Dynamical time focus shift in multiple-reflection time-of-flight mass spectrometers

Abstract

A new method is presented for making the overall flight path of ions in a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) isochronous. Here, the ions undergo an arbitrary number of turns in a TOF analyzer, which itself is tuned to be isochronous from turn to turn. The overall isochronicity from the ion source or injection trap to the detector is established by changing the voltage settings of the analyzer dynamically to a different mode for one turn. This approach combines the advantages of an MR-TOF-MS with a time focus shift reflector with the simplicity of an MR-TOF-MS with only the TOF analyzer as an isochronous tool. Measurements have been performed, in which an MR-TOF-MS was operated with this dynamical time focus shift. These are compared to measurements, in which the time focus was shifted onto the detector using a variation of the extraction field strength in the injection trap. A mass resolving power was achieved that is up to three times larger for the same time-of-flight. For Cs ions, mass resolving powers of 100,000 and 200,000 were obtained after flight times of 1.7ms and 4.9ms, respectively. These flight times are a factor of 3 shorter than those with the time focus shift with the injection trap. The smaller number of turns required for a given mass resolving power results in a larger unambiguous mass range, a higher transmission efficiency, a higher ion capacity and a shorter measurement time. This yields advantages in precision experiments in nuclear physics and for applications in analytical mass spectrometry.