Capillary Electrophoresis Separations of Inorganic Anions, Cations and Small Molecules

• Author / Creator

  Pei, Lei

• Capillary electrophoresis (CE) is a powerful separation technique. The analysis of inorganic ions using capillary electrophoresis is becoming increasingly recognized for its high resolving power, low cost, and the simplicity of design, optimization, and execution of CE experiments. To achieve better resolution and separation efficiency and to minimize the analyte adsorption on the capillary wall, control of the electroosmotic flow (EOF) and capillary surface charge are essential. Capillary wall coatings have been one of the major solutions to adjust the EOF and minimize analyte adsorption. This thesis demonstrates the optimization of inorganic ion separations using a variety of wall coatings including surfactant-based, cationic polymeric, and successive multiple ionic layered (SMIL) coatings. Specifically, the double chain zwitterionic surfactant 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (Diyne PC) was polymerized to a form neutral, semi-permanent bilayer coatings on the capillary wall which masked the surface charge of the fused silica capillary. A suppressed EOF (2.0×10-4 cm2/Vs) and better peak shape and separation efficiency (N = 300,000 plates/m) were achieved for small amine compounds. Cationic polymers such as poly(diallyl dimethyl ammonium chloride) (PDADMAC) electrostatically adsorb onto the negatively charged capillary wall to yield a semi-permanent cationic coating, resulting in a reversed EOF. However, such coatings are not stable at high pH. It is demonstrated that this instability was due to a surface catalyzed conversion of the quaternary amines of the polycations to tertiary amines. Successive multiple ionic layer coatings prepared from alternating polycation/polyanion layes demonstrated greater alkaline stability as the multiple ionic layers shield the EOF generating final layer from the surface. Alkaline separations of inorganic anions is demonstrated on both the polycation and multiple layer coatings. Fluorescence detection was investigated for inorganic anion and cation analysis for routine, in-field oilfield water analysis. Indirect fluorescence using 8-hydroxypyrene-1,3,6-trisulfonic acid as the electrolyte probe enabled detection of trace sulfate (0.5 ppm) in high salinity samples (Cl-~1000 ppm) of oilfield waters . For cation analysis, a fluorescent chelating reagent, fluorescein-thiocarbamyl-1-(4-aminobenzyl) diethylenetriamine-N, N, N’, N”, N”-penta-acetic acid (FTC-AB-DTPA) is used to complex target cations in the sample, and then a cationic polymer, hexadimethrine bromide (polybrene), was added to background electrolyte to form ion association complex (IAC) with the metal-probe complex. The difference in the mobility of the IAC is the driving force for separation and the fluorescent chelating probe enables the direct fluorescence detection of cations. This method is capable of simultaneous detection of multiple heavy metal cations (Mn2+, Pb2+, Cu2+, Cd2+, Ni2+, Zn2+ and Co2+) at lower than 10-7 M in high calcium matrix sample (Ca2+>1000 ppm).

• Subjects / Keywords

  • CE coating
  • Indirect anion detection
  • EOF modification
  • Capillary electophoresis

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3H41JX9B

• 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.