Chapters 4-6
*
Unit 3: Part 1
*
Unit 3: Part 1
DO NOW: What is glass ?
Homework: Complete Pre-lab assignment.
Today students will:
* Determine which chemical and physical properties
provide distinguishing characteristics of matter
* Determine procedure for analysis of glass fragments
* Develop an investigation plan to recognize
differences in glass fragments
*
*The forensic scientist must determine the
properties which give distinguishing
characteristics to matter, allowing for a unique
identity.
*Physical properties such as weight, volume,
color, boiling point, and melting point describe
a substance without reference to any other
substance.
*A chemical property describes the behavior of
a substance when it reacts or combines with
another substance.
*
*Temperature is a measure of heat intensity,
or the hotness or coldness of a substance.
* In science, the most commonly used temperature scale is
the Celsius scale. This scale is derived by assigning the
freezing point of water a value of 0°C and its boiling point
a value of 100°C.
*Weight is the force with which gravity
attracts a body.
*Mass refers to the amount of matter an
object contains independent of gravity.
*The mass of an object is determined by
comparison to the known mass of standard
objects.
*
*Density:
(D = M/V)
*Density is an intensive property of
matter, meaning it remains the same
regardless of sample size.
*It is considered a characteristic
property of a substance and can be
used as an aid in identification.
*
* Put water into the beaker until it is ½ full
* Place a pen or pencil into the water
* Observe what happens to the pen/pencil
* Make notes in your notebook
* Answer the following questions:
* Why do you think this happens?
* What is happening to create this effect?
* Would using a different liquid cause a different effect?
* Could this property be used to identify or compare glass
samples?
* Explain
*
* Explain your observations
* Offer possible explanations
*
*Silently read background info. (12 min)
*In small groups discuss answers to the
following question: (7 min)
*Define refraction and refraction index
*Explain how this property can be used to
identify class evidence
*Which other properties of glass will be used,
distinguish chemical and physical properties
*
*Define refraction and refraction index
*Explain how this property can be used to
identify class evidence
*Which other properties of glass will be used,
distinguish chemical and physical properties
*
* Names of lab partners
* Question you will be investigation
* Background information summary, most important to
investigation
* Hypothesis
* Explanation of the procedures to be followed in the lab
(must be in your own words, what will you do?)
VIP: A completed pre-lab is your entrance
ticket into the experiment, without it you
will not be allowed to begin working in the
lab!
*
Today students will:
* Determine which chemical and physical properties
provide distinguishing characteristics of matter
* Define refractive index.
* Distinguish crystalline from amorphous solids.
* Define double refraction and birefringence.
* Describe the dispersion of light through a prism
* Determine how glass samples are analyzed
*
*Light waves travel in air at a constant
velocity until they penetrate another
medium, such as glass or water, then they
are suddenly slowed
*This causes the rays to bend.
*The bending of light waves because of a
change in velocity is called refraction.
*Refractive index :the ratio of the velocity
of light in a vacuum to the velocity of light
in the medium under examination.
*
*Example: at 25oC the refractive index of
water is 1.333.
*This means that light travels 1.333 times
faster in a vacuum than it does in water
at 25oC.
*Like density, refractive index is an
intensive property and will serve to
characterize a substance.
*
*
*Glass is a hard, brittle, amorphous substance that
is composed of silicon oxides mixed with various
metal oxides.
*Amorphous solids have their atoms arranged randomly,
unlike crystals.
*Tempered glass is stronger than normal glass due
to rapid heating and cooling.
*Laminated glass found in car windshields has a
layer of plastic between two pieces of ordinary
window glass.
*
CRYSTALLINE SOLIDS
* Crystalline solids have the following fundamentals
properties.
* 1. They have characteristic geometrical shape.
* 2. They have highly ordered three-dimensional
arrangements of particles.
* 3. They have sharp melting and boiling points.
* Examples:
* Copper Sulphate (CuSO4), NiSO4, Diamond, Graphite,
NaCl, Sugar etc
*
AMORPHOUS SOLIDS
* Solids that don’t have a definite geometrical shape
are known as Amorphous Solids.
* 1. In these solids particles are randomly arranged in
three dimension.
* 2. They don’t have sharp melting points.
* 3. Amorphous solids are formed due to sudden cooling
of liquid.
* 4. Amorphous solids melt over a wide range of
temperature
* 5. Examples: Coal, Coke, Glass, Plastic, rubber etc
*
*For the forensic scientist, the problem of
glass comparison is one that depends on the
need to find and measure those properties
that will associate one glass fragment with
another while minimizing or eliminating
other sources.
*To compare glass fragments, a forensic
scientist evaluates two important physical
properties: density and refractive index.
*
Today students will:
*Define double refraction and birefringence.
