Patent ID: 6953929

Claim:
A mass analyzing method using an ion trap mass spectrometer which is equipped with a ring electrode and one pair of end electrodes and temporarily traps ions in a three-dimensional quadrupole field to mass-analyze a sample, comprising: a first step of applying a main high frequency voltage to said ring electrode to form a three-dimensional quadrupole field, a second step of generating ions in a mass-analyzing unit or injecting ions from the outside and trapping ions of a predetermined mass-to-charge ratio range in said mass analyzing unit, a third step of applying a supplementary AC voltage having a plurality of frequency components between said end cap electrodes and scanning said main high frequency voltage, said supplementary AC voltage having a first frequency component with a voltage value (V 1 ) at least high enough to eject ions in resonance and a second frequency component with a voltage value (V 2 ) high enough to excite ions in resonance but not high enough to eject ions in resonance, a fourth step of scanning said main high frequency voltage and ejecting ions from said mass analyzing unit and detecting them.