Theoretical analysis of a time-of-flight mass spectrometer with spherical electrodes and radial ion paths

Abstract

A general expression for the total ion flight time is derived for a time-of-flight mass spectrometer having four concentric spherical 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 spherical geometry gives space-time focusing characteristics which are at least as good as those of instruments having similarly spaced cylindrical or planar electrodes. The use of spherical electrodes also offers a large entrance area into which ions can be drawn from a surrounding plasma, provides equal sensitivity for ions entering from all directions, and allows the use of a very small ion collector such as a channel electron multiplier. It follows that this type of mass spectrometer may be a particularly attractive choice for applications requiring unusually high sensitivity.