Proteins

Ninhydrin turns milk lilac by reacting with its proteins!

Difficulty:
Danger:
Duration:
10 minutes
Proteins

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
  • Observe safety precautions when working with boiling water.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

What kind of milk should I use?

It doesn’t matter. You can use any variety of plant or animal milk.

Purple spots appeared on my skin after the experiment. What should I do?

A little bit of ninhydrin probably stained your skin. This substance is a highly effective dye even in small doses! But don’t worry – it’s harmless in the amount provided in your set. Just be sure to wash it off thoroughly with water; the color will disappear in a few days.

The purple color did not appear. What should I do?

Replace the hot water with boiling water and leave the test tube for another 5-10 minutes. If this does not help, try to repeat the experiment with a different variety of milk.

Step-by-step instructions

For this experiment, you’ll need milk or some other protein-containing liquid.

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First, prepare a sample of your protein-containing liquid.

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Ninhydrin, the reagent used to detect proteins, works best when heated.

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It takes some time for the reaction to begin.

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If your sample contains proteins, you’ll see a bright purple color appearing in your liquid.

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Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

Ninhydrin is a molecule that turns purple when it reacts with certain fragments of molecules called "primary amines." Primary amines are present in many proteins and their building blocks (amino acids). Ninhydrin can therefore be used to detect proteins in a sample. For instance, you can use it to detect proteins in egg white or in meat broth . What you shouldn't do is touch ninhydrin with your bare fingers: there are lots of proteins and amino acids on your skin and you'll have a hard time washing the purple substance off your hands. People leave these same protein and amino acid residues on the surfaces they touch. And if you apply some ninhydrin to such a surface very carefully you'll see—you guessed it—fingerprints!