Editing Chromatography (section)

==Techniques by chromatographic bed shape==

===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>

===Planar chromatography===
''Planar chromatography'' is a separation technique in which the stationary phase is present as or on a plane. The plane can be a paper, serving as such or impregnated by a substance as the stationary bed ([[paper chromatography]]) or a layer of solid particles spread on a support such as a glass plate ([[thin-layer chromatography]]). Different [[chemical compound|compounds]] in the sample mixture travel different distances according to how strongly they interact with the stationary phase as compared to the mobile phase. The specific [[Retention factor]] (R<sub>f</sub>) of each chemical can be used to aid in the identification of an unknown substance.

====Paper chromatography====
[[File:Paper chromatography in progress.jpg|thumb|Paper chromatography in progress]]
[[File:Chromatography tank.png|thumb|Paper chromatography]]
{{further|Paper chromatography}}
Paper chromatography is a technique that involves placing a small dot or line of sample [[Solution (chemistry)|solution]] onto a strip of ''[[chromatography paper]]''. The paper is placed in a container with a shallow layer of [[solvent]] and sealed. As the solvent rises through the paper, it meets the sample mixture, which starts to travel up the paper with the solvent. This paper is made of [[cellulose]], a [[Chemical polarity|polar substance]], and the compounds within the mixture travel further if they are less polar. More polar substances bond with the cellulose paper more quickly, and therefore do not travel as far.

====Thin-layer chromatography (TLC) ====
{{further|Thin-layer chromatography}}
[[File:TLC black ink.jpg|thumb|Thin layer chromatography]]
Thin-layer chromatography (TLC) is a widely employed laboratory technique used to separate different biochemicals on the basis of their relative attractions to the stationary and mobile phases. It is similar to [[paper chromatography]]. However, instead of using a stationary phase of paper, it involves a stationary phase of a thin layer of [[adsorbent]] like [[silica gel]], [[Aluminium oxide|alumina]], or [[cellulose]] on a flat, inert [[Substrate (chemistry)|substrate]]. TLC is very versatile; multiple samples can be separated simultaneously on the same layer, making it very useful for screening applications such as testing drug levels and water purity.<ref>{{cite book|title=Handbook of Thin-Layer Chromatography|last=Bernard.|first=Fried |date=2003|publisher=Marcel Dekker Inc|isbn=978-0824748661|oclc=437068122}}</ref>

Possibility of cross-contamination is low since each separation is performed on a new layer. Compared to paper, it has the advantage of faster runs, better separations, better quantitative analysis, and the choice between different adsorbents. For even better [[resolution (chromatography)|resolution]] and faster separation that utilizes less solvent, [[HPTLC|high-performance TLC]] can be used. An older popular use had been to differentiate chromosomes by observing distance in gel (separation of was a separate step).