Determination of tetracyclines in bovine milk using laccaic acid-loaded magnetite nanocomposite for magnetic solid-phase extraction.

An efficient magnetic sorbent of laccaic acid-loaded magnetite nanocomposite was successfully synthesized for extraction and preconcentration of tetracyclines (TCs) from bovine milk sample. The synthesized nanocomposite was characterized by scanning electron microscopy and Fourier transform-infrared spectroscopy. Determination of the extracted TCs was performed by high performance liquid chromatography. Parameters affecting the efficiency of magnetic solid-phase extraction were studied and optimized. The best adsorption conditions were 80 mg of sorbent, 50 mL of sample volume, pH 7, 45°C and 20 min; the elution conditions were 0.5 mL of acetonitrile, pH 5.5, 75°C and 5 min. Under optimized conditions, the preconcentration factor of TCs was 100. The calibration curves were linear at a concentration range of 10-300 μg/kg for oxytetracycline and TC, and 5-300 μg/kg for chlortetracycline and doxycycline. The limit of detection was from 3.2 to 7.1 μg/kg, the limit of quantification was from 10.7 to 23.7 μg/kg, the relative standard deviation was between 2.8 and 5.3 and the recoveries were between 95.2% and 106.2%. In terms of the proposed procedure, the developed method was successfully applied for TCs detection in bovine milk samples.