Development of a quadrupole ion trap / time-of-flight mass spectrometer for mass resolution and ion photophysics

Abstract

Development of a tandem mass spectrometer, consisting of a quadrupole ion trap (QIT) and a time-of-flight, is described for ion mass resolution and photophysics. Ions are generated externally by electrospray ionization and trapped in the quadrupole ion trap before extraction to the time-of-flight section for mass analysis. The non-parallel fields in the hyperbolic ion trap, which serves as the first acceleration region in the time-of-flight mass spectrometer, are shown to degrade spatial focusing and mass resolution. A novel short-pulse ion extraction method is shown to be useful in diagnosis of the trapped ion cloud size, energy and dispersal time. New ion trap geometries are evaluated theoretically for improvement in mass resolution as well as ion photophysics with similar ion trapping behavior compared with the existing hyperbolic ion trap. Parameters affecting mass resolutions in linear and reflectron time-of-flight modes are identified and possible improvements are discussed. An ion trap consisting of two endcaps and two ring flat electrodes is proposed and constructed on this basis. The newly optimized design is shown to yield the mass resolution of several thousand even at room temperature with moderate extraction field. Significant improvements in ion-laser interaction and photon collection are shown in the optimized design compared to the existing hyperbolic QIT. A molecular beam source is designed, fabricated and characterized for the application in ion-molecule collision experiments. Ionization methods, from solution to gas-phase, of small polycyclic aromatic hydrocarbons are developed and compared. A photo ionization source was designed and constructed to interface in the current mass spectrometer with fast switching capability with the current electrospray source.