Ninhydrin test


This test is for the identification of α – amino acids, proteins and peptides.


  • Ninhydrin, an oxidsing agent causes oxidative decarboxylation of α-amino acids.
  • It removes CO2 and NH3 and the product is one carbon lesser than the parent amino acid.
  • The reduced ninhydrin (hydrindantin) reacts with released NH3 and one more molecule of
  • Ninhydrin to produce a blue colored complex known as “Ruhemann’s purple”.


  • To 1 mL of test solution add 2-5 drops of Ninhydrin solution, mix well and heat it.
  • Observe the development of pink or purple or violet blue color.
  • Imino acids (proline and hydoxy proline) give a yellow colored complex.
  • This test also answers for proteins / peptides as they contain α-amino acids.
Last modified: Wednesday, 23 March 2011, 8:45 AM