Patent ID: 8759751

Claim:
A method of determining properties of ions within a mass analyzer comprising the steps of: (1) injecting ions into the mass analyzer; (2) causing the ions to follow a portion of a main flight path within the mass analyzer, the main flight path comprising multiple changes of direction; (3) applying a beam deflection to deflect at least some of the ions from the main flight path so that they impinge upon a detection surface located within the mass analyzer, the detection surface comprising part of an active field-sustaining electrode of the mass analyzer; (4) measuring a quantity representative of the charge arriving at the detection surface caused by the impinging ions; (5) determining, from the deflection applied, properties of a trajectory upon which the ions were travelling immediately prior to deflection, and/or determining, from the quantity measured, a value representative of the number of the ions that impinged upon the detector surface; wherein the mass analyzer utilises an analyzer field and the analyzer field in the vicinity of the detection surface is non-zero.