Electrophoresis counter current

This last point needs some elaboration. Consider in Figure 7.1.29(c), any one of tbe two ports used to withdraw two different protein products continuously. If we bave three proteins present in the feed stream, then let the liquid coming to one of the ports be pure in one protein it is clear that the liquid passing over the other port will have two other proteins therefore the liquid stream withdrawn from this port cannot be pure in one protein. This is an inherent limitation of processes where the bulk flow is parallel to the direction of the force. Here, even though we have one force perpendicular to the bulk flow, in the presence of the electrical force parallel to bulk flow, the system in continuous operation is just like the counter-current electrophoresis of Figure 6.3.4 and equations (6.3.9a,b). However, in a hatch mode, one can have multi-component separation since each species will be focused to its own zone and therefore can be withdrawn at a later time. Multicomponent separation in electrochromatography needs a different flow vs. force configuration, to he discussed further in Section 8.2. 

More recently, Wolfrom and coworkers have obtained a heparin preparation (by fractionation of the neutral barium salt) which appeared to be homogeneous in both electrophoresis and counter-current distribution studies. Consequently, it would seem that this material is the best available for structural studies. 

Over the last 20 years, separation technology for analytical testing in the pharmaceutical industry has undergone great advances. This progress was motivated by the need for better quality products, the desire for improved knowledge in product development, and, in part, regulatory requirements. Separation techniques such as TLC, HPLC, GC, LC, counter current extraction (CCE), and capillary electrophoresis (CE) are extensively employed in preformulation studies. 

The Separation of Some enantiomers by Counter Current Capillary Electrophoresis... 

The Separation of the Enantiomers of Glutamic Acid by Counter Current Capillary Electrophoresis Courtesy of LC-GC. (Ref. 21)... 

To separate the various tRNAs, numerous methods—including chromatography (on resins, silicic acid, hydroxyapatite, Sephadex, etc.), electrophoresis, and counter current—have been devised. An interesting procedure consists of treating the amino acid-charged RNA with either periodate or converting the... 

The homogeneity of heparin has been studied by electrophoresis and counter-current distribution. Electrophoretic migration values of 8 to 24 i0 cm /sec volt have been reported, depending on the d ee of sulfation and the conditions of the experiment. The molecular weight of various preparations lies between 15,000 and 20,000, consequently higher than those observed for heparan sulfate. Heparin has the lowest intrinsic viscosity of all the glycosaminoglycuronoglycans. 

Electric fields have been used to clean membranes and to try to prevent the depo on of charged particles onto a membrane surfiice by means of electrophoresis [Bowen Sabani, 1992 Wakeman and Tarleton, 1987]. Tubular metal ndcrofiltnitian membranes are particularly suited for this application a thin metal counter-electrode positioned centrally provides acceptable current distribution. A DC elecbic field is applied to provide a current d sity of 100-200 mA cmT near to the membrane sur ce. Use of a DC field creates gas bubbles at the membrane sui ce that leads to removal of the attached particles [Fairey Microfiltrex, undated]. The membrane is the cathode to prevent oxidation at the membrane sur ce causing chemical attack of the metal. 

It is important to point out that the sample components conduct the current. There is no background electrolyte (unlike zone electrophoresis Fig. 1), which means that each zone contains only the sample component and the counter ion. 

A. In the frame of Von Smoluchowski s treatment of electrophoresis deviations may result from the surface conductance of the particle In this case the electric current is concentrated in the neighbourhood of the particle In order to prevent an accumulation of electricity at the limits between the highly conducting surface layer and the weakly conducting bulk of the liquid, a counter E M F is generated and the electrophoretic velocity is decreased. 

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