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Dialytic methods for sample treatment in ion chromatography


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Laksana, S 1993 , 'Dialytic methods for sample treatment in ion chromatography', PhD thesis, University of Tasmania.

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This thesis presents the results of a systematic study of the parameters affecting
dialysis procedures, including active (Donnan) dialysis and electrodialysis, for the
pretreatment of alkaline samples prior to ion chromatographic analysis. A
preliminary study of enrichment of inorganic anions using an "Elutrap" apparatus is
also presented. Dialysis methods were investigated with a view to applying
membrane-based clean-up procedures to the determination of trace levels of
inorganic anions in various samples following sample treatment by hydroxide fusion.
Donnan dialysis was carried out by passing sodium hydroxide solutions containing
inorganic anions through a cation-exchange hollow fibre immersed in a hydrogen ion
donating medium. As the sample is passed through the lumen of the fibre, a dialysis
reaction involving exchange of sodium ions in the sample with hydrogen ions from
the surrounding medium occurs, resulting in total or partial neutralization of the
sample. Several acid solutions including slurries of cation-exchange resins were
evaluated on the basis of neutralization efficiency and penetration of the acid anion
through the membrane. Cation-exchange resins in the hydrogen form slurried with
0.1 M octanesulfonic acid gave optimal performance and when the resin was stirred
occasionally the total theoretical neutralization capacity of the resin was achieved. The use of an "Elutrap" apparatus was shown in this study to be impractical for
sample clean-up and enrichment of anions. However, factors affecting the migration
rate of inorganic anions under applied DC potential have been elucidated. An
electrodialysis process, which uses an electrical field to stimulate the migration of
ions through the membrane, was studied for off-line neutralization of strongly
alkaline samples. This method utilizes an electrodialysis cell comprising three
compartments separated from each other by cation-exchange membranes.
Experimental parameters, such as the magnitude of the applied current or power, the type of cation-exchange membrane used and the design of the cell were studied.
Under optimal conditions, recoveries of solute anions (Cl -, Br, NO3-, HPO42- and
SO42- in the range 3-10 lig/m1) from 1 M NaOH solution were close to quantitative
except for fluoride and nitrite. It is suggested that low recoveries for these ions were
due to the formation of neutral, protonated species within the membrane with
subsequent loss by diffusion.
A flow-through electrodialysis device, in which the sample was allowed to flow
during the dialysis process, was studied for the on-line pretreatment of strongly
alkaline solutions. Variations of the shape of the sample compartments and the size
of the electrodes were studied in order to optimize the flow-through cell design and
to minimize the heat generated inside the cell. Quantitative recovery for fluoride ion
could be achieved using a Neosepta CMS cation-exchange membrane and the ability
to successfully treat samples containing fluoride represented an improvement over
the off-line cell.
The on-line electrodialysis method has been successfully applied to the
determination of inorganic anions in vegetation samples obtained from the vicinity
of an aluminium smelter, following sample preparation by hydroxide fusion. This
work demonstrated that when correctly applied, the method could be used on
different sample types which have been traditionally difficult to analyse by ion

Item Type: Thesis - PhD
Authors/Creators:Laksana, S
Keywords: Ion-permeable membranes, Ion exchange chromatography, Dialysis
Copyright Holders: The Author
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Copyright 1993 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).

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Thesis (Ph.D.)--University of Tasmania, 1994

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