Transcript Chapter 5-6

Chem 113
Spectroscopy and Spectrometry
1
Chapters 5 and 6
Forensic Science
Copyright © James T. Spencer 2003-2010 All Rights Reserved
Chem 113
Spectroscopy and Spectrometry 2
Spectroscopy: study of the interaction of radiation
with matter
Spectrometry: measurement of such interactions
Used for analysis of the matter!
Organic/inorganic Chemical Analysis
What is this stuff?
Chem 113
Organic/Inorganic Analysis
3
• Organic: a substance composed of carbon, hydrogen and often smaller
amounts of oxygen, nitrogen, halogens, phosphorus, and sulfur
• Inorganic: a chemical compound not based on carbon
Chem 113
Qualitative vs. Quantitative
4
Qualitative: relates just to
the identity of the
material of question
Example - identification
of a powder may reveal
the presence of heroin
and quinine
Quantitative: requires the
determination of the
percentage combination
of the components of
the substance
Example - indicates 10%
heroin and 90% quinine
Chem 113
Combustion Reactions

5
Reaction of Hydrogen with Oxygen [COMBUSTION]
(note precautions)
» 2 H2(g) + O2(g)
2 H2O(g)
H = 232 kJ/mol H2
» Ignition temperature = 580° - 590°C
» Explosive [“when stuff gets really big really
fast” Beakman’ World]
» The rapid release of energy [-232 kJ/mol H2] into
the surrounding air causes the air to very
quickly expand. The explosion of pure H2
sounds quieter because the air expansion is
slower.
[Video No. 20-21; 4:42 +1:29 m]
[Video No. 22; 2:50 m]
Chem 113
Combustion Reactions

Combustion of Alcohol (ethanol):
C2H5OH(g) + 3 O2(g)




6
2CO2(g) + 3H2O(g)
H = -1366.2 kJ mol-1
Tesla coil produces a high voltage electric spark.
The spark is required to initiate this reaction.
Conversion of chemical energy (PE stored in
bonds) to mechanical energy.
Questions for After Demonstration
Are other types of energy are produced besides
mechanical energy?
Why can the reaction not be repeated without
Chem 113
Combustion Analysis
7
• Empirical Formula from reaction with oxygen
• Organic Compounds - C to CO2 and H to H2O
• Use CO2 and H2O to determine the amount of C
and H in original sample
H2O
furnace
absorbant
(Mg(ClO4)2)
O2 flow
sample
contaminant
catalyst (CuO);
oxidizes traces of
CO and C to CO2
CO2
absorbant
(NaOH)
Chem 113
Combustion Analysis
8
• Tells us how much of each element is present
in unknown sample
• Allows us to determine % of each element in
the sample:
% = [amount of element/amount of sample]100%
•
Compare with reference samples
Chem 113
Mass Spectrometry
•
•
•
•
Instrumental Principles and Design
Spectral Features
Spectral Interpretation and Comparison
GC-MS and LC-MS
9
Chem 113
Mass Spectrometry
Basic Ideas
10
Creates charged particles (ions) from gas phase molecules.
Electron Ionization (EI)- Uses electron impact to ionize a
molecule.
Chemical Ionization (CI)- First ionizes a molecular gas
which in turn ionizes the molecule of interest. A
“gentler” method of ionization.
Fast Atom Bombardment (FABS)- Mainly for non-volatile
compounds - very harsh.
The MS analyzes ions to provide information about the
molecular weight of the compound and its chemical
structure.
Chem 113
Mass Spectrometry
11
Basic Ideas
M
ionization
-e -
M+
M+
M+
Chem 113
Mass Spectrometry
12
Basic Ideas
M
-e -
M+
M+
acceleration
M+
Chem 113
Mass Spectrometry
13
Basic Ideas
M
-e -
M+
M+
acceleration
M+
Chem 113
Mass Spectrometer
Magnetic field deflection (quadrupole MS) 14
• Direct methods of measuring (separating) mass.
• Sample molecules are ionized by e-beam to cations (+1 by
“knocking off” one electron) which are then deflected by
magnetic field - for ions of the same charge the angle of
deflection in proportional to the ion’s mass
vacuum chamber beam of pos. ions
accelerating grid (-)
sample
Mass
Spectrum
Hg
N
200
focusing slits
ionizing e- beam
S
magnetic field
Int.
mass number (amu)
detector
Chem 113
Mass Spectrometer
Atomic Spectra - Isotopic Abundance 15
Mass
Spectrum
Cl
Int.
35
Mass
Spectrum
Int.
C
12
37
mass number (amu)
35Cl:
75% abundant
37Cl: 24% abundant
Mass
Spectrum
P
Int.
31
13
mass number (amu)
12Cl:
mass number (amu)
98.9% abundant 31P: 100% abundant
13Cl: 1.11% abundant
Chem 113
Mass Spectrometry
Molecules
16
Chem 113
Mass Spectrometry
18
Ionization produces singly charged ions. The intact charged
molecule is the molecular ion. Energy from the electron impact
and instability in a molecular ion can cause that ion to break
into smaller pieces (fragments).
The methanol ion may fragment in various ways, with one
fragment carrying the charge and one fragment remaining
uncharged. For example:
CH3OH+. (molecular ion)
(or) CH3OH+.(molecular ion)
CH2OH+(fragment ion) + . H
CH3+(fragment ion) + .OH
Chem 113
Mass Spectrometry
19
Chem 113
Mass Spectrometry
20
169
Chem 113
Mass Spectrometer
21
Unknown white powdery substance ingested by
unconscious patient.
What do you do? Is it Heroin, Cocaine, Caffeine?
In ten sity
Mass Spectrum of Unknown Compound
Mass
25
50
75
100
125 150
175
200
225
250
275
300
Chem 113
Mass Spectrometer
In ten sity
MS Library
Heroin
Heroin
43
22
other peaks at
327 and 369
268
204
215
94
Mass
25
50
75
146
100 125 150 175 200 225 250 275
194
In ten s ity
67
Mass
82
25
50
75
Caffeine
109
55
42
300
MS of Unknown
100 125 150 175 200 225 250 275
300
Chem 113
In ten sity
Mass Spectrometer
MS
Library
82
Cocaine
Cocaine
182
303
42
122
Mass
25
50
75
272
150
100 125 150 175 200 225
194
67
In ten s ity
Mass
23
250 275
300
Caffeine
109
MS of Unknown
55
82
42
25
50
75
100 125 150
175 200 225
250 275
300
Chem 113
Mass Spectrometer
MS Library
In ten s ity
67
Mass
194
Caffeine
Caffeine
109
55
82
42
25
50
75
100 125 150
175 200 225
194
67
In ten s ity
Mass
24
75
Caffeine
MS of Unknown
82
42
50
300
109
55
25
250 275
100 125 150
175 200 225
250 275
300
Chem 113
Mass Spectrometer
O
CH 3
H 3C
N
N
O
Mass Spectrum
CH 3
Caffeine
In ten sity
Mass
N
N
25
50
75
100
125 150
175
200
225
250
275
300
25
Mol. Wgt
= 194
Chem 113
Sensitivity
10pg_benzophenone01_020226184800
26
02/26/2002 06:48:00 PM
RT : 5.99 - 7.99
NL:
2.94E4
7.08
100
m/z 183
S/N 53:1
95
90
85
m/z=
182.50183.50 MS
10pg_benzop
henone01_0
2022618480
0
80
10 pg Benzophenone – S/N >10:1
75
Re la ti ve A b u nd a nc e
70
65
1 pg (picogram) = 10-12 grams!
60
55
50
45
40
35
30
25
20
6.72
6.24
6.09
15
6.06
6.03
6.43
6.40
6.16
7.39
6.65
6.52
7.32
6.59
6.81
6.32
10
7.18
6.83
6.54
6.30
7.42
7.61
7.26
7.03
6.91
7.46
6.93
7.56
7.88
7.69
7.83
7.72
7.77
6.44
5
0
6.0
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7.0
7.1
T ime (min)
Base Peak
Calculated v alues
R etention Time : 7.08
N oise Rang e : 6.84 - 7.03 minutes (22 scans)
Scan : 243
Baseline : 1851
Intensity : 29374
Sig nal To Noise : 53
Standard Deviation : 519
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.92
Chem 113
Chromatography
27
• Used to separate mixtures of compounds (most
things in nature come as mixtures)
• Based upon the differing interactions between the
components of a mixture and some other substance.
Chem 113
Chromatography
See: http://antoine.frostburg.edu/chem/senese/101/matter/chromatography.shtml
28
Chem 113
Chromatography
29
Chem 113
Chromatography
•
•
•
•
•
30
Chromatographic systems have a stationary phase (which can be
solid or liquid) and a mobile phase (usually liquid or gas).
The mixture to be separated is placed at the beginning of the
chromatographic system (stationary phase).
The mobile phase then “pushes” the components of the mixture
through the system.
Each component adsorbs on the stationary phase with a different
strength (stronger means moves more slowly through the system).
Each component comes out the end of the system at a different
time (retention time).
Chem 113
TLC
Thin Layer Chromatography
Spotting sample
31
Developing plate
Chem 113
GC-Mass Spectrometry
32
A mixture is injected into the GC where the mixture is
vaporized. The gas mixture travels through a GC column,
where the compounds become separated. Those separated
compounds then immediately enter the mass spectrometer.
MS
Chem 113
GC-Mass Spectrometry
33
The peak at 4.97 minutes is from dodecane, the peak at 6.36 minutes is from
biphenyl, the peak at 7.64 minutes is from chlorobiphenyl, and the peak at
9.41 minutes is from hexadecanoic acid methyl ester.
Chem 113
GC-Mass Spectrometry
GC of a charcoal lighter fluid standard
34
Chem 113
GC-Mass Spectrometry
MS-GC?
35
Chem 113
Street Drugs in Real Time- Know what the funny
white powder is in less than 10 minutes.36
RT: 2.80 - 7.43
100
SM: 9G
NL:
7.91E6
m/z=
43.50-44.50
F: MS
level4
80
60
Amphetamine
40
20
0
100
NL:
1.18E7
m/z=
57.50-58.50
F: MS
level4
Methamphetamine
and MDMA
80
60
40
20
0
100
NL:
5.92E5
m/z=
298.50299.50 F:
MS level4
80
60
40
Hydrocodone
20
0
100
NL:
2.17E6
m/z=
81.50-82.50
F: MS
level4
80
60
Cocaine
40
20
0
100
NL:
2.40E5
m/z=
314.50315.50 F:
MS level4
80
60
40
20
0
3.0
3.5
4.0
4.5
5.0
5.5
Time (min)
6.0
6.5
7.0
Oxycodone
Chem 113
Cases for the GC-MS
• Toxicology:
–
–
–
–
–
–
Components in blood, etc.
Toxin ID
Quality control (Tylenol murders)
Arson investigations (VOC)
Alcohol Intox.
Gunshot residues
37
Chem 113
Atomic and Molecular Spectroscopy
38
• Science: Atomic Theory
– “The strength of a science is that its conclusions are
derived by logical arguments from facts that result
from well-designed experiments. Science has
produced a picture of the microscopic structure of the
atom so detailed and subtle of something so far
removed from our immediate experience that it is
difficult to see how its many features were
constructed. This is because so many experiments
have contributed to our ideas about the atom.”
B. Mahan from University Chemistry
Chem 113
Atomic and Molecular Spectroscopy
39
• Interaction of electromagnetic radiation (“light”)
with atoms and molecules
• Absorption, transmission and emission spectra
Chem 113
Spectroscopy
Background - Electromagnetic Radiation 40
 = c
where  = wavelength,
 = frequency,
c = light speed
amplitude
1 cycle per sec = 1 hertz
wavelength ()
Chem 113
Electromagnetic Radiation
41
Chem 113
Spectroscopy
42
• When electromagnetic radiation passes through a
substance, it can either be absorbed or transmitted,
depending upon the structure of the substance.
