The application of ion optics in time-of-flight mass spectrometry

Abstract

The ion time-of-flight (TOF) through accelerating, decelerating and reflecting fields is the key to determining ion optical properties and the resolution of most TOF mass spectrometers. The initial velocity- and position-induced energy spread aberrations, as well as the role of the time lag, are considered for linear drift TOF mass spectrometers. Peak shapes for stable and metastable ions are presented for these instruments. On a specific geometry the resolution is estimated for realistic assumptions. The post source focusing method ion-optical capabilities are discussed. The ion-optical properties of the single and double stage mirrors with first and second order energy focusing in time respectively are detailed for linear and packet oblique incidence geometries. Again, illustrative peak shapes for stable and metastable ions are given. The resolution of typical mirror TOF mass spectrometers was calculated and compared with those of linear drift instruments. The TOF ion optical properties of the parabolic potential with plane and axial symmetry are described for mirrors and accelerating systems. Matrix elements are given for cylindrical electrostatic mirrors, applicable to electrostatic particle guides. Means to focus transversally and to tune ion packets to the detector i.e. electrostatic lenses and plane deflectors are briefly mentioned. The TOF basic parameters of multisector electrostatic systems are exemplified on a three deflector geometry. The main TOF ion optical parameters of four magnetic-sector analyzers are also specified.