Patent ID: 6847037

Claim:
An ion trap mass spectrometer comprising: a ring electrode and a pair of end cap electrodes placed opposite each other with the ring electrode therebetween, where an ion trap space is defined by the ring electrode and the pair of end cap electrodes; frequency determining means for determining a plurality of frequencies or a plurality of frequency channels each corresponding to a mass to charge ratio of an ion to be selected; wide-band RF signal generator for generating a wide-band RE signal having a plurality of notches each corresponding to each of the plurality of frequencies or the plurality of frequency channels, wherein the wide-band RF generator generates the wide-band RF signal by: a) generating a sinusoidal wave having one of a plurality of component frequencies composing the wide-band RF signal devoid of the plurality of frequencies or the plurality of frequency channels corresponding to the plurality of notches; b) adding the sinusoidal wave to a current temporary superposed wave to produce an addition wave; c) subtracting the sinusoidal wave from the current temporary superposed wave to produce a subtraction wave; d) selecting either of the addition wave or the subtraction wave that has a smaller amplitude as a next temporary superposed wave; and e) repeating the steps a)-d) for all the component frequencies; and a voltage controller for applying a voltage corresponding to the wide-band RF voltage to the pair of end cap electrodes, whereby ions having mass to charge ratios corresponding to the frequencies or frequency channels remain in the ion trap space but other ions are ejected from the ion trap space.