Forensic toxicology & chemical evidence

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Forensic toxicology & chemical evidence

  1. 1. Forensic Toxicology & Chemical Evidence
  2. 2. Forensic Toxicologist identifies and analyzes poisons, drugs, and chemicals studies the effect of such substances on the body Important in helping medical examiner determine cause of death in an autopsy all the blood and tissue samples undergo a toxicology screening.
  3. 3. Toxicology Tests: Chromatography – separate and quantify individual chemical compounds  Mobile phase – substance is dissolved in solvent  Stationary phase – dissolved substance is passed through a finely divided adsorbent, different compounds move at different speeds, rates of adsorption are plotted on a chart.
  4. 4. Toxicology Tests: Thin-Layer Chromatography (TLC) –  uses a glass or plastic plate covered with a thin layer of finely ground adsorbent such as silica gel or alumina  sample is deposited on the plate  locations of separated components are noted after the solvent evaporates
  5. 5. Toxicology Tests: Gas Chromatography – separates liquids and gases  material is coated on fine clay or glass beads and packed into a steel or copper column  column is heated above boiling point of liquid  gas pushes compounds through column  detectors measure emerging fractions
  6. 6. Toxicology Tests:Mass Spectrometry – identifies the chemical structure of an unknown substance  after separating a substance using gas chromatography each component enters a vacuum chamber  the components collide with a beam of high-energy electrons causing the component molecules to lose electrons and become charged ions  they then pass through a magnetic or electric field where they are separated according to their masses and can be identified
  7. 7. Toxicology Tests:Spectrophotometry - measures how much radiation from the electromagnetic spectrum is absorbed by a particular chemical
  8. 8. At the Crime Scene Crime scene technicians can  Fire accelerants conduct field tests  Blood that detect many  Explosives chemical residues  Gunshot residue found at crime  Drugs scenes, in  Cosmetic material vehicles, or on  Construction material clothing  Trace metals
  9. 9. Types of chemical evidence Solids – poisons, drugs, soil, cement, minerals, explo sive residues, gunshot residues, cosmetics, trace materials Liquids – acids, gasoline, body fluids, beverages, chemicals for drug labs, cleaning fluids, medications, poisons Gases – natural gases, refrigerants, butane, propane, tear gas, propellants

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