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Chromatography

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Black ink chromatography.jpg

Chromatography is a method used to divide and evaluate various chemical mixtures. Scientists use it for many purposes, ranging from forensics to food production. There are many different forms of chromatography, and each one allows scientists to determine components within a mixture and to separate theses components.

What is Chromatography?

Diagram displaying the concept of simple chromatography.

Chromatography is a method of dividing and evaluating various mixtures of chemicals. It is also labeled as the division of compounds by sifting it through an absorbant material to allow each component to divided into individual layers.[1] It could also be defined as a system used to separate the components of a mixture in accordance with the amounts spread between the mobile and the stationary phases. [2] The stationary phase is the stage that remains stationary (generally as a solid, thick liquid, or bonded coating). In the mobile phase, most often a liquid or gas, moves or flows.[3] In analytical chromatography, the goal is to recognize the components of various complex mixtures. Preparative chromatography, on the other hand, aims to isolate and purify particular molecules.[4]

Chromatography separates proteins, nucleic acids, and small molecules in mixtures in accordance with their various interactions with the stationary and mobile phases.[5] The Kinetic molecular motion constantly exchanges molecules in the mixture between the two phases. When the distribution of the molecules are more attracted to the fluid phase, they will travel with the stream, farther away from the molecules more attracted to the stationary phase, taking longer to disengage, and vice versa. The partition coefficient states that the ratio of time in the mobile and stationary phases equals the ratio of the concentrations in each region. Different components will travel at different rates from the other components in the mixture. The main force in the movement of the molecules is the moving fluid, while the main force constraining the movement of molecules is molecules’ attraction to the stationary phase. It is this conflict of forces that leads to the separation of the various compounds in the mixture.[2]

Forms

A gas chromatography lab.

There are many different forms of chromatography, these include:

Gas Chromatography - Is used to separate volatile organic compounds. The chromatograph (instrument used to perform chromatography) for gas chromatography has a flowing mobile phase, injection ort, separation column with the stationary phase, a detector and a system to record data.[1]

Absorption Chromatography - One of the oldest forms, this style uses either a mobile liquid or a gaseous phase. The phase is absorbed onto the surface of a stationary solid phase. The equilibrium held by the two phases results in the various solutes separating.[6]

Liquid Chromatography - Is used for mixtures of ions or molecule dissolved within a solvent.[1]

Column Chromatography - This form usually occurs on a stationary phase inside a column. Different compounds, depending on the materials to be separated, will be moved through the column as the mobile phase travels through it. This movement collects and distinguishes the small fragments of the components of the mixture.[5]

Thin-Layer Chromatography - Separates Organic Compound mixtures. It is simple and fast, and is used oftentimes to observe the progress of organic reactions and to check purity of products.[1]

Ion Exchange Chromatography - Resin is used as the stationary phase to covalently attach anions or cations to it. A solute of the opposite charge within the liquid mobile phase is attracted to the resin, leading to the separation of the mixture.[6]

Mixed-mode chromatography - Uses more than one mode of chromatography on a single resin. Because of this, the selectivity becomes more augmented., but still follows the same concept as the Ion Exchange Chromatography method.[1]

Affinity chromatography - It is the most selective form of chromatography. It uses a specific interaction between one solute molecule and another molecule immobilized on a stationary phase. As the solute in the mobile phase moves alongside the stationary phase, only the specific molecule reacts.[6]

Molecular Exclusion Chromatography - Does not have an attractive interaction between stationary phase and solute. Rather, the liquid or gas phase travels through a porous gel that separates molecules by size, allowing smaller molecule to pass through while inhibiting larger molecules.[6]

History

An example of Thin-Layer Chromatography

Chromatography was first practically applied by dye-chemists testing dye mixtures by dipping string or cloth into a dye vat, and observing the dye traveling up the material, producing bands of various colors. German chemists in the 19th century experimented with the concept of chromatography. In their experiments, they noticed that the development of colored rings when inorganic compounds were dropped in the center of a piece of filter paper. In 1861, Friedrich Goppelsröder published a paper elaborating on the technique, as well as naming it capillary analysis. Russian botanist Mikhail Tsvet is the one most often credited with the discovery of chromatography through his application of the concept rationally and in an organized manner on plant pigments in 1901. However, his discoveries were not well-known at first, because he only published his findings in German botanical journals or Russian works. In 1931, German chemist Richard Kuhn, along with his student Edgar Lederer, a French student, reported using Tsvet’s method in their experiments. [2]

