Luminol




Luminol[1]
IUPAC name 5-Amino-2,3-dihydro-
1,4-phthalazinedione
Other names o-Aminophthaloyl hydrazide
o-Aminophthalyl hydrazide
3-Aminophthalhydrazide
3-Aminophthalic hydrazide
Identifiers
CAS number 521-31-3
EINECS number 208-309-4
SMILES NC1=C(C(NNC2=O)=O)C2=CC=C1
Properties
Molecular formula C8H7N3O2
Molar mass 177.16 g/mol
Density g/cm3
Melting point

319-320 °C

Hazards
NFPA 704
1
2
0
 
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Luminol is a versatile 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. It is also used by biologists in cellular assays for the detection of cyanides.

Chemistry

Synthesis

Luminol may be synthesized beginning from 3-nitrosodium dithionite (Na2S2O4) produces luminol.


Chemiluminescence

  To exhibit its luminescence, the luminol must first be activated with an oxidant. Usually, a solution of iron compound, the hydrogen peroxide is decomposed to form oxygen and water:

2 H2O2 → O2 + 2 H2O

In a laboratory setting, the catalyst used is often Enzymes in a variety of biological systems may also catalyze the decomposition of hydrogen peroxide.

When luminol reacts with the hydroxide salt, a nitrogen to produce 5-aminophthalic acid with electrons in an excited state. As the excited state relaxes to the ground state, the excess energy is liberated as a photon, visible as blue light.



Use by crime scene investigators

Theory

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.

Drawbacks

Luminol has some drawbacks that may limit its use in a crime scene investigation:

  • Luminol also fluoresces in the presence of bleaches; and as 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.[4]


References

  1. ^ Merck Index, 11th Edition, 5470.
  2. ^ Huntress et al., J. Am. Chem. Soc., 1934, 241.
  3. ^ Synthesis of luminol
  4. ^ Technical note about Hemaglow
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Luminol". A list of authors is available in Wikipedia.