Patent ID: 6838665

Claim:
An ion trap mass spectrometer comprising a mass analyzing unit having a ring electrode and one pair of end cap electrodes; a detecting unit for detecting ions ejected from said mass analyzing unit; and a control unit for controlling a voltage applied to said mass analyzing unit, wherein said control unit applies a main high frequency voltage to said ring electrode, forms a three-dimensional quadrupole field, and applies a supplementary AC voltage having a plurality of AC voltage components having different frequencies between said ring electrode and said end cap electrodes while ions are trapped in said mass analyzing unit, and wherein said supplementary AC voltage has a predetermined frequency band (ω 1 to ω 2 ) and components of said band are swept together, wherein the voltage (V 1 ) of at least one frequency component of said supplementary AC voltage is at least high enough to eject ions in resonance, and wherein the voltage (V 2 ) of at least another frequency component of said supplementary AC voltage is high enough to excite ions in resonance but not high enough to eject ions in resonance.