Forensics

Forensics
Type	Chemistry
Category	Lab
Description	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.
Event Information
Approx. Time	50 minutes
Impound	No
Allowed Resources	Safety equipment Writing utensil Two stand-alone calculators One note sheet per participant
Rotates	No
Eye Protection	C
Latest Appearance	2024
Forum Threads
2024 2023 2022 2021 2020 2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009
Question Marathon Threads
2024 2023 2022 2021 2020 2019 2018 2017 2016 2015
Official Resources
Website	www.soinc.org/forensics-c
Division C Results
1st Ann Arbor Pioneer High School 2nd Solon High School 3rd Acton-Boxborough Regional High School

Forensics is a permanent Division C chemistry event involving the use of concepts in chemistry to solve a fictional crime scene. Participants will be given a scenario and possible suspects, as well as physical evidence from the categories outlined in the rules manual. They will be able to perform tests on the evidence and use the results to solve the crime. Each participant may bring one 8.5x11" page containing information on both sides in any form from any source, as well as a kit of lab equipment to perform tests during the event.

This event is closely associated with the Division B event Crime Busters.

Supplies and Safety

To participate in Forensics, every team of students should come prepared with the proper safety equipment. This includes:

• Category C eye protection
• An apron or lab coat
• Close-toed shoes
• Clothes that cover the skin down to the wrists and ankles (pants should be loose-fitting)

Students with shoulder-length or longer hair should also tie it back. Gloves are not required by the rules manual, but may be required by the event host. Always check the website for your specific tournament to see if they have any safety requirements not covered by the rules manual. Students not following the proper safety requirements or behaving unsafely during the event may be penalized or disqualified.

Practicing at School

To practice for the event at school, students should check with a coach to ensure that they have access to all of the potential pieces of evidence that may be tested. This includes:

• Powders: sodium acetate, sodium chloride, sodium hydrogen carbonate, sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, calcium sulfate, calcium carbonate, cornstarch, glucose, sucrose, magnesium sulfate, boric acid, and ammonium chloride
• Hairs: human, bat, cow, squirrel, and horse
• Fibers: cotton, wool, silk, linen, nylon, spandex, polyester
• Plastics: PETE, HDPE, non-expanded PS, LDPE, PP, PVC, PMMA, PC

Powders are often the easiest to find, since many of them are common household substances. When sourcing fibers and plastics, competitors should check any tags or labels on the items to ensure that they are the correct substance. Powders can be stored in old pill bottles, test tubes with lids, or even simple plastic bags. Be sure to label them properly so as to not confuse the powders. Coaches should also source iodine (KI solution), 2M hydrochloric acid, 2M sodium hydroxide, Benedict's solution, a Bunsen burner, and a wash bottle. For more information on the materials required to perform chromatography, see the chromatography section of this article.

At the Competition

Competitors are responsible for providing their own lab equipment to perform the event. The full list of allowed materials for all Division C chemistry events is available on soinc.org, but a list is also provided below. Any students that do not provide their own equipment will not be provided equipment, so it is best to bring as much as is allowed. However, students bringing non-permitted equipment may be penalized up to 10% by the event supervisor.

• 50, 100, 250, and 400 mL beakers
• Test tubes
• Test tube rack
• Test tube brush
• Test tube holder (for heating test tubes)
• Petri dishes
• Spot plate
• Microscope slides
• Cover slips
• Droppers/pipettes
• A spatula/spoon/scoopula
• Stirring rods
• Metal forceps/tweezers
• Thermometer
• pH or litmus paper
• Hand lens
• Flame loop
• Cobalt blue glass
• Conductivity tester
• Paper towels
• Pencil
• Ruler
• Magnets

Qualitative Analysis

Qualitative analysis is the first section of the rules, involving the identification of unknown powders. Competitors may be asked to identify 3-8 samples at the regional level, 6-10 samples at the state level, and 10-14 samples at the national level. All teams will have the same set of solids to identify, but some samples may occur more than once.

Fifteen different substances are included in the rules manual. These are sodium acetate, sodium chloride, sodium hydrogen carbonate, sodium carbonate, lithium chloride, potassium chloride, calcium nitrate, calcium sulfate, calcium carbonate, cornstarch, glucose, sucrose, magnesium sulfate, boric acid, and ammonium chloride. Many of these powders are accessible in local stores or available on Amazon.com.

Methods of Identification

Many competitors utilize a flow chart or table which they use to identify powders. Developing a strategy for how to test the samples can aid with time management and ensure that all the given powders can be identified accurately. Additionally, utilizing all available means of identification will give the best results and help draw a more accurate conclusion.

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

A word of caution: every compound has a unique solubility product constant (Ksp), which indicates the amount of compound that can dissolve in a given volume of water before it reaches a point where no more of that compound can dissolve in the solution. This is called saturation. Because of this, it may be possible for a powder to appear to not be dissolving in water if there is too much of it and not enough water. Be careful of this when observing solubility, and, when in doubt, go for using smaller quantities of the sample.

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 8, but there are several chemicals that have distinct pHs. For example, sodium carbonate has a pH of 10, and boric acid has a pH of 4.

There are many different kinds of pH paper, sometimes also called litmus paper, that can be used to perform this test. Any kind should do. The test involves dissolving some of the dry powder in water, dipping the end of the pH paper in the solution, and comparing the resulting color to the palette on the package to see which pH value corresponds to it.

Flame test

The flame test uses a Bunsen burner and a nichrome wire. If nichrome wire is not available, wooden splints (such as coffee stirrers) soaked in water work and dry samples of the powder on the tip of a spatula or scoopula work well too. 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: golden 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 visible
• 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 off the yellow color given by sodium in case the sample may have been contaminated. In some cases, this yellow color can appear a little golden or orangish, rather than a lemon-like tint of yellow. Some powders have been said to not give off a flame color, including, but not limited to, calcium sulfate and calcium carbonate, which will be evident. Cleaning nichrome wires should help, though that is not guaranteed. To do this, stick the wire into the flame until no color is observed (or until the wire glows orange, whichever happens first). Next, dip the wire into acid (hydrochloric acid should do the trick, as it should be readily available during the competition for obvious reasons). Finally, dip it into deionized water, and then it's ready for use again. This problem can perhaps also be solved by just bringing an abundance of utensils to decrease the chances of needing to clean any, but this method of cleaning nichrome wires should help in the case having more tools is not a viable option.

There are additional properties of some of the powders that can also be observed in a flame test. For example, heating a carbohydrate such as glucose or sucrose will cause it to melt and caramelize. Heating dry ammonium chloride for a few seconds will cause it to release white wisps of smoke. These are best observed with the method of putting dry powder on the tip of a spatula or a scoopula and holding it directly in the flame.

Tests with liquid reagents

Liquids used for identification are iodine, sodium hydroxide, and hydrochloric acid. These reagents will be provided by the event supervisor.

• 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 are 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 containing 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 reducing sugars such as 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. An important fact to note is that sucrose will not react with Benedict's solution but glucose will. Benedict's solution can also be used to test for ammonium chloride. Adding a couple of drops will turn the sample a dark blue.

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, and is the most useful for identifying ionic compounds.

Polymers

A polymer is a chain-like molecule made up of individual repeating subunits called monomers. These chains can be linear or branched, resulting in many possible polymers with different structures. Heteropolymers/copolymers are polymers made up of multiple different subunits, while homopolymers consist of one repeating subunit. Polymers can also be formed in a variety of different ways, though the two most relevant to this event are condensation and addition. When a polymer is formed by condensation it will produce a small molecule like water as a byproduct. However, polymerization by addition will not form a byproduct. Addition polymers can be more difficult to recycle as they form stronger bonds between each monomer unit. Comparatively, it is easier to break down a polymer made by condensation (which makes them more biodegradable).

There are three types of polymers in the forensics rules: plastics, fibers, and hairs. The main methods of identifying these polymers will be discussed in each section, but the three main techniques are burn tests, density tests, and examination under the microscope. Burn tests are permitted on fibers and hairs but not plastics, since burning plastic can be a hazard. However, a test writer may still provide a written description of how the plastic behaves when it burns.

Plastics

Plastics are synthetic materials typically made of petroleum derivatives. These polymers are inexpensive to produce and easy to mold or reshape, making them very desirable for producing objects quickly. The first fully synthetic plastic was Bakelite, invented in 1907 by Leo Baekeland. Since then, synthetic plastics have been produced in large quantities around the world.

Two plastics on the list (PC and PETE) polymerize by condensation while the rest polymerize by addition. In polymerization by condensation, the addition of two monomer units produces a small by-product like water or methane. In polymerization by addition, no by-product is lost.

There are two main types of plastics: thermoset and thermoplastic. Thermoset polymers undergo a process known as curing, where a plastic is irreversibly hardened from a softer resin form. This can be induced by heat, UV radiation, or mixing with a catalyst (like two-part resins). When a plastic is cured, the individual polymer chains form cross-links to create a hardened plastic. This makes it difficult to melt and reuse the plastic, which is why they are called thermoset plastics. Since these plastics cannot be melted, they also cannot be recycled commercially.

