Methods and analyzers useful for time of flight mass spectrometry are provided. A method of determining properties of ions within a time of flight or electrostatic trap mass analyzer comprises the steps of: injecting ions into the mass analyzer; 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; 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; measuring a quantity representative of the charge arriving at the detection surface caused by the impinging ions; 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; and wherein the analyzer utilises an analyzer field, the detection surface sustains the analyzer field in its vicinity, and the analyzer field in the vicinity of the detection surface is substantially non-zero.