Department of Chemistry, Washington State University , Fulmer 104B, Pullman, Washington 99164-4630, United States.
Anal Chem. 2017 Apr 4;89(7):4287-4293. doi: 10.1021/acs.analchem.7b00356. Epub 2017 Mar 23.
Digital operation of linear ion guides allows them to operate as traps and mass filters by modulating the duty cycles of the two driving waveforms. A gas-filled (5 mTorr) digitally driven quadrupole ion guide was used to demonstrate ion isolation and preconcentration. These abilities allow ion trapping mass spectrometers to be filled to capacity with only ions in the range of interest at essentially any value of m/z. Due to the unique performance characteristics of digitally operated quadrupoles, isolation with purely duty cycle enhanced waveforms was developed with three increasingly sophisticated isolation methods. First, the guide was used as a gas-filled transmission mass filter using the waveform duty cycle to generate a narrow mass window. The second method used broadband trapping to collect ions and translationally cool along the transmission axis before shifting the duty cycle to filter the trapped ions. A subsequent duty cycle change axially ejected the filtered population for measurement. The third method improved resolution by shifting the operating frequency during isolation. The resolving power was optimized with the shift frequency to yield a device limited resolving power of 400 (m/Δm). It is the temporal control of the duration of the isolation process that sets digital waveform based isolation apart from the current technology and that minimizes ion loss even when the mass is very large. Preconcentration by repeated trapping and isolation of an individual charge state was also demonstrated to saturate the ion guide with that charge state. These digital isolation and preconcentration techniques will permit the same isolation resolution (m/Δm) at any value of mass or m/z without significant ion loss as long as the secular frequencies do not significantly overlap while in the trapping mode. It is therefore ideal for the isolation and preconcentration of single charge states of large proteins and complexes.
线性离子阱的数字操作允许通过调制两个驱动波形的占空比来将其作为陷阱和质量滤波器运行。使用充满气体（5 mTorr）的数字驱动四极离子阱来演示离子隔离和预浓缩。这些能力允许离子阱质谱仪仅在实质上任何 m/z 值下，用感兴趣范围内的离子充满容量。由于数字操作的四极的独特性能特性，通过三种越来越复杂的隔离方法开发了仅使用占空比增强波形的纯离子隔离。首先，该导子被用作使用波形占空比产生窄质量窗口的充气传输质量滤波器。第二种方法使用宽带捕获来收集离子，并在沿传输轴平移冷却之前将占空比切换以过滤捕获的离子。随后的占空比变化轴向喷射过滤后的离子进行测量。第三种方法通过在隔离过程中改变操作频率来提高分辨率。通过改变频率来优化分辨率，从而产生器件限制的分辨率为 400（m/Δm）。正是隔离过程的持续时间的时间控制将基于数字波形的隔离与当前技术区分开来，并即使在质量非常大时也最小化离子损失。通过对单个电荷状态的重复捕获和隔离也证明了预浓缩，以使该电荷状态饱和离子阱。这些数字隔离和预浓缩技术将允许在任何质量或 m/z 值下保持相同的隔离分辨率（m/Δm），而不会显著损失离子，只要在捕获模式下 secular 频率不会显著重叠。因此，它是大型蛋白质和复合物的单电荷状态的隔离和预浓缩的理想选择。
