Determination of the stability of antibiotics in matrix and reference solutions using a straightforward procedure applying mass spectrometric detection

Abstract

International audienceThe stability of an antibiotic is a very important characteristic, especially in the field of antibiotic residue analysis. During method development or validation, the stability of the antibiotic has to be demonstrated no matter if the method is used for screening, confirmation, qualitative or quantitative analysis. A procedure for testing the stability of antibiotics in solutions and food samples using LC-MS/MS is described here. The procedure is based upon the assumption that the antibiotics are stable when stored at -70 °C. Representative solutions or spiked samples containing the antibiotic are stored at the temperature to be tested (-18 or 4 °C) and at -70 °C. After a selected storing time samples are moved from the chosen storage temperature to -70 °C. At the end of the study, all samples -per class of antibiotic- are analysed in one batch. By applying statistical models it is finally concluded at which circumstances the antibiotic is stable. The stability of 60 antibiotics belonging to the classes of tetracyclines, sulphonamides, quinolones, penicillins, macrolides and aminoglycosides are tested. The stability of solutions containing tetracylines and penicillins is only guaranteed for three months while stored at -18 °C. Solutions of all other antibiotics tested are stable for at least 6 or 12 months when stored at 4 °C. In muscle tissue stored at -18 °C no severe degradation of the tested antibiotics was observed with the exception of the penicillins. The presented stability data are useful as a reference for laboratories carrying out validation studies of analytical methods for antibiotic (residue) detection. It saves them time needed for long term stability testing of solutions and samples