Electrokinetic separations considerations

Theoretical Considerations in Electrokinetic Separations. Models have been proposed for electrophoretic (52) and electrochromatographic systems. Similar to developments in chromatography, we may write a model equation for these systems ... 

Capillary electrochromatography (CEC) is a rapidly emerging technique that adds a new dimension to current separation science. The major "news" in this method is that the hydrodynamic flow of the eluting liquid, which is typical of HPLC, is replaced by a flow driven by electro-endoosmosis. This increases considerably the selection of available separation mechanisms. For example, combinations of traditional processes such as reversed-phase- or ion-exchange- separations with electromigration techniques are now possible. Also, CEC is opening new horizons in the separation of non-polar compounds, and thus represents an alternative to the widely used micellar electrokinetic chromatography. 

Many more-sophisticated models have been put forth to describe electrokinetic phenomena at surfaces. Considerations have included distance of closest approach of counterions, conduction behind the shear plane, specific adsorption of electrolyte ions, variability of permittivity and viscosity in the electrical double layer, discreteness of charge on the surface, surface roughness, surface porosity, and surface-bound water [7], Perhaps the most commonly used model has been the Gouy-Chapman-Stem-Grahame model 8]. This model separates the counterion region into a compact, surface-bound Stern" layer, wherein potential decays linearly, and a diffuse region that obeys the Poisson-Boltzmann relation. 

A considerable number of CE separation methods exist for a wide variety of analytes. However, nitrosamines separation and determination by CE requires additional development for its practical use. " " For the separation of hydrophilic, low molecular weight, neutral, and polar compounds such as nitrosamines, it is necessary to develop CE techniques for enhancing the selectivity. The main reason is that these compounds do not interact strongly with the commonly used surfactants (e.g., sodium dodecyl sulfate, SDS) or other buffer modifiers such as cyclodextrins in electrokinetic chromatography. The separation depends on several factors which must be optimized to reach... 

ID Separation of Proteins There has been considerable research devoted to tbe development of nricioflu-idic platforms capable of performing small-scale protein separations. In addition to diffusion based methods [3], nearly every type of electrokineticaUy driven separation has been demonstrated in a cbip-based platform, including free-flow electrophoresis, capillary electrophoresis, capillary gel electrophoresis, isoelectric focusing (lEF), micellar electrokinetic chromatography and capillary electrochemical chromatography. 

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