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Encyclopedia > Thin layer chromatography
Thin layer chromatography

Separation of black ink on a TLC plate
Acronym TLC
Classification Chromatography
Other Techniques
Related Agarose gel electrophoresis
SDS-PAGE

Thin Layer Chromatography (TLC) is a chromatography technique used to separate chemical compounds [1]. It involves a stationary phase consisting of a thin layer of adsorbent material, usually silica gel, aluminium oxide, or cellulose immobilised onto a flat, inert carrier sheet. A liquid phase consisting of the solution to be separated dissolved in an appropriate solvent is drawn through the plate via capillary action, separating the experimental solution. Separation of black ink on TLC plate. ... For the Second Person album, see Chromatography (album). ... Digital image of 3 plasmid restriction digests run on a 1% w/v agarose gel, 3 Volts/cm, stained with ethidium bromide. ... Picture of an SDS-PAGE. The molecular marker is in the left lane SDS-PAGE stands for Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis. ... For the Second Person album, see Chromatography (album). ... In chemistry, adsorption of a substance is its concentration on a particular surface. ... Beads of silica gel Silica gel is a granular, porous form of silica made synthetically from sodium silicate. ... Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula Al2O3. ... Cellulose as polymer of β-D-glucose Cellulose in 3D Cellulose (C6H10O5)n is a polysaccharide of beta-glucose. ... Capillary action, capillarity, or capillary motion is the ability of a substance (the standard reference is to a tube in plants but can be seen readily with porous paper) to draw a substance up against gravity. ...


Its wide range of uses include

  • determination of the pigments a plant contains
  • detection of pesticides or insecticides in food
  • analysis the dye composition of fibers in forensics, or
  • identification compounds present in a given substance

It is a quick, generic method for organic reaction monitoring. Forensics or forensic science is the application of science to questions which are of interest to the legal system. ...

Contents

Plate preparation

TLC plates are made by mixing the adsorbent, such as silica gel, with a small amount of inert binder like calcium sulfate (gypsum) and water. This mixture is spread as a thick slurry on an unreactive carrier sheet, usually glass, thick aluminum foil, or plastic, and the resultant plate is dried and activated by heating in an oven for thirty minutes at 110 °C. The thickness of the adsorbent layer is typically around 0.1–0.25 mm for analytical purposes and around 1–2 mm for preparative TLC. Every type of chromatography contains a mobile phase and a stationary phase. Beads of silica gel Silica gel is a granular, porous form of silica made synthetically from sodium silicate. ... In English, to be inert is to be in a state of doing little or nothing. ... Calcium sulphate is a common laboratory and industrial chemical. ... This article is about the material. ...


Technique

Chromatogram of 10 essential oils coloured with vanillin reagent.
Chromatogram of 10 essential oils coloured with vanillin reagent.

The process is similar to paper chromatography with the advantage of faster runs, better separations, and the choice between different stationary phases. Because of its simplicity and speed TLC is often used for monitoring chemical reactions and for the qualitative analysis of reaction products. Image File history File links Size of this preview: 567 × 600 pixels Full resolution (1200 × 1269 pixel, file size: 100 KB, MIME type: image/jpeg) The scan of TLC plate (silica gel G) with 10 essential oils developed with mobile phase toluene - ethyl acetate (93:7 v/v), next sprayed... Image File history File links Size of this preview: 567 × 600 pixels Full resolution (1200 × 1269 pixel, file size: 100 KB, MIME type: image/jpeg) The scan of TLC plate (silica gel G) with 10 essential oils developed with mobile phase toluene - ethyl acetate (93:7 v/v), next sprayed... An essential oil is a concentrated, hydrophobic liquid containing volatile aromatic compounds from plants. ... Vanillin, methyl vanillin, or 4-hydroxy-3-methoxybenzaldehyde, is an organic compound with the molecular formula C8H8O3. ... Paper chromatography is an analytical technique for separating and identifying mixtures that are or can be colored, especially pigments. ... Vapours of hydrogen chloride in a beaker and ammonia in a test tube meet to form a cloud of a new substance, ammonium chloride A chemical reaction is a process that results in the interconversion of chemical substances. ...


A small spot of solution containing the sample is applied to a plate, about one centimeter from the base. The plate is then dipped in to a suitable solvent, such as ethanol or water, and placed in a sealed container. The solvent moves up the plate by capillary action and meets the sample mixture, which is dissolved and is carried up the plate by the solvent. Different compounds in the sample mixture travel at different rates due to differences in solubility in the solvent, and due to differences in their attraction to the stationary phase. Results also vary depending on the solvent used. For example, if the solvent were a 90:10 mixture of hexane to ethyl acetate, then the solvent would be mostly nonpolar. This means that when analyzing the TLC, the nonpolar parts will have moved further up the plate. The polar compounds, in contrast, will not have moved as much. The reverse is true when using a solvent that is more polar than non-polar (10:90 hexane to ethyl acetate). With these solvents, the polar compounds will move higher up the plate, while the non-polar compounds will not move as much. A solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound, and is best known as the alcohol found in alcoholic beverages. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... A solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... Capillary action, capillarity, or capillary motion is the ability of a substance (the standard reference is to a tube in plants but can be seen readily with porous paper) to draw a substance up against gravity. ... A chemical compound is a chemical substance of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition. ...


