Methods for the analysis of surfactants and proteins by Capillary
Electrophoresis (CE) were investigated. Several modifications of the system to
achieve detection and separation of these analytes were examined. These
modifications included buffer additives, sample additives and surface treatment
and modification of the fused silica capillary.
For the analysis of anionic surfactants, the addition of an anionic IN
absorbing compound to the buffer was investigated to achieve indirect detection
of the non-absorbing surfactants. The effect on detection sensitivity and
separation efficiency of the absorbing ion was examined. These parameters were
affected by differences in the electrophoretic mobilities of the analytes in
comparison to the absorbing ion. The use of organic modifiers was also
investigated to minimize micelle formation of the surfactants which leads to
zone spreading.
For the analysis of serum and urine proteins, the use of high pH buffers
was investigated to minimize solute/capillary surface interactions and achieve
separation. At high pH's the proteins are negatively charged; therefore, they
should be repelled by the negatively charged fused silica surface. To improve
reproducibility of migration times of the proteins the addition of polyvinyl
alcohol to the sample was also investigated. The polyvinyl alcohol improved
reproducibility by reversibly covering the active sites on the capillary surface to
minimize protein interactions. Migration time reproducibility was also improved
by optimizing the capillary cleaning procedure. Lastly, the addition of methyl
cellulose to the buffer to work as a dynamic molecular sieving medium was
investigated to improve resolution.
Analyte/ capillary surface interactions are a major limitation in CE
especially for the analyses of proteins. The use of coated capillaries to eliminate
these interactions has been widely investigated. However, reproducibility and
degree of surface deactivation with these coating can be poor. In this work
hydrothennal treatment of the fused silica capillary surface prior to deactivation
was examined. Hydrothennal treatment was used to produce a homogenous
surface prior to coating which leads to the production of more highly
deactivated, reproducible columns. The effects of the treatment were studied by
coating the surface with a silane and examining the influence of the coating on
electroosmotic flow and analyte adsorption.
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