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Dissertation
Mechanistic investigation of the cationization process of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
Doctor of Philosophy (Ph.D.), Drexel University
1997
DOI:
https://doi.org/10.17918/00008349
Abstract
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is a powerful tool to characterize synthetic polymers. The goal of this study is to investigate the cationization process, one of the four parts, sample preparation, desorption, ionization and detection, occurring during MALDI-TOFMS analysis of synthetic polymer samples. The investigation of the cationization process, by analyzing small ethylene glycol oligomers by observing the effect of their end groups and their MALDI behavior (e.g. affinity order to the alkali metals) using a 23 factorial experiment design model, leads to conclude that the MALDI cationization process is not an equilibrium process in the gas phase. Ideally, under normal MALDI conditions, there might be no mass discrimination in terms of cationization affinity (bonding strength) between different size oligomers in the polymer distribution of polyethylene glycol (PEG). If the mass discrimination does occur, it might result from the difference of reaction rate for different oligomers. Further study indicates that the methyl end-group increases the affinity of alkali metal cations to the small oligomers. The alkali metal cation affinities, although they have limited effect on the molecular weight distribution for the three polymers (blends which have low Mn) tested in our experiments, will have a significant impact on the analysis of polymer blends of higher molecular weight distribution when the detection signal is more important to be used for the calculation of molecular weight. It is observed that the addition of NH4DHB to the sample or the use of electrospray to dry the sample increases the resolution of the mass spectrum. The sample preparation method using IAA with silver acetylacetonate (AgAcAc) added as the ionization reagent permits the MALDI/TOFMS analysis of hydrocarbon polymers, such as polystyrene and polybutadiene, up to 125,000 amu with consistent agreement of molecular weight and polydispersity determined by conventional methods. Copper is found to be an efficient cationization reagent for low molecular weight polystyrene. Laser desorption (LD) TOFMS is developed as a simple and accurate method to characterize the molecular weight of perfluorinated polyethers (PFPEs) up to 7,000 amu. Comparison of the results of MALDI and LD for PPG and LD for PFPE demonstrates experimentally the separation function of matrix materials for the first time.
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Details
- Title
- Mechanistic investigation of the cationization process of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
- Creators
- Henry Y. Xiong
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- xxii, 179 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Arts and Sciences; Drexel University
- Other Identifier
- 991021889108204721