*Describe the dispersion of light through a
prism
*Determine how glass samples are analyzed
*Define the Becke line
*
*
*The flotation method is a rather precise and rapid
method for comparing glass densities.
*In the flotation method, a glass particle is
immersed in a liquid.
*The density of the liquid is carefully adjusted by
the addition of small amounts of an appropriate
liquid until the glass chip remains suspended in
the liquid medium.
*At this point, the glass will have the same density
as the liquid medium and can be compared to
other relevant pieces of glass which will remain
suspended, sink, or float.
*
*Crystalline solids have definite geometric
forms because of the orderly arrangement
of their atoms.
*These solids refract a beam of light in two
different light-ray components.
*This results in double refraction.
*Birefringence is the numerical difference
between these two refractive indices.
* Not all solids are crystalline in nature. For example, glass
has a random arrangement of atoms to form an
amorphous or non-crystalline solid.
*
* http://Birefringence
*
*The flotation and the immersion methods are
best used to determine a glass fragment’s density
and refractive index, respectively.
*The latter involves immersing a glass particle in a
liquid medium whose refractive index is varied
until it is equal to that of the glass particle.
*At this point, known as the match point, the
Becke line disappears and minimum contrast
between liquid and particle is observed.
*The Becke line is a bright halo near the boarder
of a particle that is immersed in a liquid of a
different refractive index.
*
*The flotation and the immersion methods are
best used to determine a glass fragment’s
density and refractive index, respectively.
*The immersion method: involves immersing a
glass particle in a liquid whose refractive index
is changed until it is equal to that of the glass
particle.
*At this point, known as the match point, the
Becke line disappears and minimum contrast
between liquid and particle is observed.
*The Becke line is a bright halo near the boarder
of a particle that is immersed in a liquid of a
different refractive index.
*
*
*Refractive Index of Glass
* Uses Becke Line - a bright halo of light that appears
around the perimeter of a particle when the indices of
refraction of the particle and surrounding medium
are different.
Glass has higher refractive index
Becke line seen inside
Rays converge
RI(glass) > RI(solvent)
Glass has lower refractive
index
Becke line seen outside
Rays diverge
CHE 113 30
RI(glass) < RI(solvent)
*
Refractive Index of Class
1. Hot stage microscope used
2. Glass is immersed in RI liquid which is higher RI than
glass. Temperature is raised until Becke line
disappears. Rate of change of RI in liquid is known (3x10-4/degree) so the RI of the unknown can be
determined
3. The point where the Becke line disappears:
RI of the sample = the RI of the liquid
*The penetration of window glass by a
projectile, whether it is a bullet or a stone,
produces cracks which radiate outward
(radial fractures) and encircle the hole
(concentric fractures).
*By analyzing the radial and concentric
fracture patterns in glass, the forensic
scientist can determine the direction of
impact.
*
* Two kinds of fractures, radial fractures (those
radiating from the center) and concentric
fractures.
*
CHE 113 33
* The direction of force in breaking a window pane can
be determined by the direction of the rib marks
(stress marks left on broken edges of glass that are
perpendicular to one side and that curve tangentially,
run almost parallel, to the other side).
*
* On radial fractures (those
radiating from the center) the
direction of the force is on the
same side as the tangential
(almost parallel) parts of the rib
marks.
* The edge of the glass where the
rib lines are perpendicular is not
the side of the glass that the force
came from. This is the little R
rule—radial cracks make right
angles to the rear.
*
* On concentric fractures, the
perpendicular part of the rib
mark is the side from which
the breaking force came. The
rib fractures DO make a right
angle to the side the force
came from.
* If you’re standing inside and
break a pane of glass, most of
the glass will land outside—
but some will fly backwards
towards you, landing inside
the house and depositing tiny
shards on your clothing.
*
*
Concentric Crack
Radial Crack
Radial cracks
make Right
angles to the
Rear.
CHE 113 37
*
Area on a windshield
where the wiper blades
cross
Area on a windshield
where only one wiper
blade sweeps
Scratches on a side
window from grit
caught in the rubber
*A high-velocity projectile such as a bullet often
leaves a hole that is wider at the exit side, and
hence its examination is important in determining
the direction of impact.
*The direction of impact can also be accomplished
by applying the 3R Rule: Radial cracks form a Right
angle on the Reverse side of the force.
*The sequence of impacts when there have been
successive penetrations of glass is frequently
possible to determine because a fracture always
terminates at an existing line of fracture.
*
*
* If a window is broken by a
bullet, it is possible to determine
the bullet's direction by noting
the side of the cone-shaped hole
left by the bullet. The small
opening is on the entrance side
and the large opening is on the
exit side.
* A determination of the sequence
of bullet holes can be made by
noting the radial fractures.
Radial fractures caused by the
passage of a bullet will stop at
any pre-existing fracture.
