A novel method for trapping ions in a quadrupole ion trap has been developed, utilizing programmed RF-voltage amplitudes and electrostatic trapping fields applied to the end-cap electrodes and/or the sample probe. This method overcomes the difficulties associated with trapping of the high kinetic energy ions produced by matrix-assisted laser desorption, and has been successful in achieving mass resolutions greater than one part in 12,000 for peptides in the range of 1000 to 1500 DL In addition, the method obviates the need for high pressures of the buffer gas normally used to retard ion velocities and, therefore, permits one to obtain high resolution mass spectra at normal scan rates. Thus far, our work has been carried out on a modified Finnigan ion trap detector (ITD), which does not have the capabilities for detection of high mass ions or for tandem mass spectrometry. We propose, therefore, to further modify the existing ITD vacuum chamber, detection system, and electronics to enable us to extend this approach to peptides in the range of 500 to 4000 daltons, and to carry out tandem experiments to obtain amino acid sequence from the (primarily) singly-charged molecular ions produced by matrix-assisted laser desorption. It is our intention to evaluate this instrumental configuration promptly for the analysis of peptides in ongoing projects of the Middle Atlantic Mass Spectrometry laboratory, with the goal of developing a compact and user-friendly instrument for routine structural analysis of peptides. Thus, the instrument will be utilized for the structural analysis of the beta-amyloid peptides associated with Alzheimer's disease, to determine phosphorylation sites on the Assembly Protein of several herpesviruses, to characterize the peptide antigens associated with the Major Histocompatibility Complex (MHC), and for several other collaborative projects.
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