What Luminol can do in Criminal Investigation?
In criminal investigation dramas, it is easy to see this scene. When polices search at the crime scene and spray something on the ground or in the corner,a certain place lit up after a while, , and the police shouted solemnly or excitedly, "I found it!" .As an editor of Desheng, I like watching criminal investigation films very much. Every time they inspect the crime scene, simulate the case, poke the layers of clues, and finally catch the prisoner, I feel really amazing! So, as a true fan of criminal investigation films, let me lead you to reveal how Luminol detects bloodstains in the reconnaissance scene!
The above image is a scene where the shape of bloodstains is detected, but these bloodstains are invisible, they are displayed by a specific method. In fact, the case is normal in many detective scenes.The bloodstains at the crime scene are often handled or cleaned. It is invisible for us, not to mention to watch the shape of the bloodstains.But if we use special methods to show these bloodstains,you can make a more effective judgment on the case according to the shape and amount of the bloodstain. It turns out that this was the famous Luminol reaction in criminal investigation, which is used to detect bloodstains at the crime scene.
Principle of Luminol luminescence
First,sodium hypochlorite(NaClO) oxidizes luminol to make it glow;
Second, hydrogen peroxide(H₂O₂) reacts with sodium hypochlorite ( NaClO) to generate oxygen to oxidize luminol to make it glow:
First is sodium hypochlorite reacts with hydrogen peroxide,NaClO + H₂O₂ == NaCl + O₂ + H₂O. Then , when luminol reacts with hydroxide and forms a double negative ion (Dianion), which can be oxidized by the oxygen decomposed by hydrogen peroxide, and generate an organic peroxide that is very unstable and immediately decomposes to nitrogen (Luminol is oxidized by an organic oxidant such as dimethyl sulfoxide to form nitrogen-containing organics instead of nitrogen) to generate excited 3-aminophthalic acid. In the transition from the excitation to normal state, the released energy exists in the form of photons with a wavelength in visible blue light.
Shortcoming of Luminol
First,luminol fluoresces with copper, copper-containing alloys, or certain bleaches, and misleading the existence of blood.
Second,luminol fluoresces with animal blood and blood in urine, so if the room to be tested contains urine or animal blood, the test results will be biased.Third,Luminol reacts with excrement and emits the same blue light as it reacts with blood.
Ways to Avoid Interference when using Luminol
1. After drying a few days of crime scene, the disturbing effect of bleach will disappear, and luminol will still glow with blood even after many years .
2. Use a compound that inhibits the interference effect of hypochlorous acid. Suitable inhibitors have been found for the chemical structure of hypochlorous acid contains with chlorine atoms.
Knowing that bloodstain detection in criminal investigation is using luminol,you’ll find that chemistry is really amazing. luminol reagent is used not only on biochemical and metal ion detection, but also as a marker in carboxylic acid and ammonia compound.With very high sensitivity,it is used in detecting bloodstain in criminal investigation.
Luminol produced by Desheng is a light yellow powder. It needs to be dissolved with lye when used and stored in the dark place!
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