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All About Chromatography

August 25th, 2015 12:54 am

Chromatography is a term which may refer to any number of different methods of separating the different components of analytes for preparative or analytical applications. While the particulars of each of type of chromatographic process vary, essentially what happens is this: an analyte or mixture containing an analyte is combined with a solvent to form a liquid or gas (or supercritical fluid in some cases) known as the mobile phase. The mobile phase is then passed through a medium fixed in place called, understandably enough, the stationary phase; this material is often silica, but varies depending on the type of chromatography being performed.

The differing physical or chemical properties of the constituent components of the mobile phase cause them to pass through the stationary phase at different rates; a process which separates the analyte from the other components of the mobile phase. These different partition coefficients, as they are known, are the basis for chromatographic preparation and analysis in the laboratory. Essentially, the less affinity which a given component in the mobile phase has for the material of the stationary phase, the more quickly it will pass through the column. It’s a bit more complicated than all that, of course, but this is the general principle behind chromatography.

In preparative chromatographic applications, the idea is to separate the constituents of the mobile phase, which are then often put to use elsewhere in the laboratory. It can be an efficient purification process with certain materials and may be done in nearly any quantity as needed. Analytical applications, on the other hand, are usually performed using much smaller volumes of material, with the chromatograph being used to provide a measurement of the concentration of components of the sample being tested. This method may also be used to find out if a given analyte is in fact present in a sample at all. While their aims may differ, preparative and analytical chromatography may in fact be performed in a single operation.

The most familiar chromatographic testing to most people is the columnar method, though paper (which relies on the different rates at which materials bond with a sheet of cellulose), planar and thin layer (which both often use a sheet of glass as a substrate underneath a layer of silica or cellulose) chromatographic methods are also common. There are in fact many different methods available, with some being better suited to specific applications or different analytes. The state and type of analyte to be tested for and the purpose of the separation largely determine whether liquid or gas chromatography and which particular type is appropriate.

These technologies are useful not only in research laboratories but are also extensively used in the production of chemicals and biotechnology products, where it is most commonly used as a separation and purification method. The precision which the chromatographic process allows for the separation of even the most complex of mixtures where the constituents have only the minutest variation. Provided the proper solvent and the proper medium as the stationary phase, virtually any mixture which is soluble can be separated this way, making chromatography one of the most common procedures in laboratories.

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November 9th, 2014 9:46 pm

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