Multi-CRAFTI: Relative Collision Cross Sections from Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Line Width Measurements
Multi-CRAFTI: Relative Collision Cross Sections from Fourier Transform Ion Cyclotron Resonance Mass Spectrometric Line Width Measurements
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Multi-CRAFTI：傅里叶变换离子回旋共振质谱线宽测量的相对碰撞截面
DOI：
10.1021/jasms.1c00297
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发表时间：
2022
影响因子：
3.2
通讯作者：
Dearden, David V.
中科院分区：
文献类型：
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作者：
Pope, Brigham L.;Joaquin, Daniel;Hickey, Jacob T.;Mismash, Noah;Heravi, Tina;Shrestha, Jamir;Arslanian, Andrew J.;Anupriya;Mortensen, Daniel N.;Dearden, David V.
利用傅里叶变换离子回旋共振（CRAFTI）技术的截面积来确定碰撞截面（CCS）受到必须知道质谱仪的捕获单元中的精确压力的要求的限制。实验还必须在高能硬球制度，使离子退相干后，与中性粒子的单次碰撞，这限制了应用程序的离子是不是更大的质量比中性粒子。为了缓解这些问题，我们在一个实验中共振激发了两个（或多个）不同m/z的离子到相同的质心动能，使它们受到相同的中性压力。我们将这种方法称为“多CRAFTI”。这便于测量相对CCS，而不需要知道压力，并且能够使用内标确定绝对CCS。当考虑到碰撞能量的差异时，用四烷基铵离子的实验产生与一次一个离子的CRAFTI方法和离子迁移谱（IMS）合理一致的CCS（由于多CRAFTI中采用的碰撞能量较高，多CRAFTI通常产生比IMS更小的CCS）。将多CRAFTI和IMS结果与分别使用投影近似或轨迹法值在M06-2X/6-31+G* 理论水平计算的结构计算的CCS进行比较，表明计算结构的CCS越来越小于实验CCS asm/z的增加，这意味着计算模型高估了烷基臂之间的相互作用。对于经历类似的碰撞退相干过程的离子，相对CCS达到恒定值，在较低的碰撞能量比绝对CCS值，这表明通过采用多CRAFTI增加可访问的upperm/zlimit的一种手段。
Determination of collision cross sections (CCS) using the cross-sectional areas by the Fourier transform ion cyclotron resonance (CRAFTI) technique is limited by the requirement that accurate pressures in the trapping cell of the mass spectrometer must be known. Experiments must also be performed in the energetic hard-sphere regime such that ions decohere after single collisions with neutrals; this limits application to ions that are not much more massive than the neutrals. To mitigate these problems, we have resonantly excited two (or more) ions of differentm/zto the same center-of-mass kinetic energy in a single experiment, subjecting them to identical neutral pressures. We term this approach “multi-CRAFTI”. This facilitates measurement of relative CCS without requiring knowledge of the pressure and enables determination of absolute CCS using internal standards. Experiments with tetraalkylammonium ions yield CCS in reasonable agreement with the one-ion-at-a-time CRAFTI approach and with ion mobility spectrometry (IMS) when differences in collision energetics are taken into account (multi-CRAFTI generally yields smaller CCS than does IMS due to the higher collision energies employed in multi-CRAFTI). Comparison of multi-CRAFTI and IMS results with CCS calculated from structures computed at the M06-2X/6-31+G* level of theory using projection approximation or trajectory method values, respectively, indicates that the computed structures have CCS increasingly smaller than the experimental CCS asm/zincreases, implying the computational model overestimates interactions between the alkyl arms. For ions that undergo similar collisional decoherence processes, relative CCS reach constant values at lower collision energies than do absolute CCS values, suggesting a means of increasing the accessible upperm/zlimit by employing multi-CRAFTI.