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Analytical Chemistry

Analytical Chemistry. The Study of Chemical Testing. Analytical Chemistry . What is analytical chemistry?. Science of obtaining, processing, and communicating information about the composition and structure of matter The art and science of determining what matter is and how much of it exists.

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Analytical Chemistry

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  1. Analytical Chemistry The Study of Chemical Testing

  2. Analytical Chemistry • What is analytical chemistry? • Science of obtaining, processing, and communicating information about the composition and structure of matter • The art and science of determining what matter is and how much of it exists

  3. Spectroscopy • What is spectroscopy? • Study of how matter interacts with energy • Based on the response of matter to certain frequencies or wavelengths of EM radiation

  4. Infrared Spectroscopy (IR) Analytical Chemistry

  5. Vibration of Bonds • What happens to covalent bonds when exposed to infrared (IR) radiation? • Behave like springs when they are exposed to a particular frequency • They can: • Stretch • Bend • Rock • Scissor • Twist • Wag

  6. Vibration of Bonds

  7. Vibration of Bonds • What is related to the IR frequency needed to vibrate a bond? • Bond enthalpy • Strong bond • High bond enthalpy • More energy is required to vibrate it • Weaker bond • Low bond enthalpy • Less energy is required to vibrate it

  8. Change in Bond Polarity • What happens to a molecule when it vibrates? • If its polarity changes, it becomes infrared (IR) active and detectable in an IR spectrometer • If its polarity doesn’t change, then it cannot be detected and it considered IR inactive

  9. Change in Bond Polarity δ+ δ- IR Active: Stretching involves a change in dipole IR Inactive: Stretching involves no change in dipole

  10. Infrared Spectrometer • What is the layout of an IR spectrometer? Mirrors Spectra IR Light Source S R Monochromator Photomultiplier And Detector

  11. Reading an Infrared Spectrum • How do you read an infrared spectra? • Absorptions are usually expressed as a wavenumber (1/λ) • High wavenumber equals higher energy • Different functional groups absorb at different wavenumbers

  12. Table 17: Infrared Data

  13. Table 17: Infrared Data

  14. Reading an Infrared SpectrumOne last thing… • What is the fingerprint region? • Complex absorption region between 1400 and 400 cm-1 • Analytical databases can ID many chemicals just based on this region

  15. Infrared Spectrum Practice #1

  16. Infrared Spectrum Practice #1

  17. Infrared Spectrum Practice #2

  18. Infrared Spectrum Practice #2

  19. Infrared Spectrum Practice #3

  20. Infrared Spectrum Practice #3

  21. Mass Spectroscopy (MS) Analytical Chemistry

  22. Mass Spectrometry • What is mass spectrometry (MS)? • Two uses: • Determine relative atomic mass based on isotope abundance • Determine the structure of an organic molecule by breaking it into pieces and analyzing fragment abundance

  23. Mass Spectrometer What is the layout of a mass spectrometer?

  24. Mass Spectrometer • How does the deflector separate the different ions? • Depends on the mass of the ion and its charge • NOTE: IB only uses charges of +1 • Large deflection: • Small mass • Small deflection: • Large mass

  25. Reading a Mass Spectrum • How does a spectra assist in determining percent isotope abundance? • Determine the total mass present • 100 + 12.8 + 14.4 = 127.2 • Divide each mass by the total mass and get a percent

  26. Reading a Mass Spectrum

  27. Reading a Mass Spectrum • How does a spectra assist in determining molecular structure? • Molecular fragments are separated based on the mass/charge (m/z) ratios • Fragments are identified and pieced back together to determine molecular structure

  28. Reading a Mass Spectrum • What is the parent peak? • Peak on the mass spectra that has the largest mass because it is the unfragmented ionized molecule • Usually represented by M+ • All other peaks will be compared to it Propanoic acid

  29. Reading a Mass Spectrum • What do the peak heights represent on a mass spectra? • Relative abundance of that particular fragment Propanoic acid

  30. Reading a Mass Spectrum - Warning • What should I be careful about when reading a spectrum? • Not all possible fragments are formed • Unexpected and unusual fragments can also occur • i.e. Only look at the peaks that you are asked to look at 

  31. Mass Spectra Practice #1 Formula CO2 What could have caused the m/z peaks at 16, 28 and 44? What is the molecular structure of this compound?

  32. Mass Spectra Practice #2 Formula C3H8 What could have caused the m/z peaks at 15, 29, 43, 44? What is the molecular structure of this compound?

  33. Mass Spectra Practice #3 – Part A Formula C3H8O What could have caused the m/z peaks at 29, 31, 45, 60? What is the molecular structure of this compound?

  34. Mass Spectra Practice #3 – Part B Formula C3H8O What could have caused the m/z peaks at 45 and 60? What is the molecular structure of this compound?

  35. H1 Nuclear Magnetic Resonance (H1 NMR) Analytical Chemistry

  36. H1 NMR • What is the function of H1 NMR spectroscopy? • To analyze each unique “chemical environment” of every hydrogen in the organic molecule

  37. Analyzing Chemical Environments

  38. H1 NMR • How can the NMR machine detect these environments? • An applied magnetic field causes all the hydrogen nuclei to align with it and spin with or against it • Nuclei in different environments will spin at different rates due to how much was energy absorbed by the radio waves

  39. H1 NMR • What do the peaks represent? • All of the hydrogens • Called a chemical shift (δ) and measured in parts per million (ppm) • The area underneath each peak is representative of the number of hydrogens in that specific environment • Also, there is always a reference peak (TMS) around zero

  40. Table 18: H1 NMR Data

  41. H1 NMR Spectra Practice #1

  42. H1 NMR Spectra Practice #2

  43. H1 NMR Spectra Practice #3

  44. Uses of NMR Spectroscopy • What are some common uses of NMR technology? • Useful in the medical field because radio waves are harmless • NMR, or MRI, is used in body scanning because it can detect protons in water, fat and carbohydrates • Can also be used to scan the brain for disease and cancer

  45. Atomic Absorption (AA) Analytical Chemistry

  46. Thinking back… • How is an emission spectrum produced? • Excite the electrons • When the electrons relax they release specific wavelengths of light • Produces a light signature

  47. Now reverse it… • What does an atomic absorption (AA) spectrometer measure? • The energy required to excite those electrons, NOT the light produced when they relax

  48. AA • What’s the layout of a double beam AA spectrometer? Light Source Monochromator Monochromatic Detector Nebulized sample in flame cell

  49. AA • What can be measured using absorption? • Light that is absorbed is directly connected to the concentration of the sample and can be measured with incredible precision • Excellent for very low concentrations of metals in water, soil, food, etc.

  50. AA • What are the biggest drawbacks of AA? • You need to know what element you are looking for • Special cathode lamps are needed for each element • i.e.Determining the concentration of lead you would need a lead cathode lamp

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