# Essay Example on Basic Principles and Modes of Capillary Electrophoresis

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From Clinical and Forensic Applications of Capillary Electrophoresis 2 Basic Principles and Modes of Capillary Electrophoresis Harry Whatley 1 BASIC PRINCIPLES OF CAPILLARY ELECTROPHORESIS 1 1 Fundamentals of Electrophoresis Capillary electrophoresis CE is a special technique that uses an electrical field in order to separate the components present in a mixture Electrophoresis in a capillary can be differentiated from other types of electrophoresis that it is done within the walls of a narrow tube To understand the functioning of molecules influenced by an electrical field inside a capillary it is important to know the phenomena that result from the geometry of a capillary 1 1 1 Basic Principles It has long been well known that molecules can possess positive or negative electrical charge When the quantity of negative and positive charges are equal the charges will cancel creating an uncharged neutral molecule If allowed to move charged particles will go for regions like an electrode having an opposite charge which means that opposites will attract Figure 1 demonstrates an electrophoresis example In this example mixture of ions is dissolved in such a suitable solvent like water Before applying an electrical field these ions are in a random motion state When the electrical field is applied charged species start moving A separation happens leading to a less random distribution of particles Cations positive ions move toward the cathode electrode of negative charge and anions negative ions move toward the anode electrode of positive charge Figure 1 also shows another point of electrophoresis in solution the effect of the mass charge ratio m z In figure 1 there are four types of ions large and small of positive charge and large and small of negative charge If each of the particles has only one single charge then will be the same absolute value of the force on each of the particles

The acceleration created by this force can be calculated by the equation Force acceleration mass F ma The separation medium viscosity opposes the acceleration with the result that a steady velocity is reached under constant conditions This means that the system is only able to separate particles of opposite charges but is also able to separate particles having the same charge when there are other differences between them The electrophoresis science is concerned with the creation of systems that utilize the differences between the molecules Antother way is that the analyst tries to make a system that creates differences between molecules Changing the pH of the separation method is an example At pH 10 0 acetic acid and glycine will have the same charge 1 At pH 7 0 glycine will have a very small net charge while acetic acid will have a charge of 1 Separation of these two molecules would differ at pH 7 0 and at pH 10 0 Many other factors other than pH affect the separations of electrophoretic These include the hydrodynamic radius of the molecules the temperature and the separation medium viscosity In real systems there are other forces in addition to the electrical field affecting the charged molecules e g the entire fluid mass may be moving relative to the vessel in which it is contained Some of these factors can affect the electrophoresis in a very complex manner for example the movement of current through a liquid can elevate the liquid temperature This temperature change can affect the electrical resistance of the system ie the current the viscosity and the velocity of the molecules moving in the field

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