*
* A bullet makes a clean-cut hole in the side of entrance and causes a
saucer-shaped or coning depression on the exit side, with a greater
diameter than the entrance hole.
* Glass fractures caused by a blunt object will show a pattern of fractures
like, but not as regular as, the pattern from a bullet.
* Fractures due to heat are wave-shaped. They do not show a regular
pattern of radial and concentric lines like fractures caused by impact.
*If even the remotest possibility exists that
glass fragments may be pieced together,
every effort must be made to collect all the
glass found.
*When an individual fit is thought improbable,
the evidence collector must submit all glass
evidence found in the possession of the
suspect along with a representative sample
of broken glass remaining at the crime
scene.
*
*The glass fragments should be
packaged in solid containers to avoid
further breakage.
*If the suspect’s shoes and/or
clothing are to be examined for the
presence of glass fragments, they
should be individually wrapped in
paper and transmitted to the
laboratory.
*
*Physical Measurements and Chemical
Composition of Glass:
* Density
* Refractive Index (most glass is the same - but can
tell if two samples are different)
* Polarizing Microscopy (determine tempered glass)
* IC-MS (inductively coupled mass spectrometer)
*
*Physical Measurements and Chemical
Composition of Glass:
* Density
*Floatation Method
*Gradient Tubes
*Volumetric Measurements (mass
measurement and volume by
displacement)
*
* Sequence the fractures on the given hand outs
*
*
Do Now: How can soil play a role in a
forensic investigation?
Today students will:
* List the important forensic properties of soil.
* Explain soils analysis techniques
* Describe the proper collection of soil evidence
* Analyze several important cases in which soil
evidence played a major role
*
*
*Mixture of organic and inorganic material
*May range from 100% inorganic (sand) to nearly
100% organic (peat)
*Inorganic part is minerals
*Organic part is decayed plant and animal
material and is sometimes called humus
*Soil is class evidence - cannot be individualized
to a particular location
*There is no classification system for soils
*Soils can be easily transported
*Soils within a few meters horizontally or vertically
differ
*
*Bulk analysis
*Density gradient
*Particle size distribution (sieving)
*Inorganic components
*Color (dissolve in water)
*Petrography - mineral analysis; Requires a good deal
of skill and practice
*
*Organic components
*Liquid chromatography: separates into
various components for identification of
individual composition
*Oxygen availability
*Bacterial DNA? - Future possibility
*
* Soil is frequently found on clothing, shoes, or tools
and in the wheel wells of vehicles.
* Most soil analysis consists of comparing two or more
samples by their mineral content, color, and density.
The presence of pesticides and herbicides have also
been used in soil comparison.
*
*
Hit and Run: - Under-fender dirt/soil deposited at
impact with the victim. matching the grease on the
victim with the grease under the car.
* Rape: - Soil on clothing of a suspected rapist placed
suspect at the crime scene.
* Murder: - Soil found on murder victims used to
determine the location of homicides, especially when the
murder occurs in one location and the body is then
moved. Using water-current measurements,
bodies/objects thrown into water can be located and
where a discovered body/object originally entered the
water determined.
* Assault: - Identifying the type of rocks used as
weapons led to the source of the rocks and helped locate
suspects.
*
* Microscopic fossils called diatoms collectively deposited
to form a sedimentary rock called diatomaceous earth.
* Some manufacturers use diatomaceous earth for
insulating safes.
* Burglary crimes have been solved by examining white
specks from suspects' hair and clothing to determine
that the specks were actually diatoms that came from
broken safes at crime scenes, and not dandruff as the
suspects had claimed.
*
*Florida v. William Kennedy Smith
*South Dakota v. Donald Eugene Moeller
*Colorado v. Walter Osborne
*The Death of a DEA agent – Enrico Camarena
*
*WKS accused of rape of Patricia Bowman
*Alleged attack on grass lawn behind Kennedy estate in
W. Palm Beach, Fl
*WKS alleged consensual sex on the beach near estate
*Jay Siegel used PLM(Polarized light microscopy)to
compare samples from clothing of victim to lawn and
beach areas
*Samples consistent with beach, not lawn
*WKS acquitted of rape
*
*Capital murder case of 9-year old Becky
O’Connell on May 8, 1990.
*Testimony by soil expert refutes defendant alibi
*Victim snatched off street, raped, killed, body
dumped in woods.
*Suspicion fell on Defendant because of prior sex
crime involvement.
*Found guilty and sentenced to death. Appeal
resulted in reversal owing to admission of
evidence of prior bad acts.
*
* SD Supreme Court reversed and reinstated conviction
* State geologist analyzed soil found in wheel wells of
defendant pickup truck. Issue was whether soil came from
crime scene South of Sioux Falls or from a road North of Sioux
Falls where defendant claimed he was at time of crime
* Geologist testified that soil could have come from crime
scene.
