Forensic Examination of Metals (and other things that emit light)
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Transcript of Forensic Examination of Metals (and other things that emit light)
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Forensic Examination of Metals (and other things that emit light)
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Examples
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• Energy: Capacity to do work• Kinetic Energy: Energy of motion• Potential Energy: Stored energy
All of these emit light when atoms or molecules in an excited state return to the ground state
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Riboflavin Demonstration
Why does the riboflavin solution glow?
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Potential Energy
• In chemistry potential energy exists in bonds of molecules
C4H10 + O2 CO2 + H2O + energy!
• Whenever bonds are broken or formed there is a potential for energy to be released and the system to do work
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• Macroscopically energy seems continuous
• Energy a molecule can possess actually exists in discrete steps
NO
Yes
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Example of a flame test
• Link
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Energy and Colors
E = hf
Where: E = energyh = Planck’s constantf = frequency
And f = c/wWhere:c = speed of lightw = wavelength of light
Color Wavelength
Red 780-622
Orange 622-597
Yellow 597-577
Green 577-492
Blue 492-455
Violet 455-390
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Sodium Potassium Lithium
• Which gap from the ground state to the excited state is largest? Smallest?
• Sodium, Potassium, or Lithium?
If energy did not have discrete energy levels, what color would the light emitted be? (Hint think about color wheel)
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Model of an Atom
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How can we make use of this forensically?• Flame tests can be
used to qualitatively identify metals
• Emission spectroscopy can qualitatively and quantitatively identify metals
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Atomic Spectra
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Metal Poisoning
• The mysterious death of Robert Curley
• How did Mr. Curley die?• Who was responsible for his death?• How was the case solved?• Where was Thallium found?
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Atomic Absorption Spectroscopy• Key to solving this case• How does this work? Movie
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Calibration Curves
• These curves relate a physical measurement to an assigned value
• Graphical analysis of data gives an equation of a line which can then be used for unknown values
Examples: thermometers
Millimeters of Hg are calibrated with specific distances on glass thermometer
• Speedometers: Rotations of tires are counted and related to speed displayed on dashboard
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Calibration makes quantitation possible
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Calibration Curve Data• Before SORAS
treatment the ground water had an absorbance of 0.28
• After SORAS treatment the ground water had an absorbance of 0.13
• What are the concentrations of As in the ground water before and after treatment?
Total As concentration
Absorbance
0 0
50mg/L 0.12
100mg/L 0.23
150mg/L 0.35
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Arsenic Concentration
People generally require about two liters of water a day and the recommended daily intake of arsenic by an adult is set at 150 micrograms (150 µg). How much arsenic would a person be expected to receive if they drink the untreated water? If they drink the water treated by the SORAS method?
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Breathalyzer
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Other Metal Detecting Instrumentation ICP/MSExcitation achieved with
plasma 7-10,000 oCHas been used in
identification & characterization of bullet & glass fragments
Are two bullets from same manufacturer/ lot?
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Antimony & Silver Concentrations in the Kennedy Assasination Bullets
Silver (ppm) Antimony (ppm)
Sample
Q1 8.8 + 0.5 833 + 9 Connally stretcher bullet
Q9 9.8 + 0.5 797 + 7 Fragments from Connally’s wrist
Q2 8.1 + 0.6 602 + 4 Large fragment from car
Q4, 5 7.9 + 0.3 621 + 4 Fragments from Kennedy’s brain
Q14 8.2 + 0.4 642 + 6 Small fragments found in car
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X-Ray Diffraction
• Used to identify compounds present in sample
• Bounces X-rays off of crystal structure
• X-ray crystal link
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Toxicology
• LD50: The lethal dose which will kill 50% of the population. Typically determined with animals for pesticides, medicines, etc.