A time of flight mass analyzer having a drift region, an ion package generator, first and second ion reflectors and at least one ion detector. The drift region has an axis, an entrance and an exit and provides for a place wherein ions may be temporarily separated according to their mass-to-charge ratios. The ion package generator injects packets of ions into the drift region at the region's entrance from a beam of ions by intermittently applying an electrostatic field such that the packets of ions enter the drift region in an initial direction which is inclined to the direction of said beam of ions. The first ion reflector is disposed at the exit of the drift region to reflect, back towards the entrance, ions which are traveling towards the reflector in the drift region. The second ion reflector is disposed in juxtaposition to the first ion reflector to reflect packets of ions back towards the first ion reflector through at least a portion of the drift region so that the packet of ions may be reflected to and fro between said first and second ion reflectors and undergo a number n of reflections at the second ion reflector. A detector is disposed to detect at least some packets of ions reflected by the first ion reflector which do not enter the second ion reflector. The number of reflections at the second ion reflector may be selected by adjustment of an inclination of the initial direction to the axis.