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8th Grade Forensic Science

T. Trimpe 2006 http://sciencespot.net/

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What is chromatography?From Wikipedia ...

Chromatography (from Greek word for chroma, colour) is the collective term for a of laboratory techniques for the separation of mixtures. It involves passing a mixturecontains the analyte through a stationary phase, which separates it from other molein the mixture and allows it to be isolated.

Which means ...Chromatography is the physical separation of a mixture into its individual componen

We can use chromatography to separate the components ofinks and dyes, such as those found in pens, markers,

clothing, and even candy shells. Chromatography can also beused to separate the colored pigments in plants.

http://members.shaw.ca/vict/chem

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A few basics ...

Mixture

Two or more substances that are mixed together, but not chemicallycombined.

Examples of mixtures ...Air mixture of gasesBowl of cereal mixture of cereal and milkSoda pop mixture of soda syrup, water, and CO2 gasFog water suspended in airKool-Aid mixture of water, sugar, and flavor crystals

Examples of compounds ...Salt Sodium and chlorine combined chemically

Water Hydrogen and oxygen combined chemicallyCarbon Dioxide Carbon and oxygen combined chemically

Compounds Two or more elements that are chemically combined.

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SolutionsSolutions are mixtures in which one substance is dissolved in another.

Solutions have two parts: solute and solventThe solute is the substance that is dissolved.The solvent is the substance that does the dissolving

Identify the solute and solvent in each solution ...

Solution Solute Solvent

LemonadeSoda pop

Ocean water

Solubility - A measure of how much of a given substance will dissolve in a liquid.

A substance that does not dissolve in water is called insoluble.A substance that does dissolve in water is called soluble.

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Types of Chromatography

Gas Chromatography is used in airports to detect bombs and is used is forensics different ways. It is used to analyze fibers on a persons body and also analyze bloodat a crime scene. Helium is used to move a gaseous mixture through a column of

absorbent material.

Liquid Chromatography is used in the world to test water samples to look for pollu

lakes and rivers. It is used to analyze metal ions and organic compounds in solutionLiquid chromatography uses liquids which may incorporate insoluble molecules.

Thin-layer Chromatography uses an absorbent material on flat glass or plastic plais used to detect pesticide or insecticide residues in food. Thin-layer chromatographalso used in forensics to analyze the dye composition of fibers.

Paper Chromatography is one of the most common types of chromatography. It usstrip of paper and capillary action is used to pull the solvents up through the paper tseparate the solutes.

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RF FactorBecause molecules in ink and other mixtures have different characteristics (such a

and solubility), they travel at different speeds when pulled along a piece of papesolvent (water). For example, black ink contains several colors. When the watethrough a word written in black, the molecules of each one of the colors bdifferently, resulting in a sort of rainbow effect with the colors separating out at drates.

We can determine the RF (or retardation factor) by measuring the distance the pigtraveled up the strip and the distance the water traveled. You will need to calculate for each of the colors that are present in a sample.

RF

=

Distance pigments traveled

Distance water traveled

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Directions

Obtain the supplies youll need from your teacher. Beaker with a small amount of water Paper strips Pencil Markers for testing Masking tape Timer

Cut the strip so that it will be at the correct heightlong enough to reach the top level of the wateWrite the pen number on the strip using a pencil or permanent marker.

Use one of the testing markers to place one line on the paper strip at about inch from the bottomdont want the ink line to touch the water.

Tape the top of the strip to a pencil and hang in the water for 5 minutes.

Remove the strip from the water and use a pencil to mark the line between the wet and dry portionstrip.

Use the ruler to make the measurements of each color for RF data and then allow the strip to dry.

Pencil

Paper

Ink

TapeLabel with marke

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