Forensic Chemistry/Trace EvidenceJen PechalYAP 2010

Forensic Chemistry

What is Forensic Chemistry?

Forensic chemistry is the use of chemical analysis as it applies to the law

Differs from toxicology in that it analyzes non-biological samples instead of biological samples Accelerants, explosive residues and physical trace

evidence

Uses Chemical techniques to identify and quantify traces of known and unknown substances and trace their origins for the purposes of criminal investigations

Areas of ApplicationArson Accelerants Incendiary Devices

Explosives Detonators, Powders

Trace Evidence Powders, Drugs and Toxins Paint Fibers Glass

Physical Match Soil, Lubricants, Cosmetics and Metals

Drug Testing

Powders

Liquids

Tablets

Capsules

Vegetable material

Drug Analysis

1. Take notes describing the contents of the case

Drug Analysis

2. Record the weight Determine misdemeanor or felony

Drug Analysis

3. Color test

Marquis reagent chemical test for heroin (left); Cobalt thiocyanate reagent chemical test for cocaine (right)

Drug Analysis

4. Microscopic crystal test

Gold chloride crystal test for cocaine viewed through crossed polarized

filters next

Sodium acetate crystal test for heroin viewed through crossed polarized

filters

Drug Analysis

Using a polarized light microscope

Gas Chromatography/Mass Spectrometry

Separate chemical components from each other

Identify each component

GC/MS Results

Resulting Mass Spectrum of cocaine

GC/MS Results

Resulting Mass Spectrum of heroin

Drug Analysis

5. Final report submitted to the agency and the District Attorney’s Office

6. Evidence is re-sealed

7. Store until the submitting agency picks it up

Arson InvestigationDuring examination of a potential arson scene, cause and origin investigators collect debris they believe to contain accelerants

Arson Investigation

Evidence is stored in airtight containers

GC/MS Analysis

Identify traces of ignitable liquid residue in these samples

They accomplish this by adsorbing the accelerant residue onto activated charcoal strips.

The concentrated accelerant is then eluted off the strip by dissolving in a solvent.

Gun Shot Residue

When a firearm is discharged, gases are generated containing burned and unburned components from both the propellant and primer of the cartridge.

GSR AnalysisEnd up on the

Victim (clothing or skin)

Hands of the person firing

GSR Analysis

Scanning Electron Microscope (SEM) fitted with a energy dispersive spectrometer

Energy Dispersive Spectrometer (EDS)Scanning Electron Microscope (SEM)

GSR AnalysisTape lifts

Presence of primer residue particles

Gunshot primer residue particles as viewed on

the SEM-EDS.

GSR AnalysisRecords the coordinates of the particle

Barium, lead and antimony = primer residue

Noxious Chemicals

Tear gasCommonly found in dye packs used by banks

Capsaicin

Trace Evidence

Powdered Substances

Paint Transfer

Fiber Analysis Glass Analysis

Trace Evidence

Microscopic and macroscopic traces of physical evidence

Found at various crime scenesHomicides

Rapes

Assaults

Automobile accidentsHit and runs

Burglaries

Trace Evidence

Various hairs viewed through the stereomicroscope

An animal hair viewed through the polarized light microscope

Hairs

Trace Evidence

Fibers viewed through the stereomicroscope

A fabric impression in automotive paint

Fibers

Trace EvidencePaint

Automobile paint chips viewed under the stereomicroscope

Trace Evidence

Soil

Soil viewed through the stereomicroscope Pollen SEM

Trace EvidencePolymers

Polymer material viewed through the stereomicroscope

Trace Evidence

Glass viewed under the stereomicroscope

Glass

Glass fragments reconstructed to reveal bullet hole, illuminated with

UV light

Trace Evidence

A footwear impression in soil

Impressions

Footwear impression in snow prepared with snow print wax

Microscopic Trace Evidence

Initial examination using a stereomicroscope

The date on a dime viewed through a stereomicroscope

Trace evidence viewed through a stereomicroscope

Microscopic Trace Evidence

Synthetic fibers are analyzed using a polarized light microscope

A fiber viewed through the polarized light microscope

Microscopic Trace Evidence

Use a comparison microscope

Microscopic Trace Evidence

More sophisticated chemical analysis on fibers and paints can be conducted using the micro-Fourier Transform Infrared Spectrometer.

Microscopic Trace Evidence

If the fibers or paints are colored these can be spectrally compared on the Visible Microspectrophotometer.

Microscopic Trace Evidence

Or if evidence beyond the capabilities of a normal microscope, the trace evidence section can utilize a state of the art digital Scanning Electron Microscope. 

Microscopic Trace Evidence

Solid materials:Paints

Fibers

Plastics

are heated, broken down and volatilized

Pyrolysis Gas Chromatograph-Mass Spectrometer

A spectrum of an unknown sample

PGC-MS Results

A comparison of two PGC-MS spectra