Patent ID: 8866077

Claim:
A mass spectrometer having an ion transport optical system in which an ion lens or an aperture plate having an opening for allowing ions to pass through is provided between a front-stage multi-pole ion guide and a rear-stage multi-pole ion guide, wherein: a voltage source for applying a radio-frequency voltage to each of the front-stage and rear-stage ion guides, the two radio-frequency voltages having a same frequency and a same phase, or a same frequency with a phase difference within a predetermined allowable range; and a relationship between a size of the opening of the ion lens or the aperture plate and a radius of an incircle of each of the ion guides is determined so that a circumferential edge of the opening of the ion lens or the aperture plate is located on or outside a circumferential surface of a virtual tubular body straightly connecting the incircle at a rear edge of the front-stage ion guide and the incircle at a front edge of the rear-stage ion guide.