Patent ID: 8097844

Claim:
A mass-analysis method for operating a mass-analysis apparatus with an ion trap for capturing ions by an electric field created within a space surrounded by a plurality of electrodes, including steps of holding ions within the ion trap, then dissociating a specific kind of ion into product ions, and subjecting the product ions to mass analysis, characterized by: a) a precursor ion selection step in which, among various kinds of ions captured within the ion trap, those ions whose mass-to-charge ratios are within a predetermined mass range including a mass-to-charge ratio of an objective ion are selectively maintained as precursor ions within the ion trap; b) a high q-value-setting step in which a frequency of an ion-capturing radio-frequency voltage applied to at least one of the electrodes is regulated so that the objective ion will be captured with a relatively high q-value; c) a dissociation-performing step in which an ion-exciting radio-frequency voltage for causing resonant excitation of the objective ion is applied to at least one of the electrodes in order to help collision-induced dissociation of the objective ion within the ion trap, and then application of the ion-exciting radio-frequency voltage is discontinued within a period of time where at least a portion of the product ions generated by the collision-induced dissociation remain in the ion trap; and d) a product ion-capturing step in which the product ions are captured after the frequency of the ion-capturing radio-frequency voltage is changed so that the product ions will be captured with a relatively low q-value, simultaneously with discontinuation of the application of the ion-exciting radio-frequency voltage, or at a delayed point in time within a period of time where at least a portion of the product ions generated by the collision-induced dissociation remain in the ion trap after the discontinuation of the application of the ion-exciting radio-frequency voltage; wherein at least the ion-capturing radio-frequency voltage is a radio-frequency voltage generated by switching a direct-current voltage.