Determination of three tetracyclines in bovine milk using magnetic solid phase extraction in tandem with dispersive liquid-liquid microextraction coupled with HPLC.

A novel analytical method namely magnetic solid phase extraction in tandem with dispersive liquid-liquid microextraction was developed and used for the extraction/preconcentration of tetracycline (TCN), oxytetracycline (OTC) and doxycycline (DC) from bovine milk sample before HPLC-UV analysis. The β-cyclodextrin functionalized silica-coated magnetic graphene oxide (Fe3O4@SiO2@GO-β-CD) was used as an adsorbent. The adsorbent was fully characterized using FT-IR, SEM, EDX and Zeta potential techniques. The effective parameters on the performance of the method such as extraction solvent type and volume, adsorbent amount, desorption solvent type and volume, disperser solvent type, desorption time, ionic strength and pH value were investigated. The limit of detection (LOD) and limit of quantification (LOQ) were obtained in the ranges of 1.8-2.9 μg L-1 and 6.1-9.7 μg L-1, respectively. The linearity was in the range of 10.0-200.0 μg L-1 with satisfactory determination coefficients (R2) higher than 0.9929 and a good precision (RSD < 8.8%). The recovery percentages for the analytes in real samples (bovine milk and water) were achieved in a range from 70.6 to 121.5%.