1. Forensic files with GC use: Deadly formula

2. Organic and Inorganic Chemical Analysis
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 Pure Substance Mixture Compound Element Homogeneous
Uniform Composition?
Heterogeneous
Can be separated
by physical methods
Pure Substance
Can it be broken down further ?
Compound
Element
Yes No
Homogeneous
(solution)
Mixture

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

8. Quantitative or qualitative required
Questions to consider in choosing an analytical (chemical) method:
Quantitative or qualitative required
Sample size and sample preparation requirements
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).

12. 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

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

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

15. 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

16. 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

17. TLC

18. 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

19. 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

20. 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

22. GC Analysis
Retention time can be used as a characteristic 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

23. Retention Time
tm is the time it takes for the mobile phase to pass through the column

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

25. 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: takes place at room temperature
Used for organic explosives that are heat sensitive as well as heat sensitive drugs

26. Underlying Ideas - Atomic and Molecular Weights
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).

27. 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.

28. 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

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

30. Allows for identifying chemical substance
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

31. Mass Spectrometer
MS Library
Heroin
MS of Unknown

32. MS
Library
Cocaine
MS of Unknown

33. MS Library
Caffeine
MS of Unknown

34. Mol. Mass = 194
Mass Spectrum
Caffeine

35. GC-Mass Spectrometry

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

39. Most useful applications of Electrophoresis
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

40. 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

41. 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 (6.626x10-34 Js)

42. 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

44. Flame Tests
Atomic Emission

46. 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

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

48. Absorption of Grape Soda
Example:
Determination of the wavelength of light absorbed by a sample of grape soda
Absorption of Grape Soda

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

50. 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 swing are sent to the laboratory.
Each sample undergoes AAS to detect if lead is present

51. The Spectrophotometer
Instrument used to measure and record the absorption spectrum of a chemical substance (compounds)

52. UV Spectrophotometry
Measures absorbance of ultraviolet and visible light of a compound as a function of wavelength or frequency
Allows tentative identification
Ex. White powder with UV spectrum comparable to that of heroin results in a tentative identification

53. UV-VIS Spectrum

54. Infrared (IR) Spectrophotometry
Different materials always have distinctively different infrared spectra
Each IR spectrum is therefore equivalent to a “fingerprint” of that substance and no other
Extensive catalogue of IR spectra of organic compounds allows for identification of organic substances

55. IR Spectrum

56. Neutron Activation Analysis (NAA)
Neutrons interact with a target nucleus to form a compound nucleus in an excited state.
The compound nucleus will decay into a more stable configuration through emission of one or more gamma rays.
This new configuration may yields a radioactive nucleus which also decays by emission of delayed gamma rays, but at a much slower rate according to the unique half-life of the radioactive nucleus.
Quantitation in parts per billion but requires a nuclear reactor

58. Neutron Activation Analysis
Rate depends on half-life of isotope
Prompt gamma ray formation
measurement taken during irradiation
Delayed gamma ray formation
measurements taken after irradiation
more common
About 70% of elements have properties suitable for measurement by NAA

59. Gamma-ray Spectra
Continuation of medium- & long-lived elements

60. Comparison of Techniques
Qual.* or Quant.
Sample Size
Detection levels
Destructive
Instr. Avail.
Mass Spec.
Qual.
0.1 mL to 10-8 mL *
Yes
Easy
Infrared
0.001 g No
UV-visible
AES
Quant.
10-4 g/L
Moderate
AAS
NAA
1 x 10-9 g
Possibly
Difficult
* Primary use is in qual. analysis, although it can be used quantitatively in some cases.