chromatography

• Formulations are complex mixtures of chemicals which have a specific use
• Chromatography


  Can be used to identify the substances present in a mixture of solutes
• Paper chromatography


  1. Draw a pencil line across the chromatography paper, 1 - 2 cm from the bottom

  2. Use a pipette or capillary tube to add small spots of each ink to the line on the paper

  3. Place the paper into a container with a suitable solvent in the bottom

  4. Allow the solvent to move through the paper, but remove the chromatogram before it reaches the top

  5. Allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent
• Chromatography is used to separate different substances dissolved in a liquid
• Chromatography can be used to separate and tell the difference between coloured substances
• R_f value


  Distance travelled by substance / distance travelled by solvent
• Measurements in millimetres are more precise than those in centimetres, and will give more precise R_f values
• Hazards and precautions


  • Harmful solvent - Skin irritation, avoid skin contact, wear gloves
  • Harmful solvent - Breathing difficulties, ensure adequate ventilation or use a fume cupboard