Practice question

Ninhydrin, or 2,2-dihydroxy-1,3-indandione, is classical colorimetric reagent for detection of alpha-amino acids on paper chromatography or electrophoretograms. Primary amines and free amino acids undergo oxidative deamination and condensation with ninhydrin to produce deep purple chromophore known as Ruhemann's purple, absorbing at 570 nanometers, enabling sensitive visualization of separated amino acid bands. Secondary amines like proline yield yellow product. It does not specifically detect lipids, sugars, or intact proteins under similar conditions, though N-terminal residues may react weakly. Lipids require Sudan dyes, sugars require anisaldehyde or orcinol reagents.