Editing Paper chromatography

{{Short description|Separation of chemicals, often colored, on paper}}
{{Refimprove|date=February 2008}}
{{Infobox chemical analysis
| name = Paper chromatography 
| image =Chromatography_tank.png
| caption = paper chromatography
| acronym = PC
| classification =[[Chromatography]]
| analytes = chromatography is a technique used for separation of the parts of a mixture of either gas or liquid solution
| manufacturers = 
| related = [[Thin layer chromatography]]
| hyphenated = 
}}
'''Paper chromatography''' is an [[analytical chemistry|analytical]] method used to separate colored chemicals or substances. It can also be used for colorless chemicals that can be located by a stain or other visualisation method after separation.<ref name=britannica>{{Cite news|url=https://www.britannica.com/science/paper-chromatography|title=Paper chromatography {{!}} chemistry|work=Encyclopedia Britannica|access-date=2018-06-01|language=en}}</ref> It is now primarily used as a teaching tool, having been replaced in the [[laboratory]] by other chromatography methods such as [[thin-layer chromatography]] (TLC).

This analytic method has three components, a mobile phase, stationary phase and a support medium (the paper). The mobile phase is generally a non-polar organic solvent in which the sample is dissolved. The stationary phase consists of (polar) water molecules that were incorporated into the paper when it was manufactured. The mobile phase travels up the stationary phase by [[capillary action]], carrying the sample with it. The difference between [[Thin-layer chromatography|TLC]] and paper chromatography is that the stationary phase in TLC is a layer of adsorbent (usually [[silica gel]], or [[aluminium oxide]]), and the stationary phase in paper chromatography is less absorbent paper.

A paper chromatography variant, [[two-dimensional chromatography]], involves using two solvents and rotating the paper 90° in between. This is useful for separating complex mixtures of compounds having similar polarity, for example, [[amino acids]].

== R<sub>''ƒ''</sub> value, solutes, and solvents ==
The [[retention factor]] (R<sub>''ƒ''</sub>) may be defined as the ratio of the distance travelled by the solute to the distance travelled by the solvent. It is used in chromatography to quantify the amount of retardation of a sample in a stationary phase relative to a mobile phase.<ref>{{GoldBookRef |title=retention factor, ''k in column chromatography'' |file=R05359 |accessdate=2018-01-19 }}</ref> R<sub>''ƒ''</sub> values are usually expressed as a fraction of two decimal places. 
* If R<sub>''ƒ''</sub> value of a solution is zero, the solute remains in the stationary phase and thus it is immobile. 
* If R<sub>''ƒ''</sub> value = 1 then the solute has no affinity for the stationary phase and travels with the solvent front. 
For example, if a compound travels 9.9&nbsp;cm and the solvent front travels 12.7&nbsp;cm, the R<sub>''ƒ''</sub> value = (9.9/12.7) = 0.779 or 0.78. R<sub>''ƒ''</sub> value depends on temperature and the solvent used in experiment, so several solvents offer several R<sub>''ƒ''</sub> values for the same mixture of compound. A solvent in chromatography is the liquid the paper is placed in, and the solute is the ink which is being separated.

==Pigments and polarity==
Paper chromatography is one method for testing the [[:wikt:purity|purity]] of compounds and identifying substances. Paper chromatography is a useful technique because it is relatively quick and requires only small quantities of material. Separations in paper chromatography involve the principle of partition. In paper chromatography, substances are distributed between a stationary phase and a mobile phase. The stationary phase is the water trapped between the cellulose fibers of the paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. Components of the sample will separate readily according to how strongly they adsorb onto the stationary phase versus how readily they dissolve in the mobile phase.

