Capillary Electrophoresis Capillary Electrophoresis Capillary electrophoresis (CE), also known as capillary zone electrophoresis (CZE), can be used to separate ionic species by their charge and frictional forces and hydrodynamic radius. In traditional electrophoresis, electrically charged analytes move in a conductive liquid medium under the influence of an electric field. Introduced in the 1960s, the technique of capillary electrophoresis (CE) was designed to separate species based on their size to charge ratio in the interior of a small capillary filled with an electrolyte. What is Capillary Electrophoresis? Capillary electrophoresis is an analytical separation technique of electrophoresis. The capillary electrophoresis is a high resolution separation technique. The separation of ions is based on the electrophoretic mobility of ions under an applied voltage. The mobility or the migration of ions depends on some factors which include charge of the ion, the viscosity, and the size of atom or its radius. The rate of migration of particles is proportional to the applied electric field. So the mobility of ions increases with increasing the strength of field.
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Only the ions migrate while the neutral species remains unaffected. The smaller ions have high migration rate due to their smaller size and so they move with less friction. The capillary electrophoresis is good and widely used due to the following advantage. 1. Theory of capillary electrophoresis The electrophoresis involves the migration of ions and the opposite charged ions are attracted towards to the oppositely charged electrodes. Thus the movement of oppositely charged ions towards electrodes is the basic phenomena of capillary electrophoresis techniques. 2. Electrophoretic mobility The ions are moved in the applied electric field. The mobility depends on the viscosity and the applied field. The ions feel a force under applied field which is equal to the product of net charge and the applied electric field strength. So the electrophoretic mobility is equal to µEP = q / f = q / (6πηr) where, q denotes the net charge and f is the force which is equal to 6πηr. The force is given by stock law for spherical particle where η and r stands for viscosity of the solvent and the radius of the atom respectively. The velocity of ion v = (µEP x E) where, E stands for the magnitude of applied electric field. The attraction of ions increases with increasing the strength of applied field because their velocity is increased. 3. Electroosmotic flow (EOF)
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The CE is used to separate the compounds contain similar structure. The separation is done successfully due to the EOF. The solution starts to move towards cathode as the field is applied across contains an electrolyte solution. This is due to high voltage. As the buffer solution initiates the migration through the silica capillary, the capillary wall becomes negatively charged due to loss of proton from the SiOH groups and the formation of SiO- ions. Thus the cation attracts towards the capillary wall and there is double layer of cation formed on the wall. One is stationary and other is diffuse layer. The inner stationary layer is not free to move like the outer diffusion layer which can move along the capillary. Thus the electro osmotic flow rate is shown by the below mentioned equation;
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