines. Based on these findings, a magnetic solid-phase extraction method coupled with HPLC-MS/MS was developed for the determination of tetracyclines in honey, involving dissolution of the sample in methanol to extract the analytes, followed by acetonitrile addition to precipitate sugars, dilution of the resulting extract with water, and subsequent purification using magnetite nanoparticles. The proposed method exhibited good reproducibility (RSD 4-16%), low matrix effects (79-108%), and high sensitivity, with limits of detection and quantification of 0.3 and 1 μg kg⁻¹, respectively.