Conversely, thermoplastic polymers do not undergo a curing process. These plastics will become moldable/malleable when heated beyond a certain point, making them suitable for use in processes like injection molding or extrusion. This also makes them suitable for commercial recycling. Every plastic on the Forensics list occurs in a thermoplastic form, but some polymers can occur in either thermoset or thermoplastic forms.

Common liquids used to test plastic densities include water, vegetable oil, isopropyl alcohol, and NaCl solution (10%, 25%, and saturated). If a plastic sample sinks in a liquid, it is more dense than that liquid. Using this information, it is possible to develop a flow chart to identify plastics based on density solutions. However, it is important to rinse and dry a sample before testing it in another solution. If this is not done, the density of the solution may change due to dilution and make the test inaccurate.

It can be difficult to tell if a plastic indicates a suspect since many of their uses overlap. Start by re-reading the suspect's bio and noting down anything associated with them that is likely to be made of plastic, like food containers or pill bottles. Then, determine what that item is likely to be made of.

Plastic	Resin Code	Density (g/cm3)	Monomer Structure	Common Uses	Burn Test Results	Additional Info
Polyethylene Terephthalate (PETE)	1	~1.37		Soft drink/beverage bottles, carpet, fiberfill, rope, scouring pads, fabric, Mylar	Shrivels with heat, burns slowly with yellow flame and light smoke	Polymerizes by condensation
High-Density Polyethylene (HDPE)	2	~0.95		Food containers, bags, lumber, furniture, flower pots, signs, trash cans, toys	Burns slowly with a yellow flame, smells like candle wax	Polymerizes by addition, monomer units more linear than LDPE
Polyvinyl Chloride (PVC)	3	~1.38		Food packaging, shampoo containers, construction (PVC pipes), tiles, credit cards	Burns with a green flame, acrid smell	Polymerizes by addition
Low-Density Polyethylene (LDPE)	4	~0.92		Food containers (specifically bags), grocery bags, plastic wrap, etc.	Burns slowly with a blue flame with yellow tip, smells like candle wax	Polymerizes by addition, ethylene monomer units branch out more than HDPE
Polypropylene (PP)	5	~0.90		Food containers, medicine containers, automobile batteries, carpet, rope, plastic wrap, lab equipment	Burns slowly with a blue flame with yellow tip, has a sweet smell	Polymerizes by addition
Polystyrene (PS)	6	~1.05		Styrofoam, tableware, coffee cups, toys, lighting, signs, insulation	Burns quickly with a yellow flame, releases a dense black sooty smoke	Polymerizes by addition, reacts with acetone
Polycarbonate (PC)	7	~1.20		Shatterproof glass, eyeglass lenses	Orange flame with black sooty smoke, has a faint sweet odor	Polymerizes by condensation, clear
Polymethyl Methacrylate (PMMA)	7	~1.16		Plexiglas, glass substitute	Light blue flame with white tip, drips, floral/fruity smell	Polymerizes by addition, reacts with acetone

Just to clarify how LDPE differs from HDPE:

(Lines represent the connected ethylene monomer units)

Fibers

See also: Crime Busters#Fibers.

There are seven fibers that competitors are responsible for: cotton, wool, silk, linen, nylon, spandex, and polyester. The main way to identify fibers is to burn them over a candle (Bunsen burners are too hot) and examine how they behave when exposed to flame. However, some tests will also provide images of the fibers for identification. Based on how they're made, the listed fibers can be divided into three broad categories:

• Wool and silk are animal fibers. These fibers are produced by animals, with wool being sourced from sheep and silk being sourced from insects (mostly caterpillars). When burned, animal fibers tend to shrivel but not melt. These fibers will also dissolve in bleach, unlike other fibers.
• Cotton and linen are vegetable fibers. These fibers are produced by plants, with cotton being made from cotton plants and linen being derived from flax. Vegetable fibers tend not to melt or shrivel, but they ignite easily and usually appear charred after being burned.
• Nylon, spandex, and polyester are synthetic fibers. These are man-made fibers, usually derived from petroleum or constructed from synthetic polymers. Synthetic fibers will melt and shrivel, fusing together when burned. Synthetic fibers tend to be very smooth and uniform, while natural fibers are more varied.

Some additional information about each fiber is included in the table below. While there are descriptions of the burn test results provided, it is highly recommended to practice performing these tests and create your own descriptions for the behavior of each one. Fabric samples can often be obtained for free from fabric stores or purchased cheaply from online retailers such as Amazon. Experience identifying each fiber is important when it comes to doing well in the event.

Fiber Information

Name of Fiber	Type of Fiber	Information	Burn Test Results	Microscopic View
Wool	Animal	Most commonly used animal fiber. Made of keratin.	Shrivels, leaving behind a brown-black residue and brittle ash. Smells like burning hair, and self-extinguishes when withdrawn from the flame.	Cylinders with scales. Scales may not be visible at lower magnifications (image above is 100x)
Silk	Animal	Smoother than wool. Made of fibroin.	Shrivels and leaves a black residue, smells like burning hair or feathers. Leaves behind a crushable black bead.	Thin, long, and smooth cylinder
Cotton	Vegetable	Most widely used plant fiber. Made of cellulose.	Burns with a steady flame, smells like burning paper, able to blow flame from a thread like a match, leaves a charred whitish ash	Irregular twisted ribbons
Linen	Vegetable	Fibers are generally longer and smoother than cotton. Made of cellulose, derived from flax.	Burns at a constant rate, does not produce smoke, smells like burning grass, produces sparks	Smooth, bamboo-like structure
Polyester	Synthetic	Fibers can be any length	Melts, only ignites when in the flame, drips when it burns and bonds quickly to any surface it drips on, produces sweet odor and hard, colored (same as fiber) ash	Completely smooth cylinder
Nylon	Synthetic	Long fibers	Curls, melts, produces black residue, smells like burning plastic (some sources say it smells like celery?), ignites only when brought into flame	Fine, round, smooth, translucent
Spandex	Synthetic	Can stretch to eight times its original length. Typically appears in blends with nylon or polyester.	Melts quickly	Flattened, ridged fibers, clustered

Hair

A diagram of the hair shaft and follicle

Hair is typically divided into two main parts: the hair shaft (the fiber that emerges from the skin) and the hair follicle (which is embedded in the skin). The hair follicle is also known as the bulb or root when it is removed from the skin, and is responsible for the growth of hair. The hair follicle is the only part of hair considered to be alive, since it is the site of all the biochemical activity in the hair. There are also other structures associated with the follicle such as sebaceous (oil-producing) glands and muscles which make the hair stand on end. The shaft can be further divided into three layers called the cuticle, cortex, and medulla.

The medulla is the innermost layer of the hair, and may or may not be present in some hairs. This region of the hair lacks the same structure that is present in the outer layers, and it is one of the most fragile layers of hair. The role the medulla plays in the hair is unclear, but recognizing certain characteristics of the medulla is essential to identifying hairs. Human hairs can have three different medulla types: fragmented, interrupted, or continuous. Fragmented medullas are the most broken pattern, and appear more like a dashed line with many gaps and fragments. Interrupted medullas will have breaks, but will be much less broken than fragmented medullas. A majority of the medulla is connected, and the gaps are small. Continuous medullas have no breaks. Human hair may also lack a medulla entirely. Animal hairs typically have thicker medullas, and can have two additional patterns called ladder or lattice. Squirrel hair is a good example of a latticed medulla. Hairs can also be characterized by the medullary index. This is measured by taking the diameter of the medulla and dividing it by the diameter of the hair as a whole. Humans typically have a medullary index of less than 0.3, while animals typically have a medullary index of greater than 0.5.

The cortex is the second layer of hair, and it is the most structurally complex of the three. The cortex gives hair its color and shape, and is also responsible for water uptake and nourishing the hair. The pigment that gives hair its color is melanin, which is the same pigment responsible for coloring skin. Melanin is found in pigment granules, which in humans tend to be distributed towards the cortex. In animals, most of the pigment is found closer to the medulla. The cortex also contains ovoid bodies, which are oval shaped structures commonly found in cattle and dog hairs (though they may also be found in human hairs). Cortical fusi are irregular air-filled pockets found near the root of human hair, though they may be present elsewhere in the shaft.

The structure of the cortex under a microscope

The cuticle is the outermost layer of the hair, and is responsible for the scale-like pattern on the outside of a strand of hair. The cuticle of the hair is responsible for protecting the inner layers and repelling water. The cuticle can have a variety of patterns that are useful for identifying hairs. Coronal scales are present on the hair of bats and rats, and they look like stacked cups or "strawberries on a stick". Spinous scales are present on cat hairs, and have points that are rounded at the ends. Imbricate scales are found on human hairs, where the scales are more rectangular and flat in shape. Many mammals also have hairs with imbricate cuticles.

