Paper Chromatography
Principles of Paper Chromatography
- A solution is a mixture that cannot be separated by filtration, therefore an alternative separation technique must be used
- Paper chromatography is used to separate a mixture of liquids that have different intermolecular interactions in a given solvent (e.g. separate the coloured inks that were used to make black ink)
- The substances can be identified by the distance they travel across a sheet of chromatography paper
- The stronger the interaction with the solvent, the farther the distance the component will travel up the chromatography paper
- The solvent will travel up the paper because the liquid molecules will have adhesive and cohesive forces with the pores of the chromatography paper
- Since the solvent moves up the paper, the solvent is called the mobile phase
- Since the chromatography paper stays in a fixed position, it is called the stationary phase
- The different components of the mixture will be separated because of the different intermolecular interactions with the mobile and the stationary phases
Conducting a Paper Chromatography analysis
- Draw a pencil line at the bottom of the chromatography paper. A sample of the mixture is placed as a spot on the top of the line. Additional spots of known reference compounds are placed to identify the components of the mixture
- Place the paper into the solvent container, making sure that the line sits above the level of the solvent. This will prevent the samples from washing into the solvent container
- Analyze the chromatography paper by comparing the sample with the reference compounds
Diagram to Show the Method of Chromatography
Analysis of the composition of ink that can be used using paper chromatography. Blue ink travels the most distance showing the strongest interaction with the solvent and the weakest interaction with the chromatography paper
- The component that travels the greatest distance along the paper has the strongest intermolecular interaction with the mobile phase and the weakest interaction with the stationary phase
- The component that travels the shortest distance along the paper has the weakest intermolecular interaction with the mobile phase and the strongest interaction with the stationary phase