Patent ID: 6756587
Filing Date: 2004-06-29
Classification: H01J

Abstract:
A time-of-flight mass spectrometer comprising:an ion source (1-24) for repetitively generating bunches of ions from a sample to be analyzed; ion accelerating means (21) for causing at least some of the ions comprised in each of said bunches to enter a drift region (24) along an axis (25) with substantially the same component of kinetic energy along said axis (25), in which drift region (24) they become separated in time according to their mass-to-charge ratios; and an ion detector (27) disposed to receive ions after they have passed through said drift region (24); characterized in that: said ion detector comprises: at least one electron multiplying means (42,32) for producing secondary electrons in response to an ion entering said ion detector (27); a first collection electrode (39) for receiving some of said secondary electrons; and a second collection electrode (36,38) for receiving others of said secondary electrons or other electrons derived from those electrons, said second collection electrode (36,38) receiving in use more electrons in response to an ion entering said ion detector (27) than said first collection electrode (39), each said collection electrode (36,38;39) having associated therewith a separate signal processing means (28,29) which has a digital output; said mass spectrometer further comprising: digital memory means (30) for storing the digital outputs of each of said signal processing means (28,29) at one or more transit times of said ions through said drift region (24) relative to the generation of a said bunch of ions; and output means (31) for accessing the data stored in said digital memory means (30) after all the ions of interest generated in one or more of said bunches have entered said ion detector (27), and retrospectively determining the quantity of ions which entered said ion detector (27) at one or more of said transit times while said ion bunches were being generated.