Identification of tylosin in bovine muscle at the maximum residue limit level by liquid chromatography-mass spectrometry, using a particle beam interface.

A particle beam liquid chromatography-mass spectrometric method is presented as a confirmatory technique for analysis of tylosin residues in bovine muscle. After chloroform extraction and a diol solid-phase extraction clean-up, on-line liquid chromatography-mass spectrometry (LC-MS) of extracts is carried out on an RP-18 bonded silica column. The analyte is introduced into the ion source by a particle beam interface and identified by negative chemical ionization with selective ion monitoring. The tylosin molecular ion is obtained with this ionization mode. The response of the ion chromatogram peak areas is linear for the three levels of spiked muscle analysed (0.5, 1 and 2 maximum residue limit). Under these LC-MS conditions, other macrolide antibiotics such as spiramycin and erythromycin do not interfere with tylosin.

Particle beam liquid chromatography-mass spectrometry method with negative ion chemical ionization for the confirmation of oxacillin, cloxacillin and dicloxacillin residues in bovine muscle.

To ensure human food safety, the European Union has defined maximum residue limits (MRLs) for veterinary drug residues in food products. Analytical methods need to be developed to confirm the presence of drugs at the MRL level. A method using particle beam liquid chromatography-mass spectrometry was developed for the confirmation of oxacillin, cloxacillin and dicloxacillin in bovine muscle at the maximum residue limit of 300 micrograms kg-1. Beta-lactams were extracted from tissues with ethyl acetate under slightly acidic conditions and separated on a C18 bonded silica column with a methanol-aqueous formic acid (2%) solution-acetonitrile mobile phase. Negative ion chemical ionization with methane as the reagent gas was used to identify the compounds. The specificity required for a regulatory confirmation procedure was achieved by monitoring five fragment ions for each compound (selected ion monitoring mode): m/z 183, 198, 213, 214 and 241 for oxacillin; m/z 196, 248, 250, 275 and 277 for cloxacillin; m/z 165, 230, 232, 274 and 276 for dicloxacillin.