Patent ID: 8368014

Claim:
An ion trap time-of-flight mass spectrometer including an ion trap composed of a plurality of electrodes and a time-of-flight mass spectrometer unit for performing a mass analysis of ions ejected from the ion trap, the mass spectrometer being constructed to temporarily capture ions to be analyzed in the ion trap, subject the ions to a cooling process in which a kinetic energy of the ions is attenuated by making the ions come in contact with a cooling gas, and create an accelerating electric field in the ion trap so as to collectively eject the ions from the ion trap into the time-of-flight mass spectrometer unit and make the ions undergo an analysis, comprising: a) a voltage applier for applying an ion-capturing radio-frequency rectangular-wave voltage to at least one of the electrodes; and b) a controller for operating the voltage applier so as to apply a radio-frequency rectangular-wave voltage to the aforementioned at least one of the electrodes during the cooling process, wherein the controller operates the voltage applier in such a manner that a rectangular-wave voltage having a predetermined frequency and a predetermined amplitude is applied to the aforementioned at least one of the electrodes so as to capture the ions with a potential having a predetermined depth, and then the frequency of the rectangular-wave voltage is increased so as to reduce the depth of the potential for a predetermined period of time immediately before the ions are ejected.