Methods+of+Blood+Detection+CEB

Blood Detection Methods:

Three typical Types: -used to confirm blood, find invisible stains, and enhance hard to see stains 1) Crystal Tests: Haem forms crystals when reacted with certain reagents. Common is pyridine (pink crystals)

2) Catalytic Tests: Haem can catalyze the breakdown of hydrogen peroxide. H2O2 breaks down another substance is oxidized producing color change. Positive doesn’t mean its blood just a possibility

3) Instrumental Methods: chromatography can be used to identify the presence of hemoglobin

Introduction: Is the stain blood or not? -Chemical reactions are faster to find out if yes or no

Chemical Methods used to Detect Blood -all methods depend on presence of hemoglobin Crystal Tests- -Test is carried out on a microscope slide - An alkaline solution of pyridine is added to the stain and, if blood is present, pink crystals of a complex between pyridine and haem form as the slide is warmed - An alkaline solution of pyridine is added to the stain and, if blood is present, pink crystals of a complex between pyridine and haem form - a positive control should always be run for comparison

Catalytic Tests- -very sensitive -are subject to many interferences

Instrumental Methods -high performance liquid chromatography (HPLC) - can also give an estimate of how old blood is

Applications: Conformation: -Sangur stick or Kastle-Meyer test Sangur Sticks- rubbed gently on the stain and moistened, pale yellow to intense greenish blue indicated probably blood KMT- phenolphthalein is kept in alkaline solution with zinc. Colorless ot bright pink means blood --for both tests must be confirmed with biological test

Detection of non-visible bloodstains: -Luminol- solution applied in a spray presence of blood comes up in a bluish luminescence for 45 seconds

Enhancement of blood stains: -Luminol can be used -Leucocrystal violet I now being used for shoeprint enhancement-light spay purple stain almost immediately, very easy to photograph unlike Luminol.

Subsequent Reactions of Stains treated with blood detecting reagents: -Should only use part of the stain to test if blood so the rest can be used to find out whose it is