Characterization of Impurities in Cefdinir Bulk Material by Online Column- Switching Liquid Chromatography and Tandem Mass Spectrometry

Column switching LC/MS methods were developed for rapid identification of impurities in cefdinir. Based on the mechanism by which cephalosporins are degraded, stress tests were designed and performed. It was found that eight main impurities were degradation products and five impurities originated from the synthesis process. Cefdinir bulk material was eluted as gradient on a C18 column, with 0.25% tetramethyl ammonium hydroxide solution (pH5.5)-acetonitrilemethanol as mobile phase. According to the retention time of different impurities, the target impurities were separated and enriched in another chromatographic column using column switching technology. Then the target impurity was desalted using an elution of 0.5% formic acid solution. Mass analysis was performed by elution with a mobile phase consisting of 1.0% formic acid-acetonitrile (3:7). The structures of ten related impurities were characterized on the bases of MS/MS data, general mass fragmentation pathway of cefdinir, and UV spectra. This study provides the material basis for the related substances of cefdinir in the Chinese Pharmacopeia 2010 edition. It also provides an effective means for the rapid identification of impurities in chromatographic systems containing non-volatile salt.