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  Journal of Spectroscopy and Dynamics 2012, 2: 2
  Research Article
 
Photon induced side-chain elimination of metronidazole: Photoionization mass spectrometric and theoretical studies
  Huijun Guo, Lidong Zhang, Liangyuan Jia, Fei Qi  
     
National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, P. R. China
   
  Abstract  
  Photon induced side-chain group elimination reactions of imidazole ring in metronidazole are investigated with vacuum ultroviolet (VUV) photoionization mass spectrometry and ab initio calculation. The typical photoionization mass spectra of metronidazole are obtained at various photon energies. Side chain hydroxyethyl and nitryl groups eliminate to generate four ionic fragments at m/e 124, 125, 126 and 127, which are assigned to C6H8N2O+, C6H9N2O+, C4H4N3O2+ and C4H5N3O2+, respectively. And the photoionization efficiency (PIE) curves of molecular ion and ionic fragments at m/e 124 and 125 are measured. The ionization energy (IE) of metronidazole is determined to be 8.84 ± 0.1 eV. The appearance energies (AEs) for the fragments of m/e 124 and 125 are determined to be 9.96 and 10.02 ± 0.1 eV, respectively, which are in faire consistent with the theoretical calculation. With the help of theoretical calculation, the dissociative pathways of metronidazole cation to lose nitryl and hydroxyethyl groups are discussed in detail, which are testified by experimental results to a cetain extent. Besides, the nitryl group elimination is proved to be the dominant dissociation pathway for metronidazole cation.
     
  Keywords  
  Metronidazole; VUV photoionization mass spectrometry; Ionization energy; Dissociative pathway; Side-chain group elimination  
     
   
   
   
   
     

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