Gas-phase ion/ion reactions with a quadrupole/time-of-flight tandem mass spectrometer: Simulations and applications to biomolecule analysis

Jian Liu, Purdue University

Abstract

With the physical separation of the three key steps in ion/ion reactions, i.e. ionization, reaction, and mass analysis, hybrid mass spectrometers such as quadrupole/time-of-flight (QqTOF) provide the highest flexibility and performance for gas-phase ion/ion reaction studies. The information power of a QqTOF platform, as well as other popular platforms, was found to be significantly improved when coupled with an ion/ion proton transfer reaction, as demonstrated in a computer simulation of protein mixture analysis and protein dissociation studies, suggesting its advantages in the electrospray based “top-down” proteomics. This predicted high informing power of the QqTOF platform with ion/ion reaction capability was confirmed by the high confidence demonstrated in the “top-down” protein identification and characterization of a priori unknown proteins in an E. coli protein mixture. In order to improve the instrument duty cycle for “top-down” protein analysis, simultaneous transmission mode collision induced dissociation and ion/ion reactions was later developed with a QqTOF instrument for fast protein identification/characterization. Electron transfer dissociation (ETD) is another subject focused on in this thesis. The study of charge state dependent dissociation of insulin cation via ion/ion electron transfer is likely to provide important implications for the electron transfer dissociation of multiply disulfide-linked whole proteins in general. A quantitative study of product partitioning into various competing ETD channels as a function of peptide charge states was also carried out as an effort to study the fundamentals of electron transfer dissociation process, which allows insights to be drawn about the electron transfer dissociation mechanism. The unique radical chemistry exhibited in the ETD process allows facile identification of the C-terminal products under most ion trap conditions. The value of knowing such product type in the protein database search was evaluated by use of computer simulations.

Degree

Ph.D.

Advisors

McLuckey, Purdue University.

Subject Area

Analytical chemistry

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