ELECTROPHORESIS. APPLICATIONS IN MEDICINE

Electrophoresis is

The motion of the dispersed phase relative to the fluid caused by an external electric field

Electrophoretic mobility is

The ratio between the terminal velocity of the dispersed phase and the electric field strength

The forces acting on the moving particle are

Electric force and the drag forc

When the forces acting on the moving particle are balanced

The particle moves with constant velocity

The electric driving force depends on

The amount of charge of the particle and on the strength of the external electric field

The drag force depends on the

Velocity of the particles

The electrophoretic mobility is determined

Experimentally from measurements of particle velocity and electric field strength

If the dispersion pH changes

The slipping plane does not move but the zeta potential changes

If the dispersion pH changes

The ionic strength and Debye length do not change but the density of the surface charge changes

If the dispersion pH changes

The density of the surface charge changes, the zeta-potential changes, the electrophoretic mobility changes

Decreasing the density of the surface charge results in

Smaller value of the zeta-potential and smaller electrophoretic mobility

Isoelectric point is

The fluid pH value at which the electrophoretic mobility of the suspended particles vanishes

At the isoelectric point

Particles in external electric field do not move

Passing through the isoelectric point changes the sign of the

Surface charge of the particles, zeta-potential and electrophoretic mobility

If the ionic strength changes

The slipping plane does not move and the density of the surface charge does not change

If the ionic strength changes

The Debye screening length changes, the zeta-potential changes;

Increasing the ionic strength of a solution results in

Smaller Debye screening length and faster decay of the electrical potential away from the particle surface

Increasing the ionic strength of a solution results in

Smaller value of the zeta-potential and smaller electrophoretic mobility

The interactions between identical charged particles in a solution depend on the relative strength of two forces

Van der Waals attractive force and electrostatic repelling force

Flocculation is

Increasing the ionic strength of the solution results in greater attractive force causing the particles to aggregate (agglomerate) and settle to the bottom

The surface charge density obtained from measurements of the

Zeta-potential can be used to evaluate the condition of the cell membrane

Separation of protein molecules or nucleic acid fragments

Molecules in a mixture have different charge to mass ratio and different electrophoretic mobility. The electrophoresis separates molecules into groups by their mobility. It is used for analytical or preparative purposes

Molecular suspensions

Are prepared in special buffers/solvents. The electric field moves the molecules along a solid porous medium (carrier) soaked in the pure buffer

The mechanism of the paper electrophoresis is

A thin stripe of the target solution is laid on the paper carrier, the electric field is turned on. Different target molecules move with different velocity and are separated sometime late

Immunoelectrophoresis is

Electrophoretic method for separation of proteins with only slightly differing electrophoretic mobilities: immunoprecipitation of proteins by antibodies and is used to discover and separate proteins