Abstract: A method and apparatus for analyzing ions by determining times of flight including using a collision cell to activate ions toward fragmentation and a deflector to direct ions away from their otherwise intended or parallel course. Deflectors are used as gates, so that particular ions may be selected for deflection, while others are allowed to continue along their parallel or otherwise straight path, from the ion source, through a flight tube, and eventually, to a detector. According to the present invention, a postselector, in the form of two deflection plates is used as an ion deflector and is encountered by ions after the collision cell as they progress through the spectrometer.