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Kaitlin Cassity P5: Blood Detection Outline

Blood Detection By Chemical Methods: Crystal tests, catalytic tests, or instrumental methods can be used to determine whether or not a stain is in fact blood. Each is dependent on the presence of hemoglobin and will yield positive results for both animal and human blood.

1. Crystal Tests: Crystals react to certain reagents, which yield a color change. a) These types of tests are rarely used, but occur on a microscope slide with reagents being added to the stain under a cover slip. b) Generally, it is accepted with the crystal tests that a positive result confirms the presence of blood. (Must always run a positive control, as a negative result does not necessarily mean blood is not present. 2. Catalytic Tests: rely on idea that hem can catalyze the breakdown of hydrogen peroxide. *A positive test does not mean the stain is blood, as various enzyme and certain metals can also give positive results. a) Rely on idea that hem group of hemoglobin possesses a peroxidase-like activity that catalyzes the breakdown of hydrogen peroxide. A visible color change is produced from the reaction. b) Tests are extremely sensitive, but are subject to a number of interferences and are therefore not totally specific to blood. *Ex: catalase and peroxidases. c) Principle: If test is negative, blood is absente, but that if a test is positive, blood is probably, not definitely present. “Presumptive tests” 3. Instrumental methods: Chromatography can be utilized to discover hemoglobin. These tests confirm the nature of the stain, the detection of a non-visible stain, and the enhancement of hard to see stains. It is imperative that the chemical reactions do not prevent later testing to help identify the person to whom the blood belongs. a) High performance liquid chromatography: the use of absorbance of hemoglobin for detection. This method can identify the species of origin from variations in the globin chains (estimate age of blood stain, adult or fetal hemoglobin?) Applications: Confirmation that Visible Stains are (Probably) Blood -“Sangur Sticks” Method: A detecting reagent is in an immobilized form is rubbed gently on the stain and moistened. An immediate change in color from pale yellow to an intense greenish blue indicates the probably presence of blood.

-Kastle-Meyer test: Test the reduced phenolphthalein is kept in alkaline solution in presence of zinc. Initially colorless, oxidation with hemoglobin and peroxide will produce a vibrant pink color.

To confirm presence of blood, antigen-antibody reactions, presence of an enzyme known to be human specific, or presence of DNA sequence specific to humans must be identified.

Non-visible Bloodstains: Luminol: Utilized in areas where blood may be present but is difficult to see or areas it has been cleaned up with traces still present. The solution is applied as a spray and the presence of blood produces a bluish luminescence which persists 45 seconds. 1. This test is not specific for blood and can also give a positive reaction with some plant enzymes, metals, and oxidizing agents. How long it last, the color it produces, and the degree of sparkle of the product can help confirm if stain is blood/blood does not sparkle. Enhancement of Blood Stains: Luminol has been used to enhance existing bloodstains. The treatment of a print with a chemical, which reacts with blood, can often produce a much more detailed print. Leucocrystal violet is used for shoeprint enhancement with considerable success. (Purple stain produced that is easily photographed).

Subsequent Reactions of Stains Treated with Blood Detecting Reagents --Tests must be chosen properly in order to determine, is it? Then Whose? The Sangur or Kastle-Meyter tests use only a small part of the stain and the major part remains for further testing. When an entire stain is treated with a reagent, subsequent tests can be affecte