A multiresidue liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method for the simultaneous quantitative determination of the tetracycline antibiotics tetracycline, oxytetracycline, chlortetracycline, their respective 4-epimers and doxycycline in eggs has been optimised and validated. Reliable detection methods are necessary because residue levels above MRL in eggs can be present if the recommended withdrawal times for tetracyclines are not respected by the poultry farmers. The drug substances were extracted with a 20% trichloroacetic acid solution (pH=0.40) while shaking. After centrifugation, the supernatant was filtered through a glass filter and a thorough sample clean-up with an OASIS HLB SPE column was carried out. The LC separation was performed with an Alliance HPLC system on a reversed-phase Alltech Alltima C18 column (3 µm, 150 x 2.1 mm i.d.) with gradient elution. A mobile phase consisting of water and a mixture of methanol/acetonitrile (70/30 v/v), each phase containing 1% formic acid, was used. The analytes were detected and identified with a Micromass tandem quadrupole mass spectrometer after electrospray ionisation in positive mode by multiple reaction monitoring. All the analytes involved in this study can be detected at residue levels between 5 and 30 µg/kg, which is much lower than the MRL level of 200 µg/kg. The decision limit, detection capability, detection limit, quantification limit and the recovery were determined conform the EU requirements for analytical methods for the detection of residues in animal products. The mean obtained recovery values for the different compounds ranged from 93 to 103%. This analytical method will be used in an integrated system for the confirmation of positive results obtained with screening methods.
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