Patent attributes
In the mass spectrometer of the present invention, the controller controls the time of changing the voltage applied to the electrode or electrodes of the ion trap from the ion trapping voltage to the ion ejecting voltage according to the polarity of the electric charge of ions to be ejected from the ion trap. Since positively charged ions and negatively charged ions move in the same direction if the phases of the RF voltage for generating the ion trapping electric field in the ion trap are reversed, the controller may reverse the phase of the RF voltage for trapping ions according to the polarity of the electric charge of ions when the ion ejecting time is fixed, irrespective of the polarity of the electric charge of ions to be ejected. Alternatively, the controller may change the ion ejecting time by half a cycle of the RF voltage depending on the polarity of the electric charge of ions when the ion trapping RF voltage is maintained the same. Owing to such a control, the ions are ejected when they are converging or are converged in the ion trap irrespective of the polarity of the electric charge of the ions. This minimizes the variation in the starting point of ions ejected from the ion trap, and reduces errors in their flight time in the subsequent TOF-MS, whereby the accuracy of the mass analysis is improved and the mass resolution is enhanced.
