Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States.
J Am Soc Mass Spectrom. 2020 Oct 7;31(10):2161-2170. doi: 10.1021/jasms.0c00263. Epub 2020 Sep 8.
Image charge detection is the foundation of charge detection mass spectrometry (CDMS). The mass-to-charge ratio, /, of a highly charged ion or particle is determined by measuring the particle's charge and velocity. Charge is typically determined from a calibrated image charge signal, and the particle velocity is calculated using the peaks from the shaped signal as they relate to the particle position and time-of-flight through a detector of known length. Although much has been done to improve the charge accuracy in CDMS, little has been done to address the inconsistencies in the particle velocity measurements and the interpretation of peak position and effective electrode length. In this work, we combine SIMION ion trajectory software and the Shockley-Ramo theorem to accurately determine the effective electrode length, peak position, and shape of the signal peaks. Six model charge detector geometries were examined with this method and evaluated in laboratory experiments. Experimental results in all cases agreed with the simulations. Using a charge detector with multiple, 12.7 mm-long cylindrical electrodes, experimental velocities across and between electrodes agreed within 0.25% relative standard deviation (RSD) when this method was used to correct for effective electrode lengths, corresponding to an uncertainty in the effective electrode length of only 40 μm. For a detector with multiple electrodes and varied electrode spacing, experiments showed that the peak amplitude and shape vary with the geometry and with the particle path through the detector, whereas all peak areas agreed to within 2.3% RSD. For a charge detector made of two printed circuit boards, the velocities agreed within 0.44% RSD using the calculated effective electrode length.
图像电荷检测是电荷检测质谱（CDMS）的基础。高度带电离子或粒子的质荷比（/）通过测量粒子的电荷和速度来确定。电荷通常通过校准的图像电荷信号确定，而粒子速度则使用整形信号的峰值计算得出，这些峰值与粒子位置和通过已知长度探测器的飞行时间有关。尽管在 CDMS 中已经做了很多工作来提高电荷精度，但在解决粒子速度测量的不一致性以及峰值位置和有效电极长度的解释方面做得很少。在这项工作中，我们结合了 SIMION 离子轨迹软件和 Shockley-Ramo 定理，以准确确定有效电极长度、峰值位置和信号峰值的形状。使用这种方法检查了六种模型电荷检测器的几何形状，并在实验室实验中进行了评估。在所有情况下，实验结果都与模拟结果一致。使用具有多个 12.7 毫米长圆柱形电极的电荷检测器，当使用这种方法校正有效电极长度时，跨电极和电极之间的实验速度在 0.25%相对标准偏差（RSD）内一致，这对应于有效电极长度的不确定性仅为 40 μm。对于具有多个电极和变化的电极间距的检测器，实验表明，峰值幅度和形状随几何形状和粒子在探测器中的路径而变化，而所有峰值面积的一致性在 2.3%RSD 内。对于由两块印刷电路板制成的电荷检测器，使用计算出的有效电极长度，速度的一致性在 0.44%RSD 内。
