1. Forensic Chemistry/Trace Evidence
Jen Pechal
YAP 2010

2. Forensic Chemistry

3. 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

4. Areas of Application Arson Explosives Trace Evidence Physical Match
Accelerants
Incendiary Devices
Explosives
Detonators, Powders
Trace Evidence
Powders, Drugs and Toxins
Paint
Fibers
Glass
Physical Match
Soil, Lubricants, Cosmetics and Metals

5. Drug Testing Powders Liquids Tablets Capsules Vegetable material
Non-drug powder

6. Drug Analysis
Take notes describing the contents of the case
heroin

7. Drug Analysis 2. Record the weight Determine misdemeanor or felony
cocaine

8. Drug Analysis 3. Color test
Marquis reagent chemical test for heroin (left); Cobalt thiocyanate reagent chemical test for cocaine (right)

9. 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

10. Drug Analysis
Using a polarized light microscope

11. Gas Chromatography/Mass Spectrometry
Separate chemical components from each other
Identify each component

12. GC/MS Results
Resulting Mass Spectrum of cocaine

13. GC/MS Results
Resulting Mass Spectrum of heroin

14. 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

15. Arson Investigation
During examination of a potential arson scene, cause and origin investigators collect debris they believe to contain accelerants

16. Arson Investigation Evidence is stored in airtight containers
to avoid possible loss of the volatile components and is transported to the laboratory for analysis.

17. 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.

18. 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.

19. GSR Analysis End up on the Victim (clothing or skin)
Hands of the person firing

20. GSR Analysis
Scanning Electron Microscope (SEM) fitted with a energy dispersive spectrometer
Scanning Electron Microscope (SEM)
Energy Dispersive Spectrometer (EDS)

21. Gunshot primer residue particles as viewed on the SEM-EDS.
GSR Analysis
Tape lifts
Presence of primer residue particles
Gunshot primer residue particles as viewed on the SEM-EDS.

22. GSR Analysis Records the coordinates of the particle
Barium, lead and antimony = primer residue

23. Noxious Chemicals Tear gas Capsaicin
Commonly found in dye packs used by banks
Capsaicin

24. Trace Evidence Powdered Substances Paint Transfer Fiber Analysis
Glass Analysis

25. Trace Evidence Microscopic and macroscopic traces of physical evidence
Found at various crime scenes
Homicides
Rapes
Assaults
Automobile accidents
Hit and runs
Burglaries

26. Trace Evidence Hairs Various hairs viewed through the stereomicroscope
An animal hair viewed through the polarized light microscope

27. Fibers viewed through the stereomicroscope
Trace Evidence
Fibers
Fibers viewed through the stereomicroscope
A fabric impression in automotive paint

28. Automobile paint chips viewed under the stereomicroscope
Trace Evidence
Paint
Automobile paint chips viewed under the stereomicroscope

29. Soil viewed through the stereomicroscope
Trace Evidence
Soil
Add palynology
Soil viewed through the stereomicroscope
Pollen SEM

30. Polymer material viewed through the stereomicroscope
Trace Evidence
Polymers
Polymer material viewed through the stereomicroscope

31. Glass viewed under the stereomicroscope
Trace Evidence
Glass
Glass viewed under the stereomicroscope
Glass fragments reconstructed to reveal bullet hole, illuminated with UV light

32. Trace Evidence Impressions A footwear impression in soil
Footwear impression in snow prepared with snow print wax

33. Microscopic Trace Evidence
Initial examination using a stereomicroscope
The date on a dime viewed through a stereomicroscope
Trace evidence viewed through a stereomicroscope

34. Microscopic Trace Evidence
Synthetic fibers are analyzed using a polarized light microscope
A fiber viewed through the polarized light microscope

35. Microscopic Trace Evidence
Use a comparison microscope

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

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

38. 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. 
The fracture surface in Figure 9 shows evidence of ratchet marks and multiple crack initiation sites, indicating relatively high applied stresses

39. 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

40. PGC-MS Results
A comparison of two PGC-MS spectra