Electrokinetic separations involving surfactants and proteins

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Virginia Tech


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.