Organic Analysis

Introduction:

Before applying physical or chemical properties to the identification and/or comparison of evidence, information on the composition of matter is necessary. ◼ For convenience matter is organic (carbon atoms) vs inorganic (no carbon atoms) ◼ Analysis for each varies greatly

Review:

An element is the simplest substance known and provides the building block from which all matter is composed. ◼ Matter is anything that has a mass and occupies space. ◼ All of the elements are listed by name and symbol in the periodic table. ◼ Two or more elements combine to form a compound. ◼ An atom is the basic particle of an element and a molecule is the smallest unit of a compound.

Matter can be classified according to the physical form it takes. ▪Solid-definite shape and volume ▪Liquid-specific volume, takes the shape of its container ▪Gas/vapor-neither a definite shape nor volume ◼ Substances can change from one phase to another without forming a new chemical species, matter is simply being changed from physical state to another. ◼ Whenever a situation exists in which a substance can be distinguished by a visible boundary, different phases exist.

Selecting a technique

The proper selection of analytical techniques that will allow the forensic scientist to identify or compare matter can best be understood by categorizing all substances into one of two broad groups: organics and inorganics. ◼ In general, organic substances contain the element carbon, commonly in combination with one or more other elements. ◼ Inorganic materials encompass all other known chemical substances. ◼ This enables an analyst to determine the appropriate lab technique

Qualitative vs Quantitative

Another consideration in selecting an analytical technique is the need for either a qualitative or a quantitative determination. ▪ qualitative- the identity of the material ▪ quantitative- determination of the percent composition of the components of a mixture ◼ Most of the evidence received by crime laboratories requires the identification of organic compounds. ▪ E.g. drugs - alcohol, marijuana, heroin, etc. ▪ Petrol products, paint products, explosives

Chromatography vs Spectrometry

Chromatography, spectrophotometry, and mass spectrometry are all readily used by forensic scientists to identify or compare organic materials.

◼ Chromatography: a means of separating and tentatively identifying the components of a mixture.

◼ Spectrophotometry: the study of the absorption of light by chemical substances.

▪ Spectrophotometer: -shining light through unknown sample→ determines what is absorbed/reflected→digital value

Types of Chromatography

  1. Gas chromatography (GC)
  2. 2. High-Performance Liquid Chromatography (HPLC)
  3. 3. Thin Layer Chromatography (TLC)