Gel filtration chromatography is a laboratory technique to separate biomolecules by size. The apparatus can be thought of as nothing more than a column filled with porous beads. As a solution of molecules travels through the column, the smaller molecules get temporarily stuck in the beads, while the larger ones pass right by them. As more solvent is poured through the column, the smaller molecules will find their way out. This means that the first fraction collected will have the largest molecules, and later fractions will have smaller ones. This is not to be confused with gel electrophoresis where smaller molecules travel faster than larger ones.
Thus, the gel seems to resemble a saturated household sponge, but it is distinguished by its colloidal size scale: the dimensions of the open spaces and of the solid objects constituting the network are smaller (usually much smaller) than a micrometer.
For example, a polyacrylamide gel (a polymer linked by covalent bonds) shrinks dramatically when it is transferred from a dish of water (a good solvent) to a dish of acetone (a poor solvent), because the polymer chains tend to favor contact with one another rather than with acetone, so the network collapses onto itself.
In fiber-optic communications, a gel resembling petroleum jelly in viscosity is used to surround a fiber, or multiple fibers, enclosed in a loose buffer tube.
Chromatography is a technique used to separate molecules based on their size, shape, or charge.
The most common types are: gelfiltration (sizing) chromatography which separates molecules based on size, ion-exchange chromatography which separates molecules based on charge, and affinity chromatography which separates molecules based on their shape or unique functional groups.
Gelfiltrationchromatography is often the first step in sorting the proteins in a large mixture.
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