Tandem time-of-flight mass spectrometer

Abstract

A tandem time-of-flight mass spectrometer includes an ion source, a velocity selector downstream of the ion source, a dissociation cell downstream of the velocity selector, and an ion accelerator downstream of the dissociation cell, the accelerator being capable of focusing ions at a space focal plane, and an ion-reflector (reflectron) downstream of the accelerator. The accelerator allows the ions to subsequently separate according to their m/z ratios and the reflectron to subsequently space-focus the ions over a broad mass range at a detector. A velocity selector includes a pair of ion defectors each having multiple electrically conductive strips, the strips including alternate positive voltage strips and alternate negative voltage strips. A method of selecting a subset of ions from a set of ions includes applying a voltage across a first ion deflector so as to deflect ions passing through the first deflector in a first direction away from a flight path, switching off the voltage applied to the first ion deflector in phase with the passage of a subset of ions having a select range of velocities so that the subset of ions is deflected less in the first direction than preceding ions, switching on a voltage applied to a second ion deflector downstream of the first ion deflector so as to deflect ions passing through the second ion deflector in a second direction and to deflect the subset of ions back along the flight path, and maintaining a voltage across the second gate so as to deflect ions following the subset of ions away from the flight path. The velocity selector also can be used in a single-deflector mode.