Apparatus for delivering ions to a mass analyzer. The apparatus includes
a time of flight ion guide, a pulsing device for receiving a continuous ion stream
containing ions of different atomic mass and for delivering pulses of ions to the
ion guide wherein ions in each of the pulses of ions exit the ion guide in ascending
order of their atomic mass, and a gating device at the exit end of the ion guide
for allowing ions of a predetermined atomic mass to pass to the mass analyzer.
