Forensic toxicologists identify and analyze poisons, drugs, and chemicals found in the body to help determine causes of death. They use various tests like chromatography, mass spectrometry, and spectrophotometry to separate and identify unknown chemical compounds in blood and tissue samples. Crime scene technicians can also use field tests to detect chemical residues like accelerants, explosives, drugs, and metals that can provide evidence found at crime scenes or on clothing.

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