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Chapter 5 ORGANIC ANALYSIS

Chapter 5 ORGANIC ANALYSIS. Introduction. 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 .

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Chapter 5 ORGANIC ANALYSIS

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  1. Chapter 5ORGANIC ANALYSIS

  2. Introduction • 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. ORGANIC ANALYSIS

  3. Introduction • 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. ORGANIC ANALYSIS

  4. Organic vs. Inorganic • 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. ORGANIC ANALYSIS

  5. Qualitative vs. Quantitative • Another consideration in selecting an analytical technique is the need for either a qualitative or a quantitative determination. • The former relates just to the identity of the material, whereas the latter requires the 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. ORGANIC ANALYSIS

  6. Chromatography vs. Spectrometry • Chromatography, spectrophotometry, and mass spectrometry are all readily used by a forensic scientist to identify or compare organic materials. • Chromatography is a means of separating and tentatively identifying the components of a mixture. • Spectrophotometry is the study of the absorption of light by chemical substances. ORGANIC ANALYSIS

  7. Chromatography • The theory of chromatography is based on the observation that chemical substances have a tendency to partially escape into the surrounding environment when dissolved in a liquid or when absorbed on a solid surface. • Those materials that have a preference for the moving phase will slowly pull ahead and separate from those substances that prefer to remain in the stationary phase. ORGANIC ANALYSIS

  8. Gas Chromatography • In GC, the moving phase is actually a gas called the carrier gas, which flows through a column. • The stationary phase is a thin film of liquid contained within the column. • After a mixture has traversed the length of the column, it will emerge separated into its components. • The written record of this separation is called a chromatogram. ORGANIC ANALYSIS

  9. Gas Chromatography • The time required for a component to emerge from a GC column is known as retention time. • Solid materials may be heated or pryolyzed to high temperatures so that they will decompose into numerous gaseous products to flow through the GC column. ORGANIC ANALYSIS

  10. Other Chromatography • Other forms of chromatography found to be applicable to forensic science problems are high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). • Both chromatographic systems, as with any chromatography, require having a moving phase and a stationary phase. ORGANIC ANALYSIS

  11. HPLC • HPLC separates compounds using a stationary phase, a column filled with fine solid particles, and a mobile liquid phase. • As the liquid carries the sample through the column, different components are retarded to different degrees, depending on their interaction with the stationary phase. • The major advantage of HPLC is that the entire process takes place at room temperature. • Substance, such as organic explosives, which are heat sensitive are more readily separated by HPLC. ORGANIC ANALYSIS

  12. TLC • TLC uses a solid stationary phase usually coated onto a glass plate and a mobile liquid phase to separate the components of the mixture. • The liquid will slowly rise up the plate by capillary action causing the sample to become distributed between the stationary phase and the moving liquid phase. • Because most compounds are colorless, the materials must be visualized by placing the plates under ultraviolet light or spraying the plate with a chemical reagent. • The distance a spot travels up a thin-layer plate can be assigned a numerical value known as the Rf value. ORGANIC ANALYSIS

  13. Electrophoresis • A technique analogous to TLC is electrophoresis. • Here, materials are forced to move across a gel-coated plate under the influence of an electrical potential. • In this manner, substances such as proteins and DNA can be separated and characterized. ORGANIC ANALYSIS

  14. Theory of Light • Two models describe the behavior of light. • Light is described as a continuous wave. • Light is depicted as a stream of discrete energy particles. • When white light passes though a prism, it is dispersed into a continuous spectrum of colors. • Visible light ranges in color from red to violet in the electromagnetic spectrum. • Waves are described in terms such as: • Wavelength, the distance between two successive crests (or one trough to the next trough). • Frequency, the number of crests (or troughs) passing any one given point per unit of time. ORGANIC ANALYSIS

  15. Theory of Light • Frequency and wavelength are inversely proportional to one another. • The electromagnetic spectrum is the entire range of radiation energy from the most energetic cosmic rays to the least energetic radio waves. • Visible light is only a small part of the electromagnetic spectrum. • As electromagnetic radiation moves through space, its behavior can be described as that of a continuous wave; however, once radiation is absorbed by a substance, it is best described as discrete particles of light known as photons. ORGANIC ANALYSIS

  16. Absorption • Just as a substance can absorb visible light to produce color, many of the invisible radiations of the electromagnetic spectrum are likewise absorbed. • Spectrophotometry, an important analytical tool, measures the quantity of radiation that a particular material absorbs as a function of wavelength and frequency. • The quantity of light absorbed at any frequency is directly proportional to the concentration of the absorbing species. This is known as Beer’s Law. ORGANIC ANALYSIS

  17. The Spectrophotometer • The spectrophotometer is the instrument used to measure and record the absorption spectrum of a chemical substance. • The components of a spectrophotometer are: • A radiation source • A monochromator or frequency selector • A sample holder • A detector to convert electromagnetic radiation into an electrical signal • A recorder to produce a record of the signal • Absorption spectra can be done in the visible, ultraviolet (UV) or infrared (IR) regions. ORGANIC ANALYSIS

  18. UVand IR Spectrophotometry • Currently, most forensic laboratories use UV and IR spectrophotometers to characterize chemical compounds. • The simplicity of the UV spectrum facilitates its use as a tool for determining a material’s probable identity, although it may not provide a definitive result. • The IR spectrum provides a far more complex pattern. • Different materials always have distinctively different infrared spectra; each IR spectrum is therefore equivalent to a “fingerprint” of that substance. ORGANIC ANALYSIS

  19. Mass Spectrometry • In the mass spectrometer, a beam of high-energy electrons collide with a material, producing positively charged ions. • These positive ions almost instantaneously decompose into numerous fragments, which are separated according to their masses. • The unique feature of mass spectrometry is that under carefully controlled conditions, no two substances produce the same fragmentation pattern. ORGANIC ANALYSIS

  20. GC and Mass • A direct connection between the GC column and the mass spectrometer allows each component to flow into the mass spectrometer as it emerges from the GC. • The separation of a mixture’s components is first accomplished by the GC. • Then, fragmentation of each component by high-energy electrons in the mass spectrometer, will produce a distinct pattern, somewhat like a “fingerprint,” of the substance being examined. ORGANIC ANALYSIS

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