Forensic Science

 A. Matter - anything that has mass & takes up space
 B. Element - cannot be broken down into simpler substances by chemical means
 C. Periodic table - chart of elements arranged in a systematic fashion
 D. Atom - smallest particle of an element that can exist and still retain its identity as that element

Mixture – Two or more substances that are mixed together, but not chemically combined.
Examples of mixtures ...
Air – mixture of gases
Bowl of cereal – mixture of cereal and milk
Soda pop – mixture of soda syrup, water, and CO 2 gas
Fog –water suspended in air
Kool-Aid – mixture of water, sugar, and flavor crystals
Compounds – Two or more elements that are chemically combined.
Examples of compounds ...
Salt –Sodium and chlorine combined chemically
Water –Hydrogen and oxygen combined chemically
Carbon Dioxide – Carbon and oxygen combined chemically

Solutions are mixtures in which one substance is dissolved in another.
Solutions have two parts: solute and solvent
The solute is the substance that is dissolved.
The solvent is the substance that does the dissolving
Identify the solute and solvent in each solution ...
Solution Solute Solvent
Lemonade
Soda pop
Ocean water
Solubility A measure of how much of a given substance will dissolve in a liquid.
A substance that does not dissolve in water is called insoluble .
A substance that does dissolve in water is called soluble .

The periodic table is a listing of all elements by increasing atomic number.

 Substances change from one state to another
 Phase - a uniform piece of matter, different phases are separated by definite visible boundaries
 There are four phases of matter: solid, liquid, gas, and plasma.

 Evaporation = Liquid -> Gas
 Condensation = Gas -> Liquid
 Melting = Solid -> Liquid
 Freezing = Liquid -> Solid
 Sublimation = Solid -> Gas

 particles vibrate but can’t move around
 fixed shape
 fixed volume
 incompressible

 particles can move around but are still close together
 variable shape
 fixed volume
 Virtually incompressible

 particles can separate and move throughout container
 variable shape
 variable volume
 Easily compressed
 Vapor - gaseous state of a substance that is a liquid or solid at room temperature

 particles collide with enough energy to break into charged particles (+/-)



 Need to know whether substance is organic or inorganic
 A. Organic - substance composed of carbon and hydrogen
 B. Inorganic - CO
2 lack carbon and all substances that
 Need to consider the need for qualitative and quantitative determination

 Spectrophotometry
 Chromatography
 Gas Chromatography (GC)
 High – Performance Liquid Chromatography
(HPLC)
 Thin – Layer Chromatography (TLC)
 Electrophoresis

 An analytical method for identifying a substance by its selective absorption of different wavelengths of light
 Most applicable to organic analysis
 Optimum utilization requires that a material be in relatively pure state


Organic mixtures are separated into their components by their attraction to a stationary phase while being propelled by a moving phase.
 Useful technique for purifying substances
 1 st observed in 1803 by William Henry (Henry’s Law)
 One phase is always made to move continuously in one direction over a stationary or fixed phase
 It’s like a race between chemical compounds.


At the beginning, all substances are mixed together.
As the race progresses, those that have preference for the moving phase will move faster and pull ahead of others.
 At the end, all the substances are separated.

 separates mixtures on the basis of their distribution between a stationary liquid phase and a moving gas phase
 used widely because of its ability to resolve a highly complex mixture into its components within a time period usually measured in minutes
 is very sensitive
 sample must be vaporized and passed through heated tube

 Different types of stationary phases (usually nonaqueous) with a liquid moving phase
 can perform process at room temperature
 used for organic explosives and drugs that are heat sensitive

 incorporates solid stationary phase & liquid moving phase
 because most compounds are colorless, uses UV light to reveal those that fluoresce
 cannot by itself provide absolute identification; has to be used in conjunction with other procedures to prove absolute identity
 powerful tool for solving analytical problems
 rapid and sensitive
 minimal cost and space requirements

 related to TLC in that it separates materials according to their migration rates on solid phase
 uses electrical current instead of moving liquid phase
 characterization of proteins, enzymes, and DNA

Liquid Chromatography
Used to identify unknown plant pigments & other compounds.
Thin-Layer Chromatography
Uses thin plastic or glass trays to identify the composition of pigments, chemicals, and other unknown substances.
Gas Chromatography
Used to determine the chemical composition of unknown substances, such as the different compounds in gasoline shown by each separate peak in the graph below.
Paper Chromatography
Can be used to separate the components of inks, dyes, plant compounds (chlorophyll), make-up, and many other substances







