Fourier Transform Ion Cyclotron Resonance Mass Resolution and Dynamic Range Limits Calculated by Computer Modeling of Ion Cloud Motion
Fourier Transform Ion Cyclotron Resonance Mass Resolution and Dynamic Range Limits Calculated by Computer Modeling of Ion Cloud Motion
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通过离子云运动的计算机建模计算傅里叶变换离子回旋加速器共振质量分辨率和动态范围限制
DOI：
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发表时间：
2012
影响因子：
3.2
通讯作者：
E. Nikolaev
中科院分区：
文献类型：
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作者：
G. Vladimirov;C. Hendrickson;G. T. Blakney;A. Marshall;R. Heeren;E. Nikolaev
粒子池（PIC）离子轨迹计算提供了最真实的傅立叶变换离子回旋共振（FT-ICR）实验的模拟，通过有效和准确地计算作用在一个系综（云）中每个离子上的力，包括库仑相互作用（空间电荷）、ICR陷阱电极的电场、陷阱电极上的成像电荷、磁场以及与中性气体分子的碰撞。最近的研究表明，离子云的集体行为是产生FT-ICR信号所必需的，有两个主要现象影响质量分辨率和动态范围。首先是在临界离子数（密度）下形成椭球状离子云（称为“凝聚”），这有利于任意几何形状的FT-ICR单元中的信号产生，因为凝聚云表现为准离子。第二个现象是峰值聚并。如果离子数（密度）超过一个阈值，则在m/z上紧密间隔的离子共振会合并成一个共振，该阈值取决于磁场强度、离子回旋半径、离子质量和质量差以及离子的初始空间分布。这两种现象通过小离子密度下云的快速消相和高离子密度下云的聚并来减小动态范围。在这里，我们使用PIC模拟来量化聚结对每个关键参数的依赖。在系统地改变离子数、磁场强度、离子半径、离子m/z、离子m/z差和离子初始空间分布（本文从离子密度分布恒定的椭圆型离子云开始）的一系列实验中，观察到独立运动和合并运动之间的转变。我们的模拟表明，在给定的磁场强度下，随着离子数的增加，质量分辨率是恒定的，直到达到临界值(N)。测定了不同m/z、等丰度和等回旋半径的两个离子群对磁场强度、回旋半径、离子质量和离子质量差的依赖关系。我们发现N和动态范围与1-21特斯拉范围内的磁场强度成二次关系。对回旋半径和Δm/z的依赖是线性的。N取决于m/z = (m/z) -2。给出了质量分辨率随各实验参数变化的经验表达式。在这里，我们首次阐述了FT-ICR MS动态范围和质量分辨率之间权衡的起源和程度（定义不是线宽，而是最接近分辨的质量之间的分离）。
Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud), including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes, the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first is formation of an ellipsoidal ion cloud (termed “condensation”) at a critical ion number (density), which facilitates signal generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius, ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength in the range 1–21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)–2. Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not as line width, but as the separation between the most closely resolved masses).
DOI：
10.1016/j.jasms.2009.10.001
发表时间：
2010-02
影响因子：
3.2
作者：
Leach FE 3rd;Kharchenko A;Heeren RM;Nikolaev E;Amster IJ
通讯作者：
Amster IJ