Theoretical analysis of a cylindrical time-of-flight mass spectrometer with radial ion paths

Abstract

Time-of-flight mass spectrometers with concentric cylindrical electrodes and ion paths directed radially inwards are potentially capable of very high sensitivity. A general expression for total ion flight time is derived for a spectrometer having four concentric electrodes which bound two accelerating regions and a drift region. The special case of negligible initial velocity is then considered and it is shown that the cylindrical geometry gives a higher order of space-time focusing than is possible with a conventional linear instrument having similarly spaced planar electrodes. The theoretical difference in resolving power amounts to a factor of at least 2–3, depending on the definition of peak width which is used. It follows that for small time-of-flight mass spectrometers a cylindrical layout offers substantially higher resolving power as well as higher sensitivity than would be possible with a more conventional electrode system.