Ion detection and structural mass spectrometry by Fourier transform ion cyclotron resonance mass spectrometry and matrix assisted laser desorption ionization

Abstract

The work presented in this thesis focuses on detection and structural mass spectrometry of large biomolecules by MALDI-FTICR. In Chapter I, overviews of the MALDI technique and advantages of FTICR are given. In Chapter II, experimental considerations and the basic operation of FTICR are described. In Chapter III performance of three ion trap geometries are compared. The ion trajectories and potential energy surfaces calculated for various ICR cells, by using SIMION program, are contrasted and the predictions based on the SIMION calculations are compared with the experimental results. Two methods for trapping the high kinetic energy biomolecule ions are described in Chapter IV; (i) the ion signal for (M+H$rbracksp+$ ions are shown to increase with increasing trapping voltages, and (ii) collisional relaxation is used for the detection of (M+H$rbracksp+$ ions of bovine insulin.The use of binary matrices and internal calibrants to improve the mass measurement accuracy in MALDI-FTICR mass spectrometry is described in Chapter V. In Chapter VI, a simple modification to an ion cyclotron resonance (ICR) cell for detection of high mass ions with large spatial and kinetic energy distributions is described. The high mass range of FTICR is extended from about 2 kDa to ca. 157 kDa. The remaining chapters deal with structural mass spectrometry of biomolecules. Laser desorption ionization and photodissociation of compounds that absorb 337 nm, e.g., vitamin B$sb{12}$ and selected porphyrins, are examined in Chapter VII. Results from two different methods of biological structural mass spectrometry are described in Chapter VIII and Chapter IX. In Chapter VIII, the use of matrices that promote fragmentation of biomolecules are discussed and the reactions of laser desorbed peptide ions with small neutral molecules (e.g., CO, CO$sb2,$ SF$sb6)$ are investigated. In Chapter IX, the reaction of laser desorbed Fe$sp+$ with small organic molecules such as N-methylformamide as models for peptides are reported and extent of electronic excitation of laser desorbed Fe$sp+$ are measured and compared with the results of electron impact. Finally, Chapter X contains concluding remarks.