Laser desorption/laser ionization time-of-flight mass spectrometry instrument design and investigation of the desorption and ionization mechanisms of matrix-assisted laser desorption/ionization.

摘要

This thesis contains two sections of related research. The first section focuses on improving the performance of laser desorption/ionization time-of-flight mass spectrometers. It begins with an investigation of the effects of the electric field inhomogeneities near wire mesh grids on the resolving power and the ion transmission in TOFMS. The results show that under special conditions, the resolving power and the ion transmission of the instrument can be limited by grid effects.;This section also contains an analysis of the effects of ion initial conditions on the mass calibration and mass accuracy in time-of-flight mass spectrometry. The results show that a third-order fit to the calibration data will improve the mass accuracy over a wider range of ion masses.;The second section of the thesis focuses on understanding the desorption and ionization processes acting during matrix-assisted laser desorption/ionization. Evidence is presented that suggests that the photodecomposition of the matrix leads to the release of analyte molecules and the formation of a supersonic expansion.;Data is presented that shows the alkali metal cationization of large molecules occurs by either an ion-molecule reaction or a molecule-molecule reaction takes place in the expanding matrix plume. The data show that the first step in the cationization process is the photodecomposition of the matrix salt to produce a low kinetic energy bare-cation that reacts in the expanding matrix plume.;During this analysis, a computer program was developed to model the ion peak shape generated by the time-of-flight mass spectrometer. The peak shape program was incorporated into an existing simplex optimization routine that optimizes the design of a TOFMS system without artificially setting any instrument parameters. The program is valuable for the design and testing of TOFMS systems.;The understanding of these processes has led to the development of new matrix compounds with special properties and analytical applications, as well as a better understanding of the initial conditions of ion formation necessary for the improvement in MALDI instrumentation and the MALDI technique.