AQA A Level Chemistry

Revision Notes

7.11.1 Chromatography

Principles of Chromatography

Principles of Chromatography

  • Chromatography is a technique that enables the separation of mixtures and includes:
    • thin-layer chromatography (TLC)
    • column chromatography (CC)
    • gas chromatography (GC)
  • All of these chromatography techniques makes use of the principle that components in a mixture when dissolved in a fluid (mobile phase), will flow through another material (stationary phase) at varying rates
  • The rate of separation depends upon how the components in the mixture interact with the stationary phase (their retention) and how soluble they are in the mobile phase

Retention times

  • Each component in a mixture will have a unique retention factor (Rf value), which is calculated by dividing the distance the compound moves by the distance moved by the solvent

Thin Layer Chromatography Basics equation

Worked Example

A mixture of amino acids is analysed by thin layer chromatography (TLC). The TLC plate produced is shown below. Identify the amino acids in the sample using the table of values for Rf.


Blue spot Rf value = \frac{2.82}{4.63} =  0.61 = Leucine

Green spot Rf value = \frac{2.45}{4.63} = 0.536 = Isoleucine

Red spot Rf value = \frac{2.04}{4.63} = 0.44 = Valine


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