Forensic Toxicology & Chemical Evidence

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.

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.

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

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

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

Toxicology Tests:

Spectrophotometry -   measures how much radiation from the

electromagnetic spectrum is absorbed by a particular chemical

At the Crime Scene

Crime scene technicians can conduct field tests that detect many chemical residues found at crime scenes, in vehicles, or on clothing

Fire accelerants Blood Explosives Gunshot residue Drugs Cosmetic material Construction material Trace metals

Types of chemical evidence

Solids – poisons, drugs, soil, cement, minerals, explosive 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