GPC for Molecular Weight
What is the principle behind the determination of the molecular weight of a polymer using gel permeation chromatography?
Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is a widely used technique for determining the molecular weight distribution of polymers. The principle behind this technique is based on the fact that the size of a polymer molecule determines its ability to penetrate a porous stationary phase, such as a gel.
In GPC, a solution of the polymer sample is passed through a column packed with a porous gel material. The column separates the polymer molecules based on their size, with smaller molecules being trapped in the pores of the gel and taking longer to elute from the column, while larger molecules pass through the gel more quickly and elute earlier. As the sample moves through the column, detectors at the outlet of the column measure the concentration of the polymer as a function of time, creating a chromatogram.
The chromatogram obtained from the GPC analysis provides information about the molecular weight distribution of the polymer sample. The elution time of each polymer molecule is related to its hydrodynamic volume, which is proportional to its molecular weight. By comparing the elution times of the polymer sample to those of known standards of different molecular weights, the molecular weight distribution of the sample can be determined.
The molecular weight distribution obtained from GPC analysis is typically represented as a graph showing the concentration of the polymer sample as a function of molecular weight. This information is useful for understanding the physical and chemical properties of the polymer, as well as for quality control in manufacturing processes.
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