Experiment 29: Paper chromatography
To understand the principles of chromatography
- Filter paper strip
- solvent (absolute alcohol)
- Take a filter paper strip and using a pencil draw a horizontal line 3cm from one end of the paper. Then draw another line lengthwise (vertically) from the centre of the paper. Name the point at which the two lines intersect as P
- Put a drop of the mixture of red and blue inks at the point P. Let it dry in air. Put another drop on the same spot and dry again, so that the spot is rich in the mixture
- Pour 20mL of denatured alcohol and water in a beaker chamber and mix it well using a glass rod. This is used as the solvent.
- Suspend the filter paper vertically in the chromatographic chamber containing the solvent in such a way that the pencil line remains about 2cm above the solvent level
- Keep the set-up undisturbed for 15-20 minutes
Observations and Findings:
- After the solvent has risen about 15 cm you will notice two different spots of blue and red colors on the filter paper. The pattern is called chromatograph.
- Over time, we see a pattern composed of various colors / components of the ink
- Most inks (and organic compounds in general) contain several impurities. Chromatography is a separation technique to extract pure compounds
- Chromatography is a laboratory technique for the separation of a mixture.
- The mixture is dissolved in a fluid (gas, solvent, water, ...) called the mobile phase, which carries it through a system (a column, a capillary tube, a plate, or a sheet) on which is fixed a material called the stationary phase.
- The different constituents of the mixture have different affinities for the stationary phase.
- The different molecules stay longer or shorter on the stationary phase, depending on their interactions with its surface sites.
- So, they travel at different apparent velocities in the mobile fluid, causing them to separate.
- The separation is based on the differential partitioning between the mobile and the stationary phases.
- Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation