Transcript Inorganic Analysis

Inorganic Analysis
Inorganic versus Organic
¾ of the weight of the earth’s
crust is composed of SILICON and
OXYGEN.

What are some inorganic materials we would encounter in the
forensic’s lab?

All tests must be designed to ultimately determine the specific
chemical identity to the “exclusion of all others”.
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May involve identification of trace elements.
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Trace elements (<1%) are invisible markers that may establish
a source or additional points for comparison.
Identifying and quantifying trace
elements.
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1. Emission
spectroscopy
- identifying inorganic
elements.
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2. Atomic absorption
spectrophotometry

- quantifying inorganic
elements.
Emission Spectra of Elements.

Display of colors from
an element is called
emission spectra.

An Emission
spectrograph can be
used to produce the
spectra which will
identify the element.
Inside an Emission Spectrometer.
Continuous versus Line spectra
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Visible light  continuous spectrum, where all the colors
“merge” together.
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Elements  line spectra, where each line represents a
definite wavelength (or frequency) that is characteristic of
that element.
Line spectra
“the cosmic barcodes”
Argon
Mercury
Sodium
Neon
ICP Emission Spectroscopy
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Inductively Coupled Plasma
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High voltage spark is applied to argon gas flowing through
a plasma torch.
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Reaches 7,000-10,000 degrees Celsius aerosol of
sample
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Uses:
- mutilated bullets
- glass fragments
ICP Emission spectroscopy
Atomic Absorption
Spectrophotometry/Spectroscopy

The filament of the radiation source must be the made of
the same element as the one being analyzed.
Specimen is inserted into an air-acetylene flame 
vaporized atoms are exposed to radiation emitted from a
radiation source called a hollow cathode tube or discharge
tube.
How do we know what elements are in the sample
we are testing?
Hollow cathode tube (discharge lamp) emits only those
frequencies/wavelengths of light that are present in the emission
spectrum of the element.
Atomic absorption spectroscopy measures the absorption of the
specific frequencies of light emitted from the discharge lamp.
From this we can determine the amount of a particular element.
Advantages and Disadvantages
Advantages:
- will detect trace elements,
one-trillionth of a gram
- Simple and low cost
Disadvantages:
Must select the discharge
lamp to match the element
under investigation.
Where do emission and absorption
spectra come from?
ATOMS !!!
Protons
about 2000x mass of electron
Positive charge
Neutron
about 2000x mass of electron
neutral charge
Electron
smallest subatomic particle.
negative charge

Popular model shows
electrons orbiting around a
central nucleus
(containing protons and
neutrons).
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Remember the atom has
no net charge, therefore,
#protons (+ charge) =
#electrons (- charge)
Atoms are neutral
Each element is a collection of atoms with the same # of
protons (or electrons), ie, electrically neutral
The Atomic
Symbol
The Atomic Number is the
number of PROTONS (or
electrons)
11
Na
22.99
The Atomic Mass is the
number of PROTONS +
number of NEUTRONS
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Electrons move around the nucleus in a fixed
path……….this is an energy orbital.

Each orbital has a definite amount of
energy…………..this is the energy level.
Theory underlying A.A.S.
(Atomic absorption spectrophotometry)
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When elements absorb energy (eg. from heat or light)
strongly they emit energy/light with a characteristic color,
as the outer electrons can easily be raised to an excited
state.

The spectral colors result from the fact that light is emitted
in discrete quanta, the energy (wavelength or color) of
which is determined by the structure of the respective
electron shells.
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If a photon of exactly the right energy "hits" an atom, it
can be absorbed and cause an electron to jump to an outer,
higher energy orbit.
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A photon of the same energy is emitted when the electron
falls back down to its original orbit.
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A photon of light can interact with an electron causing it to
jump to a higher orbit.
E = hf
Where,
E = energy difference between the two orbitals
h = Planks constant (6.626 x 10-34 J-sec)
f = frequency of absorbed light.
What does this mean?
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An element is selective in the frequency of light it will
absorb.
Thus,
we can distinguish between elements based on the
frequency of light they absorb (or transmit/release).
Neutron Activation Analysis
(N.A.A.)
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N.A.A. allows both identification and
quantification of elements.
Uses neutrons to cause a sample to emit radiation
which can be measured.
What about neutrons?
 Isotopes have same # of protons but different # of
neutrons eg. Hydrogen, deuterium, tritium.
Isotopes of Hydrogen
ISOTOPE MASS
NUMBER
SUBATOMIC
PARTICLES
hydrogen
1
1 proton
(1 electron)
deuterium
2
1 proton
(1 electron)
1 neutron
tritium
3
1 proton
(1 electron)
2 neutrons
What is radioactivity?
emission of radiation that
accompanies the spontaneous
disintegration of an unstable
nucleus.
Alpha (α) radiation
Beta (β) radiation
Gamma (γ) radiation
Back to Neutron Activation Analysis!
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Basic technique involves:
Source of Neutrons  bombard specimen  captured by the
nucleus
new “activated” isotope created  decompose and emit radioactivity
as gamma rays.
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Resulting gamma radiation can be measured to identify the elements
in the specimen.
Gamma Ray Spectrum from a pottery sample.
Neutron Activation Analysis cont..
Advantages:
1.
Nondestructive method for identifying and
quantifying trace elements.
2.
Detect one-billionth of a gram
3.
Simultaneous analysis for 20-30 elements
Disadvantages:
1.
Expensive
X-ray Diffraction
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Sometimes called “X-ray crystallography”
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Can only be used with solid or crystalline materials.
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X-rays are aimed at the crystal and how they interact with
the atoms in the substance are recorded  diffraction
pattern.
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Major disadvantage: lack of sensitivity.
Principle of X-ray Crystallography.
Producing a Diffraction pattern.