Hair grows in three stages: the anagen, catagen, and telogen phase. Occasionally a fourth phase is included known as the exogen phase, but this is largely just an extension of the telogen phase. The anagen phase is the first phase, and is also known as the growth phase. In this phase the hair grows around 1 cm per month for around three to five years. A majority of hairs (around 85-90%) on the head are in the anagen phase. The next phase is the catagen phase, also known as the transitional phase. This phase lasts around two weeks, during which the follicle shrinks and the hair is cut off from its blood supply. This forms a club hair, and causes the hair to enter the telogen phase. In this phase (also known as the resting phase), the hair is dormant and anchored in by epidermal cells lining the follicle. The follicle will eventually begin to grow again, causing the anchor point of the shaft to soften and the hair to be shed. The exogen phase is the process of shedding the hair, while the telogen phase is the hair laying dormant.

There are five types of hair to know for competition: human, squirrel, cow, horse, and bat hair. While burn tests may be performed, the hairs behave relatively similarly when burned. As a result, the best way to distinguish hairs is to examine them under a microscope.

Microscopic Images of Hairs

Type of Hair	Human	Squirrel	Cow	Horse	Bat
Image(s)
Characteristics	Scaly, imbricate cuticle Medulla is typically fragmented or interrupted, if present at all	Thick, latticed medulla	Very coarse, thick Ovoid bodies typically present in the cortex Thinner medulla than horse hair typically, may be fragmented/interrupted	Imbricate cuticle Very coarse, thick	Very fine Coronal scales on cuticle, similar to a stack of paper cups or "strawberries on a stick"

Chromatography

See also: Crime Busters#Chromatography

Chromatography refers to any technique used in the lab to separate a mixture of components. The substance being analyzed (the analyte) is dissolved in a solvent called the mobile phase. The stationary phase is a solid material which the mobile phase travels through. The stationary phase is used to separate the mixture but does not move with the components, while the mobile phase is used to separate the mixture and moves with the components. Different parts of the mixture will have more or less affinity for the stationary phase. If a part of the mixture interacts strongly with the stationary phase, it will separate out of the mixture more quickly. If a part of the mixture interacts weakly with the stationary phase, it will travel further from the point of origin. As a result, the mixture is separated based on a particular property.

In normal-phase chromatography, the stationary phase will be polar while the mobile phase will be non-polar. In reverse-phase chromatography, the stationary phase is non-polar while the mobile phase is polar. Paper chromatography is often normal-phase chromatography. The stationary phase is the cellulose in the paper, which is very polar. The mobile phase is usually a non-polar solvent like rubbing alcohol. Non-polar substances will interact strongly with the mobile phase and travel far up the paper, while polar substances will react with the mobile phase and stay close to the point of origin.

Most competitions will ask for R_f (retention/retardation factor) calculations. In some cases this can also be referred to as rate of flow. R_f will always be a value between 0 and 1. A value close to 1 means that the substance has a high affinity for the mobile phase, and a R_f value close to 0 means that the substance has a high affinity for the stationary phase. To calculate R_f, measure the distance that the analyte traveled from the point of origin as well as how far the solvent traveled. Divide the distance the analyte traveled by the distance the solvent traveled to find the R_f. For example, if the analyte traveled 4.3 cm while the solvent traveled 6.1 cm, the R_f for that substance would be 0.70. Always measure distance to the center of the band.

TLC and paper chromatography are both types of planar chromatography, where the mobile phase travels up a flat (planar) stationary phase. Another type of chromatography is column chromatography, where a bed of material is placed in a tube that the stationary phase drips through. This technique is commonly used to separate mixtures of proteins in a lab setting based on properties like size, charge, or polarity.

Other types of chromatography include gas chromatography (where gases like helium or nitrogen are used to move the gaseous mixture through absorbent material and is used to analyze volatile gases) and liquid chromatography (where liquids dissolve ions and molecules and which is used to analyze metal ions or organic compounds in solutions). Gas chromatography is often used in forensic analysis in combination with mass spectroscopy, where it is known as GC-MS. This technique is used to identify unknown substances in labs like debris or drug remnants.

The only chromatography techniques that competitors will be asked to perform are paper chromatography and thin layer chromatography (TLC). Paper chromatography utilizes a filter paper as a stationary phase and a solvent like water or rubbing alcohol as the mobile phase. TLC utilizes a thin plate made of a nonreactive substance like glass covered in an adsorbent material like silica (SiO₂) or alumina (Al₂O₃). The silica serves as the stationary phase, adhering to the material being separated by the solvent. More information about performing these techniques is included in the section below.

Performing Chromatography

A diagram depicting a paper chromatography setup. This setup uses propanone (acetone) as the solvent and a pencil to suspend the chromatography paper.

Performing paper chromatography is relatively simple and requires a short list of materials. To practice performing paper chromatography at home or school, students should have:

• Strips of filter paper (some stores like Flinn Scientific sell paper specifically for chromatography, but coffee filters or paper towels work just as well)
• A beaker (200 mL should be fine)
• A glass stir rod or dowel to suspend the filter paper above the water
• A binder clip
• A pencil
• Pens or markers to perform chromatography on (water-soluble markers or pens like Expo markers get the best results)
• Around 50 mL of solvent (typically water, but can be done with other solvents such as alcohol)

To prepare the filter paper for chromatography, draw a line in pencil around 1 cm from the bottom of the paper strip. Drawing the line in pencil is important, as pencil will not be moved by the solvent. If the line is drawn in pen, it will be difficult to read the results. Place a dot of ink on the pencil line. Next, fill the beaker with the desired solvent so that the solvent stops just before the pencil line on the paper. It is important to not submerge the dot in the solvent, as the chromatography will not work if this happens. Attach the top of the strip of filter paper to a dowel or rod using a binder clip and place the bottom of the filter paper into the beaker. The dowel or rod will suspend the paper in the solvent so it travels up the filter paper and separates the pigments in the ink. Once the pigments have stopped moving (or reached the top of the paper), remove the paper from the beaker and mark where the solvent stopped.

Performing thin layer chromatography is similar to paper chromatography. A TLC plate has two sides: a smooth, shiny side and a matte side with the silica deposited on it. Draw a line in pencil on the matte side of the plate around 1 cm from the bottom. This may disturb the silica layer, but that won't affect the results of the chromatography. Be careful when handling the plate so as to not snap it. Then, place a dot of ink on the pencil line. If the substance being analyzed is a liquid, it may be necessary to use a thin tube called a capillary or a toothpick to place the analyte on the plate. Touch the capillary/dropper into the substance, then touch it to the plate briefly. Then, treat the plate like it were a piece of paper in paper chromatography. Pour solvent into the beaker and place the TLC plate in it, leaning the plate up against the edge of the beaker. Since the plate is rigid, a dowel or rod isn't necessary to suspend it.

Chromatography can be time consuming. A common strategy is to prioritize setting it up at the beginning of the time to ensure that it is finished developing before the end of the testing period. This ensures that enough time is left for the produced chromatograms to dry and for competitors to answer any additional chromatography questions.

Mass Spectrometry

Mass spectrometry is an analytical chemistry technique which measures the mass to charge ratio (m/z) of a compound. A sample of a compound is placed in a mass spectrometer, where it is then ionized and fragmented using a process called electron impact (EI). The mass to charge ratio (m/z) of these fragments is then graphed, producing a mass spectrum. This information can then be used to determine the molecular weight and molecular formula of the compound, alluding to its identity.

Note that in the real world, mass spectrometry is often used in conjunction with other analytical chemistry techniques such as IR spectroscopy and NMR to identify compounds. As a result, it may not always be possible to perfectly distinguish between multiple compounds with the same chemical formula. However, using the techniques outlined below it's possible to get pretty close.

How a Mass Spectrometer Works

A diagram of a mass spectrometer.

The device used to perform mass spectrometry is called a mass spectrometer. The three main parts of a mass spectrometer are the ionizer, the mass analyzer, and the detector.

First, a sample of the compound to be analyzed is loaded into the mass spectrometer. The sample is then vaporized and then converted into ions through a process called electron ionization, described below. Once the compound has been converted into ions, the ions are accelerated through a negative magnetic field. This causes the ions to deflect. Uncharged fragments are not deflected and will not be picked up by the mass analyzer. Smaller ions will deflect more than larger ones, and ions with multiple charges are deflected more than ions with a charge of +1. Since the amount of deflection is inversely proportional to the mass of the ion, the mass analyzer is able to sort the ions by their mass to charge ratio (m/z). Since the ions produced are mostly cations with a charge of +1, the mass to charge ratio is a measure of the molecular mass of the fragment. The spectrometer then outputs a graph known as a mass spectrum, which plots the m/z against the relative abundance of each fragment.

Electron Ionization

Electron ionization (EI, also known as electron impact ionization or electron bombardment ionization) is the most common method of ionizing compounds for mass spectrometry. This involves hitting the compound to be analyzed with high energy electrons. When the high energy electrons strike the compound, it forces an electron to be ejected. This forms an ion that is both a radical (having an unpaired electron) and a cation (having a positive charge). As a result, the ions formed in mass spectrometry are known as radical cations. The radical cation is symbolized by [math]\displaystyle{ (M)^{+\bullet} }[/math] and is known as the parent ion or the molecular ion.

