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Retardation factor

The retardation factor, also known as retention factor or Rf value, represents the characteristic rate of movement of a component in a mixture as the mobile phase moves. The Rf value is different for different compounds. The Rf value depends on:

  • The nature of the compound

  • The mobile phase used

  • The temperature

  • The presence of impurities

  • The quality of the paper or TLC plate (the stationary phase)

The Rf value can be determined by the following equation:

The R f value can be calculated by taking the distance travelled by the substance and dividing it by the distance travelled by the solvent front. On the right of the equation is a rectangular piece of paper or T L C plate. There is a reference line marked at the bottom of the plate with 3 ticks along the line for each sample. The solvent front is marked at the opposite end of the plate. The solvent front is 10 cm from the reference line. There are 3 spots on the plate, one for each sample. The first sample is 1.5 cm from the reference line, and has an R f of 0.15. The second spot is 3 cm from the reference line, and has an R f of 0.3. The third spot is 7 cm from the reference line, and has an R f of 0.7.

Since the solvent front always moves faster than the components, the Rf value will always be less than 1. The Rf value has no units.

The Rf value is not to be confused with the retention factor k', also known as the capacity factor.

References:

  • NCERT Chromatography handbook

Referred from:

Article
Paper chromatography
Article
Separation of pigments
Article
Experimental procedure (pigments)
Article
Experimental procedure (ions)