Studies of Fundamental Theories and Retention Mechanism of Charge Transfer and Hypercrosslinked Phases in Normal Phase High Performance Liquid Chromatography

• Author / Creator

  Wu,Di

• Polar compounds in petroleum, especially compounds containing nitrogen, cause numerous problems in the processing of oil, including deactivation of catalysts, corrosion, and storage instability. Chromatographic separation helps to identify and characterize these polar compounds at different stages in the refining of petroleum. Previous research in our group showed that the custom synthesized hypercrosslinked polystyrene stationary phase HC-Tol was capable of group-type separation of nitrogen compounds under normal phase liquid chromatography conditions. Group-type separation means that the pyrroles, pyridines and polycyclic aromatic hydrocarbons (PAHs) were separated into three distinct groups. The commercial dinitroanilinopropyl (DNAP) column also separated nitrogen compounds from PAHs. Despite the potential of the HC-Tol and DNAP columns for petroleum separations, their retention mechanisms were not fully understood. In this thesis, the Snyder–Soczewiñski model and linear solvation energy relationships (LSERs) were used to gain a better understanding of the HC-Tol and DNAP columns. This thesis focuses on the fundamental theories of normal phase high performance liquid chromatography (HPLC), especially on the retention mechanisms of the HC-Tol and DNAP columns. The normal phase retention on the HC-Tol column was investigated using the Snyder–Soczewiñski model. The solvent strength of binary hexane-solvent mixtures can be predicted using the solvent strength of the pure strong solvents. The HC-Tol column was shown to be a localizing adsorptive phase with adsorption sites extending above the surface. HC-Tol was also characterized by linear solvation energy relationships (LSERs) and compared to the classical amino phase and another hypercrosslinked phase (5-HGN). On both the HC-Tol and amino columns, the solute hydrogen bond acidity (A), hydrogen bond basicity (B) and polarity (S) all contribute significantly to retention, while solute excess polarizability E has a small but negative effect on retention. Solute volume V has no impact on retention on the amino column, while V has a slightly negative influence on retention for the HC-Tol column. The differences in coefficient v between the amino and the HC-Tol columns might explain why the HC-Tol is capable of group-type separations. 5-HGN phase has smaller a and b values, which means that 5-HGN is not as basic or acidic in terms of hydrogen bonds as is HC-Tol. This suggests that the hydrogen bonding character of the HC-Tol phase arises from its silica substrate. The slope of the linear relationship between retention and the mobile phase composition (Snyder-Soczewiñski model) in normal phase liquid chromatography (NPLC) was studied for both bonded and charge-transfer phases. Knowing the slope is important for retention prediction, mobile phase adjustment, and even column selection. The Snyder model and the Soczewiñski model were compared on classic NPLC bonded phases using literature data, and on the DNAP column using experimentally collected data. Overall, the Snyder model slightly better predicted the n-slope than the Soczewiñski model. However, both models had comparable uncertainty in predicting the n-slope for a given compound. The number of aromatic double bonds was the most suitable descriptor for estimating the relative n-slope of PAHs. On the DNAP phase, a modified Soczewiñski model was suggested to allow for the significant contribution of the aromatic rings to the n-slope. Coupling the modified Soczewiñski model and one gradient run, a gradient method was developed to build a LSER for normal phase chromatography. LSER model built based on gradient separation was as good as those based on isocratic separation but required less trial and error experiments.

• Subjects / Keywords

  • Snyder–Soczewiñski model
  • LSERs
  • Normal phase liquid chromatography

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3R20SB7R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.