An Ion cyclotron resonance spectrometer comprises a first cell (8) which can be evacuated to a normal high vacuum and which is coupled with means (17, 18) for ionizing a sample substance. The first cell (8) is connected with a second cell (11) via a partition wall (15) provided with a small opening (14), which second cell (11) comprises an ion trap (27, 31) located in the homogenous area of the magnet arrangement (1, 2) and adapted for determining ion cyclotron resonances. The second cell (11) can be evacuated to a superhigh vacuum. The first cell (8) comprises an area located outside the magnet arrangement (1, 2) which lies still within the stray field of the magnet arrangement and which may be provided with an additional magnet (35) so that any desired substance can be ionized therein by any suitably adapted equipment. The ions thus produced can be displaced by means of potential grids (22, 23, 24) located within the first chamber (8), which may be caused to form ion traps by applying suitable potentials, towards the end of the first cell (8) located inside the magnet arrangement (1, 2) and transferred substantially completely to the ion trap (27, 31) arranged in the second cell (11).
