Reduction of axial kinetic energy induced perturbations on observed cyclotron frequency
Reduction of axial kinetic energy induced perturbations on observed cyclotron frequency
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DOI：
10.1016/j.jasms.2007.12.009
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发表时间：
2008-04-01
影响因子：
3.2
通讯作者：
Bruce, James E.
中科院分区：
文献类型：
--
作者：
Kaiser, Nathan K.;Weisbrod, Chad R.;Bruce, James E.
利用傅里叶变换离子回旋共振（FTICR）质谱法，通过测量离子的回旋频率来确定离子的质荷比。然而，需要将离子限制在具有电场的离子回旋共振（ICR）单元的捕获区域，这引起了与未扰动的回旋频率的偏差。对所观测到的回旋频率的额外扰动通常归因于空间电荷条件的变化。这项研究提出了一个详细的调查所观察到的离子回旋频率作为离子z轴动能的函数。在理想的三维四极场中，回旋频率与阱内的位置无关。然而，在大多数ICR单元设计中，这种理想仅在阱中心附近近似，并且当离子从阱中心径向和轴向移动时，这种理想四极场产生偏差。为了区分由空间电荷条件的变化或振荡幅度的差异引起的所观察到的回旋频率的偏差，具有相同分子量但不同轴向动能的离子，以及因此z轴运动的幅度，同时被捕获在ICR单元内。这允许一个属性的偏差，在观察到的回旋频率的平均力从不同的轴向振幅的离子所经历的径向电场的差异。实验得出的磁控管频率进行了比较，磁控管频率计算使用SIMICIN 7.0不同的轴向振幅的离子。电子促进离子相干性（EPIC）用于减小不同轴向位置处的径向电场的差异。因此，与EPIC的应用程序，观察到的回旋频率的差异最小化的不同轴向振荡幅度的离子。
With Fourier transform ion cyclotron resonance (FTICR) mass spectrometry one determines the mass-to-charge ratio of an ion by measuring its cyclotron frequency. However, the need to confine ions to the trapping region of the ion cyclotron resonance (ICR) cell with electric fields induces deviations from the unperturbed cyclotron frequency. Additional perturbations to the observed cyclotron frequency are often attributed to changes in space charge conditions. This study presents a detailed investigation of the observed ion cyclotron frequency as a function of ion z-axis kinetic energy. In a perfect three-dimensional quadrupolar field, cyclotron frequency is independent of position within the trap. However, in most ICR cell designs, this ideality is approximated only near the trap center and deviations arise from this ideal quadrupolar field as the ion moves both radially and axially from the center of the trap. To allow differentiation between deviations in observed cyclotron frequency caused from changes in space charge conditions or differences in oscillation amplitude, ions with identical molecular weights but different axial kinetic energy, and thus amplitude of z-axis motion, were simultaneously trapped within the ICR cell. This allows one to attribute deviations in observed cyclotron frequency to differences in the average force from the radial electric field experienced by ions of different axial amplitude. Experimentally derived magnetron frequency is compared with the magnetron frequency calculated using SIMICIN 7.0 for ions of different axial amplitude. Electron promoted ion coherence, or EPIC, is used to reduce the differences in radial electric fields at different axial positions. Thus with the application of EPIC, the differences in observed cyclotron frequencies are minimized for ions of different axial oscillation amplitudes.