COLLISIONAL FOCUSING EFFECTS IN RADIO-FREQUENCY QUADRUPOLES
COLLISIONAL FOCUSING EFFECTS IN RADIO-FREQUENCY QUADRUPOLES
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射频四极射中的碰撞聚焦效应
DOI：
10.1016/1044-0305(92)87067-9
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发表时间：
1992-05-01
影响因子：
3.2
通讯作者：
FRENCH, JB
中科院分区：
文献类型：
--
作者：
DOUGLAS, DJ;FRENCH, JB
在5×10~(-4)到1×10~(-2)托的较高工作压力下，研究了离子在传统的二维射频四极杆中的传输。来自质量分辨分析离子和总离子电流的信号测量表明，如果初始注入离子能量较低(1-30 eV)，通过射频四极杆出口处的小孔观察到的离子传输首先随着气体压力的增加而增加，在大约8×10(-3)托时达到最大值，然后在较高压力下减少。这与经典散射的预期形成了直接的对比。这种“碰撞聚焦”似乎类似于在三维离子陷阱中看到的效果。当质量至少达到16,950u时，碰撞聚焦随离子质量(而不是质量电荷比)的增加而增加。报道了能量损失过程的蒙特卡罗模拟，它可以为合理的碰撞截面提供与观测损失一致的结果。结果表明，在较高气压下工作的射频四极管在高(如大气)压离子源离子采样中有实际应用价值。
The transmission of ions through a conventional two-dimensional radiofrequency-only (rf) quadrupole has been studied for comparatively high operating pressures between 5 x 10(-4) and 1 x 10(-2) torr. Measurements of signals from mass-resolved analyte ions and total ion currents show that, provided the initial injection ion energy is low (1-30 eV), the ion transmission observed through a small aperture at the exit of the rf quadrupole first increases as the gas pressure increases, reaching a maximum at approximately 8 X 10(-3) torr before decreasing at higher pressures. This is in direct contrast to the expectations of classical scattering. This "collisional focusing" appears to be analogous to effects seen in three-dimensional ion traps. The collisional focusing increases with the mass of the ion (not mass-to-charge ratio) for masses up to at least 16,950 u. The collisional focusing of the ions is found to be accompanied by significant losses of axial kinetic energy. A Monte Carlo simulation of the energy loss process is reported that can provide agreement with the observed losses for reasonable collision cross-sections. The results suggest that operation of rf quadrupoles at relatively high pressure may find practical application in sampling ions from high (e.g., atmospheric) pressure ion sources.