Obtain the supplies you’ll need.
 1 large beaker (or plastic cup)
Pencil
 1 small beaker (or plastic cup) filled with water
 4 pieces of filter paper
 4 black markers for testing
 4 small pieces of masking tape
 Pencil (to attach to the top of the filter paper)
 Permanent marker
 Timer
Filter
Paper
Ink
Mark
Tape – Label with marker
Write the pen number on a piece of masking tape with a permanent marker and place it at the top of the strip.
Choose one of the testing markers and draw a thick line near the bottom of the filter paper - about ¼ inch from the bottom.
Pour a small amount of water into the large cup and then hang the paper strip in the cup. Make sure the ink line does not touch the water – only the bottom of the filter paper.
Allow the water to move up the paper for 5 minutes and then remove the strip from the water. Hang it on the side of the table to dry.
Follow these directions to test the other pens.

Complete the chart on your worksheet and then answer the questions.
Questions:
What colors did your group observe in each of the black ink samples?
Do the colors occur in the same order on all the samples?
Explain.
Did some ink samples not work? Why?

Work with your group to identify the pens used for each of the
“Mystery Marks”.
1 st – Test each of the Mystery Mark strips using the procedure from yesterday.
2 nd – Compare your strips to the strips hanging in the classroom.
3 rd – Write the number of the pen that you think matches each of the mystery marks in the space on your worksheet.
4 th – Have your answers checked by the teacher. Keep trying until you are able to identify all 6 pens!
Pen A matches # _____ Pen D matches # _____
Pen B matches # _____
Pen C matches # _____
Pen E matches # _____
Pen F matches # _____

 Carbon does not appear among earth’s most abundant elements.
 Inorganics are also encountered as physical evidence
 Metals in tools, coins, weapons, scrapings
 Pigments in paints and dyes
 Explosive formulations
 Poisons
 For ID & comparison of physical evidence

 Elements selectively absorb and emit light
 When the light passes through a prism, it is separated into its component colors or frequencies
(emission spectrum).
 Types of emission spectrums
 Continuous spectrum
 shows a continuous band of colors all blending into one another
 Ex – sunlight or light from incandescent bulb passes through a prism

 Line spectrum
 1. shows a series of lines separated by black areas
 2. Each line represents a definite wavelength or frequency
 3. Ex – light from a sodium lamp or mercury arc lamp

 instrument used to obtain and record the line spectra of elements
 Requires:
1) a means for vaporizing and exciting the atoms of elements so that they emit light
2)
3) a means for separating light into its component frequencies a means for recording the resultant spectrum
 Uses in Forensics: Rapid comparison of the elemental composition of two or more specimens


Identifies and measures elements through light emitted by excited atoms
 Uses hot plasma torch instead of electrical arc to excite atoms
 Has been applied in the area of identification and characterization of mutilated bullets and glass fragments

 When an atom is vaporized, it will absorb many of the same frequencies of light that it emits in an excited state.
 In this technique, 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.
 Provides a determination of an element’s concentration
 Useful in detecting trace amounts of elements
 Drawbacks:
 only one element at a time
 each time the proper lamp has to be selected to match the particular element under investigation

 Subatomic particles
 Proton – positive electrical charge; in nucleus
 Neutron – neutral particle; in nucleus
 Electron – negative charge; outside the nucleus
 # of protons = # of electrons in a neutral atom

 Electrons move around the nucleus and are confined to specific electron orbitals or energy levels.
 Atoms are most stable when all of the electrons are in the lowest possible energy orbitals.
 When the atom absorbs energy (heat or light), its electrons are pushed into higher energy orbitals.
(excited state)
 Only a definite amount of energy can be absorbed when moving an electron from one level to another.

 Elements are selective in the frequency of light they absorb.
 Energy levels determine the selectivity.
 If atoms are exposed to intense heat, energy is generated to push electrons into higher unoccupied energy levels.
 Normally, an electron does not remain in this excited state for long, but falls back to its original energy level. As it falls, it releases energy in the form of light.
 Because each element has its own characteristic set of energy levels, each will emit a unique set of frequency values providing a “picture” of the energy levels that surround the nucleus of each element.

 Atoms of the same element have the same number of protons.
 They do not always have the same # of neutrons.
 Atomic mass - the # of protons + # of neutrons
 Isotopes - atoms with the same # of protons but different # of neutrons
 Most elements have two or more isotopes, and most are stable.
 Isotopes that are unstable and decompose are considered radioactive.

