Ninhydrin Solid Peptide Synthesis

Ninhydrin also called (Triketohydrindane hydrate) is a chemical used to detect ammonia or primary amines. Ninhydrin is also used to monitor deprotection in solid phase peptide synthesis. Deprotection of the growing peptide chain yields blue with a ninhydrin test. If the next peptide residue is coupled then the test is colorless or yellow.

 

Ninhydrin Test Protocol

• Aliquot 20μL of resin from the reaction tube into filter tube.
• Wash the resin. Aliquot with DMF and DCM, fast flow. Rinse well.
• Dry aliquot until it is a powder.
• Transfer powder into glass culture tube.
• Add 40μL phenol / ethanol + 40μL KCN / pyridine + 20μL Ninhydrin / ethanol to the resin aliquot.
• Heat the tube at 95 °C for 2-5 minutes.
• Bluish color indicates an unfinished reaction.
• A completed reaction looks pink.