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Separations of metal ions by capillary electrophoresis using complexation with metallochromic ligands

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Macka, Miroslav (1997) Separations of metal ions by capillary electrophoresis using complexation with metallochromic ligands. PhD thesis, University of Tasmania.

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Abstract

This work deals with separations of metal ions by capillary electrophoresis (CE) using
metallochromic ligands and with some related problems in separation and detection.
In the first part, some important instrumental factors relevant to CE of metal ions using
metallochromic ligands were investigated. The positioning of the separation capillary
relative to the electrode in the electrolyte vial and buffering of the background
electrolyte (BGE) in CE have been found to have a crucial influence on the magnitude
of pH changes of the BGE in the capillary. On-capillary measurement of the pH
changes accomplished by the addition of a suitable pH indicator dye to the BGE and
employing absorbance detection in the visible region showed that pH changes of
more than 2.5 pH units occurred when the capillary end was positioned close to the
electrode surface. This effect was explained by direct observations of pH changes
around a platinum electrode placed in a photometric cell serving as a BGE reservoir
which showed a zone of altered pH being generated close to the electrode and
spreading over time through the surrounding BGE by thermal convection. Light
emitting diodes (LEDs) in the range from 563 to 654 nm were examined as light
sources for on-capillary detection in CE. The detector linearity and noise for the LEDs
were compared to mercury and tungsten lamps used with interference filters. Both a
theoretical model, taking into account both stray light and polychromatic light, and
experimental results showed stray light as the major factor which determines linearity
under typical CE operating conditions. Noise was found to be same or better for the
LEDs as for the other sources. In the second part, several factors concerning chemistry of separations of metal ions
by CE were studied. Methods for analysis of metallochromic ligands by CE and
micellar electrokinetic capillary chromatography were developed using an uncoated
fused silica capillary and an alkaline BGE containing a zwitterionic additive and a
strong complexing agent (EDTA) which was crucial for obtaining good peak shapes.
Further, it was shown that ligand purity can play a crucial role in the separations of
metal ions by CE in the form of kinetically labile complexes using addition of the ligand
to the BGE. Using separation of uranium(VI) and lanthanides with arsenazo III as a
model system, solute-wall interactions were studied and found to vary for a number of
capillary wall chemistries. Least analyte adsorption was observed in an untreated
bare fused silica pre-run coated with a hydrophilic polymer, whilst the frequently used
hydroxide treated capillary exhibited greatest adsorption. The applicability of polymer
capillaries (polypropylene and polytetrafluoroethylene) for CE of metal ions/complexes
was also investigated. Complexation equilibria in the BGE were studied and the
secondary ligand type, pH and concentrations of secondary ligand and arsenazo Ill
were found to have a strong influence on the peak shapes and on the selectivity and
sensitivity. Mechanisms for these effects are discussed. A validated method is
presented for determination of Ba" and Sr" in the presence of up to 40,000 fold excess
levels of calcium(II) and magnesium(II) using an electrolyte containing sulfonazo Ill,
with a limit of detection of approx. 50 ppb for both metals. Analytical potential of the
general approach of using metallochromic ligands in CE is discussed.

Item Type: Thesis (PhD)
Keywords: Capillary electrophoresis, Ligands
Copyright Holders: The Author
Copyright Information:

Copyright 1997 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1998. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:38
Last Modified: 21 Jul 2017 06:30
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