School of Electronic Engineering, Xidian University, Xi'an, Shaanxi 710071, China.
Division of Advanced Manufacturing, Graduate School at Shenzhen, Tsinghua University, Shenzhen, Guangdong 518055, China.
Rev Sci Instrum. 2022 Aug 1;93(8):084101. doi: 10.1063/5.0074709.
The Bradbury-Nelson gate (BNG) is a common device used for ion control in time-of-flight mass spectrometry and ion mobility spectrometry (IMS). A dual-location control model was employed in order to better understand the behavior of ions around a modulated BNG. This model illustrated that the ions are released from the starting location and truncated at the cutoff location. The shapes of the starting and cutoff locations are both curved with similar curvature, and the cutoff location is situated further back. Therefore, the distance between the two locations is a key parameter leading to the ion loss during modulation and is influenced by the gating voltage difference. Through simulations and experiments, the ion loss is verified to increase with the increase in the gating voltage difference. Taking a Fourier transform IMS as an example, by reducing the gating voltage difference from 150 to 50 V, the signal-to-noise ratio of the time domain result was improved from 91.7 to 386.5 and the resolving power was improved from 40.9 to 63.6. In addition, the superposition effect of multicycle modulation is shown and explained by the model. When the modulated frequency is too rapid and the closing time is insufficient for all the ions to be consumed, some ions continue to exist between the two locations, and the residual ions then enter the drift region during the next few cycles. This phenomenon needs to be avoided because the total number of ions entering the drift region will then increase uncontrollably.
布拉德伯里-尼尔森门（BNG）是飞行时间质谱和离子淌度谱（IMS）中常用的离子控制装置。为了更好地理解调制 BNG 周围离子的行为，采用了双位置控制模型。该模型表明，离子从起始位置释放并在截止位置截断。起始位置和截止位置的形状都是弯曲的，曲率相似，截止位置位于更靠后的位置。因此，两个位置之间的距离是导致调制过程中离子损失的关键参数，受门控电压差的影响。通过模拟和实验验证，离子损失随门控电压差的增加而增加。以傅里叶变换 IMS 为例，通过将门控电压差从 150V 降低到 50V，可以将时域结果的信噪比从 91.7 提高到 386.5，分辨率从 40.9 提高到 63.6。此外，模型还解释了多周期调制的叠加效应。当调制频率过快且关闭时间不足以消耗所有离子时，一些离子会继续存在于两个位置之间，然后在下几个周期中进入漂移区。这种现象需要避免，因为进入漂移区的离子总数将不可控地增加。