Chem 113
Spectroscopy
43
When a molecule absorbs radiation it gains energy as it
undergoes a quantum transition from one energy state
(Einitial) to another (Efinal).
The frequency of the
absorbed radiation is related
to the energy of the
transition
Efinal - Einitial = E = h = hc/
.
em ission
Chem 113
Quantization
44
• Light energy may behave as waves or as small
particles (photons).
• Particles may also behave as waves or as small
particles.
• Both matter and energy (light) occur only in discrete
units (quantized).
Quantized
(can stand only on steps)
Non-Quantized
(can stand at any position on the ramp)
Chem 113
What is Quantization
45
• Examples of quantization (when only discrete and
defined quantities or states are possible):
Quantized
Non-Quantized
Piano
Stair Steps
Typewriter
Dollar Bills
Football Game Score
Light Switch (On/Off)
Energy
Matter
Violin or Guitar
Ramp
Pencil and Paper
Exchange rates
Long Jump Distance
Dimmer Switch
Chem 113
Atomic Spectroscopy
46
Chem 113
Flame Tests
47
Atomic Emission
Chem 113
Atomic Emission
48
Chem 113
Red
Blue
364.6 nm
410.2 nm
434.0 nm
486.1 nm
656.3 nm
Hydrogen Emission
Ultraviolet
49
Chem 113
50
364.6 nm
410.2 nm
434.0 nm
486.1 nm
656.3 nm
Hydrogen Emission
Ultraviolet
Red
Blue
A Swiss schoolteacher in 1885 (J. Balmer) derived
a simple formula to calculate the wavelengths of
the emission lines (purely a mathematical feat
with no understanding of why this formula
worked).
frequency = C ( 1 - 1 ) where n = 1, 2, 3, etc...
22 n2 C = constant
Chem 113
Bohr’s Model
“Microscopic Solar System”
• Electrons in around nucleus
with quantized (allowed)
energy states
• When in a state, no energy is
radiated but when it changes
states, energy is emitted or
gained equal to the energy
difference between the states
• Emission from higher to
lower, absorption from lower
to higher
51
n=∞
n=4
n=3
n=2
electronic
transitions
n=1
Chem 113
Atomic Emission
AES
52
• Atomic Emission (AE) - uses quantitative measurement of
the optical emission from excited atoms to determine analyte
concentration. Analyte atoms in solution are aspirated into the
excitation region where they are atomized by a flame, discharge,
or plasma. These high-temperature atomization sources provide
sufficient energy to promote the atoms into high energy levels.
The atoms decay back to lower levels by emitting light. Since
the transitions are between distinct atomic energy levels, the
emission lines in the spectra are narrow.
Ch. 6: p 150.
Chem 113
Atomic Emission
AES
• Russian Icon of St. Nicholas The pigments present on this
mid-19th Century painting were
characterized by AES
spectroscopy (laser-induced
breakdown spectroscopy, LIBS)
and Raman microscopy. The
identification of pigments on the
original work along with those
applied in restoration of cracks in
the varnish and painting surface
were analyzed.
Art Restoration History and Art Forgery
53
Chem 113
Atomic Emission
AES
54
• LIBS depth profile measurements leave a minute crater in the
surface of the art object being studied. This allows
stratagraphic information to be collected. A typical cross
section of the icon is shown.
Chem 113
Atomic Emission
AES
55
• Several areas of the icon, where white paint was used,
were analyzed. The LIBS spectrum showed strong
peaks characteristic of lead. This was confirmed by the
Raman spectrum, which verified the presence of lead
carbonate, [2PbCO3·Pb(OH)2].
LIBS
Raman
Chem 113
Atomic Emission
AES
The brown pigment was
characterized as an iron-based
pigment mixed with lead
white. The LIBS spectrum
showed the presence of Fe and
Al, corresponding to an iron
oxide and an earth such as clay.
