Chromatography (AQA A Level Chemistry)

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) - sometimes called gas-liquid chromatography (GLC)

• 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

Summary Table of Chromatography Component Phases

Retention factor

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

• In gas-liquid chromatography (GLC), the term retention time is used
  • This is the time that elapses from the moment of injection to when a component exits the chromatography tube