Forensic Science (????)

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Forensic Science (????)

• IJSO Training (Phase 3)

Dr. Kendrew K. W. Mak Department of Chemistry The
Chinese University of Hong Kong
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Reference for slides 3 20 Criminalistics An
Introduction to Forensic Sciences, 7th ed. By
Richard Saferstein Prentice-Hall, NJ, c2001.
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Definition and Scope of Forensic Science
Forensic science (????) The application of
science to law.
Apply the principles and techniques of sciences
to the analysis of evidence recovered during
crime investigation. Provide expert court
testimony (??).

• The procedures and techniques used must
• have a firm scientific foundation
• be admissible (????) to the courts.

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The Basic Services Provided by Crime Laboratories

• Basic Services Provided by Full-Service Crime
  Laboratories
• Physical Science Unit
• Biology Unit
• Firearms Unit
• Document Examination Unit
• Photography Unit

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The Basic Services Provided by Crime Laboratories
Physical Science Unit Use scientific tests and
modern analytical instruments to identify and
compare crime-scene evidence. E.g. drugs, glass,
paints, explosives and soil
Biology Unit Identifying and DNA profiling of
dried bloodstain (??) and other body
fluids. Comparison of hair and fibers. Identificat
ion and comparison of plants.
Firearm Unit Examine firearms, discharged
bullets, cartridge cases (???), shotgun shells,
and ammunition (??) of all types. Detect firearm
discharge residues on garments and other
objects. Estimate the distance from which a
weapon was fired.
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The Basic Services Provided by Crime Laboratories
Document Examination Unit Study handwriting and
typewriting on questioned documents to establish
authenticity and/or source. Analysis of paper
and ink, erasures, and burned or charred
documents.
Photography Unit Examine and record physical
evidence using special photographic techniques to
make invisible information becomes visible. E.g.
digital imaging, infrared (???), ultraviolet
(???), and X-ray photography
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Optional Services Provided by Crime Laboratories

• Optional Services Provided by Crime Laboratories
• Toxicology (???) Unit
• Latent Fingerprint (????) Unit
• Polygraph (??) Unit
• Voiceprint Analysis (????) Unit
• Evidence-Collection Unit

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Processing the Crime Scene
Physical Evidence Establishing that a crime has
been committed Providing a link between a crime
and its victim or a crime and its
perpetrator. Collected by experts who are very
knowledgeable in crime laboratorys techniques,
capabilities, and limitations. Forensic science
begins at the crime scene. If a physical
evidence was not properly collected and
preserved, it is useless.
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Processing the Crime Scene

• The Key Steps
• Secure and isolate the crime scene
• Record the scene by photography, sketches and
  notes
• Conduct a systematic search for evidence
• Collect and package physical evidence
• Maintain chain of custody (??? / ????)
• Obtain controls
• Submit evidence to the laboratory
• Crime-scene safety

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Processing the Crime Scene (????)
Secure and isolate the crime scene Exclude all
unauthorized personnel from the scene - to
prevent destruction of the important physical
evidence.
Record the scene Permanently record the scene in
its original state to document the condition
of the crime site and to record the location of
physical evidence. photography, sketches, and
notes
Conduct a systematic search for evidence The
search for physical evidence at a crime scene
must be thorough and systematic to collect as
much relevant evidence as possible.
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Processing the Crime Scene
Collect and Package Physical Evidence Prevents
any change from taking place between the time it
is removed from the crime scene and the time it
is received by the crime laboratory. Avoid
contamination (??), breakage, evaporation,
accidental scratching or bending, or loss through
improper or careless packaging. All items must be
packed separately to prevents damages and
cross-contamination.
Maintain Chain of Custody Continuity of
possession, or the chain of custody, must be
established.
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Processing the Crime Scene
Obtain Controls The examination of evidence often
requires comparison with a known standard or
control (??). Such materials may be obtained
from the victim, a suspect, or other sources.
Crime-scene Safety

• Forensic and crime-scene personnel may encounter
  potentially infectious materials that collected
  from the scenes (e.g. blood)
• Alert to sharp objects, knives, hypodermic
  syringes (??????), razor blades (????), etc.
• Avoid contamination of pens, pencils, notebook,
  paper, etc.

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The Significance of Physical Evidence
Examination of physical evidence for
identification or comparison.
Identification To determine the physical or
chemical identity of a substance using modern
analytical techniques (????).
Comparison Perform the same tests and
examinations to the suspect and control specimens
to determine whether they have a common origin.
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The Significance of Physical Evidence
Common Types of Physical Evidence

• Blood, Semen (??), and Saliva (??)
• Documents
• Drugs
• Explosives
• Fibers
• Fingerprints (??)
• Firearms and Ammunition
• Glass
• Hair
• Impressions

• Organs (??) and Physiological Fluids
• Paint
• Petroleum Products (????)
• Plastic Bags
• Plastic, Rubber and Other Polymers
• Powder Residues (???)
• Serial Numbers
• Soil and Minerals (???)
• Tool Marks
• Wood and Other Vegetative Matter