 Atoms having the same number of protons but differing solely in the number of neutrons are called isotopes.
 Most elements have two or more isotopes and most are stable.
 Isotopes that are unstable and decompose are considered to be radioactive.
 Radioactivity is the emission of radiation that accompanies the spontaneous disintegration of unstable nuclei.

 Types



Alpha particles (

)– composed of a helium nucleus; positive charge 4
He
2
Beta particles (

) – electrons; negative charge

0
1 e
Gamma rays (

) – high energy form of electromagnetic radiation emitted by a radioactive element
0
0


 The technique of bombarding specimens with neutrons and measuring the resulting gamma-ray radioactivity
 Advantage – provides a non-destructive method for identifying and quantitating trace elements
 It has been employed for characterizing the trace elements present in metals, drugs, paint, soil, gunpowder residues, and hair.

 Technique for identifying crystalline materials
 As x-rays penetrate the crystal, a portion of the beam is reflected by each of the atomic planes. They interact 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” compounds
 Drawback – not very sensitive and often fails to detect the presence of substances comprising less than 5% of a mixture

 An optical instrument that uses a lens or combination of lenses to magnify and resolve the fine details of an object

 Virtual image
 Can only be seen by looking through a lens and cannot be viewed directly
 Real image
 Can be viewed directly

 Magnifying glass
 Magnification of 5-10 times
 Single lens
 Compound Light Microscope
 Comparison Microscope
 Stereoscopic Microscope
 Polarizing Microscope
 Microspectrophotometer
 Scanning Electron Microscope (SEM)

 Magnification up to 1500 times
 Multiple lenses
 Objective lens
 lower lens of a microscope that is positioned directly over the specimen
 Eyepiece lens
 lens of a microscope into which the viewer looks, same as ocular lens







base – support on which instrument rests arm – C-shaped/handle/support stage – horizontal plate upon which specimens are placed for study body tube – hollow tube on which objective and eyepiece are mounted at opposite ends coarse adjustment – focuses lenses fine focus – focuses but on smaller magnitude


Illuminator

 transmitted illumination – light that passes up from condenser and through specimen vertical or reflected illumination – illumination of a specimen from above
 Condenser – collects light rays from illuminator and concentrates them onto specimen
 Objective lens – lens closest to specimen
 most microscopes are parfocal – when an image is focused with one objective in position, the other objective can be rotated into place and then the field will remain in focus
 Eyepiece or ocular lens

 monocular – one eyepiece binocular – two eyepieces



Magnifying power : power of objective lens x power of eyepiece lens
Numerical aperture


The ability of an objective lens to resolve details into separate images instead of one blurred image is directly proportional to the numerical aperture.
Ex. A lens with a NA of 1.30 can separate details that are twice as close as compared to lens with NA of 0.65.
 Field of view
 the area of the specimen that can be seen after it is magnified
 as magnifying power increases, field of view decreases
 Depth of focus

 the thickness of a specimen entirely in focus under a microscope decreases as magnifying power increases

 Two compound microscopes combined into one unit
 Uses a bridge incorporating a series of mirrors and lenses to join them
 Very useful in forensic science when side-by-side comparisons are necessary
 Vertical or reflected illumination
 Used when comparing bullets, cartridges, other opaque objects
 Transmitted illumination
 Compare hairs or fibers

 Power of 10x to 125x
 Can present a 3-D image of object
 Formation of right side up image
 Very frequently used in crime lab
 Wide field of view and great depth of focus
 Used often for examination of paint, soil, gunpowder residues, marijuana, etc.


When a beam of light passes through certain types of substances, it emerges vibrating in only one plane.
 Plane-polarized light: Light confined to a single plane of vibration

 Polarizer: Device that permits passage of light waves vibrating in only one plane
 Second polarizing crystal – analyzer
 Can modify stereo or compound microscopes so they can detect polarized light
 Application – study materials that polarize light
 ex. Birefringent substances

 An instrument that links microscope to a spectrophotometer
 Spectrophotometer an instrument used to measure and record the absorption spectrum of a chemical substance
 Allows better comparison of substances

 Image is produced by aiming a beam of electrons onto the specimen and studying electron emissions on a closed TV circuit or computer
 High magnification
 High resolution

 High depth of focus
 Used as tool for determining whether or not a suspect has recently fired a gun
 X-ray analyzer