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Chromatography Technique and Rf Value Calculation

In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the mobile phase, which carries it through a system (a column, a capillary tube, a plate, or a sheet) on which a material called the stationary phase is fixed. As the different constituents of the mixture tend to have different affinities for the stationary phase and are retained for different lengths of time depending on their interactions with its surface sites, the constituents travel at different apparent velocities in the mobile fluid, causing them to separate.

Key Points

  • The purpose of preparative chromatography is to separate the components of a mixture for later use, and is thus a form of purification.
  • An RF value is characteristic for any given compound (provided that the same stationary and mobile phases are used).
  • The mobile phase is generally a non-polar organic solvent in which the sample is dissolved.
  • The stationary phase is a resin composed of beads, usually of cross-linked agarose, packed into a cylindrical glass or plastic column.
  • Paper chromatography is a technique that involves placing a small dot or line of sample solution onto a strip of chromatography paper.
  • The strong polarity of water is indicated by its high dielectric constant of 88 (at 0 °C).

Terms

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