1. CHROMATOGRAPHY

2. Chromatography - Definition
A method of separation and analysis of a mixture of soluble chemical substances.

3. What can chromatography be used for?
- identify additives in foods - compare fibres found at a crime scene - identify drugs and alcohol - test water samples for pollution - detect bombs in airports - detecting pesticides or insecticides in food - fingerprinting

4. Paper Chromatography – how does it work?
1. Chromatography lets us separate inks and dyes according to the size and the solubility of their particles in the solvent. 2. As the solvent (water) rises through the paper it dissolves the sample mixture, which will then travel up the paper. 3. Small particles travel further than large particles, due to the differences in solubility and their attractions with the paper. 4.Insoluble dye will be left on the base line

5. Chromatography
TASK
Write step-by-step instructions on how to carry out the separation of food dyes using this technique.
Copy this picture into your books to help you explain the steps.
Beaker
Separated ink particles
Spot of dye to be separated
Solvent

6. 1.Solvent used in chromatography
A) If substance is water soluble then water is used as a solvent.
B) If substance is water insoluble then organic solvent is used as a solvent e.g. ethanol, propanone
2.Base-line should not be drawn in ink because it interferes the result.
3.The level of the solvent must be below the base- line otherwise the dyes will be dissolved/washed off.

7. Retention factor (Rf) values
The Rf factor is used to compare the components of various samples. The Rf values of suspect samples can be compared with known samples.
Rf = distance travelled by the solute[dye] from base line
distance travelled by the solvent from the base line
Solvent front
the point at which the water stopped moving up the paper
If two substances have the same Rf value, they are likely (but not necessarily) the same compound. If they have different Rf values, they are definitely different compounds.
Spot
the point at which a band or spot of colour is
Base line
the line where the original sample was placed

8. Locating Agent
Colourless substance can be made visible by spraying the chromatogram with a locating agent.

9. Leaves chromatography