Forensics

Forensics is a Division C chemistry event that involves identification of powders, polymers, fibers, and hair samples, blood serum and fingerprint analysis, and interpretation of chromatography. Given a scenario and some possible suspects, students will perform a series of tests. These tests, along with other evidence or test results, will be used to solve a crime.

The competition will involve using pre-brought materials to analyze data. The participants may also bring one Note Sheet. This event is closely associated with the Division B event, Crime Busters.

Topics Covered

• Qualitative Analysis (powders)
• Polymers
• Chromatography/Spectroscopy
• Fingerprint Analysis
• DNA
• Glass Analysis
• Entomology
• Spatters
• Seeds and Pollen
• Tracks and Soil
• Blood
• Bullet Striations

Qualitative Analysis

Qualitative Analysis is the section of the test that involves the identification of unknown powders. At the regional level, 3-8 powders will be given. 6-10 samples will be given at state, and 8-12 powders will be given at nationals. It is helpful to include a flowchart to aid with powders identification on your cheat sheet.

There are fifteen different substances that may be given on a test: sodium acetate, sodium chloride, sodium hydrogen carbonate (sodium bicarbonate), sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, calcium sulfate, calcium carbonate, cornstarch, glucose, sucrose, magnesium sulfate, boric acid, and ammonium chloride. Utilizing all your availible means of identification will give the best results.

Methods of Identification

Flame test: The flame test uses a Bunsen burner and a nichrome wire. To perform this test, dip a clean nichrome wire in distilled water, and then dip the loop of the wire into a small sample of the dry chemical. Hold the loop of the wire in the cone of the flame, and observe the color of the burning chemical. If desired, a piece of cobalt blue glass may be used for viewing. Chemical cations determine the color of the flame, and their characteristics may indicate the chemical identity.

• Sodium: yellow flame, very distinct. Even a small amount of sodium will contaminate other compounds.
• Lithium: carmine or red flame
• Calcium: yellow-red flame
• Boric Acid: bright green flame, very visable
• Ammonium Chloride: faint green flame
• Potassium: light purple, lavender flame

Note that sodium can easily contaminate some substances, and its presence can mask the other cation colors, giving off a yellow flame. The purpose of the cobalt blue glass is to block of the yellow color given off by sodium in case the sample may have been contaminated. In some cases, this yellow color can appear a little orangish.

Tests with liquids: Liquids used for identification are iodine, sodium hydroxide, hydrochloric acid, Benedict's solution, and water. Not all liquids are applicable to all samples.

• Iodine: When iodine is added to cornstarch, the sample will turn black. If cornstarch is not present, the iodine will remain brown.
• Sodium Hydroxide: Sodium hydroxide is used simply to categorize your samples into two fields: NaOH reactive- and non-reactive. For this reason, it is extremely useful when using a flowchart. To perform this test, a few drops of NaOH is added to a small sample of chemical dissolved in water. If a milky-white precipitate forms, the sample is NaOH reactive. If a precipitate does not form, the sample is NaOH non-reactive.
• Hydrochloric Acid: Hydrochloric acid will react when added to samples contaning carbonates--therefore, it is useful in identifying calcium carbonate, sodium carbonate, and sodium hydrogen carbonate.
• Benedict's solution: Benedict's solution is used to detect glucose. To perform this test, dissolve a small sample of chemical in water in a test tube. Add two to three drops of Benedict's solution, then place the test tube in a hot water bath. If the glucose is present, the sample will react and form an orange precipitate. This test may take a few minutes; be patient.
• Water: Water is used for determining the solubility of chemical samples, and is used for making solutions.

pH: The pH data for chemicals can be useful, especially for determining between two similar chemicals. Most samples have a pH of between 5 and 7, but two are distinct: sodium carbonate has a pH of 12, while sodium bicarbonate has a pH of around 10.

Conductivity: Certain chemical samples will dissociate and become conductive when dissolved in water. To perform this test, dissolve a small sample of dry chemical in water. Using a 9-volt conductivity tester will determine whether a sample is conductive or semi-conductive. This data is especially helpful when following a flowchart.

Solubility: All samples can be divided into two fields--soluble and non-soluble. Water is used to perform this test.

• Soluble Samples: sodium acetate, sodium chloride, sodium hydrogen carbonate, sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, glucose, sucrose, magnesium sulfate, boric acid, ammonium chloride
• Non-soluble Samples: calcium sulfate, calcium carbonate, cornstarch

Polymers

Methods of Identification

• Burn test--fibers and hair only
• Density in liquids--oil, water, alcohol, etc.--plastics
• Microscope--useful for distinguishing different hairs and fibers

Hints Burn tests for fibers, when permitted, will usually be done with a small candle (Bunsen burners are too hot). Burn tests on plastics will not be permitted at the event, but burn test results may be provided. If not, it is important to know densities and other identifying properties. Common liquids used to test plastic densities include water, vegetable oil, isopropyl alcohol, and NaCl solution (10%, 25%, and saturated).

