Luminol Reaction and Its Luminescence Principle

Luminol, also known as luminescent ammonia, CAS521-31-3, can be used to detect blood that can not be observed by naked eyes at the crime scene, and can show very trace blood morphology (occult blood reaction).The chemical name is 5-amino-phthalazide.It is a blue crystal or pale yellow powder at room temperature, and is a relatively stable synthetic organic compound.Let me give a detailed introduction to the luminol, luminol reaction and its luminescence principle.

Brief introduction of luminol

Luminol is an ancient and commonly used reagent, which can be oxidized by peroxides and luminescent simultaneously under alkaline conditions. The redox reaction between luminol and peroxides requires a catalyst. This catalyst is generally multivalent metal ions, peroxidases such as iron, horseradish peroxidase, etc. This method is often used to detect the content of peroxides, heavy metals, peroxidases, etc.And the derived methods for the detection of free radicals, the analysis of toxicants and the analysis based on peroxidase and glucose oxidase.

In general, luminol reacts rapidly with hydrogen peroxide in the presence of certain catalysts.Commonly used catalysts are metal ions. In a large concentration range, the concentration of metal ions is proportional to the luminescence intensity, so that chemiluminescence analysis of some metal ions can be carried out. With this reaction, those organic compounds containing metal ions can be analyzed with high sensitivity.Secondly, using the inhibitory effect of organic compounds on luminol chemiluminescence reaction, the organic compounds with quenching effect on chemiluminescence reaction were determined.The third is the indirect determination of inorganic or organic compounds by coupling reaction.

Luminol reaction

The luminol reaction is a classical chemiluminescence reaction, and unlike fluorescence, the source of luminescence is the excited-state intermediate generated in the chemical reaction, which releases blue light when it returns to the ground state.Luminol reacts with oxidants such as hydrogen peroxide in an alkaline environment to produce luminescent intermediates, which usually require the catalysis of transition metal salts, such as iron, copper or cobalt.

Luminol luminescence principle

First, sodium hypochlorite oxidizes luminol to make it luminescent;

The second is that hydrogen peroxide reacts with sodium hypochlorite to produce oxygen to oxidize luminol and make it luminescent:

First is the equation for the reaction of sodium hypochlorite with hydrogen peroxide:

NaClO + H₂O₂ = NaCl + O₂ + H₂O

Secondly, when luminol reacts with hydroxide, it produces a double negative ion (Dianion), which can be oxidized by oxygen decomposed from hydrogen peroxide and the product is an organic peroxide.This peroxide is very unstable and immediately decomposes into nitrogen (luminol is oxidized by an organic oxidant such as dimethyl sulfoxide to produce not nitrogen but nitrogen-containing organic matter), resulting in an excited state of 3-aminophthalic acid.In the transition from the excited state to the ground state, the released energy exists in the form of photons and the wavelength is located in the blue part of the visible light.

Luminol is a strong acid, which has a certain irritating effect on eyes, skin and respiratory tract. Care should be taken when using it.Desheng R&D and production of chemiluminescent reagents for up to 15 years, has an independent R&D team and advanced production equipment, can provide high-quality luminol, acridine ester products, welcome to call detailed consultation if necessary.