Rf value =Distance of the center of spot from the starting point or the distance travelled by the sample or analyte divided by Distance of solvent front from starting point or the distance travelled by the solvent front in chromatography.
Rf value or Retention factor is the difference in rate of movement of the components in chromatography is caused by various factors.
Retention Factor depends on number of factors:
- Nature of Adsorbent: Different adsorbents will give different Rf value for same solvent.
- The Mobile phase: The purity of solvents and quantity of solvent mixed also affect Rf value.
- Activity: Temperature and storage conditions of adsorbent also affects Rf value.
- Thickness of layer: The layers may be of higher or lower thickness which also varies Rf value.
- Equilibrium: Equilibrium of chamber used for development is more important in TLC than in paper chromatography and hence saturation of atmosphere with the solvent vapour is important.
- The Temperature: Generally constant temperature must be maintain to carry out separation in order to avoid changes in solvent composition.
- Loading: Loading of sample must be small and appropriate about 10micro gram. If loading is more the spreading of spot and tailing may occur.
- Dipping Zone: Distance of starting point from the solvent surface is also a important factor.
- Chromatographic Technique: Rf value is also affected by different techniques applied for chromatogaphy.