LC/ESI-MS analysis of underivatized amino acids and mass spectrum
  We report the method of LC/ESI-MS analysis of underivatized amino acids with corresponding mass spectrum and fragmentation patterns. Diagnostic product ions determined by mass spectrometry can support the qualitative identification and quantitative estimation of individual amino acids. Therefore, the optimization of chromatographic separation using the ion-pairing reagent (i.e., Nonafluoropentanoic acid, NFPA) is useful for the evaluation of target amino acid and for further compound-specific nitrogen isotope studies of amino acids. 
Yoshinori Takano, Yoshito Chikaraishi, Naohiko Ohkouchi
physics.chem-ph