Bench-top time of flight mass spectrometer

A Time of Flight analyser comprises a flight tube 160 and a reflectron 170, wherein the reflectron is compressed against the flight tube. The reflectron may comprise a stack of electrodes 172 (e.g. ring electrodes) that remains parallel to each other under compression. Rods 178 may extend through the stack of electrodes, and resilient members 182 may be biased between the rods and the stack of electrodes to compress them towards the flight tube. Also disclosed are (i) a pusher assembly comprising a double grid electrode to provide a field-free region; (ii) a method of forming two grid electrodes, comprising applying adhesive to an upper and lower surface of an annular member and winding metal strands across the annular member so as to form two grid electrodes attached to the two surfaces; and (iii) an ion inlet device and control system configured to introduce an analyte sample or lock mass substance into a mass spectrometer and switch between the analyte sample and the lock mass substance during an analytical run.