Electric field, separations based electrophoresis

When a mixture of solutes is placed in an electrical field, the positively charged species are attracted to the anode and the negatively charged ones to the cathode. The separation of charged species based on their specific migration rates in an electrical field is termed electrophoresis. 

The motion of electrically charged particles or molecules in a stationary medium under the influence of an electric field is called electrophoresis. In such transport the electric force is applied through a potential difference between electrodes. Selective use of the Lorentz force by applying a magnetic field can also induce such movement. Electrophoresis and electroosmosis are two key modaUties of electrokinetic transport which are very useful in micro- and nanofluidics for a variety of apphcations including biomedical (bio-NEMS, etc.), fuel cell, and micro total analysis systems (/r-TASs). In electroosmosis the bulk fluid moves due to the existence of a charged double layer at the solid-hquid interface. While one-dimensional electrophoresis is more commonly used, two-dimensional electrophoresis may also become a useful tool for the separation of gel proteins based on isoelectric property. 

Electrophoresis is used primarily to analyze mix tures of peptides and proteins rather than individual ammo acids but analogous principles apply Because they incorporate different numbers of ammo acids and because their side chains are different two pep tides will have slightly different acid-base properties and slightly different net charges at a particular pH Thus their mobilities m an electric field will be differ ent and electrophoresis can be used to separate them The medium used to separate peptides and proteins is typically a polyacrylamide gel leading to the term gel electrophoresis for this technique... 

Jorgenson reported the use of glass capillaries for free solution electrophoresis 25 years ago (Jorgenson andLukacs, 1981,1983). Aplug of analyte was introduced into a buffer-filled capillary and separated at high electric fields. Capillaries of 75 im inner diameter were employed, and detection of labeled amino acids and peptides was based on fluorescence. 

Separation by capillary electrophoresis is based on the differences in electrophoretic motilities in a solution of charged species in an electric field of small capillaries. Its... 

Capillary electrophoresis systems are also likely to play an increasingly prominent analytical role in the QC laboratory (Figure 7.2). As with other forms of electrophoresis, separation is based upon different rates of protein migration upon application of an electric field. 

Electrophoresis is a separation technique that is based on the differential migration of charged compounds in a semi-conductive medium under the influence of an electric field. Its origin can be traced back to the 1880s however, it got major recognition in 1937, when Arne... 

Separation by electrophoresis is based on differences in solute velocity in an electric field. The velocity of an ion is given by... 

A variety of microscale separation methods, performed in capillary format, employ a pool of techniqnes based on the differential migration velocities of analytes under the action of an electric field, which is referred to as capillary electromigration techniques. These separation techniques may depend on electrophoresis, the transport of charged species through a medium by an applied electric field, or may rely on electrically driven mobile phases to provide a true chromatographic separation system. Therefore, the electric field may either cause the separation mechanism or just promote the flow of a solution throughout the capillary tube, in which the separation takes place, or both. 

Electromigration methods compose a family of analytical separation methods based on differences in the mobilities of charged analytes in the electric field. In this chapter, we discuss mainly such electromigration methods that are performed in thin capillaries with inner diameter (i.d.) <0.1 mm. These methods are commonly known as capillary electrophoretic methods where the most important modes are capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MEKC), capillary gel electrophoresis (CGE), and capillary electrochromatography (CEC). 

Electrophoresis is another separation process that, however, is based on the mobility of ions in an electric field. The different modes of modern capillary electrophoresis with its different separation mechanisms have paid more and more attention during the last decade. 

The acid-base properties, and hence ionic character, of peptides and proteins also can be used to achieve separations. Ion-exchange chromatography, similar to that described for amino acids (Section 25-4C), is an important separation method. Another method based on acid-base character and molecular size depends on differential rates of migration of the ionized forms of a protein in an electric field (electrophoresis). Proteins, like amino acids, have isoelectric points, which are the pH values at which the molecules have no net charge. At all other pH values there will be some degree of net ionic charge. Because different proteins have different ionic properties, they frequently can be separated by electrophoresis in buffered solutions. Another method, which is used for the separation and purification of enzymes, is affinity chromatography, which was described briefly in Section 9-2B. 

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