How to Test Using Ninhydrin

Using ninhydrin to test for the presence of amino acids is a fast and sensitive method. It also provides clear results with a dramatic color change for a positive result. The formation of an anion in the solution leads to a significant change in electron confinement, resulting in the final deep purple color. The ninhydrin test does, however, have its limitations. It is non-selective, meaning it will tell us only whether or not amino acids of some type are present, not how many different types or which ones.

Things You'll Need

• Test tube Beaker Bunsen burner 5 ml albumin 2% sample 1 ml ninhydrin 0.1% Latex gloves Safety glasses

Instructions

1. Put on safety glasses and latex gloves.

2. Place 2 ml of 2% albumin in a test tube. Albumin is a protein with water solubility that contains amino acids so we will get a positive result.

3. Add 1 ml of ninhydrin 0.1% to the test tube.

4. Heat the test tube in boiling water in a beaker over a Bunsen burner for 4 to 7 minutes, stirring gently.

5. Observe the sample for a color change. The yellow ninhydrin will develop to deep blue or purple known as Ruhemann's purple if amino acids are present.

Tips & Warnings

• The final color can vary based on the type(s) of amino acids present. Fingerprints contain trace amounts of amino acids, so ninhydrin spray can be used at crime scenes to make fingerprints visible.

• Use caution when handling ninhydrin. It is a strong oxidizing agent. Ninhydrin stains the skin blue and will take about a day to wear off if it comes in contact with your skin.