Patent ID: 8772707

Claim:
A quadrupole mass spectrometer comprising: an ion source for ionizing a sample; a quadrupole mass filter composed of four rod electrodes; a quadrupole driver for producing a composite voltage, which comprises a direct-current voltage and a radio-frequency voltage corresponding to the mass-to-charge ratio of an ion to be allowed to pass through the quadrupole mass filter, and for applying the composite voltage to the quadrupole mass filter; and a detector for detecting an ion that has passed through the quadrupole mass filter, wherein the quadrupole driver comprises: a) a memory for storing voltage-setting data corresponding to the mass-to-charge ratio and for storing a gain, a common offset and a mass-related offset as control parameters for varying the direct-current voltage corresponding to the mass-to-charge ratio during a mass-scan operation, where the gain determines the ratio of the direct-current voltage to the amplitude of the radio-frequency voltage, the common offset determines a different offset voltage according to a scan speed, independently of the mass-to-charge ratio, and the mass-related offset specifies a different offset voltage for each of a plurality of mass-to-charge ratios within a mass-scan range; and b) a direct-current voltage generator for generating a direct-current voltage to be applied to the quadrupole mass filter by adding at least three voltages during a mass-scan operation, the three voltages including: a voltage generated by retrieving from the memory the voltage-setting data according to a change in the mass-to-charge ratio, performing a digital-to-analogue conversion of the voltage-setting data, and multiplying the resultant analogue signal by a gain retrieved from the memory; a voltage generated by a digital-to-analogue conversion of the common offset obtained from the memory according to a scan speed at that point in time; and a voltage generated by a digital-to-analogue conversion of the mass-related offset obtained from the memory according to the change in the mass-to-charge ratio.