In column chromatography (CC), a solid material fills the column while a liquid solvent moves down through it.
The two phases
Stationary phase: usually powdered silica or alumina packed into a vertical glass tube. Using a powder gives a large surface area for interaction with the substances being separated.
Mobile phase: a liquid solvent, or a mixture of solvents, which travels down through the packed solid.
A filter, plug or glass wool at the lower end keeps the stationary-phase particles inside the column while the liquid is able to pass through.
Preparing the column
- Fill the glass column with powdered silica or alumina to form the stationary phase.
- Add enough solvent to wet and cover the packed solid.
- Dissolve the mixture in as little solvent as practical before loading it onto the column.
- Transfer the solution carefully onto the top of the packing so that its surface is not disturbed.
- Add further solvent, called the eluent, and allow it to travel down through the column.
| Setup point | Why it matters |
|---|---|
| Produce uniform packing | Gaps or cracks can give uneven routes through the stationary phase and reduce the quality of separation. |
| Load the sample gently | Keeping the top surface undisturbed gives the mixture a narrow starting region. |
| Maintain solvent above the packing | Additional eluent is supplied as the experiment proceeds so that the packed solid stays wet. |