Tolmachev Aleksey V, Vilkov Andrey N, Bogdanov Bogdan, Pasa-Tolić Ljiljana, Masselon Christophe D, Smith Richard D
Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
J Am Soc Mass Spectrom. 2004 Nov;15(11):1616-28. doi: 10.1016/j.jasms.2004.07.014.
Ion transfer and storage using inhomogeneous radio frequency (RF) electric fields in combination with gas-assisted ion cooling and focusing constitutes one of the basic techniques in mass spectrometry today. The RF motion of ions in the bath gas environment involves a large number of ion-neutral collisions that leads to the internal activation of ions and their effective "heating" (when a thermal distribution of internal energies results). The degree of ion activation required in various applications may range from a minimum level (e.g., slightly raising the average internal energy) to an intense level resulting in ion fragmentation. Several research groups proposed using the effective temperature as a measure of ion activation under conditions of multiple ion-neutral collisions. Here we present approximate relationships for the effective ion temperature relevant to typical operation modes of RF multipole devices. We show that RF ion activation results in near-thermal energies for ions occupying an equilibrium position at the center of an RF trap, whereas increased ion activation can be produced by shifting ions off-center, e.g., by means of an external DC electric field. The ion dissociation in the linear quadrupole ion trap using the dipolar DC ion activation has been observed experimentally and interpreted in terms of the effective ion temperature.
利用非均匀射频（RF）电场结合气体辅助离子冷却和聚焦进行离子转移和存储，是当今质谱分析中的一项基本技术。在浴气环境中离子的射频运动涉及大量离子-中性粒子碰撞，这会导致离子的内部活化及其有效的“加热”（当产生内能的热分布时）。各种应用中所需的离子活化程度可能从最低水平（例如，略微提高平均内能）到导致离子碎片化的强烈水平不等。几个研究小组提出在多次离子-中性粒子碰撞的条件下，使用有效温度作为离子活化的度量。在此，我们给出了与射频多极装置典型运行模式相关的有效离子温度的近似关系。我们表明，对于位于射频阱中心平衡位置的离子，射频离子活化会导致接近热能的状态，而通过例如外部直流电场使离子偏离中心，则可以产生增强的离子活化。使用偶极直流离子活化在线性四极离子阱中进行的离子解离已通过实验观察到，并根据有效离子温度进行了解释。
