Determination of tetracycline residues in milk by using liquid chromatography with tandem mass spectrometry

A rapid, simple and reliable liquid chromatography with tandem mass spectrometry (LC-MS/MS) method, which can be used on a routine basis, was developed for the simultaneous detection of 5 tetracylines (oxytetracycline, chlortetracycline, tetracycline, doxycycline, and minocycline) in milk. The antibiotics were extracted from milk with extraction buffer including oxalic acid and EDTA. The extract was analyzed LC-MS/MS, using a water/acetonitrile gradient containing 0.3% formic acid on a C∧8 reversed phase column. Mass spectral acquisition was achieved in an electrospray positive ion mode by applying multiple reaction monitoring(MRM) of 2 fragment ion transitions to provide a high degree of sensitivity and specificity. Average recoveries of 5 tetracyclines at three fortification levels from 25 to 100 ng/mL in milks were 83.1% for tetracycline, 88.2% for minocycline, 85.0% for oxytetracycline, 94.0% for chlortetracycline, and 84.4% for doxycycline, respectively. The percent relative standard deviation for the described method was less than 10.0% over the range of concentrations studied.