Also present are emissions
characteristic of magnesium,
lead and calcium. The peak
corresponding to iron at ~275
nm is characteristic of iron that
has been observed in studies on
pure iron oxide pigments (for
example, Mars black, Fe3O4).
56
Chem 113
Atomic Absorption
AAS
• Atomic Absorption - Atomic-absorption (AA)
57
spectroscopy uses the absorption of light to measure the
concentration of gas-phase atoms. Since samples are
usually liquids or solids, the analyte atoms or ions must be
vaporized in a flame or graphite furnace. The atoms absorb
ultraviolet or visible light and make transitions to higher
electronic energy levels. The analyte concentration is
determined from the amount of absorption.
Chem 113
Atomic Absorption
AAS
58
Typical Problem - A child becomes quite ill and is
taken to the hospital. It is found that the child is
suffering from lead poisoning. A forensic laboratory
is contacted and asked if it can determine the source
of the lead which the child has ingested. No crime has
been committed, per se, but the source must be
eliminated to prevent future danger to the child. Paint
samples from a number of objects with which the
child has had repeated contact are collected. Paint on
the child's crib, paint from his toys, and paint from
the child's swing, to name a few, are sent to the
laboratory. AA is the best method for these analyses.
Chem 113
Neutron Activation Analysis
NAA
59
Neutrons interact with a target nucleus to form a compound nucleus in
an excited state. The compound nucleus will decay into a more stable
configuration through emission of one or more gamma rays. This new
configuration may yield a radioactive nucleus which also decays by
emission of delayed gamma rays, but at a much slower rate according to
the unique half-life of the radioactive nucleus.
Chapt 6.p 163
Chem 113
Neutron Activation Analysis
NAA
60
•About 70% of the elements have properties suitable for
measurement by NAA.
•Parts per billion or better.
Gamma-ray
spectrum in a
sample of
pottery
irradiated for
24 hours,
decayed for 9
days, and
counted for
30 minutes.
Chem 113
Neutron Activation Analysis
NAA
61
An example of the gamma-ray spectrum from the activation of a
human nail used as a biological monitor of trace-element status.
Chem 113
Neutron Activation Analysis
Arsenic in Hair
Napoleon Bonaparte
One of the most brilliant individuals in
history, Napoleon Bonaparte was a masterful
soldier, grand tactician, sublime statesman and
exceedingly capable administrator. After an
extraordinary career, he was finally defeated
and exiled to Elba. He returned from Elba to
be ultimately defeated at
Waterloo. He was finally
exiled to the remote tiny
volcanic island of St. Helena,
south of the Equator. The
nearest land is Ascension
Island, 700 miles to the north.
62
Chem 113
Neutron Activation Analysis
Arsenic in Hair
Murdered or Not?
For years a controversy has raged about
Napoleon being killed on St. Helena - either
by French Royalists, persons in his exiled
entourage or the British - and all have
pointed to the high levels of arsenic in the
emperor's body as being evidence of such
behavior. The emperor's body contained
some 15 parts per million of the poison,
where the maximum safe limit is only three
parts per million. The determination was
by neutron activation analysis of his hair.
63
Chem 113
Neutron Activation Analysis
Arsenic in Hair
“So Who Done It?”
(if it was done at all)
British Authorities - The Allied heads of
state had no greater wish than to ensure that
Napoleon was permanently “out of the
way”. Strong hatred by British local
commander.
Royalists - Revenge and insurance against
Napoleon for declaring himself Emperor
and dismantling the aristocracy.
Exiled Entourage - Jealousy (romantic
triangles), intrigue, revenge.
64
Chem 113
Neutron Activation Analysis
Arsenic in Hair
The wallpaper in his room was dyed with
Scheele's Green (Paris Green), a coloring
pigment that had been used in fabrics and
wallpapers from around 1770. Named
after the Swedish chemist who invented
it, the dye contained copper arsenite. It
was discovered that if wallpaper
containing Scheele’s Green became
damp, the mould converted the copper
arsenite to a poisonous vapor form of
arsenic. Breathing the arsenic on its own
might not have been enough to kill
Napoleon, but he was ill already with a
stomach ulcer/cancer. On May 5, 1821,
the arsenic tipped the scale against "the
little corporal."
