Analysis of amino acids by paper chromatography- Theory

Chromatography is a technique for analyzing or separating mixtures of substances into their components. There are various forms of chromatography techniques. Generally all of these forms involve two distinct phases; the Stationary phase and the mobile phase.
In paper chromatography the stationary phase:- Absorbent paper, Mobile phase:- A suitable liquid or a mixture of solvents.
Mobile phase flows through the stationary phase and carries the components of the mixture with it.
The stationary phase retards the passage of components of the sample.
When components pass through the system at different rates they become separated in time.
This depend on their solubility in the solvent and how well the chromatography paper absorbs.
More soluble the component is in the solvent and the less it absorb into the paper, the faster it would move with the solvent on the paper and hence the spot appears further up the paper.
There are three types of paper chromatography.

• Ascending paper chromatography
• Descending chromatography
• 2-D paper chromatography

In paper chromatography cellulose in the form of paper sheets makes an identical support medium as it has the ability to absorb water molecules between cellulose fibers and forms a stationary hydropholic phase.

In analysis of amino acids by paper chromatography, the location of the amino acids can be determined by spraying the paper with Ninhydrin. The Ninhydrin forms a blue violet complex with an amino acid except for proline/hydroxy proline which gives a yellow color complex.