Hang Wei, Lewis Cris, Majidi Vahid
Chemistry Division, Los Alamos National Laboratory, MS K484, NM 87545, USA.
Analyst. 2003 Mar;128(3):273-80. doi: 10.1039/b209109g.
Construction details and performance evaluation of a radio frequency (rf)-only quadrupole ion guide for use with an electrospray ionization time-of-flight mass spectrometer is presented in this paper. Angiotensin III and cytochrome c were used in these experiments to investigate the ion transmission properties of the rf-only quadrupole for different m/z species. In addition, influence of ion kinetic energies along with the characteristic fragmentation due to collision induced dissociation (CID) were studied. These experiments demonstrate that the transmissions of different m/z ions were not only dependent on the frequency and magnitude of the rf waveform, which is similar to a high vacuum rf-only quadrupole ion guide, but also on the pressure inside the quadrupole chamber. For the pressure range tested, low m/z ions are better focused with increasing pressure. As expected, transmission of ions are subject to space charge limitations when significant numbers of ions are focused on the axis of the quadrupole. It is also observed that CID results are related to transverse motion and longitude motion of ions inside the quadrupole region. Consequently, CID is useful for fragmentation of linear peptides and it is not effective (in present configuration) for large bulky proteins. The kinetic energy of ions that enter the repelling region of the TOFMS is ultimately determined by the ensemble effect resulting from the dc bias potential of the quadrupole (the dominant factor), skimmer-2, pressure inside the quadrupole chamber, and jet expansion. While this system is tested with an ESI source, the operational principle and design criteria are directly applicable for improving other atmospheric pressure ionization sources with time-of-flight mass analyzers such as an inductively coupled plasma ion source.
本文介绍了一种仅用于射频（rf）的四极杆离子导向器的结构细节和性能评估，该离子导向器与电喷雾电离飞行时间质谱仪配合使用。在这些实验中使用了血管紧张素III和细胞色素c来研究仅用于射频的四极杆对不同质荷比（m/z）离子的传输特性。此外，还研究了离子动能的影响以及碰撞诱导解离（CID）引起的特征性碎片化。这些实验表明，不同m/z离子的传输不仅取决于射频波形的频率和幅度（这与高真空仅用于射频的四极杆离子导向器类似），还取决于四极杆腔室内的压力。在所测试的压力范围内，随着压力增加，低m/z离子聚焦效果更好。正如预期的那样，当大量离子聚焦在四极杆轴上时，离子传输会受到空间电荷限制。还观察到CID结果与四极杆区域内离子的横向运动和纵向运动有关。因此，CID对于线性肽的碎片化是有用的，而对于大的 bulky 蛋白质（在当前配置下）则无效。进入飞行时间质谱仪排斥区域的离子的动能最终由四极杆的直流偏置电位（主要因素）、撇油器-2、四极杆腔室内的压力和射流膨胀所产生的综合效应决定。虽然该系统是用ESI源进行测试的，但其工作原理和设计标准可直接应用于改进其他带有飞行时间质量分析器的大气压电离源，如电感耦合等离子体离子源。
