Blood+Detection+by+Chemical+Method+Trey+J

Intro: The Question asked - "Whether a particular stain is or is not blood."

Chemical Methods Used to Detect Blood

All tests are dependent on the presence of hemoglobin. Types: - Crystal Tests - Haem forms crystals when reacted with certain reagents. The most common such reagent is pyridine, which forms characteristic pink crystals. (Tests are rarely used today) General rule that a positive crystal test will confirm presence of blood.

- Catalytic Tests - These tests rely on the fact that haem can catalyse the breakdown of hydrogen peroxide. A very sensitive test which has to be carefully done or results can be skewed (another substance can be mistaken for blood).

- Instrumental Methods - Chromatography can be used to identify the presence of haemoglobin. HPLC is used to confirm idenitity of blood by useing the absorbance of haemoglobin for detection.

Application Confirmation of visible stains possibly being blood. - Uses either Sangur sticks or Kastle-Meyer Test SS- Rub gently on the stain while moistened and the stain if blood will change from yellow to an "intense green blue" KMT- reduced phenolphthalein is kept in alkaline solution in the presence of zinc. This solution is colourless. Oxidation with haemoglobin and peroxide causes an instant colour change to the well known bright pink.

Non-visible blood stains Luminol is used typically. Hydrogen peroxide can be used but yields a shorter-lived luminescence than sodium perborate. The solution is applied as a spray and the presence of blood produces a bluish luminescence which persists for about 45 seconds. Luminol needs to be used with care as there are uncertainties relating to its safety.

Enhancement of blood stains: Can use Luminol or Leucocrystal violet (however this can't be used if the scene must be left clean, no rhyme intended)

Subsequent reactions of stains treated with blood detecting reagents This is done to answer the question of whose blood it is. In this thinking only a portion of the blood should be used, this in mind the rest can be used ot determine blood type, etc. to find out whose blood it is.