In this manner, dialysis may be used to perform purification or buffer exchange for samples containing macromolecules.ĭialysis works by diffusion, a process that results from the thermal, random movement of molecules in solution and leads to the net movement from areas of higher to lower concentration (until an equilibrium is reached). Molecules larger than the pores cannot pass through the membrane but small molecules can do so freely. A dialysis membrane is a semi-permeable film (usually a sheet of regenerated cellulose) containing various sized pores. In this way, the concentration of small contaminants within the sample can be decreased to acceptable or negligible levels. Changing the dialysate buffer removes the small molecules that are no longer in the sample and allows more contaminants to diffuse into the dialysate. Sample molecules that are larger than the membrane-pores are retained on the sample side of the membrane, but small molecules and buffer salts pass freely through the membrane, reducing the concentration of those molecules in the sample. A sample and a buffer solution (called the dialysate, usually 200 to 500 times the volume of the sample) are placed on opposite sides of the membrane. Dialysis is a separation technique that facilitates the removal of small, unwanted compounds from macromolecules in solution by selective and passive diffusion through a semi-permeable membrane.
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