65
Chem 113
Molecular Spectroscopy
66
• Electronic Spectroscopy
• Vibrational Spectroscopy
• Nuclear Magnetic Resonance Spectroscopy
(NMR or MRI)
(All of these are absorption methods, but this list is far from comprehensive!)
Chem 113
Electronic Spectroscopy
UV-visible
67
When white light passes through or is reflected by a
colored substance, a characteristic portion of the
total wavelengths is absorbed.
The remaining light will
assume the complementary
color to the wavelength(s)
absorbed.
Chem 113
Electronic Spectroscopy
UV-visible
68
Visible region - photon energies to excite a electron to a higher energy
level (orbital).
Of the six transitions outlined, only the two lowest energy ones (leftmost, colored blue) are in the UV-visible region (200-800 nm).
Chem 113
Electronic Spectroscopy
UV-visible
69
Effect of Conjugation
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 70
• Radiation from 500 to 4000 cm-1 (vibrational
transitions in the molecules).
• Vibrational “mode” must have a change in dipole
moment in the transition. Energy of the transition is
dependent upon the strengths of the bonds and
geometric structure.
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 71
• For the water molecule, there are three vibrational
modes that may occur (are allowed).
•The spacing between
energy levels depends
upon the vibration being
considered.
•Each spacing requires a
photon of different
energy to cause the
transition
•expect photons of three
different energies to be
absorbed by H2O.
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 72
• For a molecule to directly absorb infrared
electromagnetic radiation, the vibrational motion must
produce a change in the dipole moment of the molecule.
• There are many molecules which, although possessing
no permanent dipole moment, still undergo vibrations
which cause changes in the value of the dipole moment
from 0 to some non-zero value. Consider the CO2
molecule:
Chem 113
IR Spectrum of CO2
73
C alculated spectrum o f co 2 B 3L Y P /6-31G (d)
595
495
a b so rb a n c e
395
O=C=O
295
O=C=O
195
95
-5
0
500
1000
1500
2000
w avenum ber/cm -1
2500
3000
3500
4000
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 74
• Different types of
bonds have
characteristic
regions of the
spectrum where
they absorb
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 75
• Forensic Applications of Infrared Spectroscopy
• Use of computer databases of IR’s of known
compounds
»
Analyzing Alcohol - The breath is
tested with a mechanism similar to a
breathalyzer (chemical oxidation) but
uses the infrared absorptions of
alcohol.
»
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 76
• Forensic Applications of Infrared Spectroscopy
• Use of computer databases of IR’s of known
compounds
»
Analyzing Drugs - The drug's
various chemical components absorb
infrared light. The absorptions are
compared to known samples using a
database.
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 77
• Forensic Applications of Infrared Spectroscopy
• Use of computer databases of IR’s of known
compounds
»
Analyzing Fibers - The expected
identity of the fiber has been
established by observing it under a
microscope. Its IR spectrum can
confirm the suspected identity.
•
Chem 113
Vibrational Spectroscopy
Infrared and Raman Spectroscopy 78
• Forensic Applications of Infrared Spectroscopy
• Use of computer databases of IR’s of known
compounds
»
Analyzing Paint - Paint has been
recovered from a crime scene. Since
there is a limited amount of paint, the
first tests to be done should be
nondestructive. Colors, layers,
texture, and other physical properties
are recorded. The individual layers of
paint are analyzed by infrared
spectroscopy. The results can be
compared to IR results of known
paint samples.
