Determination of fourteen non-steroidal anti-inflammatory drugs in animal serum and plasma by liquid chromatography/mass spectrometry

The European Union has regulated the use of non-steroidal anti-inflammatory drugs (NSAIDs) in animal production and requires its member states to detect their residues in different matrices. In this work, a detailed MS and MS/MS study by ion-trap mass spectrometry of fourteen NSAIDs is described. Two multi-residue reversed-phase LC/ESI-MS/MS methods were developed, one for the determination of salicylic acid, naproxen, carprofen, flurbiprofen, ibuprofen, niflumic acid and meclofenamic acid in the negative ion mode, and the other for the determination of ketoprofen, suxibutazone, diclofenac, mefenamic acid, tolfenamic acid, phenylbutazone and its metabolite oxyphenbutazone in the positive ion mode. It was thus possible to confirm up to 14 different NSAID residues in serum and plasma samples of farmed animals, after chromatographic separation by a linear gradient. These substances were chosen as representative of different chemical subclasses of NSAIDs. The two methods were also validated in-house at three contamination levels, evaluating specificity and calculating mean recoveries, repeatability and within-laboratory reproducibility. The MS/MS product ion spectra were successfully used for the qualitative identification of all the drugs tested. All the NSAIDs, apart from salicylic acid, were recovered in high amounts, ranging between 71.6% and 100.9%.