US Patent 9396923 Ion selection method in ion trap and ion trap system

Provided is an ion selection method capable of isolating and leaving a target ion in an ion trap within a short period of time and with high separating power. In a digital ion trap, after ions over a wide range of m/z near a target ion are selectively retained by rough isolation using an FNF signal or the like (S11), unnecessary ions on a low-mass side are removed with high separating power by changing the duty ratio of a rectangular voltage (S12). Furthermore, unnecessary ions on a high-mass side are removed with high separating power by resonant excitation discharge (S13).