Determination of ten sulphonamides in egg by liquid chromatography–tandem mass spectrometry Original Research Article

A precise and reliable method for the determination of 10 sulphonamide antibiotics (sulfadiazine, sulfathiazole, sulfamerazine, sulfamethazine, sulfamethoxypyridazine, sulfachloropyridazine, sulfamethoxazole, sulfamonomethoxine, sulfadimethoxine and sulfaquinoxaline) in egg by liquid chromatography–tandem mass spectrometry (LC–MS/MS) has been developed. Drugs were extracted using a mixture of dichloromethane/acetone (50:50, v/v), acidified with acetic acid and then cleaned-up on a cation-exchange solid-phase extraction (SPE) cartridge. The chromatographic separation was performed by gradient on a C18 column with a mobile phase of methanol–water containing 0.1% formic acid and 5 mM ammonium acetate, then sulphonamides were detected in a triple-quadrupole mass spectrometer operated in positive electrospray ionization mode (ESI+). The method was validated at 15, 30 and 45 μg kg−1. These levels were much lower than the corresponding maximum residue limit of 100 μg kg−1 set for sulphonamides in several matrices but not in eggs, where the presence of such residues is not permitted. Results were quantitated against the selected internal standard 13C6-sulphamethazine and also according to the matrix-matched approach. The within-laboratory reproducibility, expressed as a relative standard deviation, never exceeded 21%. All decision limit (CCα) values lied in the range between 16.1 and 20.5 μg kg−1 and the corresponding results for detection capability (CCβ) were 16.9 and 25.7 μg kg−1. Ruggedness was estimated according to the Youden robustness test.