1. Forensic Toxicology &
Chemical Evidence

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. 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. 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. 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. 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. Toxicology Tests:
Spectrophotometry -
 measures how much radiation from the
electromagnetic spectrum is absorbed by a
particular chemical

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. 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