Liquid-Solid Electrophoretic Flow

Electroosmosis Liquid-liquid electroosmotic flow Liquid-solid electrophoretic flow... 

Key Research Findings Liquid-Solid Electrophoretic Flow... 

Electroosmosis refers to the movement of the liquid adjacent to a charged snrface, in contact with a polar liquid, under the influence of an electric field applied parallel to the solid-liquid interface. The bulk fluid of liquid originated by this electrokinetic process is termed electroosmotic flow. It may be prodnced either in open or in packed or in monolithic capillary columns, as well as in planar electrophoretic systems employing a variety of snpports, such as paper or hydrophilic polymers. The origin of electroosmosis is the electrical donble layer generated at the plane of share between the snrface of either the planar support or the inner wall of the capillary tube and the surronnding solntion, as a consequence of the nneven distribntion of ions within the solid/liquid interface. 

When the solid phase is fixed (e.g., as a capillary, membrane, or porous plug), an electric field induces a flow of liquid termed electro-osmosis. The character of the flow depends on the construction of the apparatus. For example, in an electrophoretic cell, the liquid flows in one direction near the walls and in the opposite direction in the center of the cell, and the net flow across the cell cross-section is zero (Figure 2.2). Electro-osmosis can also be demonstrated as a difference in pressure (height of a water column) generated as a result of an electric field applied to a capillary, membrane, or porous plug. 

Besides equilibria in the liquid phase (proteolytic, complex forming, etc.) that influence directly the values of effective mobilities of compounds to be separated, it is necessary to also establish, in the electrophoretic system, equilibria between the liquid and solid phase. In electrophoretic techniques which use solid stabilizing media adsorption of solutes on the sorbent surface is the main consideration. In capillary methods, and with colloid particles, similar effects have also to be considered (the surface of the solid phase that is in contact with the liquid phase is, with respect to the volume of the liquid, rather large). In both these latter cases the interaction between the solid and liquid phases participates in the formation of the electric double layer that conditions the electro-osmotic flow, and attributes the electric charge to colloid particles. 

Oddy and Santiago used micro-PIV techniques to study small particles in AC and DC electro-osmotic flow [10]. Independent measurements of the particle motion in the two fields can be correlated to determine the electrophoretic mobility of the particle and electro-osmotic mobility of the solid-liquid interface. The electrophoretic mobility of the fluorescent polystyrene particles was found to be —3.76 ib 0.05 pm cm/Vs and the zeta potential of the glass/water interface for a pH of 7 was — 115 zb 10 mV. 

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