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Dissertation
Investigation into the ionization mechanism occurring in matrix assisted laser desorption ionization and factors affecting ion flight time in MALDI time-of-flight mass spectrometry
Doctor of Philosophy (Ph.D.), Drexel University
Nov 2009
DOI:
https://doi.org/10.17918/etd-3161
Abstract
This thesis focuses on understanding and improving the fundamental aspects of MALDI TOFMS by examining the various elements operating within the technique. Sample preparation, ionization mechanisms, and ion flights times are investigated. A modified aerospray device was utilized to deposit mostly aqueous samples onto the sample probe. Initial attempts resulted in very poor analyte signal precision, therefore a two-level plus center point factorial design experiment was performed on five device parameters. From the first factorial, two device parameters (gas pressure and spray distance) were identified as having a significant effect on the signal reproducibility. A second factorial was performed varying these parameters to further improve signal precision. The spray-to-spray reproducibility of the device was improved 4.5-fold, while the within-sample reproducibility improved 3-fold. The same modified aerospray device was used to prepare samples for investigation into the primary ionization mechanism occurring in the MALDI process. To confirm that photoexcitation and energy pooling occur within the MALDI plume, the signal of amino acids was monitored in the presence of increasing concentrations of halide salts. As the concentration of the halide increased, the analyte and matrix signals decreased due to collision spin-orbit coupling of the matrix and halide ions. Other analyte techniques were performed in order to rule out other possibilities as causes for the observed reduced signals. The effect of changes in ion parameter values was performed. Various amounts of ammonium salt were added to the sample and caused time-of-flight (TOF) shifts. A TOF model was attempted, and although the calculated TOFs matched fairly accurately, the instrument parameters were not realistic. By performing the experiment at various pulsed ion extraction (PIE) delays and comparing the ratios of the PIE to the TOFs, it was determined that the ion velocities were increasing as the ammonium salt was added. Evaluation of qualitative and quantitative MALDI analysis using novel microwell plates was performed. The effect of the pore diameters and depths was investigated. The microwell plates were assessed based on sensitivity, mass accuracy, resolution, metal coatings, and manufacturing process. Other studies focused on the microwell plates' ability to perform polymer analysis and alkali scrubbing.
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Details
- Title
- Investigation into the ionization mechanism occurring in matrix assisted laser desorption ionization and factors affecting ion flight time in MALDI time-of-flight mass spectrometry
- Creators
- April M. Holcomb - DU
- Contributors
- Kevin Glenn Owens (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Arts and Sciences; Chemistry; Drexel University
- Other Identifier
- 3161; 991014632256304721