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Blood Spatter

Blood Spatter. Is it blood? Is it human? How did it get there?. Is it blood?. Kastle-Meyer test Phenophthalein + hydrogen peroxide Hemoglobin acts as peroxidase —accelerates oxidation with peroxide Presumptive : potatoes and horseradish also give a positive test. Molecule flattens out

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Blood Spatter

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  1. Blood Spatter Is it blood? Is it human? How did it get there?

  2. Is it blood? • Kastle-Meyer test • Phenophthalein + hydrogen peroxide • Hemoglobin acts as peroxidase—accelerates oxidation with peroxide • Presumptive: potatoes and horseradish also give a positive test Molecule flattens out -bond conjugation leads to color

  3. Other Blood Tests • Hemastix (sold to identify blood in urine) • Wet stain with distilled water • Rub stain with swab • Rub swab on Hemastix • Turns green in presence of blood • Does not interfere with subsequent DNA testing

  4. Other Blood Tests • Luminol • Extremely sensitive—luminesces blue • Detectable after 300,000 X dilution • Does not interfere with DNA tests later • Interferences from bleach, copper, horseradish

  5. Luminol Chemistry Catalyzed by Fe in hemoglobin Light is emitted

  6. Luminol at the Crime Scene

  7. Other Blood Tests • Microcrystalline tests • Teichmann—NaCl+acetic acid • Takayama--pyridine hematin

  8. Is it human? • The overall strategy • Use animal hosts to make specific antibodies that react with species specific blood proteins (antigens) • Antibodies and antigens both have multiple sites that can react with each other Antibody Antigen

  9. Is it human? • Precipitin test • Rabbit injected with human or other blood to make specific antibodies • Rabbit blood serum isolated • Has antibodies to specific species injected • Visible precipitin line formed if matching antibody and antigen meet • Test tube, gel, gel electrophoresis

  10. Precipitin Test

  11. Precipitin Test

  12. What makes one liquid different from another? • Density • 1.035 g/mL for blood • Viscosity • Plasma 1.3X water • Blood 2.4X plasma = 3.1X water • Blood is a suspension

  13. Size and Shape of Drops • Determined by • Velocity • Direction • Distance from point of origin • Texture of surface • Higher the impact energy, the smaller the droplets • Drops are large (> 3 mm) • Impact spatter from beating and knife attacks are medium sized (> 1 mm) • Spatter from gunshot wounds, machinery, sneezes is fine (< 1mm)

  14. Texture of Surface Smooth Surface Textured Surface http://brazoria-county.com/sheriff/id/blood/bloodspatter_general.htm

  15. Forces Acting on Drops • Gravity • Projectile motion • Causes parabolic trajectory in vertical direction • Viscosity • Surface Tension • Droplet is a sphere in flight

  16. Angle of Impact http://www.bergen.org/EST/Year5/images/splatterangle.jpg

  17. Angle of Impact http://home.iprimus.com.au/ararapaj/craigslea_testbed/Forensic%20Web%20Test%20Site/blood_spatter_analysis.htm

  18. Angle of Impact • Tail of drop points in direction of travel • Proper length of ellipse is symmetric about widest point http://en.wikipedia.org/wiki/Blood_pattern_analysis_at_crime_scenes

  19. Angles from origin •  angle from vertical • sin  = width/length • tan  = tan /sin 

  20. Volume of Convergence • Obtained from long axis of ellipse • 2-D convergence • Height obtained from shape of ellipse http://home.iprimus.com.au/ararapaj/craigslea_testbed/Forensic%20Web%20Test%20Site/blood_spatter_analysis.htm

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