Patent ID: 6759652
Filing Date: 2004-07-06
Classification: H01J

Abstract:
An ion-trap mass analyzing apparatus comprising:an annular ring electrode; two end cap electrodes disposed opposite to each other so as to sandwich said ring electrode, and wherein said end cap electrodes are formed asymmetrically with respect to a reference plane; a radio-frequency voltage power supply for generating a radio-frequency voltage applied between said ring electrode and said end cap electrodes to generate an RF electric field in an inter-electrode space formed between said ring electrode and said end cap electrodes, wherein absolute values of said voltages applied to the end cap electrodes are substantially equal to each other; an ion source for generating ions; means for capturing the generated ions in said inter-electrode space in which said RF electric field is generated; and means for detecting ions having a specific mass-to-charge ratio among all the ions captured in said inter-electrode space by emitting said ions having said specific mass-to-charge ratio from said inter-electrode space while separating mass successively in accordance with the mass-to-charge ratio in order to resonantly excite said ions having said specific mass-to-charge ratio in said inter-electrode space, wherein said ion-trap mass analyzing apparatus further comprises means for making the RF electric field distribution asymmetrical with respect to a reference plane when a plane containing a center point of said ring electrode and perpendicular to a rotational symmetry axis of said ring electrode is used as said reference plane the RF electric field distribution being generated in said inter-electrode space to capture ions; and wherein said means for making the ion-capture electric field distribution generated in said inter-electrode space asymmetrical includes means for shaping said two end cap electrodes asymmetrically with respect to said reference plane.