However, this radical cation is very unstable and can undergo a process known as fragmentation. Since the parent ion undergoes fragmentation, the ionization process will generate many different cations. This is responsible for the variety of fragments seen on a mass spectrum.

Reading a Mass Spectrum

The mass spectrum of methane. Click to view in greater detail.

A mass spectrum is the output of a mass spectrometer. It is a graph with two axes: the x-axis represents the mass to charge ratio or m/z, and the y-axis represents the relative abundance of each detected ion. Each line on the graph is known as a peak, where the tallest peak is the base peak. This is often also the molecular ion peak, but not always. The molecular ion peak is simply the peak represented by the molecular ion, which is the ion formed by removing one electron from the original compound. Since the mass of the electron is so small, the mass of the molecular ion is nearly identical to the original compound. This peak is also known as the [math]\displaystyle{ (M)^{+\bullet} }[/math] peak, and provides the weight of the original compound.

Inspect the image to the right. This is the mass spectrum of methane, [math]\displaystyle{ CH_4 }[/math]. The tallest peak is located at 16. This means that the base peak is located at 16. It has a relative abundance of 100%, meaning that the height of every other peak is described relative to the base peak. The base peak in this case is also the molecular ion peak, though this is often not the case for large molecules.

This mass spectrum also has peaks located at 15, 14, 13, and 12. Since methane is a small molecule, there are only a few ways for it to fragment and produce ions. Losing one hydrogen atom produces a fragment with a m/z = 15, which can then lose another hydrogen atom to produce a peak at m/z = 14. This continues until all 4 hydrogen atoms have been lost, leaving peaks from 12 to 15.

Isotope Peaks

It might seem like every peak is accounted for. However, there is still a small peak at m/z = 17. The molecular ion peak, or [math]\displaystyle{ (M)^{+\bullet} }[/math] peak is at 16, since 16 is the mass of methane. How can a peak be present with a m/z greater than that of the molecular ion?

The peak at 17 is due to the presence of carbon-13, an isotope of carbon. Isotopes are different forms of elements that have the same number of protons but different numbers of neutrons. 98.93% of carbon atoms are carbon-12, the isotope of carbon with 6 protons and 6 neutrons. Carbon-13 (also written as [math]\displaystyle{ ^{13}C }[/math]) has 7 neutrons, occurring with an abundance of 1.1%. This means that while 98.93% of the ions contain carbon-12, 1.1% of them will contain carbon-13. Methane molecules which incorporate carbon-13 will have a mass of 17, which is why there is a small peak at m/z = 17. This peak is known as the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peak, since the m/z is one greater than the [math]\displaystyle{ (M)^{+\bullet} }[/math] peak.

The mass spectrum of chlorobenzene. Click to view in greater detail.

Since the abundance of carbon-13 is 1.1%, the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] is 1.1% of the height of the [math]\displaystyle{ (M)^{+\bullet} }[/math] peak. Larger compounds containing more carbon atoms will have taller [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peaks. Take decane ([math]\displaystyle{ C_{10}H_{22} }[/math]) for example. Decane has 10 carbon atoms compared to methane's 1. This means that decane is 10 times more likely to contain an atom of carbon-13. As a result, the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peak is 11% as tall as the molecular ion peak, since 1.1 * 10 is 11%. This means that by comparing the relative heights of the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] and [math]\displaystyle{ (M)^{+\bullet} }[/math] peaks, it is possible to determine the number of carbons in a compound. This will be discussed in the worked example below.

Many elements such as carbon only have one dominant isotope. However, an element like chlorine has two major isotopes. Chlorine-35 represents 75.8% of all chlorine atoms, while chlorine-37 represents 24.2% of all chlorine atoms. Since chlorine-37 has 2 additional neutrons, molecules containing chlorine will have a strong [math]\displaystyle{ (M+2)^{+\bullet} }[/math] peak. This [math]\displaystyle{ (M+2)^{+\bullet} }[/math] peak will be approximately 1/3 the height of the [math]\displaystyle{ (M)^{+\bullet} }[/math] peak, as chlorine-37 is approximately 1/3 as abundant as chlorine-35. The mass spectrum of chlorobenzene ([math]\displaystyle{ C_{6}H_{5}Cl }[/math]) is shown to the left. The molecular ion or [math]\displaystyle{ (M)^{+\bullet} }[/math] peak is at m/z = 112, which places the [math]\displaystyle{ (M+2)^{+\bullet} }[/math] at m/z = 114. The peak at m/z = 114 is approximately 1/3 the height of the molecular ion peak, which lines up with the abundance of the two isotopes.

Bromine is another element with a particular pattern, having two isotopes that appear in almost equal amounts. This means that bromine-containing compounds will have [math]\displaystyle{ (M)^{+\bullet} }[/math] and [math]\displaystyle{ (M+2)^{+\bullet} }[/math] peaks of almost equal heights.

Degrees of Unsaturation

The degrees of unsaturation (also known as the hydrogen deficiency index) of an atom indicates how many double bonds or aromatic rings are present in its structure. Without this information, it is nearly impossible to predict the structure of a compound from its formula. Many chemicals will share a common molecular formula, but the degrees of unsaturation can help distinguish between them. The formula for degrees of unsaturation is [math]\displaystyle{ DoU=\frac{(2C+2+N-H-X)}{2} }[/math] where C is the number of carbons, N is the number of nitrogens, H is the number of hydrogens, and X is the number of halogens. For example, for the compound [math]\displaystyle{ C_{11}H_{8}ClBrO }[/math] the degrees of unsaturation is 7. This means that there are 7 double bonds or ring structures in the compound. A molecule with a DoU of 0 cannot have any double bonds or rings, and a molecule with a DoU of 1 can have a double bond or a ring, but not both.

Example

This section will walk through determining the likely identity of a compound from start to finish, using only the mass spectrum shown to the right.

1. The first step to identifying the compound depicted is locating the molecular ion peak. This is most likely the tallest fragment with the highest m/z. For this compound, the molecular ion peak is located at m/z = 86. This means the molecular weight of the compound is 86. The molecular weight can say a lot about a compound, such as whether or not it contains nitrogen. Compounds with an even molecular weight likely do not contain nitrogen or have an even number of nitrogen atoms. Compounds with an odd molecular weight likely contain an odd number of nitrogen atoms. Since the molecular weight of this compound is even, it is too soon to say whether or not it contains nitrogen.
2. Calculate the number of carbons in the compound. This is done by comparing the [math]\displaystyle{ (M)^{+\bullet} }[/math] and [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peaks. It's difficult to tell with this scale, but the relative abundance of the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peak is around 1.2%. However, the molecular ion peak is not the base peak. The base peak appears at m/z = 43. While the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peak is around 1.2% as tall as the base peak, you want to compare the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peak to the [math]\displaystyle{ (M)^{+\bullet} }[/math] peak. To do this, divide by the relative abundance of the molecular ion peak before multiplying by 100%. Since the relative abundance of the [math]\displaystyle{ (M)^{+\bullet} }[/math] peak is around 21, the [math]\displaystyle{ (M+1)^{+\bullet} }[/math] peak is around 5.7% as tall as the molecular ion peak. Dividing this number by 1.1 for the abundance of carbon-13 gives a value of 5.2. Rounding to the nearest whole number indicates that there are 5 carbon atoms in this molecule.
3. Examine the [math]\displaystyle{ (M+2)^{+\bullet} }[/math] peak. This compound doesn't have a [math]\displaystyle{ (M+2)^{+\bullet} }[/math] peak, so it likely does not contain a halogen like chlorine or bromine.
4. Analyze the mass of the molecule. By inspecting the molecular ion peak, we know that this unknown molecule weighs 86 amu. In step 2, we determined that there are likely 5 carbon atoms present in this molecule. These 5 carbons weigh 12 amu each, meaning that they weigh 60 amu in total. Subtracting 60 from 86 means that the rest of the atoms in the molecule weigh 26 amu total. There's no way to draw a structure which has 5 carbon atoms and 26 hydrogen atoms, so that means there must be another element present.
5. Identify any heteroatoms. Heteroatoms are elements other than carbon or hydrogen. Remember, we ruled out any [math]\displaystyle{ (M+2)^{+\bullet} }[/math] atoms in step 3. The most common heteroatoms are nitrogen and oxygen. However, in step 1 we established that the compound likely does not contain nitrogen as it has an even molecular weight. This means that the compound likely has one oxygen atom.
6. Put it all together. The molecular weight of the original compound as defined by the molecular ion peak is 86 amu. In step 2 we calculated that there are likely 5 carbons in the compound weighing 60 amu total. Determining that there is one oxygen atom in the compound which weighs 16 amu means that there are 10 hydrogen atoms in the compound. As a result, this compound's molecular formula is most likely [math]\displaystyle{ C_{5}H_{10}O }[/math].

Remember, it is often not possible to determine the exact molecular formula of a compound solely given its mass spectrum. It depends on the amount of information given and the possible fragments the compound can produce. Many potential fragments can have the same or very similar molecular weights, which can make discerning the actual compound more difficult.

Fingerprints

See also: Crime Busters#Fingerprints.

