Stability of thirteen antimicrobials in incurred samples of animal tissues, milk, eggs, and honey after freeze-storage.

Monitoring of antimicrobials residues in food of animal origin is performed by control laboratories to ensure public health, and knowledge of the stability of antimicrobials during storage is essential for the reliability of results. For stability studies, analysis of incurred samples is preferential to fortified samples due to the possible conversion of antimicrobial metabolites back to parent compounds during sample preparation, storage, and analysis of the incurred samples, resulting in an increased concentration of the analyte. We have analyzed the concentrations of 13 antimicrobials from 8 groups (tetracyclines, fluoroquinolones, phenicols, sulfonamides, aminoglycosides, penicillins, macrolides, and nitroimidazoles) at different time points of freeze-storage (1 week; 1, 2, and 3 months) using HPLC-MS/MS. Incurred samples were prepared from muscle tissue, liver, kidneys, eggs, and milk taken from different animals (cows, pigs, poultry, goats, and fish). Incurred and fortified samples of honey were investigated as well. The results have shown that all analytes in all samples were stable during the investigated periods regardless of animal species, matrix, and concentration levels.