Chem 113
Infrared Spectroscopy
79
• “With infrared radiation, forensic scientists can determine
the exact ink type and pen that a death threat was written
in, or the very model and year of a suspect's automobile in
a hit-and-run accident. Using infrared spectromicroscopy,
forensic investigators have been able to identify samples
from inks and paint chips to fibers and drugs. Researchers
at Lawrence Berkeley National Laboratory have now
expanded the boundaries of infrared forensics with the use
of synchrotron radiation from the Lab's Advanced Light
Source (ALS) facility…..” (Daily Californian, Wednesday,
September 18, 2002)
Chem 113
Magnetic Resonance Spectroscopy
NMR (MRI)
80
• Visualize soft tissue by measuring proton (nuclear)
magnetic alignments relative to an external
magnetic field.
Review Electron Spin Properties First.
Chem 113
Nuclear Spin
81
• Like electrons, nuclei spin and because of this
spinning of a charged particle (positively charged),
it generates a magnetic field. Two states are
possible for the proton (1H).
N
S
+
+
S
N
Chem 113
Magnetic Fields
82
Chem 113
Nuclear Spin
Similar to a canoe paddling
either upstream or
downstream
83
S
Antiparallel
Degenerate
E
N
N
N
S
Parallel
S
N
External Magnetic Field
S
Chem 113
84
Magnetic Resonance Imaging MRI
• Hydrogen atom has two nuclear spin quantum numbers
possible (+1/2 and -1/2).
• When placed in an external magnetic field, 1H can either
align with the field (“parallel” - lower energy) or against
the field (“antiparallel” - higher energy).
• Energy added (E) can raise the energy level of an electron
from parallel to antiparallel orientation (by absorbing
radio frequency irradiation).
• Electrons (also “magnets”) in “neighborhood” affect the
value of E (i.e., rocks in stream).
• By detecting the E values as a function of position within
a body, an image of a body’s hydrogen atoms may be
obtained.
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MRI
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• Advantages (first three are not really important for
forensics)
– non-invasive.
– no ionizing or other “dangerous” radiation (such as Xrays or positrons).
– Can be done frequently to monitor progress of
treatment.
– images soft tissues (only those with hydrogen atoms
(almost all “soft” tissues).
– images function through the use of contrast media.
• Disadvantages
– Relatively expensive equipment.
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MRI; Hardware
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MRI
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MRI
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MRI
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MRI
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MRI
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Forensic MRI/CT
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• Used to reconstruct facial images from skulls. Use
for ancient mummies to modern skulls.
• Allows a very fine discrimination between materials
with different densities providing an enormous
amount of information about the mummy and its
skeleton.
• The level of automation reached in building models
from CT data, reconstruction, texture application
and visualization allow to the user to complete
whole process in 2-3 hours on a PC or graphic
workstation.
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Forensic MRI and CT
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• The “Virtopsy” focuses on four goals:
• radiological digital imaging methods as main diagnostic tools in
forensic pathology, ultimately leading to "minimally invasive
autopsy" analogous to "keyhole surgery" in clinical medicine.
• three-dimensional optical measuring techniques - a reliable,
accurate geometric presentation of all forensic findings (the body
surface as well as the interior).
• 3D surface scanning in forensic reconstruction.
• Producing and validating of a post-mortem biochemical profile to
estimate the time of death.
• The implementation of an imaging database as a technical basis of a
"center for competence in virtual autopsy”.
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Forensic MRI
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Virtopsy, a new imaging horizon in forensic pathology:
virtual autopsy by postmortem multislice computed
tomography (MSCT) and magnetic resonance imaging (MRI)
- 40 forensic cases were examined and findings were verified by
subsequent autopsy. Results were classified as follows: (I) cause of death,
(II) relevant traumatological and pathological findings, (III) vital
reactions, (IV) reconstruction of injuries, (V) visualization. In these 40
forensic cases, 47 partly combined causes of death were diagnosed at
autopsy, 26 (55%) causes of death were found independently using only
radiological image data. Radiology was superior to autopsy in revealing
certain cases of cranial, skeletal, or tissue trauma. Some forensic vital
reactions were diagnosed equally well or better using MSCT/MRI.
Radiological imaging techniques are particularly beneficial for
reconstruction and visualization of forensic cases.
