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Luminol

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Luminol is a versatile chemical that exhibits chemiluminescence, with a striking blue glow, when mixed with an appropriate oxidizing agent. It is a white to slightly yellow crystalline solid that is soluble in water and most polar organic solvents.

Luminol is used by forensic investigators to detect trace amounts of blood left at crime scenes as it reacts with iron found in hemoglobin. It is also used by biologists in cellular assays for the detection of copper, iron, and cyanides.

Use by CSIsEdit

Luminol is used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed. The investigator prepares a solution of luminol and the activator and sprays it throughout the area under investigation. The iron present in any blood in the area catalyzes the chemical reaction that leads to the luminesence revealing the location of the blood. The amount of catalyst necessary for the reaction to occur is very small relative to the amount of luminol, allowing the detection of even trace amounts of blood. The glow lasts for about 30 seconds and is blue. Detecting the glow requires a fairly dark room. Any glow detected may be documented by a long exposure photograph.

LimitationsEdit

  • Luminol also fluoresces in the presence of copper or an alloy of copper, horseradish, and certain bleaches; and, as a result, if a crime scene is thoroughly cleaned with a bleach solution, residual bleach will cause the entire crime scene to fluoresce, effectively camouflaging any organic evidence, such as blood.
  • Luminol will also detect the small amounts of blood present in urine and it can be distorted if animal blood is present in the room that is being tested.
  • Luminol reacts with fecal matter, causing the same glow as if it were blood.
  • Luminol's presence may prevent other tests from being performed on a piece of evidence. However, it has been shown that DNA can be successfully extracted from samples treated with luminol reagent.
  • Using too much luminol on a blood sample can dissolve the hemoglobin, causing the DNA to become unusable.

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