Chapter 9, Part 2: Determination of Metals and GSR

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Chapter 9, Part 2 Determination of Metals and GSR
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Forensic Analysis of Elements

• Forensic scientists analyze for chemical elements
  present in tools, coins, weapons, explosives,
  poisons, and metal scrapings as well as trace
  components in paint, glass and gunshot residue.
• Many manufactured products and most natural
  materials contain specific amounts of trace
  elements, present in concentrations of less than
  1 percent.
• The presence of trace elements provide
  invisible markers that may establish the source
  of a material.

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Forensic Analysis of Elements

• Inductively coupled plasma (identification)
• X-ray fluorescence (identification quantitation)
• Atomic absorption spectrophotometry
  (quantitation)
• Scanning Electron microscopy with Energy
  Dispersive X-ray (identification and
  quantitation)

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Inductively Coupled Plasma Optical Emission
Spectroscopy
ICP-OES has been applied to the identification
and characterization of mutilated bullets and
glass fragments.
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Inductively Coupled Plasma Optical Emission
Spectroscopy

• The sample, in the form of an aerosol, is
  introduced into a hot plasma, creating charged
  particles that emit light of characteristic
  wavelengths corresponding to the identity of the
  elements present.

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ICP-OES

• Argon ions are accelerated by an oscillating
  radiofrequency and form a closed annular torch
  that reaches 10,000 C.
• Samples are carried into the torch by argon
  flowing through the devices central quartz tube.
• As an excited metal atom leaves the tube, it
  cools down, relaxes to the ground state, and
  releases a photon of light (optical emission).
• Measurement of the wavelength of the emissions
  can identify the elements present.

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ICP-OES

• ICP-OES accepts only solution samples. The sample
  is usually dissolved in high purity acids.
• ICP-OES method is most often used to measure the
  concentration of 10 elements Al, Ba, Ca, Fe, Mg,
  Mn, Na, Ti, Sr, Zr, such as those in glass.
• Probability of two glass fragments from different
  vehicles being indistinguishable is 1 in 1080.
• This method alone is not used to determine
  concentrations of elements but ICP-OES-MS can.

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Inductively Coupled Plasma Mass Spectrometer
http//www.esslab.com/icp-ms.jpg
Make Ions in plasma by knocking off electrons
Sort ions by mass in Mass Spec by pushing them
around with electric fields
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Comparing Trace Elements in Different Samples at
ppm
A jury friendly data displayIt easy to tell the
samples apart!
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X-ray Fluorescence Spectrometry

• A sample is bombarded by high energy x-rays that
  force electrons out of inner electron shells.
  When electrons in other shells move to fills the
  gaps, they emit x-rays whose energy equals the
  gap.

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X-ray Fluorescence Spectrometry

• Is used for bulk analysis and is non-destructive
• Is a surface techniquereports the elements
  present on the samples surface
• It doesnt work well for light atoms (Z lt 11).

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XRF Analysis of Lead in Paint

• XRF can be used to determine the presence and
  quantity of lead in paint using a handheld
  spectrometer.
• The instrument is held flush against the painted
  surface to be tested.
• During the analysis, a small amount of radiation
  is released from an enclosed radioactive source,
  Cobalt 57.

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XRF Analysis of Lead in Paint

• The radiation excites many elements in the paint.
• As the atoms return to a stable state the paint
  emits characteristic x-rays for many elements
  including lead.
• A microprocessor eliminates the effects of the
  substrate to determine the amount of lead on a
  surface in ng/cm2.

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Gunshot Residues
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Gunshot Residues (GSR)

• When a gun is fired, the primer undergoes a
  chemical reaction that leads to the detonation of
  the smokeless powder in the cartridge.
• This reaction does not always consume all of the
  primer and powder.
• The burned and unburned primer and powder expand
  around the gun in all directions including back
  toward the shooter.

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Gunpowder Residue Patterns
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Gunshot Residue Analysis

• Gunshot Residue (GSR) Analysis is the examination
  of items to attempt to determine the distance of
  the muzzle of a firearm to the target.
• The basis for this examination is that gunpowder
  residue is dispersed from a firearm in a
  reproducible manner.
• The pattern developed on the garment of a
  shooting victim can be compared to test patterns
  made by a suspect firearm.

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Gunpowder Residue Patterns
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Gunpowder Residue

• If the weapon is less than one inch from the
  target, a star-shaped tear around the bullet hole
  entrance, surrounded by a rim of a smokeless
  deposit of vaporous lead is usually present.
• A halo of lead (smoke) around a bullet hole
  indicates a discharge of 12-18 inches or less.
• The presence of scattered specks of powder
  without any soot is often observed at distances
  of 25-36 inches.
• More than three feet will usually not deposit any
  powder residues. The only indication is a dark
  ring around the hole, known as a bullet wipe.

