Lecture4 - Electrophoresis in practice Gel electrophoresis...

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1 Physical Chemistry Lecture 4 Electrophoresis and light scattering Motion of charged particles In an electric field E a charged particle ( Ze ) moves, the force being proportional to the electric field (for an isotropic medium) The movement is resisted by the viscous drag of the fluid Drag force is proportional to the speed At steady state, the molecule moves with a speed determined by the balance of the drag and electric forces E f Ze v F F state steady At v f F ZeE F ss viscous electric viscous electric Electrophoretic mobility The proportionality coefficient, , between steady-state speed and electric field is the electrophoretic mobility Assumption of a spherical particle of radius r gives an equation for Friction coefficient from Stokes-Einstein theory Depends on charge on particle Depends on “size” of particle Depends on viscosity of the medium Difficult to make quantitative Ionic environment Reduction of ef ective charge by bond ions Reduction of electric field by local ions that also contribute to the electric field Viscous ef ect of oppositely charged particles movement in the opposite direction in the field – electrophoretic ef ect Effects of shape Used as a semiquantitative tool Mobility is directly proportional to Z Mobility is inversely proportional to the friction coefficient E f Ze E v r Ze  6 Electrophoresis in practice Gel electrophoresis Uses an acrylamide or agarose gel Apply electric field for a given time After electrophoresis, the gel is visualized with a stain Various dyes can be added Fluorescent molecules can be
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This note was uploaded on 02/02/2012 for the course CHEM 419 taught by Professor Staff during the Fall '10 term at University of Delaware.

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Lecture4 - Electrophoresis in practice Gel electrophoresis...

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