Plastics

Plastic	Abbreviation	Density	Monomer Unit Structure	Other Key Features	Commonly Used to Make
Polystyrene	PS	~1.05 g/cm^3	File:Sty01.gif	Polymerizes by addition, reacts with acetone	styrofoam, tableware, coffee cups, toys, lighting, signs, insulation
Polypropylene	PP	~0.90 g/cm^3		Polymerizes by addition	food containers, medicine containers, automobile batteries, carpet, rope, plastic wrap, lab equipment
Polyvinyl Chloride	PVC	~1.38 g/cm^3	File:Pvc01.gif	Burns green, polymerizes by addition	food packaging, shampoo containers, construction (ahem PVC pipes ... you see them often), tiles, credit cards
Low Density Polyethylene	LDPE	~0.92 g/cm^3		Polymerizes by addition, ethylene monomer units branch out more than HDPE	food containers (specifically bags), grocery bags, plastic wrap, etc.
High Density Polyethylene	HDPE	~0.95 g/cm^3		Polymerizes by addition, monomer units more linear	food containers, bags, lumber, furniture, flower pots, signs, trash cans, toys
Polycarbonate	PC	~1.20 g/cm^3		Polymerizes by condensation, clear	shatterproof glass, eyeglass lenses
Polyethylene Terephthalate	PETE	~1.37 g/cm^3	File:Polyethylene terephthalate svg.jpg	Polymerizes by condensation, shrivels with heat	soft drink bottles, carpet, fiberfill, rope, scouring pads, fabric, Mylar
Polymethyl Methacrylate	PMMA	~1.16 g/cm^3		Polymerizes by addition, reacts with acetone	Plexiglas, glass substitute

Just to clarify how LDPE differs from HDPE ...

(Lines represent the connected ethylene monomer units)

Fibers

There are three types of fibers: animal, vegetable, and synthetic/man-made. Each of these types of fibers behave differently in different tests, but generally fibers of the same type will react in a similar way.

Burn Test

• Animal fibers shrivel, but don't melt
• Synthetic fibers melt and shrivel, and loose ends fuse together
• Vegetable fibers do not melt or shrivel, but they ignite easily and usually appear charred after being burned.

Other Useful Facts

• Animal fibers dissolve in bleach, but the other types will not react at all (nice to know although the bleach test isn't available during competition)
• Smoother fibers are more likely to be synthetic
• Synthetic fibers are generally uniform in thickness whereas natural fibers vary.

Individual Fiber Information

Wool (Animal)

• most commonly used animal fiber
• burn test: shrivels, leaves brown-black residue, smells like burning hair
• looks like cylinder with scales under the microscope

Silk (Animal)

• SMOOTHER THAN WOOL
• burn test: shrivels, leaves black residue, smells like burning hair
• looks like a thin, long and smooth cylinder under the microscope

Cotton (Vegetable)

• most widely used plant fiber
• rather short fibers
• burn test: burns with a steady flame, smells like burning paper, able to blow flame from thread like a match, leaves behind a charred, whitish ash
• looks like an irregular twisted ribbon under the microscope

Linen (Vegetable)

• fibers generally longer and smoother than cotton
• burn test: burns at a constant rate, does not produce smoke, smells like burning grass, produces sparks
• looks like bamboo under a microscope

Polyester (Synthetic)

• fibers can be any length
• burn test: melts, only ignites when brought into the flame, drips when it burns and bonds quickly to any surface it drips on, produces sweet odor and hard, colored ash (color according to the color of the fiber itself)
• looks like a completely smooth cylinder under microscope

Nylon (Synthetic)

• long fibers
• burn test: curls, melts, produces black residue, smells like burning plastic (some sources say it smells like celery?), ignites only when brought into flame
• looks kind of like bamboo under microscope

Spandex (Synthetic)

• can stretch to eight times its original length
• burn test: melts quickly

Chromatography

There are two types of chromatography, which are paper chromatography and TLC (thin layer chromatography). Paper chromatography is just paper, and TLC is a glass slide with a thin silicone layer, but they both do the same thing, and you can set both up using the same process. There are plenty of youtube videos out there that can show how to set it up.

There is also ink chromatography and juice chromatography. Likewise, both are set up the same way, but with juice chromatograms, the sample must be applied to the paper or TLC slide by another instrument.

Most competitions ask for Rf calculations. Rf is retention factor or rate of flow.

Formula: [math]\displaystyle{ Rf=\frac{p}{s} }[/math], where p is the distance the pigment (the ink or juice) travels and s is the distance the solvent (usually water or alcohol) travels.

