Simultaneous residue monitoring of four tetracycline antibiotics in fish muscle by in-tube solid-phase microextraction coupled with high-performance liquid chromatography

An on-line simple and rapid method for the simultaneous determination of tetracycline (TC), oxytetracycline (OTC), chlortetracycline (CTC) and doxycycline (DC) residues in fish muscle was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with a photodiode array detector. Biocompatible poly (methacrylic acid–ethylene glycol dimethacrylate) monolithic capillary was selected as the extraction medium, and no precipitating protein and removing fat steps were required prior to extraction. In order to optimize the extraction of these compounds, several in-tube SPME parameters were investigated. Simply performed by extracting with 0.01 M EDTA–MacIlvaine buffer solution (pH 4.0) and centrifugation, the sample then could be directly injected into the device for extraction. The limits of detection of tetracycline, oxytetracycline, chlortetracycline and doxycycline were calculated to be 22, 16, 30 and 21 ng/g, respectively. The calibration curves showed linearity in the range of 100–10,000 ng/g with a linear coefficient R2 value above 0.9980. Excellent method reproducibility was found by intra- and inter-day precisions, yielding the R.S.D.s less than 4.22% and 5.71%, respectively.