*Opinion
based on:
* Colors and general characteristics
* Soil was much lighter or could not have come from other roads in
area
* “Sharp, clean” hornblende crystals much more likely to have come
from crime scene area
*
*Part of appeal called for striking geologist’s
testimony as being too speculative as to
conclusions
*At 2nd trial, geologist came into more evidence
from scene and wheel well: dark green to black
gahnite found at scene and in evidence from
truck. This mineral extremely rare.
*
*Defense argued that geologist erred in identifying gahnite
only by visual inspection.
*Claimed that PLM should have been used (to confirm that
gahnite is isotropic) and that x-ray diffraction should
have been used to confirm.
*Appeals court rejected appeal
*There was no discussion at trial whether the finding of
both hornblende and gahnite near Sioux Falls was a rarity
or could be due to processing after mining elsewhere.
* Bedrock of Sioux Falls contains neither hornblende nor gahnite.
*
*Osborne botches kidnapping of Adolph Coors from his
ranch near Morrison and kills Coors
*Ranch is near “Dakota Hogback” which is made of
Dakota sandstone underlain by gray, green and maroon
clay stones, shales, more sandstone and limestone.
*Dirt road near ranch was essentially eroded, pulverized
components of hogback.
*
* During kidnapping, a fight broke out and Osborne shot Coors.
Fled in Osborne’s yellow Mercury with body. Fled south onto
an unpaved road in next county. Then went west and
climbed. Road made of muddled dust; pink-feldspar. Dust
was granite, but compared to bedrock was deficient in iron
and magnesium.
* As he climbed further, came into Pike’s Peak granite – very
distinctive.
*
*At 7200 ft, Osborne dumped body in dump used
by an Ashram. Body would not be found for 7
months.
*Osborne went east and went on an unpaved
road of black slags and drifted sands on a New
Jersey barrier island. He hid car and torched it
with gasoline.
*
*FBI investigation turned up Osborne in New Jersey
*Although Osborne (discovered to be Joseph Corbett,
Jr) covered his tracks well but was writing his
itinerary on the bottom of his car.
*4 depositional strata found:
* 4th contained material from around New Jersey dump
where he burned car
* 3rd contained pink feldspars of Pike’s Peak granite – near
where body was found
* 2nd had materials from Morrison hogback formation –
around Coor’s ranch
* 1st had pink feldspars of other Front Range granites –
generally related to Rocky Mountain Front Range
*
* Story of how FBI geologist, Ron Rawalt was able to determine,
with certainty, where Camarena body was buried, thus
showing that Mexican govt. lied about how he was killed.
* He noticed a TV report of the killings.
The body was shown
with soil clinging to it. The soil was obviously of a different
color than the soil from the alleged burial site.
*
* He told the govt. that he could prove, with soil analysis
alone, that Mexican govt. was lying about the murder.
* He went to Mexico and collected a spoonful of soil from
Camarena body. He compared that to the soil from the
alleged burial site and found them to be entirely different.
*
*Soil from body
*Spoke of mountains
*98% rhyolite ash (clean, high in silica, angular,
vesicular) – could be described as “airfall pumice”
*Bixbyite – blacker than coal
*Pink glass of exceptional depth and richness of color,
he had never seen anything like it, except in candy
*2 kinds of cristobalite: opalized and clear, elongate
and faceted, clear polygonal columns (octehedrons).
Resembled branch coral. Very rare to find both types
together.
*
* Pinpointing location
* Research with Geological Survey and Smithsonian minerologists
located specific location – A Jalisco state park called Bosques de
la Primvera. Cristabolite was the result of a third-event calderea
formation.
* Location is on upslope of mountain in park or park itself
* Rawalt flew to Mexico as “DEA agent” (FBI agents were not
allowed in to investigate
*
* While Rawalt was in Mexico searching for the area of burial,
FBI was approached about a French consultant, Loic Le
Ribault. He was the head petrologist for the French national
oil company and was said to be able to do things geologically
speaking, that other people couldn’t do. Show him a few
grains of sand and he could tell you where they came from
*
*Le Ribault
*FBI tested him by giving him 3 samples:
* Ash from Mt. St. Helens
* Alluvium from river delta in S. Carolina related to recent
murder
* Dirt from girders taken from bomb site in Beirut, Lebanon
*Ribault’s results:
* Got location of ash from Mt. St. Helens within a few miles of
source
* River basin in American Southest
* Bekaa valley in Lebanon – soil had been subjected to explosion
*
* Le Ribault’s contribution to Camarena case
*Was showed samples from park and body.
He said
“you are there, but not there”. Right elevation, but
these are samples (from park) from an area washing
north. The site is an area washing south.
