Column chromatography (CC) works on the same principle as TLC, but is used to separate and collect larger amounts of the components of a mixture, for example to purify the product of a synthesis.The stationary phase is a solid such as silica or alumina powder, packed into a vertical glass column with a tap at the bottom. The mobile phase is a liquid solvent, called the eluent.Method:
1. Pack the column with the solid, usually as a slurry in the solvent, making sure there are no air bubbles or gaps.
2. Add the mixture, dissolved in a small volume of solvent, to the top of the column.
3. Keep adding solvent at the top so it runs down through the column. The column must not be allowed to run dry.
4. The components move down at different rates. A component that is more soluble in the solvent and less strongly adsorbed onto the solid moves faster and comes out of the bottom first.
5. Collect the liquid leaving the column in a series of separate portions, called fractions.
Coloured components can be seen as bands moving down the column. For colourless compounds, each fraction is tested, for example by TLC, to find which fractions contain which component. Fractions containing the same pure component are combined, and the solvent is evaporated to leave the pure substance.The separation can be improved by using a longer column or a different solvent. Compared with TLC, column chromatography is slower, but it lets you recover useful quantities of each separated substance.
1. Pack the column with the solid, usually as a slurry in the solvent, making sure there are no air bubbles or gaps.
2. Add the mixture, dissolved in a small volume of solvent, to the top of the column.
3. Keep adding solvent at the top so it runs down through the column. The column must not be allowed to run dry.
4. The components move down at different rates. A component that is more soluble in the solvent and less strongly adsorbed onto the solid moves faster and comes out of the bottom first.
5. Collect the liquid leaving the column in a series of separate portions, called fractions.
Coloured components can be seen as bands moving down the column. For colourless compounds, each fraction is tested, for example by TLC, to find which fractions contain which component. Fractions containing the same pure component are combined, and the solvent is evaporated to leave the pure substance.The separation can be improved by using a longer column or a different solvent. Compared with TLC, column chromatography is slower, but it lets you recover useful quantities of each separated substance.