Question

1. What is Rf value? List three factors that affect the Rf value.

Answer 1

The retention factor for a chemical is the vertical distance moved by the chemical from the spot where it was originally applied to the plate, divided by the distance traveled by the solvent — measured from the same starting point.

Rf value = Distance travelled by chemical (solute) /Distance travelled

by solvent

Retention factor values in thin layer chromatography are affected by the absorbent, the solvent, the chromatography plate itself, application technique and the temperature of the solvent and plate.

The plate used in this process can also affect the value of the retention factor of a particular chemical. Depending on the coating on the plate, which could be either alumina or silica, the variance in the chemical’s affinity in comparison to the solvent can alter the retention factor.The type of solvent used affects the retention factor. If the solvent has a bias to a certain chemical, it will allow the chemical to move further up within a particular period. Each technician has a different technique when making the application. This diversity can easily alter the retention factor. The temperatures of either the solvents or the plates can make inaccurate the results of chemicals present in a mixture. If the temperatures are high, the solvents can dissolve the chemicals better unlike in cooler temperatures.