Brenton A G, Krastev T, Rousell D J, Kennedy M A, Craze A S, Williams C M
Institute of Mass Spectrometry, School of Medicine, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK.
Rapid Commun Mass Spectrom. 2007;21(18):3093-102. doi: 10.1002/rcm.3186.
A method to control the duty cycle of a time-of-flight mass spectrometer is described. The method relies on one or more ion gates placed in the beam path that have the function to transmit or stop the beam. These ion gates can switch from the open state to the closed state in tens of nanoseconds and effectively select portions of the mass range. The method is useful in circumstances where recording the complete mass spectrum is not an essential requirement, for example, in the analysis of known compounds where sensitivity and speed of operation are more important. It will be of benefit for applications in separation sciences with techniques involving fast chromatographic separations, where hundreds of mass spectra may be required per second. In such circumstances analytical identification may require only a limited number of masses (or mass regions) to be continuously monitored. Improvement of the duty cycle is particularly important for orthogonal-acceleration time-of-flight (oa-TOF) mass spectrometry instruments whose performance suffers from a low duty cycle. The duty cycle is not a constant for an instrument design but is a mass-dependent function and is least for smaller masses. The method described here is capable of raising the duty cycle to 100%. A theory is developed for one or more ion gate arrangements, for both linear- and reflectron-TOF systems. For a two-gate system the relationship between the positions of the first and second gates is described by a '2/3 rule'. Experimental results are shown for one-gate and two-gate operation, both in linear and in reflectron modes of operation, on an oa-TOF system built in-house.
描述了一种控制飞行时间质谱仪占空比的方法。该方法依赖于放置在束流路径中的一个或多个离子门，这些离子门具有传输或阻挡束流的功能。这些离子门可以在几十纳秒内从打开状态切换到关闭状态，并有效地选择质量范围的部分区域。该方法在记录完整质谱不是必要要求的情况下很有用，例如，在分析已知化合物时，灵敏度和操作速度更为重要。对于涉及快速色谱分离的分离科学应用将是有益的，在这种应用中可能每秒需要数百个质谱。在这种情况下，分析鉴定可能只需要连续监测有限数量的质量（或质量区域）。对于占空比低而性能受影响的正交加速飞行时间（oa-TOF）质谱仪，提高占空比尤为重要。占空比对于仪器设计不是一个常数，而是一个与质量有关的函数，对于较小质量的情况最小。这里描述的方法能够将占空比提高到100%。针对线性和反射式TOF系统的一个或多个离子门排列开发了一种理论。对于双门系统，第一个和第二个门的位置之间的关系由“2/3规则”描述。在内部构建的oa-TOF系统上，展示了单门和双门操作在线性和反射式操作模式下的实验结果。