*Sand deposited by water 4-5 ft. deep in a draw.
of draw <10 degrees. Shade predominates.
*Rawalt found exact location from this data.
*
Slope
*The value of soil as evidence rests with its prevalence at
crime scenes and its transferability between the scene
and the criminal.
*Most soils can be differentiated by their gross
appearance.
*A side-by-side visual comparison of the color and texture
of soil specimens is easy to perform and provides a
sensitive property for distinguishing soils that originate
from different locations.
*
*In many forensic laboratories, forensic geologists
will characterize and compare the mineral
content of soils.
*Some crime laboratories utilize density-gradient
tubes to compare soils.
*These tubes are typically filled with layers of
liquids that have different density values.
*When soil is added to the density-gradient
tube, its particles will sink to the portion of
the tube that has a density of equal value.
*
*Standard/reference soils are to be collected at
various intervals within a 100-yard radius of the
crime scene, as well as the site of the crime,
for comparison to the questioned soil.
*Soil found on the suspect, such as adhering to a
shoe or garments, must not be removed.
*Instead, each object should be individually
wrapped in paper, and transmitted to the
laboratory.
*
*
Do Now: What type of chemical are
most narcotics?
Chapter 5
* Today students will
* Understand basic chemical substances
* Apply chromatography
* Understand separation techniques
*
*An element is the simplest substance known
and provides the building block from which
all matter is composed.
*Matter is anything that has a mass and
occupies space.
*All of the elements are listed by name and
symbol in the periodic table.
*Two or more elements combine to form a
compound.
*An atom is the basic particle of an element
and a molecule is the smallest unit of a
compound.
*
*Matter can be classified according to the physical
form it takes.
*Solid-definite shape and volume
*Liquid-specific volume, takes the shape of its
container
*Gas/vapor-neither a definite shape nor volume
*Substances can change from one phase to another
without forming a new chemical species,
* matter is simply being changed from physical state to
another.
*Whenever a situation exists in which a substance can
be distinguished by a visible boundary, different
phases exist.
*
*The proper selection of analytical techniques
that will allow the forensic scientist to identify
or compare matter can best be understood by
categorizing all substances into one of two
broad groups:
1.
2.
organics
inorganics.
*Organic substances contain the element
carbon, commonly in combination with one or
more other elements.
*Inorganic materials include all other known
chemical substances.
*
*Another consideration in selecting an analytical
technique is the need for either a qualitative or
a quantitative determination.
*Qualitative relates just to the identity of the
material, whereas quantitative requires the
determination of the percent composition of the
components of a mixture.
*Most of the evidence received by crime
laboratories requires the identification of
organic compounds.
*
*
* All of the following are readily used by a forensic scientist
to identify or compare organic materials.
* Chromatography,
* Spectrophotometry
* Mass spectrometry
* Chromatography is a means of separating and tentatively
identifying the components of a mixture.
* Spectrophotometry is the study of the absorption of light by
chemical substances.
*
*Chromatography is based on the observation
that chemical substances have a tendency to
partially escape into the surrounding
environment when dissolved in a liquid or
when absorbed on a solid surface.
*Those materials that have a preference for
the moving phase will slowly pull ahead and
separate from those substances that prefer to
remain in the stationary phase.
83
* Place a single dot of the unknown substance on
the filter paper, near the bottom
* Place the paper carefully into the test tube
with just enough water to keep the bottom
wet, but not enough to touch the dot
* Allow it to “run” for about 10 minutes
* Record your observations
*
*
*In GC, the moving phase is actually a gas
called the carrier gas, which flows through a
column.
*The stationary phase is a thin film of liquid
contained within the column.
*After a mixture has traversed the length of
the column, it will emerge separated into its
components.
*The written record of this separation is
called a chromatogram.
85
*
*The time required for a component to
emerge from a GC column is known as
retention time.
*Solid materials may be heated or pryolyzed
to high temperatures so that they will
decompose into numerous gaseous products
to flow through the GC column.
86
*
*Other forms of chromatography found to be
applicable to forensic science problems are
high-performance liquid chromatography
(HPLC) and thin-layer chromatography (TLC).
*Both chromatographic systems, as with any
chromatography, require having a moving
phase and a stationary phase.
87
*
*HPLC separates compounds using a stationary
phase, a column filled with fine solid particles,
and a mobile liquid phase.
*As the liquid carries the sample through the
column, different components are slowed down
to different degrees, depending on their
interaction with (attraction to) the stationary
phase.
*The major advantage of HPLC is that the entire
process takes place at room temperature.
*Substance, such as organic explosives, which
are heat sensitive are more readily separated
by HPLC.
88
*
*TLC uses a solid stationary phase usually coated onto
a glass plate and a mobile liquid phase to separate
the components of the mixture.