Mass Spectrometry

Mass spectrometry is an analytical method used to determine the mass to charge ratio of charged particles. [1](Sample mass spec graph of dodecane)

A few things to note about said graph: -The y-axis is a measure of the percent abundance -The x-axis is the m/z ratio (molar mass) -The lines are known as peaks

Reading graphs of mass spec (aka everyone's least favorite part of Forensics):

1) The largest peak will be the mass to charge ratio of the most prevalent molecule

To be continued...

Fingerprints

Fingerprints are formed by the arrangement of volmer (or volmar) pads. They are made mostly of sweat and water but can also contain various organic and nonorganic compounds.

Patterns

There are eight fingerprint patterns to know. They are:

• Plain Whorl
• Ulnar Loop
• Radial Loop
• Plain Arch
• Tented Arch
• Central Pocket Loop
• Double Loop
• Accidental Whorl

Whorls have two or more deltas. The presence of more than two deltas indicates an accidental whorl.

Loops have one delta. The difference between an ulnar loop and a radial loop is that ulnar loops "enter and exit" on the side facing the pinky while radial loops do so on the side facing the thumb.

Arches have no deltas. Tented arches are easily distinguishable by the triangular core.

Types of Prints

Fingerprints can be in different forms when found.

• Visible: As the name suggests, these ones can easily be seen because they were made with a substance like ink or blood. They can also easily be photographed without development.

• Impression: Made in soft material such as clay. Less easy to detect than visible fingerprints, but can still be photographed without development.

• Latent: Invisible fingerprints. These must be developed before photographed.

Methods of Development

Latent prints must be developed in order to be seen. The four methods of fingerprint development are:

• Dusting: Powder applied to prints sticks to fatty acids and lipids.
• Iodine Fuming: Self-explanatory by its name. It was one of the earliest methods of fingerprint development. The iodine reacts with body fats and oils in prints.
• Ninhydrin: a chemical method useful for lifting latent prints on paper. It reacts with amino acids in prints.
• Cyanoacrylate (Superglue) Fuming: Also self-explanatory by its name. It also reacts with moisture in the air as well as reacting with substances in the prints, forming sticky white material along ridges. Good for nonporous surfaces.

Features

DNA

Although many competitions that have include DNA as evidence require matching of DNA fingerprints, questions about basic DNA physiology and principles come up along with them. PCR (Polymerase Chain Reaction), a method of synthetic DNA replication, also comes up sometimes.

Ground Facts You Should Know

• DNA stands for deoxyribonucleic acid (yes, sometimes they ask this)
• The four nucleotides that compose DNA are adenine, cytosine, thymine, and guanine.
• With a DNA fingerprint, larger fragments of DNA are located on the right side while smaller ones are located on the left.
  • This is because of gel electrophoresis, which make the fingerprints. When the current runs through the gel during this process, because DNA is negatively charged, it will move towards the positive end of the box. Smaller fragments of DNA will obviously move farther through the gel filter than larger ones.

PCR

PCR, as already stated, stands for Polymerase Chain Reaction; it is a method of synthetic DNA replication developed in the late 20th century. PCR has been very crucial to molecular biology and forensics, then and now, so its development earned a Nobel Prize.

Glass

The Rule to Remember!

If the glass's refractive index is the same or close to that of a liquid, then the piece of glass will not be visible in that liquid (use exact same liquids that are used for plastics)

Other Facts about Cracks:

• Cracks end at existing cracks
• A small force forms circular cracks
• Radial cracks and chonchoidal cracks make right angles, but face different ways
• A force very close to the glass before impact will completely shatter the glass

Entomology

Stages of insects found on a dead body can tell how long the victim has been dead. The most common are the blowfly and the beetle. Blowflies appear first, within minutes of death. Beetles usually arrive after the blowflies. Certain amounts of time lapse between each life stage, which can tell this time. For example, if maggots were found on the dead body, that means the victim probably died less than twenty-four hours ago.

Life Cycle of Blowflies

Blood Spatters

Blood Spatters are generally classified by velocity at which they form.

Blood Spatters

	Low Velocity Formation.	Appears to be droplike and forms at speeds less then 5f/s
	Medium Velocity Formation	Appears in a linear type of drop pattern 5-25 f/s
	High Velocity Formation	Appears in essentially a random pattern around 100 f/s

Angle of Impact: The angle at which a spatter hits a surface. The formula for it is:

[math]\displaystyle{ \theta=\arcsin(W/L) }[/math]

Where theta is the angle, W is the width of the spatter, and L is the length.

Note that arcsin is also known as inverse sine.

Bullet Striations

Bullet striations are pretty much just like tracks. Pretty much the only thing you have to do is try to match the one of the suspects' bullet striation to that of the one found at the scene.

See Also

Crime Busters

Links

2005 Qualitative Analysis Hints

Science Olympiad Official Resources for Forensics

Good site for paper chromatography

Mass Spectrometry