Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Edward S. Yeung

Abstract

Matrix-assisted laser desorption (MALD) is a technique for converting large biomolecules into gas phase ions. Some characteristics of the commonly used UV matrices are determined. Solubilities in methanol range from 0.1 to 0.5 M. Solid phase absorption spectra are found to be similar to solution, but slightly red-shifted. Acoustic and quartz crystal microbalance signals are investigated as possible means of UV-MALD quantitation. Evidence for the existence of desorption thresholds is presented. Threshold values are determined to be in the range of 2 to 3 MW/cm[superscript]2. A transient imaging technique based on laser-excited fluorescence for monitoring MALD plumes is described. Sensitivity is well within the levels required for studying matrix-assisted laser desorption, where analyte concentrations are significantly lower than those in conventional laser desorption. Results showing the effect of film morphology, particularly film thickness, on plume dynamics are presented. In particular, MALD plumes from thicker films tend to exhibit higher axial velocities. Fluorescent labeling of protein and of DNA is used to allow imaging of their UV-MALD generated plumes. Integrated concentrations are available with respect to time, making it possible to assess the rate of desorption and the rate of fragmentation. The spatial and temporal distributions are important for the design of secondary ionization schemes to enhance ion yields and for the optimization of ion collection in time-of-flight MS instruments to maximize resolution. Such information could also provide insight into whether ionization is closely associated with the desorption step or whether it is a result of subsequent collisions with the matrix gas (e.g., proton transfer). Although the present study involves plumes in a normal atmosphere, adaptation to measurements in vacuum (e.g., inside a mass spectrometer) should be straightforward.

DOI

https://doi.org/10.31274/rtd-180813-11932

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Theodore William Heise

Language

en

Proquest ID

AAI9334987

File Format

application/pdf

File Size

102 pages

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