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Forensic files with GC use: Deadly formula

Forensic files with GC use: Deadly formula

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Forensic files with GC use: Deadly formula

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  1. Forensic files with GC use: Deadly formula

  2. Chapter 5 and 6 Organic and Inorganic Chemical Analysis

  3. Ch 5/6: Chemical Analysis (Analytical Methods) • Elements and compounds • Solids, liquids, and gases (phase changes) • Organic vs. inorganic compounds • Qualitative vs. quantitative analysis • Chromatography • Retention time and Rf value • Electrophoresis • Spectrophotometry and spectrometry

  4. Phase Changes: (physical state changes) • Melting: change from the solid directly into the liquid state • Freezing: change from the liquid directly into the solid state • Vaporization: change from the liquid directly into the gaseous state • Condensation:change from the gas directly into the liquid state • Sublimation: change from the solid directly into the gaseous state • Deposition:change from the gas directly into the solid state

  5. Phase Diagrams:

  6. Matter Can be separated by physical methods No Yes Pure Substance Uniform Composition? Can it be broken down further ? Yes No Yes No Compound Element Homogeneous (solution) Heterogeneous Mixture

  7. Selecting an Analytical Technique • Organic: a substance composed of carbon and hydrogen (oftencontainsmaller amounts of oxygen, nitrogen, chlorine, phosphorus, or other elements) • Inorganic:a chemical compound not based on carbon

  8. Questions to consider in choosing ananalytical (chemical) method: • Quantitative or qualitative required • Sample size and sample preparationrequirements • What level of analysis is required (e.g., ± 1.0% or ± 0.001%) • Detection levels • Destructive or non-destructive • Availability of instrumentation • Admissibility

  9. What Is Chromatography? • Laboratory technique for separating mixtures into their component compounds • Uses some version of a technique in which two phases (one mobile, one stationary) flow past one another

  10. Chromatography • Chromatographic systems have a stationary phase (can be solid or liquid) and a mobile phase (usually liquid or gas). • The mixture is placed at the beginning of the chromatographic system ( on the stationary phase). • The mobile phase then “pushes” the components of the mixture through the system. • Each component adsorbs on the stationary phase with a different strength (stronger means moves more slowly through the system). • Each component comes out the end of the system at a different time (retention time).

  11. When the molecules reach the far end of the surface, they are detected or measured one at a time as they emerge • Chromatography is non-destructive

  12. Street Drugs in Real Time Amphetamine Methamphetamine and MDMA Hydrocodone Cocaine Oxycodone

  13. Types of Chromatographic Separation • Paper Chromatography • Thin Layer Chromatography (TLC) • Gas Chromatography (GC) • High Performance Liquid Chromatography (HPLC)

  14. Paper Chromatography • Stationary phase:a sheet or strip of paper • Mobile phase: a liquid solvent (substances must be soluble in the solvent) • Mixture is spotted onto the paper • Capillary action moves mobile phase across the stationary phase • Components appear as separate spots spread out on the paper after drying

  15. Thin Layer Chromatography (TLC) • Stationary Phase:a thin layer of adsorbent coating on a sheet of plastic or glass • Mobile Phase:a liquid solvent • Sample mixture spotted onto the adsorbent material • - Solids must first be dissolved • - Liquids can be directly applied • Some components bind to the TLC plate strongly, others weakly • Components appear as separate spots after development

  16. TLC

  17. Measuring Retention Factor (Rf) • Quantitative indication of how far a compound travels in a particular solvent • Good indicator of whether an unknown and a known compound are similar, if not identical • Rf= distance the solute (D1) moves divided by the distance traveled by the solvent front (D2) • Rf= D1 / D2

  18. Gas Chromatography (GC) • Stationary phase:a solid or very syrupy liquid lines a tube (column) • Mobile phase:an inert gas ( also called a carrier gas) • Usually nitrogen or helium GC Columns

  19. Schematic of a GC • A mixture is injected into the GC and is vaporized • The carrier gas “pushes” the mixture through a GC column, where the compounds become separated and enters a detector. • Detectors measure separation as a function of time. • Each peak corresponds to a component

  20. GC Analysis • Retention time can be used as acharacteristic of a substance BUT may not be unique • An extremely sensitive technique • allows quantitation of sample • area under a peak is proportional to the quantity of substance present • Retention time: time between when the sample is injected and when it exits the column reaching the detector

  21. Retention Time tmis the time it takes for the mobile phase to pass through the column

  22. Pyrolysis Gas Chromatography • Used when a sample does not readily dissolve in a solvent (paint chips, fibers)

  23. High Performance Liquid Chromatography (HPLC) • Stationary phase: fine solid particles that are chemically treated packed into a column • Mobile phase: liquid solvent pumped through the column • Advantage:takesplace at room temperature • Used for organic explosives that are heat sensitive as well as heat sensitive drugs

  24. Mass Scale Underlying Ideas - Atomic and Molecular Weights • Uses Atomic Mass Scale • Most elements in nature exist as mixtures of isotopes (atoms of an element that have different numbers of neutrons but same number of protons).

