Kaiser Nathan K, Skulason Gunnar E, Weisbrod Chad R, Wu Si, Zhang Kai, Prior David C, Buschbach Michael A, Anderson Gordon A, Bruce James E
Department of Chemistry, Washington State University, Pullman, WA 99164-4630, USA.
Rapid Commun Mass Spectrom. 2008 Jun;22(12):1955-64. doi: 10.1002/rcm.3574.
Fourier transform ion cyclotron resonance (FTICR) mass spectrometers function such that the ion accumulation event takes place in a region of higher pressure outside the magnetic field which allows ions to be thermally cooled before being accelerated toward the ICR cell where they are decelerated and re-trapped. This transfer process suffers from mass discrimination due to time-of-flight effects. Also, trapping ions with substantial axial kinetic energy can decrease the performance of the FTICR instrument compared with the analysis of thermally cooled ions located at the trap center. Therefore, it is desirable to limit the energy imparted to the ions which results in lower applied trap plate potentials and reduces the spread in axial kinetic energy. The approach presented here for ion transfer, called restrained ion population transfer or RIPT, is designed to provide complete axial and radial containment of an ion population throughout the entire transfer process from the accumulation region to the ICR cell, eliminating mass discrimination associated with time-of-flight separation. This was accomplished by use of a number of quadrupole segments arranged in series with independent control of the direct current (DC) bias voltage applied to each segment of the quadrupole ion guide. The DC bias voltage is applied in such a way as to minimize the energy imparted to the ions allowing transfer of ions with low kinetic energy from the ion accumulation region to the ICR cell. Initial FTICR mass spectral data are presented that illustrate the feasibility of RIPT. A larger m/z range for a mixture of peptides is demonstrated compared with gated trapping. The increase in ion transfer time (3 ms to 130 ms) resulted in an approximately 11% decrease in the duty cycle; however this can be improved by simultaneously transferring multiple ion populations with RIPT. The technique was also modeled with SIMION 7.0 and simulation results that support our feasibility studies of the ion transfer process are presented.
傅里叶变换离子回旋共振（FTICR）质谱仪的工作原理是，离子积累过程发生在磁场外压力较高的区域，这使得离子在被加速进入ICR池之前能够进行热冷却，在ICR池中离子会减速并重新捕获。由于飞行时间效应，这种转移过程存在质量歧视。此外，与分析位于阱中心的热冷却离子相比，捕获具有大量轴向动能的离子会降低FTICR仪器的性能。因此，希望限制赋予离子的能量，这会导致施加的阱板电位降低，并减少轴向动能的分散。这里介绍的离子转移方法称为受限离子群体转移（RIPT），旨在在从积累区域到ICR池的整个转移过程中，对离子群体提供完整的轴向和径向约束，消除与飞行时间分离相关的质量歧视。这是通过使用多个串联的四极杆段来实现的，对施加到四极杆离子导向器每个段的直流（DC）偏置电压进行独立控制。施加直流偏置电压的方式是使赋予离子的能量最小化，从而允许低动能的离子从离子积累区域转移到ICR池。给出了初始FTICR质谱数据，说明了RIPT的可行性。与门控捕获相比，展示了肽混合物更大的m/z范围。离子转移时间的增加（从3毫秒到130毫秒）导致占空比降低了约11%；然而，通过使用RIPT同时转移多个离子群体可以改善这一点。还用SIMION 7.0对该技术进行了建模，并给出了支持我们对离子转移过程可行性研究的模拟结果。
