Forensic analysis of blood using luminol
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Forensic Analysis of Blood using Luminol. 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

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Forensic Analysis of Blood using Luminol

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Forensic analysis of blood using luminol

Forensic Analysis of Blood using Luminol


Luminol

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

Luminol

5-Amino-2,3-dihydro-1,4-phthalazinedione


Chemiluminescence

Chemiluminescence

  • Chemical reaction produces an excited state compound

  • Excited state compound passes through intermediate

    • Decays to ground state

    • Emits a photon

http://en.wikipedia.org/wiki/File:Luminol2006.jpg


Chemical reactions

Chemical Reactions

  • Luminol must be activated by hydroxide salt forming a dianion:

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

    2H2O2 O2 + 2H2O

-2 OH-

2 H20 +

Luminol

Dianion

Dianion

Fe


Forensic analysis of blood using luminol

+O2

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

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

Triplet Dianion(excited state)

Dianion

Intersystem

Crossing

hv

Triplet Dianion

(excited state)

Singlet Dianion

(excited state)

Ground State

*intersystem crossing is radiationless transition between different states of spin multiplicity


Chemiluminescence1

Chemiluminescence

Triplet Dianion

Singlet Dianion

Energy

Ground State

Dianion

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 disadvantages

Advantages & Disadvantages

  • Advantages:

    • Fast

    • Easy

  • Disadvantages:

    • Fluoresces in the presence of other compounds, including bleach & horseradish

    • Can prevent other testing

    • Possible carcinogen


Application

Application

  • Luminol can be used in a healthcare setting for contamination assessment


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