The magic key of the murder scene—luminol

Many people are very interested in detecting cases, because the confusing case is often more attractive, you never know what the truth is. The murderer often smashes the scene after committing the crime and destroys the traces of the crime. But the witty police always find out those "invisible clues" at the crime scene, which uses Luminol.

What is Luminol

Luminol, also known as luminescent ammonia. A reagent that can detect blood that can not be observed by the naked eye at the crime scene, it can show a very small amount of blood (octal blood reaction). The chemical name is 3-aminophthalic acid hydrazide. It is a blue crystal or beige powder at room temperature and is a relatively stable synthetic organic compound. The chemical formula is C₈H₇N₃O₂. At the same time, luminol is a strong acid, which has a certain stimulating effect on eyes, skin and respiratory tract.

The test principle of Luminol

Luminol was synthesized in 1853. In 1928, chemists first discovered that this compound has a wonderful property that emits blue light when it is oxidized. A few years later, some people thought of using this feature to detect blood. The blood contains hemoglobin, and the oxygen we inhale from the air is transported to all parts of the body by this protein. Hemoglobin contains iron, which catalyzes the decomposition of hydrogen peroxide, turns hydrogen peroxide into water and monooxygen, and monooxygen oxidizes luminol to make it glow. In the examination of blood marks, hemoglobin, a protein in hemoglobin responsible for transporting oxygen, catalyzes the reaction of luminol with hydrogen peroxide, showing blue-green fluorescence. This method of detection is extremely sensitive and can detect blood in the form of only one part per million, even if a small drop of blood is dripped into a large tank of water. The amount of catalyst required for this reaction is very small, so luminol can detect traces of blood. The illumination lasts for about 30 seconds and can be observed with long exposure photos, and the surrounding environment should not be too bright.

Shortcomings of the luminol reaction

Although this reaction can accurately detect the blood on the scene, the chemical reaction will destroy other evidence on the crime scene, which will hinder the investigation. Therefore, under normal circumstances, the police will not spray luminescent ammonia on the surface of all objects as soon as they enter the crime scene.

Luminescent ammonia also has some drawbacks. It also illuminates substances such as copper and bleach rather than blood. Moreover, the use of luminescent ammonia to detect blood can also destroy blood evidence, although studies have shown that a DNA match that can be produced by itself is often found in luminescent ammonia blood tests. The last point is that it is unclear whether luminescent ammonia is a carcinogen.

Luminous ammonia is only responsible for assisting the investigation of the crime scene in the criminal investigation. It just proves whether there is blood. It is only one step in the investigation process.

Related links: Luminol

Edited by Suzhou Yacoo Science Co., Ltd.