Fingerprints are the arrangement of friction ridges/epidermal ridges on the tips of fingers. They are formed during fetal development when the middle (basal) layer of skin cells starts to grow faster than the layers above it, forming ridges. There are three points on the finger where these ridges can originate: the center of the fingertip, the end of the fingertip, and the crease between the fingertip and the final joint of the finger. Depending on when and how each location forms ridges, this will determine the pattern an individual's fingerprint has. An individual's fingerprint is also influenced by external factors like genetics and density of amniotic fluid in the womb, making every set of fingerprints unique.

Fingerprints are stable over an individual's lifetime and can even regrow if damaged. Individuals have succeeded in removing fingerprints using harsh methods like surgical removal or burning them with acid, but small injuries typically result in reformation of the print. Since fingerprints are unique and relatively permanent, they are one of the most commonly utilized biometric identifiers.

Fingerprint examiners will use a system known as ACE-V to identify fingerprints. This stands for Analysis, Comparison, Evaluation, and Verification. First, an examiner will analyze the fingerprint to determine if it is suitable for use in a comparison. After it is cleared for use, a known print will be compared with the suspect print. Known prints may be collected from suspects, or pulled directly from databases like IAFIS. IAFIS (Integrated Automated Fingerprint Identification System) is a database used by the FBI starting in 1999 to store and organize fingerprints collected in the United States. Since 2011, the FBI has made use of NGI (Next Generation Identification) instead of IAFIS. Once the two prints have been compared, the examiner will evaluate whether or not they are from the same source. Verification occurs when another examiner independently analyzes the prints and either supports or refutes the claims of the original examiner.

Skin

The layers of the epidermis.

See also: Anatomy/Integumentary System.

Skin has three major layers: the epidermis, the dermis, and the hypodermis. The epidermis is the outermost layer of skin, while the hypodermis is the deepest layer of skin. There are two types of skin, thick and thin skin. Thick skin is found on the fingertips and palms of the hands and soles of the feet. This is the skin that fingerprints are made of.

The most important layer of the skin in the context of fingerprints is the epidermis, which is the outer layer of skin. Cells begin their life in the basal layer and are constantly pushed upwards, moving through the layers of skin. This ensures that dead skin cells can be shed and replaced. The epidermis can be further divided into five layers in thick skin:

• Stratum corneum (cornified layer) is the outermost layer of the epidermis. It is formed from dead cells almost entirely filled with keratin. These cells are continuously shed and replaced.
• Stratum lucideum (clear layer) is an additional layer only present in thick skin.
• Stratum granulosum (granular layer) is where keratin filaments that were formed in the stratum spinosum are bound together. Cells begin to die once they reach this layer of the skin, as they no longer receive nutrients from the capillaries in deeper layers.
• Stratum spinosum (spiny layer) is a layer featuring cells bound together in structures called desmosomes. Keratin production begins when cells are in this layer.
• Stratum basale (basal layer) is the innermost layer of the epidermis. This is the layer responsible for fingerprint formation in the womb. When the basal cells present in this layer form ridges, small projections called epidermal ridges form. This also helps the epidermis obtain nutrients from the dermis.

Patterns and Minutiae

There are eight fingerprint patterns to know. They are:

• Plain arch
• Tented arch
• Radial loop
• Ulnar loop
• Plain whorl
• Central pocket whorl
• Accidental whorl
• Double loop whorl

Arches have no deltas. The ridges rise in the center of the fingertip, forming an arch. Tented arches are easily distinguishable by the triangular core (though this is different from a delta). They are the rarest fingerprint, with only around 5% of fingerprints being arches.

Loops have only 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 (the side of the wrist containing the ulna) while radial loops do so on the side facing the thumb (the side of the wrist containing the radius). This is the most common fingerprint pattern, with around 65% of fingerprints being loops.

Whorls have two or more deltas. The presence of more than two deltas indicates an accidental whorl. To distinguish between plain whorls and central pocket whorls, draw a line between the two deltas on the fingerprint. If the line intersects with the central pattern (the swirling part of the whorl), it is a plain whorl. If it does not, it is a central pocket whorl. Double loop whorls are easy to identify, since they have two loop patterns in the core area of the whorl. Whorls make up around 30% of fingerprints.

Minutiae are small features of fingerprint ridges, separate from the main fingerprint pattern. Examples can be seen to the right.

• Ridge Ending: A ridge that ends abruptly
• Bifurcation: A single ridge that divides in two
• Dot: A ridge with approximately equal length and width
• Island or short/independent ridge: A single small ridge that is not connected to other ridges
• Lake/ridge enclosure: A ridge that bifurcates and then reforms to continue as one ridge
• Spur: A bifurcation where a short ridge branches off of a larger ridge
• Bridge/crossover: A short ridge that runs between two parallel ridges
• Delta: A Y-shaped formation where two ridges meet
• Core: A circle in the ridge pattern (seen in whorls)

Types and Development

The word "fingerprint" mostly refers to the impression left behind when a finger interacts with a surface. Fingerprints are made mostly of sweat and water, but can also contain various organic and inorganic compounds like amino acids or ions. These trace compounds are essential when it comes to fingerprint development, or the process of making invisible fingerprints visible. Some fingerprints can be seen with the naked eye, but others can't. There are three types of fingerprints:

• Visible/Patent: 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.

• Plastic: 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.

There are various methods that can be used for latent print development. Many of them involve chemicals that will react with trace compounds left behind in prints like amino acids or lipids.

Dusting

Powder applied to prints sticks to fatty acids and lipids. Generally, this method involves using a special brush, usually made of camel hair, to lightly spread the powder over the area where prints may be found, usually smooth or nonporous surfaces.

There are numerous different fingerprinting powders used in dusting, and their usages vary depending on the surface and the scene environment. For example, it would make more sense to use a dark-colored powder on a light-colored surface or a fluorescent powder on a dark-colored surface. The exact compositions of such powders vary, as most formulas are kept proprietary by their manufacturers.

Iodine Fuming

One of the earliest methods of fingerprint development, this method uses iodine to visualize latent fingerprints. It is fast and inexpensive, reacting with body fats and oils in prints. Iodine is a solid but it easily sublimes, forming a dark purple vapor. By placing the fingerprint in a chamber with some iodine, the iodine vapor will adhere to the oils in the fingerprint. This produces a temporary fingerprint that will fade in a few days. To "fix" the fingerprint and keep it permanently, the fingerprint is then treated with a starch solution which reacts with the iodine and turns black. This method of development works well on surfaces like paper or cardboard.

Ninhydrin

A chemical method that is useful for lifting latent prints on paper. The object with the print is dipped in or sprayed with ninhydrin, then left to develop for 24 hours. It reacts with amino acids left behind in prints and results in purple fingerprints.

Cyanoacrylate (Superglue) Fuming

This form of development utilizes cyanoacrylate (CA), also known as superglue. A special chamber is used, and the CA is heated in order to form a vapor. This vapor will react with moisture and organic molecules in the fingerprint, forming a white fingerprint. This works best on nonporous surfaces like glass, plastic, and metal.

Other Methods

The methods above are specifically mentioned in the rules manual, but they are not the only methods utilized to detect fingerprints. Some additional methods are outlined below.

• Silver Nitrate: The object with the fingerprint is dipped in or sprayed with silver nitrate, which reacts with chlorides in the fingerprint and turns grey when exposed to light. This technique is commonly used for surfaces like wood or styrofoam.
• Small Particle Reagent (SPR): Not as common as the other methods used, but still important. SPR is used for wet surfaces and reacts with the lipids present in fingerprints.
• Wetwop: a special pre-mixed liquid formula that is designed to lift latent prints on the sticky sides of adhesive surfaces (i.e. most kinds of tape)
• Alternate Light Sources: Lasers and LEDs in combination with certain filters or dyes are used to reveal the location and pattern of fingerprints.
• Columnar Thin Film (CTF): Deposits a thin-film coating on the fingerprint in a specific chamber, allowing for preservation of the ridges and topography of the fingerprint.

DNA

See also: Heredity#DNA

Although many competitions simply require competitors to match DNA fingerprints, basic questions about the structure of DNA may appear on tests. DNA stands for deoxyribonucleic acid, and is composed of four nitrogenous bases: adenine, cytosine, thymine, and guanine. The base unit of DNA is known as a nucleotide, and is composed of a deoxyribose sugar, a phosphate group, and one of these four bases. These nucleotides link up, forming long strands of DNA. DNA is a double helix, made up of two strands that twist together. Because each DNA molecule is made up of two strands, the nitrogenous bases must pair together--adenine pairs with thymine, and guanine pairs with cytosine.

Gel electrophoresis apparatus

DNA fingerprints are created through a process known as gel electrophoresis. DNA molecules are placed into a box containing a buffer solution and a gel (typically agarose), as well as positive and negative electrodes. DNA is placed into wells in the gel, and the current is turned on. Because the DNA is negatively charged, it will migrate through the gel towards the positive electrode. Shorter DNA fragments travel further away from the wells through a process known as sieving. The agarose gel is a matrix, and it is much easier for the short fragments to move through the pores in the gel. Long DNA fragments will get caught and tangled, and stop moving as a result. This separates the fragments, producing the compete fingerprint. To determine if an individual's DNA matches the DNA at the crime scene, simply match the bands on the fingerprints. If the bands don't match, the DNA isn't the same and the suspect was not the one whose DNA was found at the crime scene.

