Determination of ten sulphonamides in egg by liquid chromatography-tandem mass spectrometry

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 C(18) column with a mobile phase of methanol-water containing 0.1% formic acid and 5mM 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 microgkg(-1). These levels were much lower than the corresponding maximum residue limit of 100 microgkg(-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 (13)C(6)-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 (CCalpha) values lied in the range between 16.1 and 20.5 microgkg(-1) and the corresponding results for detection capability (CCbeta) were 16.9 and 25.7 microgkg(-1). Ruggedness was estimated according to the Youden robustness test.