Editing Size-exclusion chromatography (section)

==Applications==

===Biochemical applications===
In general, SEC is considered a low-resolution chromatography as it does not discern similar species very well, and is therefore often reserved for the final step of a purification. The technique can determine the [[quaternary structure]] of purified proteins that have slow exchange times, since it can be carried out under native solution conditions, preserving macromolecular interactions. SEC can also assay protein [[tertiary structure]], as it measures the hydrodynamic volume (not molecular weight), allowing folded and unfolded versions of the same protein to be distinguished. For example, the apparent [[hydrodynamic radius]] of a typical protein domain might be 14 Å and 36 Å for the folded and unfolded forms, respectively. SEC allows the separation of these two forms, as the folded form elutes much later due to its smaller size.

===Polymer synthesis===

SEC can be used as a measure of both the size and the [[polydispersity]] of a synthesized [[polymer]], that is, the ability to find the distribution of the sizes of polymer molecules. If standards of a known size are run previously, then a [[calibration curve]] can be created to determine the sizes of polymer molecules of interest in the solvent chosen for analysis (often [[THF]]). In alternative fashion, techniques such as light scattering and/or [[viscometry]] can be used online with SEC to yield absolute molecular weights that do not rely on calibration with standards of known molecular weight. Due to the difference in size of two polymers with identical molecular weights, the absolute determination methods are, in general, more desirable. A typical SEC system can quickly (in about half an hour) give polymer chemists information on the size and polydispersity of the sample. The preparative SEC can be used for [[polymer fractionation]] on an analytical scale.