A diagram of the process of PCR

However, the DNA used in gel electrophoresis has to come from somewhere. Polymerase Chain Reaction (PCR) is a method of synthetic DNA replication used to amplify fragments of DNA for use in fingerprinting. It has three steps: denaturing, annealing, and synthesis/elongation. In denaturing, the DNA is heated to approximately 95 C in order to break apart the two strands so that new DNA can be created. In the annealing stage, the DNA is cooled to anywhere between 50 and 56 C so that a primer can be attached to the DNA strands. This primer is essential for the replication of DNA, which occurs in the final stage. During synthesis/elongation, new DNA is created using the primer as a starting point. An enzyme known as Taq polymerase creates a new DNA strand, using the starting strand as a template. Knowing that adenine pairs with thymine and guanine pairs with cytosine, it can put the nucleotides in the correct order and create a complete strand of DNA. PCR can be repeated for dozens of cycles, creating plenty of new DNA strands which can be used in forensic analysis.

Glass

Glass is an amorphous solid made primarily of silicon dioxide (SiO₂), also known as silica. Forensic analysis of glass typically involves testing glass fragments to determine if they have the same origin or not. Since stress patterns and breakages are unique to a common origin, they can be viewed and analyzed to tie a suspect to the crime. Glass evidence can also help relay the order of events of a crime as fractures form in particular ways depending on the direction of force, order of impact, or type of glass impacted.

Glass can be made with a variety of different additives and impurities which make it better suited for different tasks. Some of these include:

• Silicate glass (also known as fused silica glass or fused quartz glass) is made of 100% pure silicon dioxide. This makes it very difficult to work with, and as a result it is relatively uncommon.
• Soda-lime glass is the most common type of glass, made using primarily sodium carbonate (Na₂CO₃) as an additive. However, if only sodium carbonate was added the resulting compound would be water-soluble and not particularly durable. As a result multiple other compounds such as lime (CaO), magnesium oxide (MgO), and aluminum oxide (Al₂O₃) are added. Typically, soda-lime glass is 60-75% silica, 12-18% sodium carbonate, and 5-12% lime. Another 5% will typically come from other oxides added for durability.
• Borosilicate glass is typically sold for cooking and baking under brand names like Pyrex. It incorporates 5-13% boron trioxide (B₂O₃) which gives it resistance to temperature change. Though it is more difficult to manufacture than soda-lime glass, its durability makes it common in the kitchen and in laboratories where it is used for beakers and flasks.
• Lead glass (also known as crystal or flint glass) is glass which incorporates a high percentage of lead oxide (around 18-40%). This glass is softer and denser than other types of glass, but it has a high refractive index which makes it more reflective and brilliant. This desirable appearance led to its use in decorative serving glasses and bowls. However, lead glass has largely been replaced with modern alternatives in these purposes. Modern crystal glass is used to make wine glasses and other stemware and typically consists of barium oxide or zinc oxide instead of lead. However, since lead glass is softer and easier to work with it is commonly used in artisan glass projects.

Glass type	Density (g/cm3)
Fused silica	2.18
Borosilicate glass	2.2-2.5
Soda-lime glass	2.4-2.8
Lead crystal	3.1

Since each type of glass incorporates different additives and has different compositions, that makes them relatively unique. There are entire databases dedicated to the properties of different compositions of glass, so chemical analysis is typically used to get a more conclusive result. However, tests like density and index of refraction can still give an idea of what type of glass was found at a crime scene.

Each type of glass has a different density due to differences in composition. See the table to the right for common densities of a few types of glass. Since the densities are so similar in some cases, measurements have to be relatively precise to distinguish types of glass. As a result, density isn't commonly the first test performed in analysis. One of the main distinguishing tests is the refractive index of a piece of glass, which will determine if two pieces of glass originate from the same source.

A Brief Lesson in Optics

Optics is the field of science dedicated to studying the behavior and properties of light. Light can interact with surfaces in two main ways: reflection or refraction. The main concern for this event is refraction, the way that light bends when it travels through different mediums.

A common example of refraction is what happens when a straw or other object is submerged in a glass of water. The submerged portion of the straw will appear displaced or broken, while the portion that isn't submerged remains unchanged. While the speed of light in a vacuum is constant, light can change speed when traveling through different materials. Light travels faster in air than it does in glass or water, so the light is bent or refracted.

The angle at which light is refracted depends on how quickly it travels through the different materials. This can be characterized by a material's index of refraction. Index of refraction is typically defined as the ratio of the speed of light in a vacuum to the speed of light in the medium (written as n = c/v). The refractive index of a vacuum will always be 1, as the speed that light travels does not change between two mediums. Air has a very low refractive index of 1.0003, hardly bending light at all. However, water has a much higher refractive index of 1.33.

However, the speed of light in a medium isn't always known. To calculate the refractive index of a piece of glass, an equation named Snell's law is used. Snell's law is [math]\displaystyle{ n_1 \sin\theta_1 = n_2 \sin\theta_2 }[/math] where [math]\displaystyle{ \theta_1 }[/math] is the angle of incidence (the angle the light is traveling at in the first medium) and [math]\displaystyle{ \theta_2 }[/math] is the angle of refraction (the angle the light is traveling at in the second medium). In turn, [math]\displaystyle{ n_1 }[/math] corresponds to the index of refraction of the first medium and [math]\displaystyle{ n_2 }[/math] is the index of refraction of the second medium.

Material	Index of refraction
Vacuum	1.00
Air	1.0003
Water	1.33
Vegetable oil	1.47
Borosilicate glass	1.47
Soda-lime glass	1.51
Lead crystal	1.57-1.67

For example, light enters a piece of glass at an angle of 47° and exits at an angle of 28.77°. Recalling that the refractive index of air is 1.0003, using Snell's law the equation is [math]\displaystyle{ 1.0003 \sin(47^{\circ}) = n_2 \sin(28.77^{\circ}) }[/math]. Putting it into a calculator reveals that the refractive index of the glass is 1.52. If two pieces of glass have the same index of refraction, they likely originate from similar sources.

Index of refraction can also be determined qualitatively. If the glass's refractive index is the same or close to that of a liquid, then the piece of glass will seem to disappear in that liquid. This is commonly done as a demonstration with beakers and cooking oil, as borosilicate glass and vegetable oil both have indices of refraction around 1.47. If two unknown pieces of glass seem to disappear in the same liquid, they likely have similar indices of refraction and are likely the same type of glass. The refractive indices of a few common materials are present in the table to the left. These values can be used to estimate the type of glass present based on its index of refraction.

Fractures

Another way pieces of glass evidence can be evaluated is by examining any fractures that are present. Glass forms two main types of fracture lines: radial lines and concentric lines. Radial lines are the first to form, and occur first on the opposite side to the impact (e.g. if the impact came from the inside, the outside would have failed). These fractures "radiate" out from the site of the impact like spokes on a bike wheel. Concentric fracture lines appear first on the same side as the impact, forming a circle around the breaking point.

Cracks will always end at existing cracks. This information can be used to determine the order in which fractures occurred. In the image to the left two fractures are present: fracture A and fracture B. The radial fracture lines from fracture B are stopped by fracture lines from fracture A. This means that fracture A was present before fracture B was formed.

Stress lines on the edge of a piece of glass will also provide information as to what direction the force came from. Remember the 3R rule: radial fractures make right angles to the reverse side of impact.

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 or hours of the death. Flesh flies can arrive at the same time as blowflies but generally arrive slightly later. Certain amounts of time lapse between each life stage, which can tell this time. For example, if only maggots were found on the dead body, that means the victim probably died less than twenty-four hours ago. Beetles usually arrive well after the blow and flesh flies and are generally the last insect left on the body after months of decomposition. Mites are also generally present with these beetles initially because they help suppress maggots, and as such allow certain types of beetles.

Life Cycle of Blowflies

Fly Life cycle

Insects Involved in Forensic Entomology

Blood

Blood is a body fluid which allows for the transport of substances like oxygen, nutrients, and waste products throughout the body. Blood is made up of two parts: blood cells and blood plasma. Blood cells include red and white blood cells as well as platelets, and they make up approximately 45% of blood fluid. The other 55% is plasma, an amber liquid which contains things like proteins, sugars, and electrolytes. The most common type of blood cell is red blood cells, which are full of iron-rich hemoglobin that helps transport oxygen.

Blood can be identified at crime scenes using indicators such as luminol or phenolphthalein. These tests are not specific to blood, however, and a confirmatory test specific to blood will need to be performed if it is suspected to be present. Some exams may ask about the differences between human, avian, mammalian, and reptilian/amphibian blood. Human and mammalian blood are impossible to distinguish under a microscope, and even more sophisticated tests often give false positives. New techniques have been developed which use infrared spectroscopy to distinguish between human and mammalian blood, but they are too new to be used in the field. Human/mammal red blood cells are small and round, lacking a nucleus. Avian/reptilian blood is easy to distinguish from human/mammalian blood, as birds and other vertebrates have oval-shaped blood cells with nuclei. However, it can also be difficult to distinguish between avian and reptilian blood. Reptilian and amphibian red blood cells tend to have proportionally smaller nuclei compared to avian red blood cells, but this is not always the case. Some images are included below to display the difference between the types of blood.

