forensic chemistry/trace evidence jen pechal yap 2010
Post on 26-Dec-2015
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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 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
Gas Chromatography/Mass Spectrometry
Separate chemical components from each other
Identify each component
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
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 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.
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 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
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
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