Gas-phase ion -molecule reaction studies and development of laser -induced acoustic desorption of neutral organic molecules for FT -ICR mass spectrometry
Abstract
Chemical ionization (CI) is a useful soft ionization technique that can provide structural, molecular weight, and reactivity information for many types of compounds. Yet, the applicability of CI is limited to only those compounds that can be evaporated as neutral molecules into a mass spectrometer. We have examined laser-induced acoustic desorption (LIAD) as an evaporation method for analysis of neutral nonvolatile organic and biological molecules via chemical ionization in a Fourier-transform ion cyclotron resonance mass spectrometer. In particular, this work focuses on the development, characterization and application of laser-induced acoustic desorption desorption/chemical ionization in FT-ICR to further chemical analysis of interesting and important nonvolatile molecules. The work discussed here was accomplished with a transmission-mode LD probe and a specially designed LIAD probe. Desorption via LIAD and subsequent chemical ionization of a wide variety of molecules, such as small peptides, organic salts, steroids, sugars, components of nucleic acids and synthetic polymers is shown to be reproducible and relatively routine. Characterization of the energetics of molecules desorbed via LIAD was carried out by velocity distribution measurements and bracketing experiments. The results indicate that the LIAD process does not deposit much internal or kinetic energy into the molecules. LIAD coupled with ion-molecule reactions has been used to investigate the thermochemical properties of the nucleobase radical cations, probe the radical reactivity of small biomolecules, and analyze saturated hydrocarbon polymers with polar end groups. Combined with post-desorption chemical ionization, LIAD shows promise as a useful method for the analysis of thermally labile, non-volatile molecules.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry
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