Separation and characterization of polycyclic aromatic hydrocarbons and azaarenes using normal phase liquid chromatography and electrospray ionization mass spectrometry

• Author / Creator

  Jiang, Ping

• Normal phase liquid chromatography (NPLC) is widely used for separating petroleum into compound classes, such as polycyclic aromatic hydrocarbons (PAHs) and polar nitrogen containing compounds. The charge-transfer and hypercrosslinked polystyrene NPLC phases provide unique selectivities for PAHs. However, their retention mechanisms are not well understood. In this thesis, I evaluate various methods for the determination of the fundamental parameter, void volume, on charge-transfer phases: pycnometry; the minor disturbance method based on injection of weak solvent; the tracer pulse method; the hold-up volume based on unretained compounds; and the accessible volume based on Martin’s rule and its descendants. The accurate measurement of void volume assures accurate retention and selectivity calculation for further understanding of the retention mechanism. Based on accurate measurement of void volume, Chapter Three studies the retention, selectivity, and thermodynamic behavior of PAHs on charge-transfer and hypercrosslinked polystyrene phases under NPLC conditions. The retention of PAHs on these phases is mainly caused by π-π interaction and dipole-induced dipole interactions. Charge-transfer columns possess weaker π-π interaction and greater planarity selectivity than hypercrosslinked polystyrenes for PAHs. This suggests that the charge-transfer phase interacts with PAHs through a disordered phase arrangement, while hypercrosslinked polystyrene behaves as an ordered adsorption phase. Electrospray ionization mass spectrometry (ESI-MS) has been used widely for characterization of mixtures. But ESI-MS alone cannot differentiate molecular isomers and suffers from uneven response for different analytes. Richer molecular composition information for petroleum can be obtained by coupling NPLC to ESI-MS. However, it is challenging to couple NPLC to ESI-MS due to the incompatibility of the NPLC eluent with ESI ion generation. The latter half of this thesis explores techniques that enable hyphenation of NPLC with ESI-MS, using azaarenes analysis as an example. Chapter Four reviews the strategies for both off-line and on-line NPLC-ESI-MS. The application of post column solvent addition, sheath liquid interface, and ambient ionization for on-line NPLC-ESI-MS are discussed and compared. Chapter Five compares post column solvent addition and ambient ionization for ionization of azaarenes in non-ESI solvent. Both methods enhance ionization of azaarenes in hexane, but neither method eliminates the ion suppression caused by the compounds within the azaarenes class. Thus, azaarenes are separated on charge-transfer phase with NPLC mobile phase prior to ESI-MS analysis in Chapter Six. A 30 min NPLC separation coupled to ESI-MS through post column solvent addition of isopropanol provides detection limits for individual azaarene in the range of 0.8 – 120 ng/mL, which is low enough for general environmental monitoring.

• Subjects / Keywords

  • Polycyclic aromatic hydrocarbons
  • Azaarenes
  • Mass-spectrometry
  • Normal phase liquid chromatography
  • Electrospray ionization

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3VM43B40

• 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.