Electrophoretic mobility profiles

Figure 13.10. Changes in the electrophoretic mobility profile with 0.3% methylcellulose in the 25 mM carbonate buffer pH 9.3 (CGE) versus profile without methylcellulose (CZE).

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. 

Fig. 3. Agarose gel after electrophoretic separation of amplified DNA of Chlamydia trachomatis without (A), and with the addition of Ce-AR (B) in the electrophoretic system at exposure by transilluminator at 254 nm for 5 (1), 30 (2), 300 (3) and 600 (4) seconds, and profiles of the electrophoretic mobility (C).

Overbeek and Booth [284] have extended the Henry model to include the effects of double-layer distortion by the relaxation effect. Since the double-layer charge is opposite to the particle charge, the fluid in the layer tends to move in the direction opposite to the particle. This distorts the symmetry of the flow and concentration profiles around the particle. Diffusion and electrical conductance tend to restore this symmetry however, it takes time for this to occur. This is known as the relaxation effect. The relaxation effect is not significant for zeta-potentials of less than 25 mV i.e., the Overbeek and Booth equations reduce to the Henry equation for zeta-potentials less than 25 mV [284]. For an electrophoretic mobility of approximately 10 X 10 " cm A -sec, the corresponding zeta potential is 20 mV at 25°C. Mobilities of up to 20 X 10 " cmW-s, i.e., zeta-potentials of 40 mV, are not uncommon for proteins at temperatures of 20-30°C, and thus relaxation may be important for some proteins. 

In CZE, proteins are separated from each other based on the differences in their electrophoretic mobilities. The electrophoretic mobility is a function of the molecular charge and hydrodynamic size of a protein. In a given environment, the electrophoretic mobility is an intrinsic property of the protein, similar to the isoelectric point. Therefore, the mobility can be used to distinguish proteins from each other. This is the basis for using CZE as a simple identity test for final product and package labeling. As an example, the CZE profiles of six... 

FIG. 12.12 Electrophoresis patterns for human serum (a) schematic of schlieren profiles and (b) semilog plot of protein molecular weight versus electrophoretic mobility for particles electro-phoresed on cross-linked polyacrylamide. (Reprinted with permission from K. Weber and M. Osborn, J. Biol. Chem., 244, 4404 (1969).)... 

Electrodriven separations, such as capillary electrophoresis (CE) and capillary electrochromatography (CEC), are based on the different electrophoretic mobilities in an electric field of the molecules to be separated. They provide a higher separation efficiency then conventional HPLC since the electrophoretic flow (EOF) has a plug-flow profile. Whereas the mobile phase in CE is driven only by the electro-osmotic flow, it is generated in CEC by a combination of EOF and pressure. CEC has a high sample capacity which favours its hyphenation with NMR. 

Figure 3 shows typical pH-dependent particle mobility profiles across the diameter of a closed cylindrical chamber for a negatively charged particle and chamber surface. In the closed cell, fluid flow at the surface is compensated by a return How dowm the center of the cell, resulting in a parabolic distribution of particle velocities. Particle velocity at a given location is the sum of the intrinsic electrophoretically induced particle velocity and fluid velocity. 

It has now been shown that the majority, if not all, of the strains of Ps. aeruginosa produce a basal level of /3-lactamase which is inducible in the presence of penicillins and cephalosporins [182], The majority of Pseudomonas strains tested produce between 0.002-0.006 International Units of enzyme/mg protein (with cephaloridine as substrate) which can be induced over 100-fold [122,183]. The basal and inducible enzymes are indistinguishable on the basis of substrate profile and electrophoretic mobility [184]. Table 7.6 shows the substrate profile of the inducible /3-lactamase. The enzyme shows greater affinity for cephaloridine than for... 

The parabola method makes it possible to measure the potential of cell walls. Usually, the cell is made of quartz, and the parabola method thus offers the possibility of determining the lEP of one material that has already been extensively studied. The potentials of macroscopic specimens of other materials can also be determined from the mobility profile [273-275] by replacement of the original cell wall of a commercial electrophoretic cell by a flat specimen of the material of interest. For example, in [276], the lEP of a basal plane of mica found from the mobility profile was different from the lEP of a mica dispersion. Only a few types of electrophoretic devices (most of which are no longer available on the market) can be used to determine potentials by means of electro-osmosis. 

The adsorption process can more likely be attributed to electrostatic interaction. In fact, the increase in temperature raises the surface charge density on the thermally sensitive particle, as evidenced by electrophoretic mobility vs. temperature. In addition, the amount of water is at least close to 30% above the volume phase transition temperature. This adsorption profile (reduced adsorbed amount vs. temperature, as reported in Figure 12.22) is generally observed when the adsorption temperature is well controlled in the case of attractive electrostatic interactions and only the plateau is drastically affected by the pH, salinity, and surface charge density. 

The removal of neuraminyl residues from pure arylsulfohydrolase A by bacterial neuraminidase does not alter the specific activity, kinetic properties, and general stability but does change the elution profile through a DEAE-cellulose column (Fig. 1) and the electrophoretic mobility on a polyacrylamide gel (Graham and Roy, 1973 Farooqui and Srivastava, 1979). Das and Bishayee (1980) claimed that the treatment of partially purified sheep brain arylsulfohydrolase A with bacterial neuraminidase did not cause a... 

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