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Electrokinetics: Understanding Electroosmosis and Electrophoresis

Explore the principles of electrokinetics, including electroosmosis and electrophoresis. Learn how electric double layers form and how they can be used to move fluids. Understand the factors that influence electrophoresis and the importance of the medium and buffer solution.

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Electrokinetics: Understanding Electroosmosis and Electrophoresis

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  1. Electrokinetics By Dan Janiak and Mark Hanna September 15 2003

  2. Electrokinetics • Electroosmosis- Mark • Electrophoresis- Dan

  3. Electric Double Layer Solid Liquid • These layers form automatically when an electric field is applied to the system • The attraction between + and – can be used to move the fluid along the channel

  4. Electroosmosis • Negative charges evenly distributed on liquid/solid interface driven by E field • Positive ions attracted to moving negative ions, are pulled along dragging the liquid with them

  5. Electroosmotic Flow Profile • Relatively uniform flow profile compared to pressure driven flow

  6. Flow Profiles Compared • Pressure driven flow is not uniform due to indirect driving force • Electroosmotic driven flow is more uniform due to a direct driving force on each atom

  7. + Generated naturally when a potential field is applied Flow can be controlled with voltage adjustments Flat, symmetrical flow profile - Sensitive to solution and surface chemistry Requires homogenous fluid and constant surface conditions Flow needs to be monitored so it is possible to account for these changes Electroosmosis + and -

  8. In the presence of an electric field, molecules in a solution will move. Medium Basics of Electrophoresis - + Cathode Anode

  9. Factors influencing electrophoresis Electrophoresis, the Basics D.M. Hawcroft

  10. Molecular Structure • Size • Shape • Charges • Distribution Electrophoresis + + + + + + + - - - + + 2 - - - 1 - - 3 - - - 4 + + - - - + - - + - - + + - - - + + - + + - + + + - + -

  11. Medium Properties of the medium and buffer solution Sample molecules must be solvated, ionized. Concentration and pH play a large role in electrophoresis. Paper Cellulose acetate Gels

  12. Movement of molecules E * Q E = Strength of applied electric field Q = Molecular charge Molecules with greater charge densities move faster and farther than ones with smaller charge densities Molecules move toward electrodes of opposite polarity Electrophoretic mobility  = V / E

  13. Restriction of Movement Size Shape ( Rod, Elliptical, Cone) Entanglements Viscosity Movement of molecules (cont’d) Nature of buffer solution and sample ions Support medium Temperature

  14. Summary Electrokinetics Electroosmosis (Surface Interaction) Electrophoresis (Separation) Processes occur simultaneously

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