The major goal has been to develop a matrix-assisted laser desorption/ionization (MALDI) quadrupole ion trap (QIT) as a high performance tandem mass spectrometer for the amino acid sequencing of peptides from complex biological mixtures. High performance characteristics include high sensitivity, high mass accuracy, unit mass resolution in both MS and MS/MS modes, unit mass selection in tandem experiments, efficient collisional activation, and the ability to record wide mass ranges (multichannel advantage) in each cycle. During the past three years a novel method has been developed for efficiently trapping MALDI ions that ramps the fundamental RF voltage as the ions enter the trap, a method for modulating the supplementary RF voltage during mass scans that provides high linearity and mass accuracy, broadband and stretched in time SWIFT techniques for monoisotopic mass selection and isolation, and pulsed heavy gas introduction during excitation that enables one to lower the low mass cutoff for recording a wider range of product ion masses. It is now proposed to expand this effort by the addition of a reflectron time-of-flight (reTOF) mass analyzer. Current QIT/TOF configurations provide (primarily) a means for interfacing continuous ionization methods (e.g. electrospray) to the TOF analyzer, but do not exploit the high performance characteristics of the QIT. In the proposed instrument, the reTOF would serve first as a rapid, multichannel recording device for ions collisionally activated in the trap. Additionally, it would provide the ability to carry out high-energycollisions for ions mass-selected in the trap, with multichannel recording achieved using a curved -field reflectron. Finally, the investigator will also develop a high mass MALDI QIT/reTOF instrument from rapid sequencing of DNA oligomers in the mass range of 5,000 to 20,000 daltons, using a fundamental RF supply that is continuously variable with respect to both frequency and amplitude.
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