Ninhydrin test protocols

Updated November 21, 2016

Ninhydrin is a chemical substance mostly used in biochemical laboratories as a reagent for amino acids, which are small molecules that form proteins, as well as in forensics to detect finger prints and faint blood stains, according to the Australian Federal Police. Ninhydrin protocols include the ninhydrin test for amino acids, fingerprints revelation and ninhydrin test for peptide synthesis.

Ninhydrin Test for Amino Acids

Ninhydrin react with amino acids, producing a coloured solution. This protocol is used to detect the presence of amino acids in certain substances by using a solution of alcohol, ninhydrim and water. Technicians mix some drops of the analysed substance to the ninhydrim solution, boiling it for 15 to 20 seconds. If the substance contains amino acids, it becomes blue-violet. However, if it contains an amino acid called proline, it turns yellow, according to the Central Connecticut State University.

Fingerprint Revelation

This protocol uses a solution of ninhydrin and alcohol to reveal fingerprints. According to the International Association for Identification, technicians should first immerse the examined item in the solution for five seconds. Alternatively, they can spray the item. Later, they heat up to 80 degrees Celsius at 60 per cent to 70 per cent relative humidity. If on the item, fingerprints become visible and are later examined under special lights.

Ninhydrin Test for Peptide Synthesis

According to Peptide Station website, this protocol is used to detect ammonia in certain substances and to monitor peptide synthesis, which is related to a laboratory synthesis of proteins. Technicians use a solution of phenol or ethanol, the organic compound pyridine, ninhydrin and the analysed substance, previously prepared as a resin. The mixture is heated for up to 5 minutes at 95 degrees Celsius. A bluish colour indicates an unfinished peptide synthesis, while pink indicates a completed reaction.

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