Development and application of magnetic solid phase extraction in tandem with liquid–liquid extraction method for determination of four tetracyclines by HPLC with UV detection

A novel HPLC-UV method was developed for the determination of four tetracyclines based on magnetic solid phase extraction in tandem with liquid–liquid extraction. The water-soluble amino functionalized magnetite nanoparticle (MNP-NH(2)) was used as an adsorbent for extraction/preconcentration of tetracycline, oxytetracycline, chlortetracycline, and doxycycline from bovine milk samples. Fourier transform infrared spectrometer, transmission electron microscope, X-ray diffraction, and elemental analyze techniques were used to characterize the material. Some key parameters which influence liquid–liquid extraction and magnetic dispersive solid-phase extraction procedure, including volume of extraction solvent, the amount of adsorbent, the pH, extraction and desorption time, the composition of the eluent, and elution frequency were investigated. The proposed method exhibited a linear range of 50.0–2500.0 μg L(−1) (r(2) = 0.9941) with and good reproducibility (RSD