Patent ID: 7999223

Claim:
A multi-reflection or closed orbit ion trap assembly, comprising: an ion trap; an electrode arrangement including an ion gate, the ion gate being switchable between a first gating state wherein ions, when following a path within the ion trap, are directed along a first ion path, and a second gating state wherein ions, when following a path within the ion trap, are directed along a second ion path; and a system controller arranged to permit identification, from within a plurality of species of charged particles introduced into, or formed within the ion trap, a plurality n(≧2) of ion species of interest each of which n identified ion species undergoes substantially isochronous oscillations or orbits along the path within the ion trap, the oscillations or orbits having period characteristic of the respective mass to charge ratio m/z n of that species, and which period is distinct for each of said n identified species, the system controller being further arranged to switch the ion gate into the first gating state at a plurality of times T x , a first subset of which times, T a (a≧1) being determined by the characteristic period of ions of a first of the n identified species of interest, a second subset of which times, T b (b≧1) being distinct from the first subset and being determined by the different characteristic period of ions of a second of the n identified species of interest, and so forth for any further (n−2) of the n identified species of interest; whereby the ions of those species identified to be of interest are separated from those ions not so identified.