When a colored [[chemical sample]] is placed on a filter paper, the colors separate from the sample by placing one end of the paper in a [[solvent]]. The solvent [[diffuse]]s up the paper, [[dissolution (chemistry)|dissolving]] the various molecules in the sample according to the [[Chemical polarity|polarities]] of the molecules and the solvent. If the sample contains more than one color, that means it must have more than one kind of molecule. Because of the different chemical structures of each kind of molecule, the chances are very high that each molecule will have at least a slightly different polarity, giving each molecule a different [[solubility]] in the solvent. The unequal solubility causes the various color molecules to leave solution at different places as the solvent continues to move up the paper. The more soluble a molecule is, the higher it will migrate up the paper. If a chemical is very non-polar it will not dissolve at all in a very polar solvent. This is the same for a very polar chemical and a very non-polar solvent.

When using water (a very polar substance) as a solvent, the more polar the color, the higher it will rise on the papers.{{cn|date=October 2024}}{{or|date=October 2024}}

==Types==
[[File:T.baccata-paper chromatography.jpg|thumb|80px|''[[Taxus baccata]]'' paper chromatography.]]
===Descending===
Development of the chromatogram is done by allowing the solvent to travel down the paper. Here, the mobile phase is placed in a solvent holder at the top. The spot is kept at the top and solvent flows down the paper from above.

===Ascending===
Here the solvent travels up the chromatographic paper. Both descending and ascending paper chromatography are used for the separation of organic and inorganic substances.
The sample and solvent move upward.

===The ascending and descending method===
This is the hybrid of both of the above techniques. The upper part of ascending chromatography can be folded over a rod in order to allow the paper to become descending after crossing the rod.

===Circular chromatography===
A circular filter paper is taken and the sample is deposited at the center of the paper. After drying the spot, the filter paper is tied horizontally on a [[Petri dish]] containing solvent, so that the wick of the paper is dipped in the solvent. The solvent rises through the wick and the components are separated into concentric rings.

===Two-dimensional===
In this technique a square or rectangular paper is used. Here the sample is applied to one of the corners and development is performed at a right angle to the direction of the first run.

== History of paper chromatography ==
The discovery of paper chromatography in 1943 by [[Archer Martin|Martin]] and [[Richard Laurence Millington Synge|Synge]] provided, for the first time, the means of surveying constituents of plants and for their separation and identification.<ref name=haslam07/> [[Erwin Chargaff]] credits in Weintraub's history of the man the 1944 article by Consden, Gordon and Martin.<ref name="consden44">{{cite journal |doi=10.1042/bj0380224|title=Qualitative analysis of proteins: A partition chromatographic method using paper|year=1944|last1=Consden|first1=R.|last2=Gordon|first2=A. H.|last3=Martin|first3=A. J. P.|journal=Biochemical Journal|volume=38|issue=3|pages=224–232|pmid=16747784|pmc=1258072}}</ref><ref name="weintraub06">{{cite journal |last1=Weintraub |first1=Bob |title=Erwin Chargaff and Chargaff's Rules |journal=Chemistry in Israel - Bulletin of the Israel Chemical Society |date=September 2006 |issue=22 |pages=29–31 |url=https://drive.goo-gle.com/file/d/13dBvbCTMVmko67B7GZGH7ck_HwIVmJ_2-rT7MbU_dqQUGQz6YeRpb-rY1ucz/edit?usp=sharing}}</ref> There was an explosion of activity in this field after 1945.<ref name=haslam07>{{cite journal |doi=10.1016/j.phytochem.2007.09.009 |title=Vegetable tannins – Lessons of a phytochemical lifetime |year=2007 |last1=Haslam |first1=Edwin |author-link1=Edwin Haslam |journal=Phytochemistry |volume=68 |issue=22–24 |pages=2713–21 |pmid=18037145|bibcode=2007PChem..68.2713H }}</ref>

== References ==
{{Reflist}}

==Bibliography==
*{{cite book|last1=Block|first1=Richard J. |last2=Durrum|first2=Emmett L. |last3=Zweig|first3=Gunter |title=A Manual of Paper Chromatography and Paper Electrophoresis|url={{Google Books |aC4XBQAAQBAJ|page=4|plainurl=yes}}|date=1955|publisher=Elsevier|isbn=978-1-4832-7680-9|pages=4|via=Google Books}}

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{{DEFAULTSORT:Paper Chromatography}}
[[Category:Chromatography]]