Mormann Michael, Peter-Katalinić Jasna
Institute for Medical Physics and Biophysics, Biomedical Analysis Department, University of Münster, Robert-Koch-Str. 31, D-48149 Münster, Germany.
Rapid Commun Mass Spectrom. 2003;17(19):2208-14. doi: 10.1002/rcm.1163.
A novel pulse sequence improving the efficiency for electron capture dissociation (ECD) of an unmodified Fourier transform ion cyclotron resonance (FTICR) mass spectrometer by more than an order of magnitude is presented. Commercially available FTICR instruments are usually equipped with a filament-based electron source producing an electron beam that has a rather small cross section. An ideal overlap between the rotating ion cloud and the electron beam appears to be a prerequisite for a high ECD efficiency. A reduced interception of the ion cloud and the electron beam is probably due to the contribution of the magnetron motion to the trajectory of the ions, resulting in a precession about the z-axis of the instrument. By increasing the kinetic energy and therefore increasing the cyclotron radii of the precursor ions by resonant excitation, the overlap of the rotating ion cloud with the electron beam is improved. By use of this protocol the efficiency of electron capture is substantially increased and consequently the acquisition time of ECD spectra is reduced significantly. The capability of resonant excitation of the precursor ions during the irradiation with electrons is demonstrated for standard peptides. This approach is particularly valuable for analysis and characterization of O-glycosylated peptides. In addition to amino acid sequence information, the attachment site of the labile glycan moiety is determined, and also radical-site-induced fragmentations of the glycosidic bonds are observed.
本文介绍了一种新型脉冲序列，它可将未修饰的傅里叶变换离子回旋共振（FTICR）质谱仪的电子捕获解离（ECD）效率提高一个数量级以上。市售的FTICR仪器通常配备基于灯丝的电子源，产生具有相当小横截面的电子束。旋转离子云与电子束之间的理想重叠似乎是高ECD效率的先决条件。离子云和电子束的拦截减少可能是由于磁控管运动对离子轨迹的贡献，导致围绕仪器z轴的进动。通过增加动能，从而通过共振激发增加前体离子的回旋半径，旋转离子云与电子束的重叠得到改善。通过使用该方案，电子捕获效率大大提高，因此ECD光谱的采集时间显著减少。对于标准肽，证明了在电子照射期间前体离子的共振激发能力。这种方法对于O-糖基化肽的分析和表征特别有价值。除了氨基酸序列信息外，还确定了不稳定聚糖部分的连接位点，并且还观察到糖苷键的自由基位点诱导的断裂。
