Full explanation of the luminol reaction

Luminol is also called aminophthalic hydrazide. In 1928, some researchers discovered that it has the wonderful property of emitting blue light under the condition of oxidation. After continuous development, some people try to detect blood stains through this feature, because blood contains hemoglobin, when the human body inhales oxygen, it is then transported to the whole body.

When detecting bloodstains, luminol reacts with heme in the blood, showing blue light. This test method is highly sensitive. Even if the bloodstains have been scrubbed for a long time, the presence of components in blood cells can be identified.

In fact, to put it simply, at the crime scene, as long as there is blood stained place, no matter what method is used to clean it, even if it takes a long time, as long as it is sprayed with luminol reagent and observed in a dark environment, the original blood stained will automatically fluoresce.

This is because after spraying, the blood in the blood will quickly catalyze light, the light-emitting time is about 30s, the surrounding environment is not easy to be too bright, and the amount of catalyst used in this reaction is very small.

In the case of no change, Luminol is a yellow powder with stable performance, but it is also a strong acid, which is irritating to human skin to a certain extent. It only emits light when it is oxidized. Usually, an aqueous solution of H2O2 and an alkaline mixed aqueous solution of hydroxide are used as activators. After the catalysis of iron compounds, the aqueous hydrogen peroxide solution is decomposed into oxygen and water.

At the same time, when it is combined with hydroxide, it produces two negative ions, and the O2 decomposed by H2O2 is oxidized and becomes an organic peroxide. Because the composition is unstable, it will immediately decompose oxygen, thereby generating excited state 3- Aminophthalic acid.

In the process of converting the excited state to the ground state, it is released in the form of photons, and blue light appears, but it should be noted that it will also react with other substances with oxidative properties, but the time and length of the display are different from those of the blood test.

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