Time of flight mass spectrometer and dual gain detector therefor

This invention relates to a time-of-flight mass spectrometer and its associated ion detection system. It provides apparatus for detecting ions in a time-of-flight mass spectrometer, and methods of operating that apparatus, which result in improved performance at a lower cost when compared with prior spectrometers. An ion detector () for use in a time-of-flight mass spectrometer () is disclosed. The ion detector (), which has an extended dynamic range, comprises at least one microchannel plate electron multiplier () together with first and second collection electrodes (). The second collection electrode () is arranged such that in receives more electrons per ion entering the ion detector () than the first collection electrode (). In one embodiment the collection electrodes () are formed in an array consisting of a larger plate-like collection electrode () and a smaller plate-like collection electrode (). In an alternative embodiment a second microchannel plate electron multiplier is arranged between the first collection electrode () and the second collection electrode (). In this embodiment the first collection electrode consists either of a grid electrode () or more preferably of a wire electrode, and the second collection electrode consists of a plate-like electrode ().