Dialysis (biochemistry)

Dialysis (from the Greek dialysis = resolution) is a concentration- driven membrane process (see membrane), by which one can remove very small particles (typically ions or small molecules ) from solutions.

Laboratory dialysis

Dialysis is a method of working in a chemical laboratory. It serves to small molecules and ions, such as salt or sugar share, while large molecules such as proteins or nucleic acids are retained.

In a dialysis method often applied a thin-walled tube of swollen in water acetyl cellulose is used, which is vaguely reminiscent of a sausage skin. One end of a hose piece is tied, and then filled with a solution containing, for example, proteins or nucleic acids. Also the other end of the tube is tied, so that the solution is trapped. The tube is then gently swirled in a much larger quantity of a particular salt or buffer solution and left in it.

After a night in the interior of the tube approximately the same salt concentration has been established, as it existed in the outer salt solution, in which the tube was previously introduced. The proteins or nucleic acids are retained in the tube, because only molecules with a molecular weight below the pore diameter ( this may be dalton ultrafiltration membranes depending on the use of between about 3000 and 50,000 ) through the wall of the tube can pass (see osmosis). Such a membrane is therefore called semi-permeable ( semi-transparent ). Therefore, the proteins or nucleic acids could not leave the tube, the salt concentrations of the two solutions were able to adjust due to the smaller size of the ions. Since the volume of the solution was considerably higher outside the tube, their salt concentration is also inside the tube. In this way the concentration of the initially present undesirable salts can be reduced to a negligible level.

Electrodialysis

If we separate electrical voltages to help to target electrically charged species, it is called electrodialysis.

In an electrodialysis separator, the space between two electrodes separated by a stack of alternating anion and cation exchange membranes. Each pair of ion exchange membranes forms a separate "cell". These stacks consist of more than two hundred pairs of membranes in technical systems. , A direct electric voltage applied to the electrodes, the anions migrate to the anode. The anions can easily change the positively charged anion- happen, but they are stopped in each case at the nearest negatively charged cation exchange membranes.