Electrophoresis vs Electroosmosis
Physical separation methods like filtering, distillation, column chromatography are not easy methods when comes to separation of some molecules. Electrophoresis and electro-osmosis are two other separation techniques which can be used to separate charged particles.
What is Electrophoresis?
Electrophoresis is a technique of separating molecules based on their sizes. Fundamental for this separation is the charge of the molecule and their ability to move in an electric field. This is the most common and main technique in molecular biology to separate molecules, especially DNA and proteins. This is mostly in use because it is relatively easy and inexpensive. The apparatus for the electrophoresis can be bit complicated, and preparation of it takes some time. But we can easily make an electrophoresis apparatus from the things we have in the laboratory. Electrophoresis techniques can vary depending on our purposes. We can use one dimensional electrophoresis for the separation of DNA or protein. Two dimensional electrophoresis is used when more resolved samples are required (as in the case of finger printing). A gel is used as the support medium to separate the molecules. This gel can be prepared as flat sheets or in tubes. Basis of this procedure is to separate molecules depending on their rate of movement through a gel when an electric field is supplied. Negatively charged molecules like DNA tend to travel towards the positive pole in this electric field while positively charged molecules tend to travel to the negative pole. Two types of gels are used in electrophoresis as agarose and polyacrylamide. These two have different resolving powers. The gel acts as a sieve to filter the different sizes of molecules. The electrostatic charges set up in the gel act as the force.
Separation depends upon the mobility of the ions.
F= force acting on a particle
V= average migrating velocity
Z= charge of the migrating particle
E= strength of the electric field
The necessary conditions for the electrophoresis are relatively simple. When making the gel and running the sample, a buffer is used. Markers and dyes are used for the visualization purposes.
What is Electro-osmosis?
This is the process of moving a liquid through a material using an applied electric field. The movement can be through a porous material, along a capillary, membrane etc. This can be used as a separation technique (especially capillary electro-osmosis). The velocity of the liquid is linearly proportional to the applied electric field. It is also dependent on the material used to build the channel and the solution used. In the interface, solution and material have obtained opposite charges and, this is known as an electrical double layer. When an electrical field is applied to the solution, the electrical double layer moves by the resulting Coulomb force. This is known as the electro-osmotic flow.
What is the difference between Electrophoresis and Electro-osmosis?
• In electrophoresis, solid particles (macromolecules like nucleic acids or proteins) are moved using an electric field. But in electro-osmosis a liquid is moving.
• In electrophoresis, the support solid material is a gel. But it electro-osmosis it can be a gel, membrane, capillary, etc.