A tandem time-of-flight mass spectrometer is described. The spectrometer includes a pulsed source of ions that focuses a packet of ions substantially within a predetermined mass-to-charge ratio range onto a focal plane in a flight path of the ions. An ion selector receives the focused packet of ions and selects ions substantially within the predetermined mass-to-charge ratio range and rejects substantially all other ions. An ion fragmentor that fragments a fraction of the selected ions is positioned in the flight path of the selected ions. A pulsed ion accelerator that accelerates the selected ions and fragments thereof is positioned in a flight path of the selected ions and fragments thereof after the ion fragmentor. An electrode is positioned in the flight path of the accelerated selected ions and fragments thereof after the pulsed ion accelerator. In operation, the electrode is biased with a time varying bias voltage that increases the energy of the fragments relative to the selected ions.