During a halt period of time when the introduction of ions is temporarily discontinued to change an objective
ion to be selected by a first
mass separator in the previous stage, a pulsed
voltage having a polarity opposite to that of the ions remaining in a collision
cell (4) is applied to an entrance lens
electrode (42) and exit lens
electrode (44). The ions are pulled by the DC
electric field created by this
voltage, to be neutralized and removed by colliding with the lens electrodes (42, 44). Thus, the residual ions, which may cause a
crosstalk, can be quickly removed from the inner space of the collision
cell (4) without contaminating an
ion guide (5) to which a radio-frequency is applied. Since no radio-frequency
voltage is applied to the lens electrodes (42, 44), the circuit for applying the pulsed voltage can have a simple configuration. Thus, the cost increase is suppressed.