(AOM) Analytical Techniques Lesson

Analytical Techniques

The term, "Organic", refers to materials or chemical compounds containing carbon and which are generally living things or derived from living things. Inorganic materials are chemical compounds that do not contain carbon. When analyzing evidence, the techniques vary based on the type of material and the type of result needed. Tests can be either qualitative or quantitative. Qualitative tests analyze the properties or qualities of the material, such as color or opacity. Quantitative tests yield results concerning the number or percent composition of the material. Examples of quantitative results include measurements such as boiling point, temperature and concentration of a substance. Organic evidence typically involves body fluids or materials such as saliva, blood or samples of DNA, but can also include a number of other pieces of evidence, such as illicit drugs or certain accelerants used in arson. In order to analyze these types of evidence, certain techniques must be used. Common techniques include various types of Electrophoresis, Chromatography, Spectrophotometry, and Mass Spectrometry. Electrophoresis will be covered in detail in the DNA unit, but it is considered a very important method of organic evidence analysis due to its use in DNA analysis. Briefly, it is a method of separating substances, especially proteins, and analyzing molecular structure based on the rate of movement of each component in a colloidal suspension while under the influence of an electric field. The pattern of deposited DNA fragments creates a distinct "DNA fingerprint", which can then be used to identify a person.

To understand organic evidence analysis, recall that everything is made up of matter. Matter is anything that has mass and takes up space. Matter is generally categorized as a gas, liquid or solid, depending on its state. Particles within matter, known as atoms, are the building blocks of all substances. In gases, atoms move freely to fill the container they are in. They take on the shape and volume of the container and move freely in random directions. In liquids, the atoms are closer together and assume the shape of the portion of the container they are kept in. The atoms in a liquid can't move as freely as in gases, but they still slide past each other easily. In solids, the atoms are tightly packed next to each other. Solids retain their own shape and volume. The atoms can't move past each other, but instead vibrate in place. See the images below.

Interactivity: Chemistry Review

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