The relative abundances of the fragment ions increased with increase in the cone voltage. The experimental results were explained by the favorability of the intermediate structure and the stability of the fragment ion structure. The specific fragmentation patterns could be used for differentiating underivatized AAs.
The number and abundances of the negative product ions were much greater than those of the positive ones. Mechanism for the formation of [2Gln - H - NH3](-) and [His+AA - H - NH3](-) was examined by deuterium replacement of the amine and hydroxide groups to distinguish the deamination and dehydration reactions with a single quadrupole mass spectrometer. The [His + AA - H - NH3](-) ion is formed by ion-molecule reaction between the [His-H](-) ion and a neutral AA.
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