Dynamically Harmonized FT-ICR Cell with Specially Shaped Electrodes for Compensation of Inhomogeneity of the Magnetic Field. Computer Simulations of the Electric Field and Ion Motion Dynamics
Dynamically Harmonized FT-ICR Cell with Specially Shaped Electrodes for Compensation of Inhomogeneity of the Magnetic Field. Computer Simulations of the Electric Field and Ion Motion Dynamics
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DOI：
10.1007/s13361-012-0480-1
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发表时间：
2012-12-01
影响因子：
3.2
通讯作者：
Nikolaev, Eugene N.
中科院分区：
文献类型：
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作者：
Kostyukevich, Yury I.;Vladimirov, Gleb N.;Nikolaev, Eugene N.
最近推出的用于FT-ICR质谱仪的具有动态协调功能的离子阱显示出对中等质量500-1000 Da（肽）离子以及高达200 kDa（蛋白质）的极高质量离子的最高分辨能力。对于磁场均匀性非常高的超导磁体，得到了这样的结果。对于均匀性较低的磁体，瞬态持续时间会较小。在用于FT-ICR质谱的超导磁体中，轴向磁场的不均匀性是影响离子云同步运动的主要因素。这种不均匀性导致回旋频率依赖于离子阱势阱中轴向振荡的幅度。因此，离子云中的离子变得失相，这导致信号衰减和分辨率降低。离子回旋频率也受电场径向分量的影响。因此，通过适当地调节电场，可以补偿磁场的不均匀性并在z振荡的整个振幅范围内对准回旋频率。提出了一种动态协调FT-ICR池中磁场不均匀性补偿的方法，该方法基于将额外的电极添加到池中，该池以这样的方式成形，即由这些电极产生的平均电场产生对由不均匀磁场引起的力的反作用力。
The recently introduced ion trap for FT-ICR mass spectrometers with dynamic harmonization showed the highest resolving power ever achieved both for ions with moderate masses 500-1000 Da (peptides) as well as ions with very high masses of up to 200 kDa (proteins). Such results were obtained for superconducting magnets of very high homogeneity of the magnetic field. For magnets with lower homogeneity, the time of transient duration would be smaller. In superconducting magnets used in FT-ICR mass spectrometry the inhomogeneity of the magnetic field in its axial direction prevails over the inhomogeneity in other directions and should be considered as the main factor influencing the synchronic motion of the ion cloud. The inhomogeneity leads to a dependence of the cyclotron frequency from the amplitude of axial oscillation in the potential well of the ion trap. As a consequence, ions in an ion cloud become dephased, which leads to signal attenuation and decrease in the resolving power. Ion cyclotron frequency is also affected by the radial component of the electric field. Hence, by appropriately adjusting the electric field one can compensate the inhomogeneity of the magnetic field and align the cyclotron frequency in the whole range of amplitudes of z-oscillations. A method of magnetic field inhomogeneity compensation in a dynamically harmonized FT-ICR cell is presented, based on adding of extra electrodes into the cell shaped in such a way that the averaged electric field created by these electrodes produces a counter force to the forces caused by the inhomogeneous magnetic field.