Doctor of Philosophy (PhD)
Instrument and technique development and modeling of ionization methods using infrared (IR) laser desorption and ablation for mass spectrometry (MS) analysis of chemical and biochemical samples are described. Infrared lasers are highly efficient at sample removal and post-ablation ionization of materials removed by IR laser can be used to improve ionization efficiency. Fundamental studies of the physical processes in laser ablation mass spectrometry can help elucidate the mechanism. In this research, an infrared/ultraviolet two-laser matrix-assisted laser desorption ionization (MALDI) MS was developed for analysis of biomolecules. An infrared laser was used to ablate a mixture of analyte and matrix, and the ablated material was post-ionized by an ultraviolet (UV) laser. Factors affecting ion yield, including IR and UV laser fluences and the delay time between the laser pulses, were studied using a peptide standard. Protein samples were tested and the observed signals suggested that ionization occurs through a UV MALDI mechanism. A continuous flow infrared matrix-assisted laser desorption electrospray ionization (CF IR MALDESI) mass spectrometry was developed for study of chemical and biochemical reactions. Samples in aqueous solution were flowed through a silica capillary to form a liquid bead at the capillary tip. An IR laser was used for sample ablation and the ejected sample was entrained in an electrospray to form ions. Ions were sent to an ion trap mass spectrometer for analysis. The chelation reaction of 1,10-phenanthroline with iron (II), the denaturation reaction of insulin with 1,4-dithiothreitol, and tryptic digestion of cytochrome c were on-line monitored. A two-dimensional finite element model was developed to simulate IR laser ablation of glycerol. The laser fluence was varied from 1 to 6 kJ/m2, and the wavelength was varied from 2.7 – 3.7 µm that covered the OH and CH stretch absorption region of glycerol. The results showed a strong temperature dependence on laser wavelength and fluence. The peak temperature of glycerol was obtained as the laser wavelength tuned to OH stretch absorption at 3 µm, and was sufficient for phase explosion to occur. The simulation results showed a good agreement with previous particle sizing and plume imaging results.
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Huang, Fan, "Infrared laser ablation for biological mass spectrometry" (2012). LSU Doctoral Dissertations. 2235.
Murray, Kermit, K.