Microscopic Images of Blood

Type of Hair	Human	Avian	Mammalian	Reptile/Amphibian
Image(s)
Characteristics	RBCs lack nuclei Appears identical to mammalian blood	Ovoid shape Larger platelets than human blood	RBCs lack nuclei Appears identical to human blood	Ovoid shape RBCs may have irregular borders or irregular nuclei

Blood Typing

Blood typing is a system of categorizing blood based on proteins called antigens which are present on the surface of red blood cells. There are 44 different human blood group systems recognized internationally, but the two most important ones are ABO and Rh. The ABO blood group system deals with the presence or absence of A and B antigens, while the Rh blood group system mostly deals with the presence or absence of a Rh(D) antigen.

There are four blood types seen in humans using the ABO system: A, B, AB, and O. These are named for the antigens they possess: A has A antigen, B has B antigen, AB has both A and B antigens, and O has neither antigen. Each of these blood types can also be positive or negative for the Rh(D) antigen (also known as the rhesus or Rh factor). Combining the two systems means that there are eight total blood types: A+, A-, B+, B-, AB+, AB-, O+, and O-. The rarest blood type is AB-, while the most common blood type is O+.

Since antigens are what determine someone's blood type, you can determine the type of blood that someone has using antibodies. Antibodies are proteins made by the immune system designed to keep foreign entities out of the body. There are antibodies which will react to certain antigens present on the surface of the red blood cell, causing blood to agglutinate. Agglutination might occur naturally if someone was given the wrong blood type in a blood transfusion. The antibody detects the antigen, causing the blood cells to clump together. In this case, seeing clumps of blood will confirm that the antigen you're testing for is present on the blood cell.

Examine the chart to the right. Since Anti-A antibodies are designed to interact with the A antigen, type A and AB blood will agglutinate when exposed to Anti-A serum. Similarly, since Anti-B antibodies will interact with the B antigen, both B and AB will agglutinate when exposed to Anti-B serum. Since type O blood lacks both the A and B antigens, it will not agglutinate when exposed to either serum. If a lab scenario uses a simulated blood kit, there may be plates or similar pieces of equipment to perform the tests. If not, use a well plate. Place a small amount of the blood sample in a well, and then place a small amount of the serum. Wait a moment for the "blood" to react, and then record the results. Be sure to keep track of which serums are placed in each well.

Some simulated blood typing kits will only have Anti-A and Anti-B serums, but some will also include an Anti-Rh or Anti-D serum. This behaves similarly to the Anti-A and Anti-B serums in that it will cause cells that have the Rh(D) antigen to agglutinate. If a blood sample clumps up when exposed to this serum, the blood type is positive. If it does not, the blood type is negative.

Inheritance

Some tests may ask questions about how blood types are inherited, or what blood type an individual would have given their parents blood types. To solve these types of questions, it's important to have an understanding of Punnett squares. For a more in-depth explanation on Punnett squares, see Heredity#Inheritance.

Genotype	Phenotype
IAIB	AB
IAIA, IAi	A
IBIB, IBi	B
ii	O

Blood types are inherited from both parents. Doing a Punnett square for blood types can be tricky at first since there are three possible alleles: I^A, I^B, and i. The first two alleles are both dominant, with I^A representing the A antigen and I^B representing the B antigen. This is because blood type is a codominant trait, which means there can be two dominant alleles expressed at once. This is how the AB blood type is possible: if an individual has the I^AI^B genotype, they will have the AB phenotype. The i allele is recessive, and represents a lack of an antigen. Since the i allele is recessive, it is possible for individuals with A and B blood types to carry that allele and pass it down to their children. This also means that only individuals with the ii genotype will have type O blood. Two individuals with AB blood will also never be able to have type O children as they cannot carry the i allele. A list of possible genotypes and their corresponding phenotypes is included to the right.

For example: what are the odds that an individual with the I^AI^A genotype and an individual with the I^Bi genotype will have a child with the AB phenotype?

Answer There is a 50% chance that these two individuals will have a child with the AB phenotype. Examine the filled out Punnett square above. Two of the four possible genotypes are IAIB. Since 2 of the 4 possibilities correspond to AB blood, the odds of these two individuals having a child with AB blood are 50%.

Spatters

Spatters and blood are separate topics in the Forensics rules, but they are typically associated with one another. Bloodstain pattern analysis (BPA) is a subject of forensic science in which practitioners will analyze bloodstains found at a crime scene in the hopes of putting together a sequence of events. Spatter patterns are distinct from drip stains in that drip stains are only acted on by gravity and not any other external force. Spatters are typically caused by blunt force impacts or by someone shaking blood off a weapon. Competitors are responsible for being able to determine the angle, velocity, and origin direction of a spatter based on images or real spatters.

Blood spatters are generally classified by the velocity at which they form, or the intensity of the impact which created them. The table below has some example images of blood spatters and their classifications.

Blood Spatters

Image	Velocity	Description
	Low velocity (formed at <5 f/s)	Typically large and drop-like. Droplets are often several mm in diameter. These may be formed by dripping from a self-inflicted or accidental wound.
	Medium velocity (formed at 5-25 f/s)	Often appear as a linear sequence of drops. Typically result from blunt force injuries, though they may also occur when a blunt instrument covered in blood is swung (known as cast-off).
	High velocity (formed at ~100 f/s)	Usually a large collection of very small droplets in an almost random pattern. Typically result from injuries such as gunshot wounds, though they can also be caused by blunt instruments if hit with enough force. Droplets are typically less than 1 mm in diameter.

The angle of impact is the angle at which a spatter hits a surface. Blood droplets are spherical, and will remain spherical until it collides with a surface or is acted upon by some force. Using this knowledge, it is possible to use the width and length of a spatter to determine its angle of origin. Use the formula [math]\displaystyle{ \theta=\arcsin\frac{W}{L} }[/math] where theta (θ) is the angle, W is the width of the spatter, and L is the length. Arcsin (or [math]\displaystyle{ \sin^{-1} }[/math]) is also known as inverse sine, and solves for the angle that gives a certain value of sin. The more acute the angle, the more elongated the spatter will be--that is to say, smaller angles will produce more elliptical spatters. To determine where an impact came from, analysts will typically measure the angle of impact of several different spatters and find the point of convergence where they all likely originated. This may be done using a process called stringing, where strings are run from the measured blood spatters at the calculated angles to determine the point of convergence.

The "tail" or pointed end of a blood spatter is going to indicate its direction of travel. Calling it a tail is a bit misleading, as the pointed part of a blood spatter is always pointing towards the direction of travel. That means the "tail" is located at the front! That means that the droplet to the right was traveling from top to bottom when it formed this spatter. Additionally, when measuring the width and length of a spatter, don't include the tail in the measurement. Just include the main droplet. Going back to the image to the right: since the width is 9mm and the length is 18mm, that means to find the angle of impact for this blood spatter one would need to calculate the value of [math]\displaystyle{ \theta=\arcsin\frac{9}{18} }[/math]. Putting this into a calculator, it resolves to a 30° angle of impact.

Seeds and Pollen

An image of a lily flower. The pollen-producing anther are the yellow formations in the center of the flower, while the stigma is the white stalk in the center.

Pollen and seeds are formations on plants designed to help them reproduce. Only "seed plants" (spermatophytes) produce pollen and seeds, which include all flowering plants as well as conifers like pine trees. In flowering plants, the flowers contain the plant's reproductive organs. These include formations like the stigma, stamen, and ovary. Pollen is produced by flowers in the anther, which is located at the tip of the stamen. It is then transferred to the stigma, either of the same flower (self-pollination) or a different flower (cross-pollination). When the pollen interacts with the stigma, the pollen grain germinates and forms a structure called a pollen tube. This pollen tube travels towards the plant's ovules, fertilizing the reproductive cells inside and allowing for production of a seed. Seeds are just undeveloped plant embryos. They're formed from the fertilized ovules of a plant while the surrounding ovary continues to develop into a fruit.

Pollen from a variety of plants, taken with an electron microscope.

Pollen grains are incredibly small and must be examined under microscopes. They have three main parts: an inner cytoplasmic portion which contains the nuclei, an inner wall called an intine or endospore, and an outer wall called an exine or exospore. The intine is made up of cellulose, similar to the cell wall in plants. The extine, however, is made up of an incredibly tough compound called sporopollenin. This compound is a biopolymer which is incredibly resistant to degradation, which makes its structure very difficult to study. Since it is so hardy, this makes pollen evidence very difficult to wash off or get rid of. Pollen grains are very good at attaching to surfaces and can even embed into clothing, making them very difficult to remove. This is also due in part to the unique structure of the exine, which is visible in microscope images. Exine structures differ wildly between different plant species, and by studying the structure of the pollen grain it is possible to determine what type of plant it came from.

