Ion trap mass spectrometer

Abstract

A technique for performing precursor isolation with a desired mass-to-charge ratio (m/z) in a digital ion trap while maintaining the q value at a substantially constant value is provided. A data obtained by digitizing an FNF signal having a notch is stored beforehand in an FNF waveform memory. In the process of precursor isolation, a main voltage timing controllerand a main voltage generatorgenerate a rectangular-wave voltage based on a reference clock signal CK. An auxiliary signal generatorreads data from the FNF waveform memoryand generates an FNF signal by performing digital-to-analogue conversion of the data in accordance with a clock signal synchronized with the reference clock signal CK. Under the command of a controller, a reference clock generatorproduces the reference clock signal CK having a frequency corresponding to the m/z value of a target ion. Accordingly, a change in the m/z of the target ion leads to a change in the frequency of the reference clock signal CK, which causes the frequency of the rectangular-wave voltage and the central frequency of the notch of the FNF signal to change in the same proportion.