1 / 20

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

mercury
Download Presentation

Blood Spatter

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related