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The retardation factor, also known as retention factor or Rf价值,代表了特点stic rate of movement of a component in a mixture as the mobile phase moves. The Rfvalue is different for different compounds. The Rf价值取决于:

  • 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 Rfvalue 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 Rfvalue will always be less than 1. The Rfvalue has no units.

The Rfvalue is not to be confused with theretention factor k', also known as the capacity factor.

References:

  • NCERT Chromatography handbook
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