Date of Award
Doctor of Philosophy (PhD)
Patrick A. Limbach
In this study, polyaromatic hydrocarbon compounds including anthracene, pyrene, acenaphthene and perylene were investigated as nonpolar matrices in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for the analysis of selected nonpolar analytes. First, the influence of matrix and the analyte ionization potentials on a charge-transfer ionization mechanism were determined. Results of these studies demonstrated that formation of radical molecular cations in MALDI-MS depends on the ionization energy difference between the matrix and the analyte. Charge-transfer ionization occurs only when the ionization potential of the matrix is higher than that of the analyte. Next, nonpolar matrices were investigated for the analysis of low molecular weight nonpolar polymers including polybutadiene, polyisoprene, and polystyrene. Conventionally, these types of polymers are analyzed by MALDI-MS using acidic matrices, such as all-trans-retinoic acid, with an additional metal salt as a cationization reagent. Nonpolar matrices were shown to be more effective than acidic matrices, as nonpolar matrices provide better matrix isolation and enhanced spectra reproducibility. Potential difficulties associated with background silver salt clusters present during the analysis of nonpolar polymers by MALDI-MS are reported. Silver cluster ions are observed with m/z values ranging from 1500 to about 7000 when acidic, polar matrices are used with silver salts. It was found that these background signals could be greatly reduced by the use of the nonpolar matrices. Alternatively, using copper salts with acidic matrices instead of silver salts substantially improves the mass spectral quality due to reduced background signals. Finally, the nonpolar matrices were applied to other polymeric compounds including amine functionalized polystyrene, platinum (II) linked modified polystyrenes, and poly[(o-cresyl glycidyl ether)- co-formaldehyde] (PGF). These studies demonstrated that nonpolar matrices can be used for the MALDI-MS analysis of polymers of varying polarity. As with the prior studies, nonpolar matrices were found to be generally more effective for the analysis of these analytes than acidic matrices. Taken together, these studies demonstrate that nonpolar matrices provide high quality MALDI mass spectra of nonpolar and moderately nonpolar polymers. These improvements arise due to improved matrix-analyte miscibility as well as reduction in background salt clusters when silver salts are used as cationization reagents.
Macha, Stephen Francis, "Analysis of Hydrocarbon Materials by Use of Nonpolar Matrices in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS)." (2001). LSU Historical Dissertations and Theses. 296.