The forensic use of pollen grains is known as forensic palynology. Since pollen is too small to be seen with the naked eye, it is easy for suspects to pick up and transfer pollen grains without realizing it. This can be used to tie a suspect to a given location or even determine a possible location for a crime if it is not known. Though forensic palynology is an unpopular practice in the U.S., it has seen some success in countries like New Zealand where pollen evidence has been used in courts since the 1970s.

Most questions asked about this subject will require participants to compare the evidence from the crime scene to that which is found on the suspects. They may also be required to match certain types of seeds or pollen to a region of the nation or world. It is, however, helpful to have a general knowledge about various kinds of pollen and common regionally identifiable plants. This may include plants such as cotton or rice, which can only grow in specific climates. Seeds and pollen rarely appear on exams, but it is still important to be prepared for questions that may be asked about them.

Tracks and Soil

Tracks

In this section, most observations will be qualitative. Often, the only necessary action is to compare the given photographs to the track provided at the "scene." These tracks can be footprints or tire tracks, both of which can be identified by the tread that is left on the ground. Checking the pattern, shape, and size of each distinct part of the sole on a shoe is generally necessary to make a 100% accurate match.

Soil

See also: Crime Busters#Soil

Soil can be used to tie suspects to the scene or area of a crime based on the type of soil found. There are three main types of soil which are categorized based on their texture: sand, silt, and clay. Sand is the most coarse of the three textures, with its particles having the greatest diameter and having a pH of 4.5-5.5. Sand is primarily made of pieces of eroded rock, and is typically found on beaches or in arid climates like deserts. Silt is also a sediment but its grains are finer than that of sand. Silt is typically found around riverbanks and other waterways as the water erodes rock and deposits it onto land. It can also be carried into valleys by floodwaters. Silty soil tends to have a pH of around 4.5-5.5, similar to sand. Clay is the third major category of soil and has the finest grains of the three. Clay soil can be found in most places in the U.S., though it can be common around lakes and other large bodies of water. Clay soil tends to have a pH of around 5.5-7.0.

These three types of particulate can appear in different proportions in a given sample of soil, determining the type of soil it is. For example, a soil sample that is mostly sand with a small percentage of silt or clay may be sandy loam while a sample that is mostly silt with a little sand may be silt loam. Loamy soil is a mixture of all three types of particulate as well as organic matter, making it optimal for most garden plants. Loamy soil tends to have a pH of 5.5-6.5, but certain additives and fertilizers may alter it based on the plants growing in it. Another type of soil is peat, composed largely of organic material on the top layer of soil. Peaty soil is acidic and high in nutrients, but harvesting it is problematic for the wetlands it's found in. As a result, alternatives are used to promote soil drainage and nutrient absorption.

To categorize a soil sample, a chart called a soil triangle is used. For example, a given soil sample may have a composition of 20% clay, 60% silt and 20% sand. By examining each side of the triangle and following the diagonal line from each number to where they intersect, it can be determined that this sample is silt loam. Reading these charts can take some practice, but it's important to know how to read one.

Some exams may also expect competitors to do lab tests on soil, like testing the soil's pH to determine its composition. Typically this will either involve a test strip, meter, powder, or liquid. The event supervisor will likely provide instructions based on the specific test to be performed, but it usually involves adding water or the test reagent and shaking the soil sample to ensure even distribution. Then, either test the soil with the strip/meter or wait for the sample to change color. By comparing with a given color legend it's possible to determine the soil's pH and make an educated guess at its composition.

Bullet Striations

This image compares two bullets: one recovered from the crime scene (left) and one test bullet fired from the same gun (right). Notice how the grooves match up between the two bullets.

Bullet striations are microscopic ridges on the surface of a bullet. They are created when the bullet exits the barrel of a gun. Each gun barrel has unique grooves known as rifling. The purpose of this rifling is to give the bullet a spin as it travels, which improves the spin on the weapon. Since the barrel is harder than the bullet, these ridges will imprint on the surface of the bullet when the gun is fired. Since the rifling of every gun barrel is unique, it is possible to match the grooves between a bullet and a gun to see which gun the bullet was fired from. However, not all guns can be analyzed in this way. Some manufacturers employ polygonal rifling instead of traditional rifling, making the rifling more smooth (and thus impossible to analyze).

Guns can be distinguished based on a variety of characteristics: the gauge of the weapon (the size of the inner diameter of the barrel, typically used with reference to shotguns), the caliber (diameter) of the bullet that was fired, how many grooves are present inside the gun barrel, and whether these grooves run clockwise or counter-clockwise. Even if the gun used at the scene was not recovered, it may still be possible to determine the type of weapon used from any casings or ammunition left behind. A majority of the questions related to this topic will ask competitors to match striations on bullets, determining if a given gun was used to commit the crime.

Analysis

The analysis is the final (and most essential) part of the exam, worth more points than any other section. It requires competitors to put together every piece of evidence they've gathered and determine who was the most likely person to commit a crime. Typically, not much prompt is given besides asking who committed the crime and why. However, a good analysis is more than just a list of names. Competitors should be sure to address each suspect and address why they did or did not commit the crime. This justification should come from a combination of a careful reading of the crime scene, accurate analysis of the physical evidence, and general deductive reasoning. Writing a good analysis (and doing it quickly) can take some practice, and the best way to do it is by taking practice tests and learning from your mistakes.

Here are some additional things to remember when writing an analysis:

• It's okay to guess. Even if you're unsure who did it, writing down a name is better than nothing at all. Guessing completely randomly is more likely to get points than leaving the page blank.
• Include as much as possible. Don't just write about why the culprit did it, write about why the other suspects didn't. A good way to do this is by taking notes when reading through the scenario for the first time, noting down what objects each suspect is known to use or certain traits about them that can give hints to their motives. Having a list of evidence to draw from can be important when trying to include evidence in the analysis.
• You don't have to use full sentences. Unless a test states to do so, it's often just fine or even encouraged to make a bulleted list or use another format to structure the analysis.
• Look at examples. Practice tests posted on the Test Exchange Archive often have answer keys with an analysis included. Learn from what supervisors expect you to include and do your best to incorporate that on future exams.

Scoring

Forensics is a hybrid lab/study event, and scoring is based on the highest score that a team gets on the written exam. However, certain sections are weighted to place more emphasis on lab-based portions of the event like the powder and polymer testing. Listed below is the percentage of the total points that each section should roughly be worth. Not all test authors will take this into account, but it may serve as a general guideline when considering what to emphasize when studying.

• Qualitative Analysis (powders): 20%
• Polymers (plastics, fibers, and hairs): 20%
• Chromatography and Spectroscopy: 15%
• Physical Evidence (topics like blood and DNA): 15%
• Analysis of the Crime: 30%

Ties will be broken based on which team had the higher score on the analysis section. Certain penalties may also be given (up to 10%) if teams do not clean up their area after the event or if they bring prohibited lab equipment to the event.

Competition Strategies

Forensics can be an intimidating event to tackle, but with a few strategies it can be made much more manageable.

• Time is of the essence. Forensics is an event with a lot of topics which can make the tests very long. Developing a strategy to compete efficiently is essential to scoring as many points as possible. Competitors often include dichotomous keys or flowcharts in their notes, developing a routine for lab tasks. If you are asked to do chromatography, start it as soon as possible so the chromatograms have time to fully develop.
• Arrive prepared. Ensure that before you head to the event you have your required lab equipment and any safety equipment, as well as a pen or pencil. If you don't have these they will not be provided, and you may have to sprint back to your team's location and find them. This can cut into the time you have available, or even prevent you from competing. It's important to ensure that as soon as you walk into the testing room, you have everything you'll need.
• Prepare in advance. A good set of notes is a crime solver's best friend. Much of the work during the actual competition is managing your time, and by either memorizing information or being able to reference it in your notes quickly you can save a lot of time. By knowing what you're going to do ahead of time, you take out a lot of the guesswork.
• Divide and conquer. Work with your partner to decide your plan of action. Remember--time is of the essence, and by splitting up the work you can work on different things at the same time. This helps you make sure that you don't run out of time to write an analysis (which is 30% of your total score!). Oftentimes one partner will tackle powders/qualitative analysis while the other will tackle polymers. These sections are each worth 20% of the exam, and are the most time consuming part of the event.
• Don't forget the analysis. It's very easy to get caught up in cleaning up and finishing especially if you didn't have time to get to every section. However, something is always better than nothing. The analysis is supposed to be worth 30% of your final score, so even an incomplete analysis can be the difference between placing and not placing. At the bare minimum, leave enough time to guess at which suspect committed the crime.

Resources

• The Forensics Library
• Forensics Science Simplified
• Forensic Resource Council (designed for attorneys, very information-dense)
• 2005 Qualitative Analysis Hints
• Paper Chromatography page on chemguide
• Mass Spectrometry Resource from Michigan State University
• National Event Supervisor's Resource Website (archived copy, not all links may still work)
• Hair Image Gallery
• Glass Presentation