Nikolay Izmaylov and Maria Shrayber, pharmacists from Russia, reported in 1938, findings looking into thin-layer chromatography, but the potential was not truly understood until 1956. Archer J. P. Martin and Richard L. M. Synge, both British chemists, began to study sheep wool’s amino acid composition in 1941. They utilized the same technique as Tsvet, and it became known as the partition chromatography. There were drawbacks to this form of chromatography: namely the difficulty in reproducing results. Martin and Synge sought to develop a more consistent method using a sheet of filter paper for their stationary medium, and in the 1940’s, paper chromatography became widespread in the use of analyzing biological compounds. In 1942, the Manhattan Project utilized chromatography. [2] Gas chromatography was first used in Austria in 1944 by Erika Cremer. Because of their work in chromatography, Martin and Synge received the Nobel Prize in 1952. American chemist J. Calvin Giddings summarized necessary conditions needed for liquid chromatography to be as powerful as gas chromatography in 1964. Pedro Cuatrecasas and his colleagues described affinity chromatography for the first time in 1968.

Uses

Equipment used to perform chromatography.

Chromatography has many uses, most of which are unknown to most people. A very common use is in chemical plants, separating contaminants out. Chemical industries also utilize chromatography in the removal of pesticides or insecticides from groundwater. In the pharmaceutical field, chiral compounds (compounds similar in atomic weight, element composition and physical properties existing in different forms) are identified, so accurate medicines can be produced. Chromatograhy is also used to separate toxic materials from water, a well as monitoring air quality. [7]

Chromatograhy is also used to determine the quality of food. It is able to detect additives,[8] vitamins, and preservatives, as well as proteins and amino acids. [7] It can also identify a food’s vitamin count and it’s nutritional quality. Scientists also utilize chromatography in food spoilage detecting and process control in foods.[8]

Chromatography has also been utilized to fight diseases. Recently, it was used by scientists to fight ebola. It was determined to be a useful tool in the research of the disease. Scientists utilized chromatography to determine what antibodies were the most effective to neutralize ebola. Although there has been no decisive approval for a drug yet, chromatography helped to develop an experimental immunization drug. Chromatography still being used to further research the disease.[9]

Chromatography also helps to detect chemicals and residue in the aftermath of a fire or explosion, leading to authorities being ble to solve various cases. Forensic science uses it in fiber analysis and DNA / RNA fingerprinting. It can also be used to identify the presence of substances such as alcohol, drugs or medication in human blood and urine.[7]

Video

A simple explanation of Chromatography.

References

  1. 1.0 1.1 1.2 1.3 1.4 Definition of Chromatography Chemicool. Web. Accessed 11 April 2015. Unknown Author.
  2. 2.0 2.1 2.2 2.3 Giddings,J. Calvin. Chromatography Encyclopedia Britannica. Web. Last updated 10 September 2014.
  3. Marsella, Gail. What is Chromatography Study.com. Web. Accessed 9 April 2015.
  4. Chromatograhy Bio-Rad. Web. Accessed 10 April 2015. Unknown Author.
  5. 5.0 5.1 Types of Chromatography Bio-Rad. Web. Accessed 10 April 2015. Unknown Author.
  6. 6.0 6.1 6.2 6.3 Types of Chromatography RPI. Web. Accessed 8 April 2015. Unknown Author.
  7. 7.0 7.1 7.2 Pandey, Kunden. Uses of Chromatography Buzzle. Web. Updated March 2, 2015.
  8. 8.0 8.1 Chromatography in Food Production Bio-Rad. Web. Accessed April 10, 2015. Unknown Author.
  9. . 5 Uses of Chromatography in Everyday Life Chromatography Today. Web. Accessed 15 April 2015.