Question

Compare and contrast membrane electrophoresis and capillary electrophoresis. What are the similarities and what are the differences.

Answer 1

Membrane electrophoresis is the separation technique based on charge density. The basic concept of membrane electrophoresis is that they have a known isoelectric point and buffering capacity is at its isoelectric point. The electrophoretic characteristics of such a membrane are known and calibrated. There will be only a very small or virtually no net charge on the membrane. There is a pH gradient encompassing a narrow range about a specific pH, which can be designated as the isoelectric pH. During the electrophoretic process, because of its buffering power, the membrane will remain under stable isoelectric conditions. Therefore there will be little or no tendency for electroendosmosis to occur during electrophoresis. The matrix exerts little effect on diffusion so that the separated zones are relatively wide while the resolution and limit of detection are low.

Capillary electrophoresis is an analytical technique for the separation of ions based on their electrophoretic mobility (under the influence of an applied voltage). The electrophoretic mobility depends on the charge of the molecule, the viscosity, and the atom's radius. The rate of movement of the particle is directly proportional to the applied electric field--the greater the field strength, the faster the mobility. Only ions move with the electric field and if two ions are of the same size, the one with greater charge will move faster. For ions of the same charge, the smaller particle has less friction and overall faster migration rate. On the other hand they are easy to handle and separation and staining are rapid.

Membrane and capillary electrophoresis, both of which are based on the same principle of size and charge based fragment separation.

Differences:

Capillary electrophoresis (CE) can be used to separate ionic species by their charge and frictional forces and hydrodynamic radius. Capillary electrophoresis is used most predominately because it gives faster results and provides high resolution separation. It is a useful technique because there is a large range of detection methods available.
Membrane electrophoresis is a method used in clinical chemistry to separate proteins by charge and or size (IEF agarose, essentially size independent) and in biochemistry and molecular biology to separate a mixed population of DNA and RNA fragments by length, to estimate the size of DNA and RNA fragments or to separate proteins by charge.