| 摘要 |
The instrument initially assesses the purity of a given candidate parent. If the candidate parent is contaminated with an isobaric signal(s), it promptly focuses on the alternative charge state(s) for the same neutral mass. Specifically for every peptide mass there are almost universally several charge states (usually 1-4 for tryptic peptides) present in the ESI spectrum. An optional step may be used for more complex situations where alternative (lower) charge states are not evident in the spectrum. In this case, proton transfer is performed on a higher charge state. Next, if the reduced ion parent is isobarically pure, a higher energy collisionally activated dissociation is performed on the reduced ion parent. Alternatively, a dedicated targeted isolation can be performed for low abundant precursors at calculated m/z if they fall below LOD of the analyzer full scan.
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