Patent ID: 8907274

Claim:
A quadrupole mass spectrometer including a quadrupole mass filter composed of a plurality of electrodes, a quadrupole power source for applying a predetermined voltage to each of the electrodes of the quadrupole mass filter so as to selectively allow an ion having a specific mass-to-charge ratio to pass through the quadrupole mass filter, and a controller for giving the quadrupole power source an instruction on a target voltage corresponding to the mass-to-charge ratio of a target ion, the quadrupole power source having a wave detector for detecting a radio-frequency voltage applied to the quadrupole mass filter and generating a DC detection output, a detection output adjuster for adjusting a gain of the detection output generated by the wave detector, a radio-frequency power source which includes a signal generator for generating a radio-frequency signal with a variable frequency and which produces a radio-frequency voltage whose amplitude is based on a comparison between an output of the detection output adjuster and the target voltage and whose frequency is equal to or proportional to the frequency of the radio-frequency signal, a direct-current power source for producing a direct-current voltage based on the output of the detection output adjuster, and a superimposer for superimposing the direct-current voltage produced by the direct-current power source and the radio-frequency voltage produced by the radio-frequency power source, where the radio-frequency voltage superimposed by the superimposer is applied to the quadrupole mass filter after being increased by an LC resonation circuit including, as a component thereof, a stray capacitance between the electrodes of the quadrupole mass filter, and where the LC resonance circuit is tuned by adjusting the frequency of the radio-frequency signal, wherein the detection output adjuster in the quadrupole power source includes an amplifier for amplifying a voltage with a constant gain independent of the frequency of the radio-frequency signal and a first corrector for correcting a voltage at a stage of input to or output from the amplifier according to a ratio of a frequency change so that the radio-frequency voltage applied to the quadrupole mass filter maintains a constant amplitude when the frequency of the radio-frequency signal is changed from a standard frequency for a purpose of tuning, and the quadrupole power source further includes a second corrector for correcting the target voltage according to a square of the ratio of the frequency change when the aforementioned frequency change for the tuning is made.