Paper chromatography
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paper chromatography
(′pā·pər ′krō·mə′täg·rə·fē)
(analytical chemistry) Procedure for analysis of complex chemical mixtures by the progressive absorption of the components of the unknown sample (in a solvent) on a special grade of paper.
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Paper chromatography
Britannica Concise Encyclopedia:
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paper chromatography
Type of chromatography using filter paper or other special paper as the stationary phase. Spots of sample and reference materials are applied, usually as liquids, near one edge (or corner, for two-dimensional PC) of the paper. The edge of the paper is dipped in a solvent, which travels along it by capillarity, moving the components of the sample at rates depending on their relative solubilities in the solvent. In two-dimensional PC, the paper is then turned 90 and the new edge dipped in a different solvent. The components of the sample mixture, visible as separated spots, are identified by comparing the distances they have traveled with those of the known reference materials. PC is especially useful for complex mixtures of amino acids, peptides, carbohydrates, steroids, and many other organic compounds and inorganic ions.
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Paper Chromatography
The separation of components that can be visually analyzed by spreading a liquid system along paper. A paper is first dipped into, for example, a mixture of colors. After a while the colors will separate into bands according to their respective rates of dispersion along the paper, and a separation of individual colors will appear.
Oxford Dictionary of Biochemistry:
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paper chromatography
abbr.: PC; a technique of chromatography, applicable to microgram quantities of soluble substances, in which specially prepared filter paper, chromatography paper, forms the support for the stationary phase. The latter is commonly a film of water held by adsorption on the cellulose fibres of the paper and in equilibrium with a water-immiscible liquid or liquid mixture, which forms the mobile phase. A solution of a sample is applied near one end of a strip of paper, allowed to dry, and the mobile phase allowed to flow over the strip from that end. If the sample consists of only one component, development using an appropriate method of detection will reveal a single spot at a characteristic distance from the origin relative to that travelled by the mobile phase; in general, a mixture will give rise to a number of spots each occupying a different and characteristic position. Separations occur essentially by partition between the mobile and stationary phases, with some contribution, under certain conditions, attributable to adsorption or ion-exchange onto the paper support. An elaboration of the technique uses a square of paper on which two successive separations are effected at right-angles using mobile phases of differing separatory powers to produce a two-dimensional pattern of spots on the paper. With suitable treatment of the paper and an appropriate choice of the composition of the two phases, reversed-phase partition chromatography on paper may be effected. Since cellulose is chiral, some enantiomer separations are possible.
| paper chromatogram, papaverine, papain | |
| paper electrophoresis, papovavirus, par+ |
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categories related to 'paper chromatography'
- Tools and Techniques - paper chromatography: use of solvent to separate amino acids on filter paper
- Tools, Tests, Units, and Scales - paper chromatography: chromatographic technique in which the stationary phase is paper
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Paper chromatography
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This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2008) |
 Chromatography jar |
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| Classification | Chromatography |
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| Other techniques | |
| Related | Thin layer chromatography |
Paper chromatography is an analytical method technique for separating and identifying mixtures that are or can be colored, especially pigments. This can also be used in secondary or primary colors in ink experiments. This method has been largely replaced by thin layer chromatography, however it is still a powerful teaching tool. Two-way paper chromatography, also called two-dimensional chromatography, involves using two solvents and rotating the paper 90° in between. This is useful for separating complex mixtures of similar compounds, for example, amino acids.
Rƒ value
The retention factor (Rƒ) may be defined as the ratio of the distance traveled by the substance to the distance traveled by the solvent. Rƒ values are usually expressed as a fraction of two decimal places but it was suggested by Smith that a percentage figure should be used instead. If Rƒ value of a solution is zero, the solute remains in the stationary phase and thus it is immobile. If Rƒ value = 1 then the solute has no affinity for the stationary phase and travels with the solvent front. To calculate the Rƒ value, take the distance traveled by the substance divided by the distance traveled by the solvent (as mentioned earlier in terms of ratios). For example, if a compound travels 2.1 cm and the solvent front travels 2.8 cm, (2.1/2.8) the Rƒ value = 0.75
Pigments and polarity
Paper chromatography is one method for testing the purity of compounds and identifying substances. Paper chromatography is a useful technique because it is relatively quick and requires small quantities of material. Separations in paper chromatography involve the same principles as those in thin layer chromatography. In paper chromatography, like thin layer chromatography, substances are distributed between a stationary phase and a mobile phase. The stationary phase is usually a piece of high quality filter 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 on 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 diffuses up the paper, dissolving the various molecules in the sample according to the 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 solubilities cause 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 nonpolar it will not dissolve at all in a very polar solvent. This is the same for a very polar chemical and a very nonpolar solvent.
It is important to note that when using water (a very polar substance) as a solvent, the less polar the colour, the lower it will rise on the paper.
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