Determination of Tetracycline Residues in Milk by On-line Coupling of Restricted Access Material Solid Phase Extraction with High Performance Liquid Chromatography

A new method has been developed for the determination of tetracycline residues in milk by on-line restricted access material solid phase extraction-HPLC analysis. Restricted accessed poly (styrene-co-divinylbenzene) bonded silica, synthesized by atom transfer radical polymerization, was used as solid phase extraction material in the experiment. This material played both functions of tetracylines extraction and biomacromolecule exclusion. Tetracyclines extracted from milk sample were back-flushed into a reversed phase C-18 analytical column and oxytetracycline, tetracycline and chlortetracycline were separated and quantified by HPLC analysis. The exclusion ratio of bovine serum albumin from the restricted access material column was 96.0%, which indicated that the restricted access material had the ability to exclude large biological molecules. The recoveries of three tetracylines in milk samples were 88.3% - 101.5% with relative standard deviations < 8.0%. The detection limits of 50 - 80 mu g/L and the linear ranges from 0.05 mu g/mL to 2.0 mu g/mL for the analytes were obtained. The results demonstrated that the method could be used in the determination of tetracycline residues in milk samples with good sensitivity and efficiency.