In order to understand differences in fragmentation between [M+H]
+ and [M+A]
+ ions (A=Li, Na, K, Rb, and Cs) in more detail, dissociation reactions of [M+H]
+ and [M+Li]
+ ions of
N-t-butoxycarbonyl (Boc)-α-methylalanine (BMA) and
N-t-Boc-α-methylalanine methyl ester (BMAM) in fast atom bombardment mass spectrometry (FAB-MS) were examined. Fragmentation and structural features of the [M+H]
+ and [M+Li]
+ ions are interpreted by using tandem mass spectrometry (MS/MS). The order of the activity of dissociation reaction [M+H]
+[M+Li]
+ is suggested from the relative peak intensities in the FAB mass spectra,
I[M+H-fragment]
+/
I[M+H]
+ and
I[M+Li-fragment]
+/
I[M+Li]
+. Furthermore, MNDO optimized structures of the [M+H]
+ and [M+Li]
+ ions are compared with the structures of the [M+H]
+ and [M+Li]
+ ions proposed by FAB-MS.
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