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GSR Elements

• The major primer elements are Lead (Pb), Antimony
  (Sb) or Barium (Ba)
• All three must be present within 1 particle to be
  considered specific for GSR
• Less common elements include aluminum, sulfur,
  tin, calcium, potassium, chlorine and/or silicon
• Lead from other sources can mimic GSR
• Lead residues may travel up to 30 feet but the
  blast pattern is not directional

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Visual Examination for GSR
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Chemical Testing of GSR

• Modified Griess Test
• Specific for partially burned and unburned
  gunpowder particles
• most specifically, nitrates found in the
  partially burned gunpowder
• Sodium Rhodizonate Test
• Specific for lead
• Vaporous lead is usually found closer than arms
  length

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Chemical Testing of GSR
Griess Paper
Sodium Rhodizonate
Untreated
3 inches
9 inches
15 inches
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GSR Hand Tests

• Swabs or stubs are used to take samples from the
  suspected shooter(s) hands
• Studies suggest it stays on the hands
  approximately for 6 hours
• A control swab is collected using nitric acid
• Negative results may be caused by
• Washing the hands
• Shooter may have been wearing gloves
• Lead free ammunition
• A rifle or shotgun may not deposit GSR on hands

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Gunshot Residue Analysis

• The major methods for detection of primer
  residues are
• Neutron Activation Analysis (NAA)-requires a
  nuclear reactor
• Inductively Coupled Plasma (ICP)-identifies
  elements only
• Atomic Absorption Spectrophotometry
  (AAS)-identify concentrations only
• Scanning Electron Microscopy with Energy
  Dispersive X-ray (SEM-EDX)-identifies
  concentration and identity of elements
• For these methods, samples must be obtained from
  the skin surfaces of a shooters hand at the
  scene.

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Atomic Absorption (AAS)
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Atomic Absorption Spectroscopy

• GSR for AAS is collected with dilute nitric acid
  swabs and used to make a solution for analysis.
• An atomic absorption spectrometer with a
  flameless graphite furnace atomizer determines
  the elements present in the sample
• Measures one element at a time
• Can determine the concentration of lead,
  antimony, and barium released from the primer

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Atomic Absorption (AAS)
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Atomic Absorption (AA)

• The specimen is heated to a temperature that is
  hot enough to vaporize its atoms while leaving a
  substantial number of atoms in an unexcited
  state.
• The vaporized atoms are then exposed to radiation
  from a light source specific for a particular
  element.
• If the element is present in the material under
  investigation, a portion of the light will be
  absorbed.
• The concentration of the absorbing element will
  be directly proportional to the quantity of the
  light absorbed.

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Atomic Absorption (AAS)
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GSR Collection for SEM-EDX

• GSR is collected with adhesive tape or stub.
• Alternatively, GSR may be collected with
  polyvinyl alcohol (useful if skin is partially
  covered in blood).

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GSR Sample in SEM-EDX
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Energy-dispersive X-ray spectroscopy (EDX)

• An EDX detector that measures the energy of the
  X-ray photons is attached to the SEM.
• Its elemental range is limited to elements larger
  than beryllium.
• SEM can be used to search the surface of the tape
  for individual particles of residue.
• A major advantage is SEM can reveal the actual
  surface details of the particles examined for
  comparison with known examples of gunshot residue.

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Energy-dispersive X-ray spectroscopy (EDX)
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Energy-dispersive X-ray spectroscopy (EDX)
GSR (blue) can be identified on cloth fibers and
distinguished from other metal pieces by their
elemental composition.
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Energy-dispersive X-ray spectroscopy (EDX)

• The proportion of elements present in GSR differ
  slightly.
• Databases of GSR from different manufacturers can
  be used to identify what ammunition was used in a
  crime.

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GSR Case Study

• Dayton, OH Police were called to a report of a
  suicide.
• There were no witnesses other than the man who
  called it in James Hawn.
• He was later charged and tried for the murder of
  his girlfriend, Sue Jack.

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GSR Case Study

• Because of their stormy relationship, Hawn
  claimed that he had once come home to find his
  girlfriend, Sue Jack, sitting on the bed with his
  revolver. She said that sometimes she thought
  she ought to shoot herself.
• He asked Sue why are you doing that?, took the
  gun from her, wiped it off and returned it to
  the night stand drawer he kept it in.

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GSR Case Study

• Hawn testified that on the night of the shooting,
  he came home and immediately went to bed.
• Then Sue came out of the bathroom and slapped him
  on the face. So he took off his glasses and laid
  back down.
• She then threw a fan across the room and went to
  the night stand to get the gun. I was lying in
  bedthe shot that went off sounded like that
  Hawn said thumping his chest.

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GSR Case Study

• The victims clothing was visually and
  microscopically inspected for the presence of
  GSR.
• The area around the hole was examined for
  burning/singing fabric, ripping, and smoke/soot
  deposit.
• The results of this exam were negative.

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GSR Case Study

• The sweater was processed for the presence of
  nitrites (burnt gun powder) with negative
  results.
• The absence of gun powder indicated that the
  firearm was beyond the point at which powder
  would have been deposited.
• Test firing the firearm revealed it would deposit
  powder to a distance of five feet.
• Therefore, the firearm was in excess of five feet
  at the time of discharge so Sue jack could not
  have committed suicide.

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GSR Case Study