Identification and quantification of five macrolide antibiotics in severaltissues, eggs and milk by liquid chromatography-electrospray tandem mass spectrometry

We present an electrospray high-performance liquid chromatographic tandem m ass spectrometric (HPLC-MS-MS) method capable of determining in several tis sues (muscle, kidney, liver), eggs and milk the following five macrolides: tylosin, tilmicosin, spiramycin, josamycin, erythromycin. Roxithromycin was used as an internal standard. The method uses extraction in a Tris buffer at pH 10.5, followed by protein precipitation with sodium tungstate and cle an-up on an Oasis solid-phase extraction column. The HPLC separation was pe rformed on a Purospher C-18 column (125x3 mm LD.) protected by a guard colu mn, with a gradient of aqueous 0.1 M ammonium acetate-acetonitrile as the m obile phase at a how-rate of 0.7 ml min(-1). Protonated molecules served as precursor ions for electrospray ionisation in the positive ion mode and fo ur product ions were chosen for each analyte for multiple reaction monitori ng (MRM). A validation study was conducted to confirm the five macrolides b y MRM HPLC-MS-MS analysis of a negative control and fortified samples. All of the samples analysed were confirmed with four ions. The ion ratio reprod ucibility limit ranged from 2.4 to 15%. All compounds could be detected and quantified at half-maximum residue limits (MRLs). The method is specific, quantitative and reproducible enough to conform to European Union recommend ations within the concentration range 0.5 MRL-2 MRL (accuracy: 80 to 110%, relative standard deviation: 2 to 13%). This whole method allows extraction and analysis of up to 50 samples per day. (C) 2001 Elsevier Science B.V. A ll rights reserved.