What is luminol, and how is it used in crime scene investigations?

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ncchemist's profile pic

ncchemist | eNotes Employee

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Luminol is an organic chemical compound.  I cannot draw it here, but it consists of two fused 6 membered rings, one being an aniline and the other being a di-lactam (cyclic amide).  Its official chemical name is 5-amino-2,3-dihydro-1,4-phthalazinedione.  This structure gives luminol some distinct photochemical properties.  It can react with a base like hydroxide anions to produce a dianion.  This dianion can then react with oxygen (O2) to produce an unstable organic peroxide with an electron in an excited state that then immediately breaks down to release the energy as a photon (light energy), thus producing a blue glow.  This photochemical emission process is called chemiluminescence.

Luminol can be used in crime scene investigations to help detect the presence of blood.  The luminol is dissolved in a solvent with base and hydrogen peroxide mixed in as an activator.  The iron found in hemoglobin in blood can break down the hydrogen peroxide into water and oxygen (O2), thus reacting with the luminol to produce the chemiluminescence effect.  Since only a catalytic amount of iron is required for the chemical reaction, trace amounts of blood can be detected this way.  Luminol can also be used to detect metals like copper and iron in other applications as well.

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udonbutterfly's profile pic

udonbutterfly | Student, College Freshman | (Level 1) Valedictorian

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Luminol is a light producing compound that is a powdery and made of nitrogen, hydrogen, oxygen and carbon. Its written form is C8H7O3N3. Luminol is usually used to in crime investigations to expose traces of blood that may have been attempted to be cleaned. The luminol powder reacts with the blood to produce a blue glow in a dark room.

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