*The liquid will slowly rise up the plate by capillary
action causing the sample to become distributed
between the stationary phase and the moving liquid
phase.
*Because most compounds are colorless, the materials
must be visualized by placing the plates under
ultraviolet light or spraying the plate with a chemical
reagent.
*The distance a spot travels up a thin-layer plate can
be assigned a numerical value known as the Rf value.
*
* A technique analogous to TLC is electrophoresis.
*Here, materials are forced to move
across a gel-coated plate under the
influence of an electrical potential.
*In this manner, substances such as
proteins and DNA can be separated
and characterized.
*
DO NOW: Explain the principle of
chromatography, how does it work?
* Today students will
* Understand basic properties of light
* Interpret light as particle and wave
* Apply understanding of light to chemical analysis
of substances
*
*
* A technique analogous to TLC is electrophoresis.
*Here, materials are forced to move
across a gel-coated plate under the
influence of an electrical potential.
*In this manner, substances such as proteins
and DNA can be separated and characterized.
*
*Two models describe the behavior of light.
*Light is described as a continuous wave.
*Light is depicted as a stream of discrete energy
particles.
*When white light passes though a prism, it is
dispersed into a continuous spectrum of colors.
94
* Visible light ranges in color from red to violet in the
electromagnetic spectrum.
* Waves are described in terms such as:
* Wavelength, the distance between two successive
crests (or one trough to the next trough).
* Frequency, the number of crests (or troughs)
passing any one given point per unit of time.
*
*
*Frequency and wavelength are inversely
proportional to one another.
*The electromagnetic spectrum is the
entire range of radiation energy from the
most energetic cosmic rays to the least
energetic radio waves.
*Visible light is only a small part of the
electromagnetic spectrum.
*As electromagnetic radiation moves through space, its
behavior can be described as that of a continuous wave;
* However, once radiation is absorbed by a substance, it is
best described as discrete particles of light known as
photons.
*
*Just as a substance can absorb visible light to
produce color, many of the invisible
radiations of the electromagnetic spectrum
are likewise absorbed.
*The quantity of light absorbed at any
frequency is directly proportional to the
concentration of the absorbing species. This
is known as Beer’s Law.
*
98
*
*Spectrophotometry, an important analytical tool,
measures the quantity of radiation that a particular
material absorbs as a function of wavelength and
frequency.
*
*The spectrophotometer is the instrument
used to measure and record the absorption
spectrum of a chemical substance.
*The components of a spectrophotometer are:
*A radiation source
*A monochromator or frequency selector
*A sample holder
*A detector to convert electromagnetic radiation
into an electrical signal
*A recorder to produce a record of the signal
*Absorption spectra can be done in the
visible, ultraviolet (UV) or infrared (IR)
regions.
100
*
*Most forensic laboratories use UV and IR
spectrophotometers to characterize chemical
compounds.
*The simplicity of the UV spectrum makes it a useful
tool for determining a material’s probable identity,
although it may not provide a definitive result.
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*The IR spectrum provides a far
more complex pattern.
*Different materials always
have distinctively different
infrared spectra;
*each IR spectrum is therefore
equivalent to a “fingerprint”
of that substance.
*
*
DO NOW: How can the properties of light
allow it to be used for chemical analysis?
* Today students will:
* Finish Applying chemistry concepts to the
analysis of organic materials
* Compare analysis techniques for precision
* Explain the concepts of Inorganic Trace element
analysis
* List the Six techniques available to forensic
scientists for determining the elemental
composition of materials
*
*
*In the mass spectrometer, a beam of high-energy
electrons collide with a material, producing
positively charged ions.
*These positive ions almost instantaneously
decompose into numerous fragments, which are
separated according to their masses.
105
•Under carefully controlled conditions, no two
substances produce the same fragmentation
pattern.
*
*
*A direct connection between the GC column
and the mass spectrometer allows each
component to flow into the mass spectrometer
as it emerges from the GC.
*The separation of a mixture’s components is
first accomplished by the GC.
*Then, fragmentation of each component by
high-energy electrons in the mass
spectrometer, will produce a distinct pattern,
somewhat like a “fingerprint,” of the
substance being examined.
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*
(15 minutes)Work Independently and silently to answer the
following questions
You may use your own notebook, but no other resources!
1.
2.
3.
4.
5.
6.
7.
Explain the basic properties of light
Under what conditions does light behave like a particle?
Under what conditions does light behave like a wave?
How can our understanding of light be used for chemical analysis of
substances?
How does combining Gas Chromatography and Mass Spectrometry effect
the evidence produced from a sample?
Which of the analysis techniques result in specific identification of a
substance?
Which of the analysis techniques result in quantifying of a substance?
*
*
*Inorganic, or non-carbon containing
substances, will often be encountered as
physical evidence.
