Electro-osmosis mobility

Electroosmotic flow in a capillary also makes it possible to analyze both cations and anions in the same sample. The only requirement is that the electroosmotic flow downstream is of a greater magnitude than electrophoresis of the oppositely charged ions upstream. Electro osmosis is the preferred method of generating flow in the capillary, because the variation in the flow profile occurs within a fraction of Kr from the wall (49). When electro osmosis is used for sample injection, differing amounts of analyte can be found between the sample in the capillary and the uninjected sample, because of different electrophoretic mobilities of analytes (50). Two other methods of generating flow are with gravity or with a pump. 

The molecular simulations also showed that electro-osmosis is also observed in aqueous electrolyte solutions, as long as the external electric field is reversed periodically to prevent the ions from accumulating near the membrane. An example of this is shown in Fig. 10, which shows the effect of an electric field on a 4.67 mole percent aqueous LiCl solution at 25°C. It is quite clear that the mobility of the solvent molecules increases as a result of... 

Lasagna uses electro-osmosis to mobilize contaminants into installed in situ treatment zones where contaminants are removed by adsorption, immobilization, or degradation. The technology is currently undergoing field demonstrations and is not yet commercially available. It will be marketed by Envirogen, a subsidiary of Monsanto Company. 

Electric sector, 295 Electrochromatography, 119 Electrode potential, 348 Electromagnetic separator, 294 Electromigration, 114, 117 Electron capture detector, 36 Electron ionisation, 307 Electro-osmosis, 115 Electro-osmotic flow, 114 Electrophoregram, 113 Electrophoretic mobility, 114 Electrospray, 312 ELISA, 336... 

Electro-osmosis, in which an electric field is applied causing mobile liquid to move relative to a stationary charged surface (Figure 4.5). 

To characterize a surface electrokinetically involves the measurement of one of the above electrokinetic effects. With disperse colloidal systems it is practical to measure the particle electrophoretic mobility (induced particle velocity per unit applied electric field strength). However, for a nondisperse system one must measure either an induced streaming potential or an electro-osmosis fluid flow about the surface. 

The basic experimental approach when using electro-osmosis to characterize surfaces is to measure fluid mobility at a surface when electro-osmosis is in-... 

FIG. 3 Apparent panicle mobility in 7.5 mM NaCI of a sulfated polystyrene latex particle across the diameter of a closed quart/, cylindrical chamber. Profiles are associated with varying degrees of electro-osmosis at pH 2 (O). pH 6 ( ). and pH 11... 

Electro-osmosis at a sample plate wall can then be taken from a single particle mobility measurement. 

Though the model presented and used does not give a complete account of the interface and the origin of measured electro-osmotic fluid mobility, it was proven useful in interpretation of surface properties. The range of electrolyte concentration that can be used in the manual particle electrophoresis chamber developed in this work is limited, and this limits the model of the origin of electro-osmosis that can be tested, such as inclusion of a Stern layer. 

Electro-osmosis If we have a fixed surface (i.e., a capillary wall or a porous plug) in an electrolyte solution and apply an electric field, E, the mobile part of the diffuse layer will move as shown in Figure... 

Figure 4.6. Electro-osmosis In a plug, contained In a capillary between two walls Wj and Wj. The applied electric field exerts a force to the left on the mobile positive charges In the liquid, leading to a liquid flow In that direction. For simplicity the countercheu ge Is only represented by plus signs.

Table 4.2. Electrokinetic potentials of negative polystyrene latex particles obtained from electro-osmosis, electrophoresis and conductivity. In the conversion of mobilities surface conduction behind the slip plane was ignored. (Data from A.G. van der Put, PhD. thesis. Agricultural University Wagenlngen. NL (1980) as elaborated by O Brlen, J. CoOoid Interface Set 110 (1986) 477.)...

Another class of "difflcult" particles Involves systems which are porous. Then they may no longer be classified as dielectric. Ion transport and electro-osmosis may then take place inside the particles. Miller et al. ) found theoretically that porosity tends to increase or decrease the mobility for high and low respectively. Such studies may also be Interesting for the Interpretation of the electrophoresis of aggregates of particles. 

It is best to match the mobility of the reagent to the average mobilities of the solutes to minimize electrodispersion, which causes band broadening [7]. When anions are determined, a cationic surfactant is added to the BGE to slow or even reverse the electro-osmotic flow (EOF). When the EOF is reversed, both electrophoresis and electro-osmosis move in the same direction. Anion separations are performed using reversed polarity. 

Using SI units, the velocity of the electro-osmotic flow is expressed in meters per second (m/s) and the electric field in volts per meter (V/m). Consequently, in analogy to the electrophoretic mobility, the electro-osmotic mobility has the dimension square meters per volt per second. Because electro-osmotic and electrophoretic mobilities are converse manifestations of the same underlying phenomenon, the Hehnholtz-von Smoluchowski equation applies to electro-osmosis as well as to electrophoresis. In fact, when an electric field is applied to an ion, this moves relative to the electrolyte solution, whereas in the case of electro-osmosis, it is the mobile diffuse layer that moves under an appUed electric field, carrying the electrolyte solution with it. 

During analyte migration, electrophoresis and electro-osmosis are taking place. The velocity cm/s) and mobility ( c, cm /V s) of the solute are defined by the following equations ... 

Choosing an internal standard to correct errors due to sample preparation and injection reduced the impact of variability on the final trueness and precision of the developed method. Peak area can be corrected (peak area/migration time) to avoid the migration time drift influence, because of the temperature affecting both electro-osmosis and electrophoretic mobilities as well as buffer electrolysis, adsorption into the capillary wall and so on. 

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