Håkansson K, Axelsson J, Palmblad M, Håkansson P
Ion Physics Division, Angström Laboratory, Uppsala University, Sweden.
J Am Soc Mass Spectrom. 2000 Mar;11(3):210-7. doi: 10.1016/S1044-0305(99)00144-0.
The degree and onset of fragmentation in multipole storage assisted dissociation (MSAD) have been investigated as functions of several hexapole parameters. Strict studies of hexapole charge density (number of ions injected) and hexapole storage time were made possible by placing a pulsed shutter in front of the entrance to the mass spectrometer. The results obtained show that the charge density is the most critical parameter, but also dependencies on storage time, radio-frequency (rf) -amplitude, and pressure are seen. From these data, and from simulations of the ion trajectories inside the hexapole, a mechanism for MSAD, similar to the ones for sustained off-resonance irradiation (SORI), and for low energy collisionally induced dissociation in the collision multipole of a triple quadrupole mass spectrometer, is proposed. It is believed that, at higher charge densities, ions are pushed to larger hexapole radii where the electric potential created by the rf field is higher, forcing the ions to oscillate radially to higher amplitudes and thereby reach higher (but still relatively low) kinetic energies. Multiple collisions with residual gas molecules at these elevated energies then heat up the molecules to their dissociation threshold. Further support for this mechanism is obtained from a comparison of MSAD and SORI spectra which are almost identical in appearance.
已研究了多极存储辅助解离（MSAD）中的碎片化程度和起始情况，作为几个六极杆参数的函数。通过在质谱仪入口前放置一个脉冲快门，得以对六极杆电荷密度（注入离子数）和六极杆存储时间进行严格研究。所获得的结果表明，电荷密度是最关键的参数，但也观察到了对存储时间、射频（rf）振幅和压力的依赖性。基于这些数据以及对六极杆内离子轨迹的模拟，提出了一种MSAD机制，类似于持续非共振辐照（SORI）以及三重四极杆质谱仪碰撞多极杆中的低能碰撞诱导解离机制。据信，在较高电荷密度下，离子被推至更大的六极杆半径处，此处射频场产生的电势更高，迫使离子径向振荡至更高振幅，从而达到更高（但仍相对较低）的动能。在这些较高能量下与残余气体分子的多次碰撞随后将分子加热至其解离阈值。通过比较外观几乎相同的MSAD和SORI光谱，进一步支持了这一机制。
