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What is Separation Science
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From Wikipedia, the free encyclopedia.  Link to complete article here.
(from Greek: "chroma" which means color and "graphein" which means to write) is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated.


Chromatography may be preparative or analytical. Preparative chromatography seeks to separate the components of a mixture for further use (and is thus a form of purification). Analytical chromatography normally operates with smaller amounts of material and seeks to measure the relative proportions of analytes in a mixture. The two are not mutually exclusive.
Chromatography terms

  • The analyte is the substance that is to be separated during chromatography.
  • Analytical chromatography is used to determine the existence and possibly also the concentration of analyte(s) in a sample.
  • A bonded phase is a stationary phase that is covalently bonded to the support particles or to the inside wall of the column tubing.
  • A chromatogram is the visual output of the chromatograph. In the case of an optimal separation, different peaks or patterns on the chromatogram correspond to different components of the separated mixture.  Plotted on the x-axis is the retention time and plotted on the y-axis a signal (for example obtained by a spectrophotometer, mass spectrometer or a variety of other detectors) corresponding to the response created by the analytes exiting the system. In the case of an optimal system the signal is proportional to the concentration of the specific analyte separated.
  • A chromatograph is equipment that enables a sophisticated separation e.g. gas chromatographic or liquid chromatographic separation.
  • Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in a definite direction.
  • The effluent is the mobile phase leaving the column.
  • An immobilized phase is a stationary phase which is immobilized on the support particles, or on the inner wall of the column tubing.
  • The mobile phase is the phase which moves in a definite direction. It may be a liquid (LC and CEC), a gas (GC), or a supercritical fluid (supercritical-fluid chromatography, SFC). A better definition: The mobile phase consists of the sample being separated/analyzed and the solvent that moves the sample through the column. In one case of HPLC the solvent consist of a carbonate/bicarbonate solution and the sample is the anions being separated. The mobile phase moves through the chromatography column (the stationary phase) where the sample interacts with the stationary phase and is separated.
  • Preparative chromatography is used to purify sufficient quantities of a substance for further use, rather than analysis.
  • The retention time is the characteristic time it takes for a particular analyte to pass through the system (from the column inlet to the detector) under set conditions.
  • The sample is the matter analysed in chromatography. It may consist of a single component or it may be a mixture of components. When the sample is treated in the course of an analysis, the phase or the phases containing the analytes of interest is/are referred to as the sample whereas everything out of interest separated from the sample before or in the course of the analysis is referred to as waste.
  • The solute refers to the sample components in partition chromatography.
  • The solvent refers to any substance capable of solubilizing other substance, and especially the liquid mobile phase in LC.
  • The stationary phase is the substance which is fixed in place for the chromatography procedure. Examples include the silica layer in thin layer chromatography.





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