The appropriate solvent in context of Thin layer chromatography will be one which differs from the stationary phase material in polarity. If polar solvent is used to dissolve the sample and spot is applied over polar stationary phase TLC, the sample spot will grow radially due to capillary action, which is not advisable as one spot may mix with the other. Hence, to restrict the radial growth of sample-spot, the solvent used for dissolving samples in order to apply them on plates should be as non-polar or semi-polar as possible when the stationary phase is polar, and vice-versa.


Analysis

As the chemicals being separated may be colorless, several methods exist to visualize the spots:

  • Often a small amount of a fluorescent compound, usually Manganese-activated Zinc Silicate, is added to the adsorbent that allows the visualization of spots under a blacklight(UV254). The adsorbent layer will thus fluoresce light green by itself, but spots of analyte quench this fluorescence.
  • Iodine vapors are a general unspecific color reagent
  • Specific color reagents exist into which the TLC plate is dipped or which are sprayed onto the plate

Once visible, the Rf value of each spot can be determined by dividing the distance traveled by the product by the total distance traveled by the solvent (the solvent front). These values depend on the solvent used, and the type of TLC plate, and are not physical constants. Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... BlackLight Is a Rock Band set up April 2006. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Standard atomic weight 126. ... A reagent is a material used to start a {[chemical reaction]}. For example hydrochloric acid is the chemical reagent that would cause calcium carbonate to release carbon dioxide. ...


Applications

In organic chemistry, reactions are qualitatively monitored with TLC. Spots sampled with a capillary tube are placed on the plate: a spot of starting material, a spot from the reaction mixture, and a "co-spot" with both. A small (3 by 7 cm) TLC plate takes a couple of minutes to run. The analysis is qualitative, and it will show if starting material has disappeared, product has appeared, and how many products are generated. Unfortunately, TLC's from low-temperature reactions may give misleading results, because the sample is warmed to room temperature in the capillary. One such reaction is DIBALH reduction of ester to aldehyde. Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting primarily of carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, halogens as well... This article does not cite any references or sources. ... Diisobutylaluminium hydride, DIBAL, DIBAL-H or DIBAH, is a reducing agent with the formula (i-Bu2AlH)2, where i-Bu represents isobutyl (-CH2CH(CH3)2). ...


As an example the chromatography of an extract of green leaves (for example spinach) in 7 stages of development. Carotene elutes quickly and is only visible until step 2. Chlorophyll A and B are halfway in the final step and lutein the first compound staining yellow. Binomial name Spinacia oleracea L. Percentages are relative to US recommendations for adults. ... β-Carotene represented by a 3-dimensional stick diagram Carotene is responsible for the orange colour of the carrots and many other fruits and vegetables. ... Chlorophyll gives leaves their green color Space-filling model of the chlorophyll molecule Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. ... Lutein (LOO-teen) (from Latin lutea meaning yellow) is one of over 600 known naturally occurring carotenoids. ...

In one study TLC has been applied in the screening of organic reactions [2] for example in the fine-tuning of BINAP synthesis from 2-naphtol. In this method the alcohol and catalyst solution (for instance iron(III) chloride) are place separately on the base line, then reacted and then instantly analyzed. Organic reactions are chemical reactions involving organic compounds. ... (S)- and (R)-BINAP Ball and stick model of BINAP viewed as above In organic chemistry, BINAP, an acronym used for 2,2-bis(diphenylphosphino)-1,1-binaphthyl, is an important chiral ligand widely used in asymmetric synthesis. ...


References

  1. ^ Vogel's Textbook of Practical Organic Chemistry (5th Edition) (Hardcover) by A.I. Vogel (Author), A.R. Tatchell (Author), B.S. Furnis (Author), A.J. Hannaford (Author), P.W.G. Smith ISBN 0582462363
  2. ^ TLC plates as a convenient platform for solvent-free reactions Jonathan M. Stoddard, Lien Nguyen, Hector Mata-Chavez and Kelly Nguyen Chem. Commun., 2007, 1240 - 1241, doi:10.1039/b616311d
  • Hand book of Thin Layer Chromatography,Sherman, J.and Fried, B. (authors) 3rd ed. Marcel Dekker, New York.

Chemical Communications or ChemComm is a is a peer-reviewed scientific journal in the chemical sciences published since 1996 by the Royal Society of Chemistry. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

See also


  Results from FactBites:
 
Thin Layer Chromatography module (0 words)
Thin layer chromatography (TLC) is a method for identifying substances and testing the purity of compounds.
TLC is a useful technique because it is relatively quick and requires small quantities of material.
The stationary phase is a thin layer of adsorbent (usually silica gel or alumina) coated on a plate.
  More results at FactBites »

 
 

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