The reaction of ninhydrin with an amino acid to form a purple colored product.

Scheme 8

B. Ion-Exchange Chromatography:
In this technique, a column is packed with an insoluble ion-exchange resin. Then, a solution of a mixture of amino acids is loaded on the top of the column, and eluted with aqueous solutions of increasing pH. Since the amino acids bind with the resin at different extent, during the elution, the weakly bound amino acid can flow faster compared to that bound strongly, which can be collected as different fractions. Scheme 9 presents the structure of section of a commonly used resin and diagram of the ion-exchange chromatography separation.

 

Scheme 9