Editing Chromatography (section)

===Column chromatography===
{{further|Column chromatography}}
[[File:Column chromatography sequence.png]]

Column chromatography is a separation technique in which the stationary bed is within a tube. The particles of the solid stationary phase or the support coated with a liquid stationary phase may fill the whole inside volume of the tube (packed column) or be concentrated on or along the inside tube wall leaving an open, unrestricted path for the mobile phase in the middle part of the tube (open tubular column). Differences in rates of movement through the medium are calculated to different retention times of the sample.<ref>{{cite journal|doi=10.1351/pac199365040819|title=Nomenclature for chromatography (IUPAC Recommendations 1993)|journal=Pure and Applied Chemistry|volume=65|issue=4|pages=819–872|year=1993| vauthors = Ettre LS |doi-access=free}}</ref><ref>{{cite web | vauthors = Manish T |title=How does column chromatography work?|url=http://brightmags.com/how-does-chromatography-work/|publisher=BrightMags|access-date=7 April 2017|archive-url=https://web.archive.org/web/20170421085642/http://brightmags.com/how-does-chromatography-work/|archive-date=21 April 2017|url-status=dead}}</ref>
In 1978, W. Clark Still introduced a modified version of column chromatography called ''flash column chromatography'' (flash).<ref>{{cite journal | vauthors = Still WC, Kahn M, Mitra A | year = 1978 | title = Rapid chromatographic technique for preparative separations with moderate resolution | journal = [[J. Org. Chem.]] | volume = 43 | issue = 14 | pages = 2923–2925 | doi = 10.1021/jo00408a041 | citeseerx = 10.1.1.476.6501 }}</ref><ref name="Harwood-1989">{{cite book | vauthors = Harwood LM, Moody CJ | title = Experimental organic chemistry: Principles and Practice | edition = Illustrated | pages = [https://archive.org/details/experimentalorga00harw/page/180 180–185] | isbn = 978-0-632-02017-1 | date = 1989 | publisher = WileyBlackwell | url = https://archive.org/details/experimentalorga00harw/page/180 }}</ref> The technique is very similar to the traditional column chromatography, except that the solvent is driven through the column by applying positive pressure. This allowed most separations to be performed in less than 20 minutes, with improved separations compared to the old method. Modern flash chromatography systems are sold as pre-packed plastic cartridges, and the solvent is pumped through the cartridge. Systems may also be linked with detectors and fraction collectors providing automation. The introduction of [[Diffusion|gradient]] pumps resulted in quicker separations and less solvent usage.

In [[expanded bed adsorption]], a fluidized bed is used, rather than a solid phase made by a packed bed. This allows omission of initial clearing steps such as centrifugation and filtration, for culture broths or [[Slurry|slurries]] of broken cells.

[[Phosphocellulose]] chromatography utilizes the binding affinity of many DNA-binding proteins for phosphocellulose. The stronger a protein's interaction with DNA, the higher the salt concentration needed to elute that protein.<ref>{{cite book | vauthors = Bourgeois S, Pfahl M| chapter = Repressors | veditors = Anfinsen CB, Edsall JT, Richards FM |title=Advances in Protein Chemistry|isbn=978-0-12-034230-3 |year=1976|pages=6–7 | volume = 30 | publisher = Academic Press | doi = 10.1016/S0065-3233(08)60478-7 | pmid = 779429 }}</ref>