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

We present an electrospray high-performance liquid chromatographic tandem mass spectrometric (HPLC-MS-MS) method capable of determining in several tissues (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 clean-up on an Oasis solid-phase extraction column. The HPLC separation was performed on a Purospher C18 column (125 x 3 mm I.D.) protected by a guard column, with a gradient of aqueous 0.1 M ammonium acetate-acetonitrile as the mobile phase at a flow-rate of 0.7 ml min(-1). Protonated molecules served as precursor ions for electrospray ionisation in the positive ion mode and four product ions were chosen for each analyte for multiple reaction monitoring (MRM). A validation study was conducted to confirm the five macrolides by 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 reproducibility 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 recommendations 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.

Determination of a method for detecting and quantifying azaperone, azaperol and carazolol in pig tissues by liquid chromatography-tandem mass spectrometry.

A quick, simple method for quantifying carazolol, azaperol and azaperone is described. Liquid extraction was followed by a clean-up on an Oasis SPE cartridge. The analytes were separated by HPLC and analysed by MS-MS with atmospheric pressure chemical ionisation in the positive mode. The method was applied to muscle and kidney from untreated pigs, the samples being spiked with the three molecules of interest. Recovery was between 70 and 106%. Quantification parameters were also good: the accuracy was between 80 and 110% and the coefficient of variation did not exceed 16%, being below 8% for 90% of the samples. Linearity was good from MRL/4 to 2MRL. For unequivocal identification of each analyte, four ions were detected. The method proved very suitable for routine analysis.