*Such as tools, coins, weapons, explosives,
poisons, and metal scrapings as well as trace
components in paints and dyes.
*Many manufactured products and most
natural materials contain small quantities of
elements, known as trace elements:
* present in concentrations of less than 1
percent.
*
*The presence of these trace elements is
particularly useful
*They provide “invisible” markers that may:
*establish the source of a material
*or at least provide additional points for
comparison.
*In each case, the forensic scientist must
perform tests that will ultimately determine
the specific chemical identity of the
questioned material, to the exclusion of all
others.
*
*Six techniques available to forensic scientists
for determining the elemental composition of
materials are:
* Emission spectroscopy
* Inductively coupled plasma
* Atomic absorption spectrophotometry
* Neutron activation analysis
* X-ray diffraction
* X-ray analyzer (to be discussed in Chapter 7)
*
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*An emission spectrograph vaporizes and heats samples
to a high temperature
* So the atoms present in the material achieve an
“excited” state.
*Under these circumstances, the excited atoms will emit
light.
*If the light is separated into its components, one
observes a line spectrum.
*Each element present in the spectrum can be identified
by its characteristic line frequencies.
*Emission spectra can than be matched line for line in a
comparison between samples.
*
*Inductively coupled plasma emission spectrometry
(ICP)
* 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.
*Two areas of forensic casework where ICP has been
applied are the identification and characterization of
mutilated bullets and glass fragments.
*
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* In atomic absorption
spectrophotometry, 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 emitted
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 by the substance.
* The concentration of the
absorbing element will be
directly proportional to the
quantity of the light absorbed
and many elements can now be
detected at levels that approach
one-trillionth of a gram.
*
116
*An atom is composed of a nucleus containing protons
and neutrons, with electrons found outside the
nucleus in electron orbitals.
*The orbitals are associated with a definite amount of
energy called an energy level.
*
117
* Each element has its own set of characteristic
energy levels at varying distances from the nucleus.
* Because energy levels have fixed values, an atom
will absorb only a definite value of energy, which
may come from heat or light.
* This absorbed energy pushes the electrons into
higher energy level orbitals and the atom is now
considered in an excited state.
*
*Atomic absorption spectrophotometry measures the amount
of light energy absorbed by an atom when exciting
electrons.
*Normally, the electrons will not stay in this excited state
for long, and they will quickly fall back to their original
energy level, releasing energy in the form of light emission.
*Emission spectroscopy collects and measures the various
light energies given off by the atom.
*The specific frequency of light absorbed or emitted can be
determined by the relationship E=hf, where E is the energy
difference between two orbitals, h is a universal constant
called Planck’s constant, and f is frequency.
*Because each element has its own characteristic set of
energy levels, each will emit a unique set of frequencies.
*
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* Observe the emission spectra (5 min)
* Record your observations
*
* Working in pairs: (15 min)
* Read the given article and determine which type
of analysis was needed to evaluate the evidence
from the 1963 assassination
* Determine if you believe the correct person was
arrested
* Prepare to share out
*
*
Do Now: What evidence was extensively
study in the Kennedy assassination case?
*Today students will:
*Explain the concepts of Inorganic Trace
element analysis
*Understand the processes of Neutron
Activation and x-ray diffraction.
*Analyze the case of “Death by Radiation
Poisoning”
*
* Which type of analysis was needed to evaluate
the evidence from the 1963 assassination?
* Does the evidence show that the correct
person was arrested?
*
* Made up of:
* Protons (+)
* Neutrons (0)
* Atomic number: refers to the number of protons
* Is different for every atom
* Determines the atoms identity
* The number of P + the number of N = the atomic mass
number
* Atoms with the same number of protons can have different
numbers of neutrons (O can have atomic mass of 15 or 16)
* Isotopes are atoms of the same element which have
different numbers of neutrons therefore have different
mass numbers
* Nuclear notation indicates the atomic number and the mass
number of isotopic elements
*
*Radioactivity is the spontaneous emission of radiation
by an unstable atomic nucleus.
*Radioactive decay is the release of radiation by
radioactive isotopes.
*The three types of decay are:
*Alpha
*Beta
*Gamma decay
*
*Alpha decay is the release of alpha
particles (2 protons and 2 neutrons).
*Alpha particles are represented as
or α.
•Alpha particles, which
are large in
size, collide with objects around them.
*Do not penetrate very deeply
*Are easily stopped by a thin layer of
material.
*
Parent
Daughter
alpha particle
The parent element turns into a
daughter element
*
Two protons and
neutrons are lost
The protons and neutrons
leave as an alpha particle.
+ Energy!
*
Beta decay is the release of beta particles from
a decaying nucleus.
*A beta particle is a high energy electron with a 1charge.
