Exploration of the fundamentals and quantitative applications of matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI TOFMS) in polymer analysis

Electrospray deposition (ESD) is used to prepare synthetic polymer samples for analysis by MALDI-TOFMS. Detailed surface characterization of these samples using atomic force and optical microscopy was undertaken to improve the precision of the sample preparation process, which is particularly important when ESD is utilized for deposition of the matrix for mass spectral imaging experiments. It is demonstrated that the degree of matrix solution saturation is a critical parameter affecting the size of the solid droplets on the surface and the surface coverage. MALDI mass spectrometry is developed as a method to measure both the surface coverage and thickness of the ESD samples. The method enables determination of the minimum spray time required to obtain one monolayer of ESD droplets, and it can be used to characterize the sample spot profile with regards to sample coverage as well as the sample thickness.The effect of time in vacuum on the matrix stability, solid droplet size and surface coverage is also demonstrated. Significant evaporation of the sample during vacuum exposure is shown to decrease surface coverage and affect the MALDI analyte signal.The importance of both the matrix-to-analyte and salt-to-analyte ratios on the cationization of synthetic polymer samples in MALDI is studied using a series of poly(ethylene glycol) (PEG) and poly-(ethylene glycol) monomethyl ether samples of various molecular weights. This work suggests a competition between the matrix, higher matrix clusters and the analyte for the cationization reagent in the MALDI experiment.Visually unusual “donut-like” sample spots are recorded for samples electrosprayed using CHCA matrix containing high salt concentrations. Confocal laser scanning microscopy reveals that spherical nano-particles are located in the outer ring while more cylindrical particles are found in the center of the spot. The polymer analyte signal shows an enhancement in the central portion of the spots, while salt-adducts of the matrix show enhanced signal in the outer ring.A combined MALDI standard additions/internal standard method is developed and used to measure the amount of residual PEG in a series of ethoxylated surfactant samples with various hydrophobic-hydrophilic balance values. Good quantitative results are obtained as verified by standard HPLC methodology.Ph.D., Chemistry -- Drexel University, 201