Radiosterilization of cefotaxime: investigation of potential degradation compounds by liquid chromatography–electrospray mass spectrometry

The nonvolatile radiolytic compounds produced by irradiation of cefotaxime were studied by a liquid chromatography–electrospray mass spectrometry method. Full scan LC–MS was first performed in order to obtain the m/z value of the protonated molecules of all detected peaks. LC–MS–MS was then carried out on the compounds of interest. A comparison between the MS–MS spectrum of cefotaxime and those of the radiolytic compounds showed that their fragmentation patterns were very similar suggesting that they were structural analogues of the main drug. The examination of the two main fragmentation pathways also permitted the location of the modified substructures. Moreover, it was shown that some stereoisomers appeared with the irradiation process. The complete fragmentation pattern of cefotaxime was studied by MSn and used to obtain information about the structure of the radiolytic compounds. A complete structure was proposed for four of these.