Forensic Analysis of Blood using Luminol

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Luminol
  • Redox reaction with oxygen in the presence of catalyst produces a bright blue glow.
  • Used in forensic analysis for detection of blood
  • Iron in hemoglobin acts as catalyst
  • Other common catalysts
    • Biological: copper and cyanide
    • Laboratory: potassium ferricyanide
Chemiluminescence
  • Chemical reaction produces an excited state compound
  • Excited state compound passes through intermediate
  • Decays to ground state
  • Emits a photon characteristic to compound
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Sample of Lumniol
source: http://en.wikipedia.org/wiki/File:Luminol2006.jpg


Chemical Reactions

1.) Luminol must be activated by hydroxide salt forming a dianion:

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In the presence of iron (catalyst), hydrogen peroxide decomposes to form oxygen

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The dianion reacts with oxygen producing the unstable organic peroxide intermediate:

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This intermediate decomposes from higher energy states to the ground state, emitting a photon. 

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intersystem crossing is radiationless transition between different states of spin multiplicity

Chemiluminescense

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Chemiluminescense Energy Diagram.
  As shown by the red dot, Luminol is excited into the triplet dianion
 state chemically.  Through intersystem crossing, the molecule is able to transtion into the singlet dianion state of
 the same energy.  Finally, the molecule fluoresces from the singlet dianion state to the ground state dianion
emitting a photon of energy hv.

Advantages
  • Fast
  • Easy
Disadvantages
Application
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Luminol can be used in a healthcare setting for contamination assessment (Bergervoet, et. al. 2008). 

References


P.W.M.
Bergervoet, N. van Riessen, F.W. Sebens, W.C. van der Zwet.  "Application of the forensic Luminol for blood in infection control.J of Hospital Infection.  68 (2008): 329-333. 


http://www.3dchem.com/molecules.asp?ID=334


http://www.experiencefestival.com/a/Luminol_-_Use_by_Crime_Scene_Investigators/id/1732139