Which test reacts with all alpha-amino acids upon heating to produce an intense purple-blue color (Ruhemann's purple)?
Answer and explanation
Correct answer: D. Ninhydrin test
- Step 1: Ninhydrin (triketohydrindene hydrate) is a strong oxidizing agent. Step 2. It decarboxylates and deaminates alpha-amino acids, forming a condensation complex known as Ruhemann's purple (absorption max at 570 nm). Answer: Ninhydrin test. Why not the others: Biuret tests peptide bonds; Iodoform tests methyl carbonyls; Xanthoproteic tests aromatic amino acids with nitric acid.
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