By Dan Janiak and Mark Hanna September

Electrokinetics Electroosmosis- Mark Electrophoresis- Dan

Electric Double Layer 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 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 Solid Liquid

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 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

Electroosmotic Flow Profile Relatively uniform flow profile compared to pressure driven flow

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 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

Electroosmosis + and - + Generated naturally when a potential field is applied Flow can be controlled with voltage adjustments Flat, symmetrical flow profile + 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 - 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

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

Factors influencing electrophoresis Promoting FactorsRetarding FactorsPotentially either VoltagePhysical resistancepH CurrentViscosityBuffer ions High surface chargeInteractionsBuffer additives Low massLow surface chargeBuffer concentration Molecular dissociation High mass Molecular association Non-spherical shape Electrophoresis, the Basics D.M. Hawcroft

Electrophoresis Molecular Structure Size Shape Charges Distribution

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

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  = V / E

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

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