Summary
Summary Alevel Chemistry - Column Chromatography (CC)
- Institution
- AQA
Column Chromatography (CC)
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Column Chromatography (CC)Used for purifying an organic product.
This needs to be done to separate it from unreacted chemicals or side products.
1. It involves packing a glass column with a solid absorbent material such as aluminium oxide
coated in water - called a slurry.
2. A solvent is then run down slowly and continually down the column. The solvent is the
mobile phase.
3. As the mixture is washed through the column its components separate out according to
how soluble they are in the mobile phase and how strongly adsorbed they are to the
stationary phase (retention).
4. Once the sample is added more solvent (eluent) is added on top as the solvent runs
through so that it does not dry out.
5. Each component will spend some time adsorbed onto the stationary phase and some time
dissolved in the mobile phase.
An inert solid (usually powdered silica gel or alumina) is the stationary phase which is
placed in the column.
A liquid solvent phase, mobile phase, is added into the column until it is saturated with
solvent.
The sample flows down the column via gravity and this can be done using a gas syringe to the
top of the column.
The longer a component spends dissolved in the mobile phase the quicker it travels down the
column.
If a component spends a long time adsorbed onto the stationary phase (greatest attraction and
affinity) it will take a long time to travel down the column. The more soluble a compound is the
quicker it passes through the column.
As a component of the mixture reaches the end of the column it is collected. It can then be
identified using the time taken to pass through the column (retention time) or mass
spectroscopy.
If the components are coloured they can be identified using Rf values.
If the components are colourless then other techniques such as fluorescence under UV
light to show the position in the column.
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