Ninhydrin spray is used to detect invisible and blood-based fingerprints on porous surfaces such as paper, cardboard, money, raw wood, plasterboard, plywood, etc.
The detection of sweat and grease stains with a ninhydrin solution is based on its reaction with amino compounds (alpha-amino acids) contained in human skin secretions (e.g. sweat).
Ninhydrin stains the stains with a color that can vary from orange to purple, depending on the chemical composition of the stain and the processing conditions. After applying the solution, the area with the stains is kept in a dry place for 48 hours (placing the object in a dark place is not necessary), sometimes the development of stains can take several weeks, but the reaction can be accelerated by heating to 80-90 degrees or moistening. With the help of ninhydrin, stains from 2 years ago are revealed (there are cases of detecting older stains on paper).
In old traces, proteins contained in the sweat and fat layer break down over time into amino acids, with which ninhydrin reacts, coloring the trace blue-violet or bright red. In fresh traces, the percentage of monomers (amino acids) is lower, which affects the saturation and speed of coloring of the detected trace.
In practice, there were cases when even after a long time (up to 6 months after treatment with ninhydrin), the reaction continued, and initially faint traces eventually appeared and acquired a rich color. To increase the shelf life and ease of use, it is packaged in aerosol cans with a volume of 400 ml.
Ninhydrin spray in aerosol cans allows you to process objects both in laboratory conditions and at the scene of the incident.
When working with ninhydrin solution, safety precautions must be observed: process objects in a well-ventilated area and in rubber gloves; avoid contact with skin and mucous membranes.