(J Forensic Sci. 2003, 48, 386-403)
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Forensic MRI
Validating of a post-mortem analysis
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Complex scull fracture
system following motor
vehicle accident (victim was
overrun by automobile).
3D reconstructed MSCT image.
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Forensic MRI
Validating of a post-mortem analysis
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Injury due to vehicle impact in a motor vehicle accident
(pedestrian). (right) finding at autopsy; right lower leg showing
fracture of the fibula. (left) 3 D reconstructed MSCT;
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Forensic MRI and CT
Facial Reconstructions
Egyptian Mummy Head
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The method uses the tables combined with the warping of a
3D model of a reference scanned head, until the relevant
surface to bone distances are correct. Texture mapping is
used to provide colors and aesthetic features.
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Forensic MRI and CT
Mummy Facial Reconstruction
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Model skin (blue) and
mummy skull (white)
Face shape
generated
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Forensic MRI and CT
Mummy Facial Reconstruction
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Texturized model of reconstructed soft
tissues of the mummy
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X-ray Methods
• X-ray Diffraction (XRD and CT)
• Energy Dispersive X-ray Fluorescence
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Bragg’s Law and X-ray Diffraction
101
incoming
light

E
D
B
d
lattice in a
crystal
C
Since BCD = 2d sin  is the limiting condition for
observing a reflection then because of wave addition
and cancellation;
Bragg’s Law:
n = 2d sin 
where n = 1, 2, 3, etc...
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Energy-Dispersive X-ray
Fluorescence (EDXRF)
•Did your luxury purchase
originate in a mine deep in the heart
of Central America, or the bottom of
a silty river tributary in Africa, or
perhaps even a flask in a laboratory
in Chicago or Minsk?
•Metal ions such as V3+, Cr3+, Mn2+,
Mn3+, Fe2+, Fe3+, Ni2+, Cu2+, and
UO22+ are responsible for the colors
of most common gemstones and
minerals.
•U.S. Federal Trade Commission
says consumers must be informed
of alterations in gemstones.
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Energy-Dispersive X-ray
Fluorescence (EDXRF)
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•Among the most sensitive and
popular of the nondestructive
spectroscopic techniques used for
trace-metal determination is
EDXRF. In this technique, X-rays
excite the gemstone to fluoresce and
the fluorescent line spectrum
indicates which chemical elements
are present.
EDXRF can also be used to differentiate freshwater from saltwater pearls on the
basis of the greater concentration of magnesium present in the former.
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Energy-Dispersive X-ray
Fluorescence (EDXRF)
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•EDXRF has been called 'the curator's dream instrument'
because measurements are non-destructive and usually
the whole object can be analyzed, rather than a sample
removed from one. The technique involves aiming an Xray beam at the surface of an object; this beam is about 2
mm in diameter.
•The interaction of X-rays with an object causes
secondary (fluorescent) X-rays to be generated. Each
element present in the object produces X-rays with
different energies. These X-rays can be detected and
displayed as a spectrum of intensity against energy: the
positions of the peaks identify which elements are
present and the peak heights identify how much of each
element is present.
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Energy-Dispersive X-ray
Fluorescence (EDXRF)
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An incoming X-ray ejects a K-shell electron from an atom of the target. An
electron in the M or L-shell loses energy as it transitions to the vacant K-shell. It
given off energy in the form of fluorescence.
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Energy-Dispersive X-ray
Fluorescence (EDXRF)
http://www.thebritishmuseum.ac.uk/science/techniques/sr-tech-xrf.html
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Analytical Methods
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• Questions to consider in choosing an analytical
(chemical) method:
– Quantitative or qualitative required
– Sample size and sample preparation requirements
– What level of analysis is required (e.g., ± 1.0% or ±
0.001%)
– Detection levels and useful analytical concentration ranges
– Destructive or non-destructive
– Availability of instrumentation
– Admissibility (e.g., are all lead pipes compositionally the
same or are there sufficient variations among “known” Pb
pipes of the world to link two samples)
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