  25. Mass Spectrometry (MS or mass spec) • Basic Principle: • Creates charged particles (ions) • Separation of ions –according to mass-to-charge ratio • Detection of ions • The differences in mass spectrometer types are the different ways they carry out these three functions • The MS analyzes ions to provide information about the molecular weight of the compound and its chemical structure.

  26. Mass Spectrometer (MS) • As each gas particle leaves the GC, it enters the mass spec • A beam of electrons is “shot” at the substance breaking it down into fragments and giving them a charge • These fragments pass through an electric field which separates them by their masses • The fragment masses are then recorded on a graph • Each substance breaks down into its own characteristic pattern

  27. Mass Spectrometer Atomic Spectra Mass Spectrum Mass Spectrum Mass Spectrum Int. Int. Int. P Cl C 35 31 12 37 13 mass number (amu) mass number (amu) mass number (amu) 31P: 100% abundant 35Cl: 75% abundant 37Cl: 24% abundant 12Cl: 98.9% abundant 13Cl: 1.11% abundant

  28. Under carefully controlled conditions, no two substances produce the same fragmentation pattern! • Allows for identifying chemical substance Unknown white powdery substance ingested by unconscious patient. What do you do? Is it Heroin, Cocaine, Caffeine? Mass Spectrum of Unknown Compound

  29. Mass Spectrometer MS Library Heroin MS of Unknown

  30. MS Library Cocaine MS of Unknown

  31. MS Library Caffeine MS of Unknown

  32. Mol. Mass = 194 Mass Spectrum Caffeine

  33. GC-Mass Spectrometry

  34. Electrophoresis • Separates materials based on their migration rates on a stationary solid phase • Passes an electrical current through and allows for classification of proteins

  35. Most useful applications ofElectrophoresis • Characterization of proteins and DNA in dried blood • Proteins migrate at speeds that vary according to their electrical charge and size resulting in characteristic band patterns

  36. Spectroscopy and Spectrophotometry • Based on the study of absorption of light by chemical substances • Used for identification of various organic materials or for presence of trace elements • Electromagnetic spectrum – entire range of “light waves” • Visible Light (colors) • Ultraviolet or infrared radiation (either side of visible region) • X-ray – high energy, short wavelength

  37. Photon - small packet of electromagnetic energy that carries a quantum • Each photon contains a specific amount of energy • E = hν • E = energy of a photon (Joules) • ν = frequency of radiation (the number of waves that pass per second) • h = Plank’s constant (6.626x10-34Js)

  38. Atomic Emission Spectroscopy (AES) • Used to detect the types of elements present in a sample • Can use measurement of the emissions from excited atoms to determine concentration. The Hydrogen Discharge Tube • H2 molecules are split into excited H atoms by an electric discharge • As the atoms return to lower energy states, light is emitted

  39. Flame Tests Atomic Emission

  40. Atomic Absorption Spectroscopy (AAS) • Atoms exposed to radiation emitted from a discharge tube • Atoms absorb radiation and become excited • The amount of radiation absorbed is recorded • Usually used to determine the presence of specific elements

  41. Beer’s Law:absorption is proportional to the concentration • The amount absorbed is determined based on a calibration curve

  42. Example: • Determination of the wavelength of lightabsorbed by a sample of grape soda Absorption of Grape Soda

  43. Example: • Determination of the amount of dilution of a sample of grape soda

  44. Atomic Absorption (AAS) Example: • A child becomes ill and is taken to the hospital • It is found that the child is suffering from possible lead poisoning. • A forensic laboratory is contacted and asked if it can determine the source of the lead which the child has ingested. • Paint samples from a number of objects are collected • Paint on the child's crib, paint from his toys, and paint from the child's swingare sent to the laboratory. • Each sample undergoes AAS to detect if lead is present