Abstract: To investigate the characteristics of mass spectra of roxithromycin and its metabolites, human urine samples which were collected from healthy volunteers after a single dose of 150 mg roxithromycin were analyzed using electrospray ion trap mass spectrometry in a multi-stage MS full scan mode performed on a Finnigan LCQ instrument. The mass spectrometry was operated in the positive mode. The obtained mass spectra were analyzed assisted with the software Mass Frontier 1.0 for their fragmentation passways. Besides roxithromycin, ten of its metabolites were identified in the urine samples by LC/MS. The full scan MS² and MS³ spectra of each compound gave characteristic fragment ions of descladinose and dedesosamine respectively, and a series of dehydration ions were also found. The difference of fragmentation between the roxithromycin derivatives and the erythromycin oxime derivatives lied in the loss of different fragment ions containing nitrogen. These characteristics can be used for future structure elucidation in the studies of metabolism of roxithromycin and its analogues.

Key words: Roxithromycin, Metabolite, Electrospray ion trap spectrometer