Lumino in criminal investigation

Details:

Luminol

In the criminal investigation play, it is easy to see this scene. The police searching the scene sprayed something on the ground or corner. After a while, a certain place lit up, and the police shouted solemnly or excitedly, "found!" As a Xiaobian of Desheng, I like watching criminal investigation films very much. Every time they go through the investigation of the scene, the reasoning simulation of the case, remove layers of clues, and finally catch the prisoner, they really feel so powerful! Then, as the true love powder of the criminal investigation film, I will lead you to uncover how Lumino detected blood at the reconnaissance scene!

The above picture is a scene in which the shape of blood is detected, but these blood stains cannot be seen by the naked eye, but are displayed in a specific way. In fact, this is true in many detective scenes. The blood stains at the crime scene have often been treated or cleaned. It is difficult for our naked eyes to see the existence and shape of the blood stains, but if we show these blood stains with special methods, we can make a more effective judgment on the case according to the shape and quantity of the blood stains. Originally, this is the famous luminol reaction in criminal investigation, which is used to detect the traces of blood at the scene.

First, sodium hypochlorite oxidizes luminol to make it glow;

Second, hydrogen peroxide reacts with sodium hypochlorite to generate oxygen to oxidize luminol and make it glow:

The first is the equation of the reaction between sodium hypochlorite and hydrogen peroxide: NaClO + H2O2 = = NaCl + O2 + H2O

Secondly, luminol reacts with hydroxide to form a dianion, which can be oxidized by oxygen decomposed by hydrogen peroxide, and the product is an organic peroxide. The peroxide is very unstable and immediately decomposes into nitrogen (luminol is oxidized by organic oxidants such as dimethyl sulfoxide to form nitrogen-containing organic matter instead of nitrogen) to form excited 3-aminophthalic acid. In the transition from excited state to ground state, the released energy exists in the form of photons, and the wavelength is located in the blue part of visible light.

Luminol luminescent defect

1. Luminol fluoresces in the presence of copper, copper containing alloy or some bleach, which will strongly cover up the presence of blood.

2. Luminol can detect a small amount of blood in animal blood and urine. Therefore, if the room to be tested contains urine or animal blood, the test results will be biased.

3. Luminol reacts with excreta and emits the same light as blood.

Luminol's method of avoiding interference

1. After drying on site for a few days, the interference effect of bleach will disappear, and luminol can glow even after many years.

2. Use a compound that can inhibit the interference of hypochlorous acid. People have found suitable inhibitors for the chemical structure of hypochlorous acid, such as the chlorine atom it contains.

Knowing that the principle of detecting blood stains in criminal investigation is luminol reaction, do you think chemistry is really magical! Luminol reagent is not only used for biochemical detection, labeling of carboxylic acid and ammonia compounds and detection of metal ions, but also often used for criminal investigation blood detection, with very high sensitivity. Luminol produced by Desheng is light yellow powder, which needs to be dissolved in lye when in use. It is prepared now and stored away from light!