Doctor of Philosophy
Department of Chemistry
Lee, Young-Joon, Combining capillary electrophoresis and mass spectrometry for the characterisation of humic acids, Doctor of Philosophy thesis, Department of Chemistry, University of Wollongong, 1994. http://ro.uow.edu.au/theses/1125
Capillary electrophoresis (CE) which is a relatively new method capable of fast, highly efficient separations has been used to separate complex mixtures of isomeric substituted benzoic acids as model compounds for humic acid digests. There is evidence to suggest that these high molecular weight organic substances which are found in soil and water can be degraded to form substituted phenolic compounds.
The effects of CE parameters i.e., pH, applied voltage, buffer concentration, and composition have been examined to determine their relation to EOF and μep to get good separation. For the separation of benzoic acid isomers the most critical parameter appears to be solvent pH which determines both the mobilities of the analyte and degree of dissociation of substituted isomers. It is shown that the separations can be described by simple capillary electrophoresis theory. Modified CE methods using organic modifiers and micellar electrokinetic capillary chromatography (MECC) have been applied for improving the separation of components in the complex mixtures.
It was hoped the results of the separation of model components could be use to aid the separation of more complex materials such as humic acids. Some separation of whole humic acids was achieved with negative polarity and ammonium acetate buffer. The optimum separation of the humic acid digests was achieved using negative polarity at acidic buffer conditions (< pH 3).
As with the benzoic acid mixtures, the buffer p H had the greatest influence on the separation of the humic acid digests. The use of CTAB to enable MECC separations is shown to provide the best overall selectivity for the digests.
A commercial CE-MS interface has been implemented with some minor technical considerations impeding progress in this area. Preliminary results for the separation of a benzoic acid mixture and CE-MS of a humic acid digest demonstrate the value of the approach for the characterisation of these complex materials.