Really informative & simple explanation 🙂

It's Avagadbro

The Ninhydrin Test is used to test for the presence of amino acids (NOT proteins).

Ninhydrin degrades amino acids into aldehydes, ammonia, and CO₂  (carbon dioxide) through a series of reactions; the net result is ninhydrin in a partially reduced form hydrindantin:

 (reaction 1)

Ninhydrin then condenses with ammonia and hydrindantin to produce a blueish-purple pigment.

(reaction 2)

The typical positive result is a blueish-purple color, as seen in the image below:

(Image credit: pdecell)

But, there is an amino acid that gives a yellow result. This amino acid is PROLINE.

(Image Credit)

As you can see, proline has a ring structure (secondary amino acid).

The blueish-purple result is usually associated with primary amino acids. In these amino acids, the N is free to react with ninhydrin. However, in proline, the N is not available for reaction as it is locked…

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