Determination of molecular weight by Gel permeation chromatography (GPC)

Gel permeation chromatography (GPC)

Gel permeation chromatography is also called size exclusion chromatography (SEC).

In gel permeation chromatography, the solvent is allowed to form two phases, namely stationary phase and mobile phase, in the column packed with microporous gel particle, such that the stationary phase is made up of the part of solvent which is inside the gel while the moving phase is made up of the flowing part of solvent which is outside the gel particle, during the process.

The gel used are hard and incompressible polymer. The gel commonly used are microporous glass bead and microporous polystyrene gel.

A known amount of polymer in known volume of solvent is injected in the solvent stream flowing down the gel packed column. The entry of large size polymer molecules into the gel pores are mostly restricted or completely hindered due to small size of pores and they flow outside the gel beads, thus spend less time in gel and are eluted faster from the column. On the contrary, the small size polymer molecules enter into the pores of the gel and spend more time in the gel and are eluted after a very long time from the gel column.

Thus the large size molecules are eluted faster from the gel column and the small size molecules are eluted slower. This technique is called gel permeation chromatography, which allows fractionation of polymer molecules according to their size as shown in fig below.