Multiple Ion Isolation in Multi-Reflection Systems

A method of acquiring a continuous or near-continuous mass spectrum across a desired m/z range containing a plurality of ion species of interest by operating a multi-reflection or closed orbit ion trap assembly, comprising the steps of:

• (a) identifying n(≧2) ion species from a superset of ion species injected into, or formed within, an ion trap, each of which identified species undergoes substantially isochronous oscillations or orbits along a path within the ion trap, the oscillations or orbits having a period characteristic of the respective mass to charge ratio m/zn of that species and which period is distinct for each of the n identified species;
• (b) switching an ion gate located in or adjacent the ion trap between a first gating state in which ions of the identified species passing along the path within the ion trap are directed along a first ion path for further processing, and a second gating state in which ions not of the identified species passing along the path within the ion trap are directed along a second, different path for further storage or disposal;
• wherein the ion gate is switched into the said first gating state at a plurality of times Tx(x=1, 2, . . . ), a first subset of which times, Ta(a≧1) being determined by the characteristic period of ions of a first of the n identified species, a second subset of which times, Tb(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, and so forth for any further (n−2) of the n identified species;
• and
• repeating steps (a) and (b) for a second superset of ion species injected into, or formed, within,
• the ion trap thereby to identify p(≧2) ion species different to the n ion species identified in the first superset with respective changes to the gating times Ta, Tb and so forth.

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/za 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 Tx, a first subset of which times, Ta(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, Tb(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.

A mass spectrometer 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/zn 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 Tx, a first subset of which times Ta(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, Tb(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;
• and
• an ion detection arrangement, the system controller being arranged to switch the ion gate into an ion detection state once the n identified ion species have been separated from those not identified, at a time when it is determined by the system controller that m of the n species of trapped ions will be in the vicinity of the ion gate (m≧1;m≦n);
• wherein the system controller is further arranged to direct the m ion species in the vicinity of the ion gate towards the ion detection arrangement for detection there when in the ion detection state.