*Beta particles are written as β- or
*Beta particles pass more easily through matter than
alpha particles and require sheets of metal, blocks of
wood or specialized clothing to be stopped.
*
*
•A neutron becomes a proton (which stays in
the nucleus) and electron (which is ejected
from the atom).
•ADD A PROTON and LOSE an ELECTRON
+ ENERGY
*Gamma decay is the release of gamma
rays from a nucleus.
*A gamma ray is a high energy form of
electromagnetic radiation with out a change
in mass or charge.
*
*Gamma rays have high
penetrating ability and are very
dangerous to living cells.
*To stop gamma rays thick blocks of lead or
concrete are needed.
*
*
*When gamma decay is expressed in an equation
it is expressed as γ.
*Electron from beta decay is captured to cause gamma
particle to emit.
* The following equation shows both gamma and alpha decay
occurring.
*
Decay Type
Alpha
Beta
Gamma
Gives off
Changes Nuclear
notation by:
Radiation
penetration and
harm to cells
Alpha
Decay
Type
*
Gives off
Changes Nuclear
notation by:
Radiation penetration and harm
to cells
2 protons & 2
neutrons=
Alpha
particle=
•Mass number
decreases by 4
•Atomic number
decreases by 2
•Large particle, easily stopped
by cloth
•Very low risk
Atomic number
increases by 1
The mass number
stays the same
•These high energy particles pass
more easily through matter
•Need metal sheets to stop
•Moderate risk to cells
4
2
He
Gamma
Beta
Beta particle
= electron =
e
0
-1
A gamma ray a •No change in mass
high energy
or atomic number
form of
•BUT does not occur
electroalone
magnetic
•Accompanied by
radiation
alpha or beta.
•Gamma rays have high
penetrating ability
•To stop gamma rays thick blocks
of lead or concrete are needed.
• Very dangerous to living cells.
*Radiation can be detected with Geiger
counters and scintillation counters.
*Geiger counters detect ionizing
radiation.
*Scintillation counters register the
intensity of radiation by detecting
light.
*
*Half-life
is a term used to describe the
time it takes for half of a given amount of
a radioactive isotope to decay.
*Half-life varies greatly depending on the
isotope
*However, Each Isotope decays at a
particular rate
*
*
Uranium-238 (t½ = 4.5 billion years)
*Nuclear chemistry provides a new tool for
identifying and quantitating the elements.
*A nuclear reactor is simply a source of neutrons
that can be used for bombarding atoms
* This bombardment causes some neutrons to be
captured to produce radioactive isotopes.
*To identify the radioactive isotope, it is
necessary to measure the energy of the
gamma rays emitted as radioactivity.
*
141
(15 min)
*Read the brief case study
*Identify the detection techniques
used in this case
*What was the method of death
*Prepare to Discuss
* Analyze the case of “Death by
Radiation Poisoning”
*
Do Now:
?
* Today students will
*
*
Decay Type
Alpha
Beta
Gamma
Gives off
Changes Nuclear
notation by:
Radiation
penetration and
harm to cells
Alpha
Decay
Type
*
Gives off
Changes Nuclear
notation by:
Radiation penetration and harm
to cells
2 protons & 2
neutrons=
Alpha
particle=
•Mass number
decreases by 4
•Atomic number
decreases by 2
•Large particle, easily stopped
by cloth
•Very low risk
Atomic number
increases by 1
The mass number
stays the same
•These high energy particles pass
more easily through matter
•Need metal sheets to stop
•Moderate risk to cells
4
2
He
Gamma
Beta
Beta particle
= electron =
e
0
-1
A gamma ray a •No change in mass
high energy
or atomic number
form of
•BUT does not occur
electroalone
magnetic
•Accompanied by
radiation
alpha or beta.
•Gamma rays have high
penetrating ability
•To stop gamma rays thick blocks
of lead or concrete are needed.
• Very dangerous to living cells.
*Neutron activation analysis
*measures the gamma-ray frequencies of specimens
that have been bombarded with neutrons.
*provides a highly sensitive and
nondestructive analysis for simultaneously
identifying and quantitating 20 to 30 trace
elements.
*neutron activation analysis has been used on
find trace elements in metals, drugs, paint, soil,
gunpowder residue, and hair.
*Because this technique requires access to a
nuclear reactor, it has limited value to forensic
analysis.
*
147
*X-ray diffraction is applied to the study of solid,
crystalline materials.
*As the X-rays penetrate the crystal, a portion of
the beam is reflected by each of the atomic planes.
*As the reflected beams leave the crystal’s planes,
they combine with one another to form a series of
light and dark bands known as a diffraction
pattern.
*Every compound is known to produce its own
unique diffraction pattern, thus giving analysts
a means for “fingerprinting” inorganic
compounds.
*
148