| 研究実績の概要 |
Isomer differentiation will become even a bigger challenge under ambient in situ ionization setup where no chromatography is available. In principle, isomers may be differentiated based on differences in mass spectral fragmentations. However, identification based on MS/MS spectral pattern matching would be unreliable except for matching between spectra with same machine and exactly same conditions as fragmentation patterns depend on both rate constants of each competing decomposition channels and internal energy of the ions of interests. For example, threonine (Thr) and its diastereomer, allo-threonine (allo-Thr) may be differentiated based on spectral patterns; it is known that the diastereomers show different tendency to loose water. However, as the spectral patterns are highly sensitive to CID conditions, Thr spectrum can change into allo-Thr-like one depending on collision energy.
We've found that breakdown diagrams obtained by energy-resolved (ER) MS/MS experiments are useful for differentiation of isomers including diastereomers, such as Thr and allo-Thr. The difference between energy dependence of the water-loss fragmentation channel for each isomer was clearly visualized in their breakdown diagrams and consistent to the previously proposed fragmentation mechanisms. Consequently, the ER-MS/MS approach was found to be useful for reliable isomer differentiation of small molecules, for which numbers of observable product ions are limited and isomer differentiation would be necessary to rely on relative intensities of observed peaks.
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