Patent ID: 7759638

Claim:
A mass spectrometer comprising: an ion source, a reaction cell and a mass analyser; the mass spectrometer defining a main ion path and a branch ion path, wherein the main ion path extends between the ion source and the mass analyser, and the main ion path meets the branch ion path at a junction comprising ion optics operable to guide selectively ions travelling downstream from the ion source along either the main ion path or the branch ion path, the branch ion path rejoining the main ion path upstream of the mass analyser either at the junction or at a further junction comprising further ion optics operable to guide ions towards the mass analyser that are incident from both the main ion path and the branch ion path, wherein the reaction cell is positioned on a separated portion of the branch ion path and wherein the ion optics immediately upstream of the mass analyser are operable to guide pulses of ions along the main ion path to the mass analyser.