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Fundamental Principles of Fingerprints
1st Principle A fingerprint is an individual
characteristics. Theoretical calculation 64
billion different fingerprints. No two have even
been found to be identical.
2nd Principle A fingerprint will remain
unchanged during an individuals lifetime.
3rd Principle Fingerprints have general ridge
(?) patterns that permit them to be
systematically classified.
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Methods of Detecting Fingerprints
Three Types of Fingerprints
Visible prints
Made by fingers touching a surface after the
ridges have been in contact with a colored
material such as blood, paints, grease (??), or
ink.
Plastic prints
Ridge impressions left on a soft material such as
putty (??), wax, soap, or dust.
Latent prints
Or invisible prints. Impressions caused by the
transfer of body perspiration (??) or oils
present on finger ridges to the surface of an
object.
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Methods of Detecting Fingerprints
The method used for visualizing a latent print
depends on the type of surface that is being
examined.
Hard and nonabsorbent surfaces (e.g. glass,
mirror, tile, and painted wood)
Developed by the application of a powder (adhere
to perspiration residues and/or body oils left on
the surface) or treatment with Super Glue
Soft and porous (??) surfaces (e.g., papers,
cardboard, and cloth)
Treatment with one or more chemicals e.g. Iodine
(?), ninhydrin (????), and silver nitrate (???).
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Methods of Detecting Fingerprints
Super Glue Fuming Super glue consists of almost
pure ethyl-2-cyanoacrylate.
The invisible fingerprints residues react with
the CA (cyanoacrylate - ??????) fumes and
atmospheric moisture to form a white polymer
(polycyanoacrylate) on the fingerprint ridges and
become visible to the naked eyes.
Spray with Ninhydrin Solution
Ninhydrin reacts with the residual amino acids
(???) present in trace amounts of perspiration
and forming visible purple-blue colored prints.
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Different Types of Chromatography (?????)
Thin-layer chromatography (???????)
Column chromatography (??????)
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Thin-Layer Chromatography
A very important technique for rapid and
qualitative analysis (????) of small amounts of
material.
Suitable for the analysis of mixtures in small
and microscale experiments, without the need for
expensive instrument.
solvent front
TLC sheet containing a thin layer of adsorbent
(???)
solvent move up by capillary action (?????)
separated components
time
Original sample spot
Recall your experience with paper chromatography.
(??????)
immense in eluting solvent
The original spot should not be immersed in the
eluent (???).
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Chromatographic Method

• Chromatography - the separation technique based
  on the selective distribution of chemicals
  between a stationary phase (???) and a mobile
  phase (???)
• Due to the selective interaction of chemicals
  with the stationary and mobile phases, separation
  is achieved after a certain period of time.

Types of Chromatography

• Thin-Layer Chromatography (TLC) (a more
  effective version of paper chromatography)
• Column Chromatography
• Instrumental Technique
• Gas Chromatography (??????? ) (GC or GLC)
• High-Performance Liquid Chromatography (????????)
  (HPLC)

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Thin-Layer Chromatography (TLC)The Adsorption
Process
Adsorption (????)

• Strictly a surface process
• Depends on electrostatic forces (???)
  (dipole-dipole, ion-dipole and H-bonds)

Common adsorbents for TLC

• Silica gel (??) (SiO2) has polarized (??) Si-O
  and O-H bonds that interact with dipole (??)
  in the solutes (??)
• Alumina (???) (Al2O3)

(The activity of the stationary phase partially
depends on its water content)
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Thin-Layer Chromatography (TLC)The Adsorption
Process
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Equipment For Thin-Layer Chromatography
TLC Plate Silica gel coated on an aluminium
backing sheet
TLC Developing Chamber
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Procedure For Thin-Layer Chromatographic Analysis

• Carefully apply a small drop of the sample
  solution to a chromatographic plate near the edge
  of a narrow end.(Handle the strip only by the
  sides to avoid contaminating the plate with oils
  from your fingers.)

• Prepare the developing chamber.

• Place the TLC plate with spotted end down in a
  closed jar.(The level of the eluent should be
  just below the sample spot)

• When the solvent front has advanced nearly to the
  top of the TLC plate, the development of the
  chromatogram (????) is complete, and the plate is
  withdrawn from the developing chamber.

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Visualizing The Developed Plate
(Fluorescent Indicator?????)
If the compounds in the sample are colorless,
they must be made visible by some visualizing
reagents or methods.
Visualization with fluorescent indicator
Many commercially available pre-made TLC plates
are coated with fluorescent indicator (?????).
When a developed TLC plate is held under
ultraviolet (UV) irradiation, spots that either
quench or enhance fluorescence can be seen.
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Visualizing The Developed Plate (Fluorescent
Indicator)
TLC adsorbents come with zinc sulfide (???)
(will fluoresce green under 254 nm wavelength
light) A dark spot appear where there is an
eluted substance which quenches this fluorescence.
Applications

• Compounds that absorb UV at 254 nm
• Aromatic compounds (??????)
• Conjugated alkenes (????)
• Conjugated carbonyl compounds (???????)
• (ketones ? , aldehydes ? , esters ? )