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Organic Analysis (2)

Organic Analysis (2). What is light?. 1. Light as a continuous wave 2. Light as a stream of discrete energy particles (photons). Neither theory completely explains all the properties of light. “The Wave Theory” Wavelength ( λ ) and frequency (f) of light. Electromagnetic radiation spectrum.

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Organic Analysis (2)

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  1. Organic Analysis (2)

  2. What is light? • 1. Light as a continuous wave • 2. Light as a stream of discrete energy particles (photons). • Neither theory completely explains all the properties of light.

  3. “The Wave Theory”Wavelength (λ) and frequency (f) of light.

  4. Electromagnetic radiation spectrum • All electromagnetic radiations travel at the speed of light. • Distinguishable by their different wavelengths and frequencies. Gamma rays ~ X-rays ~ UV~ Visible ~ IR ~ microwave ~ Radio rays VIBGYOR Decreasing frequency  Increasing wavelength 

  5. Frequency and wavelength of visible/white light

  6. Coherent vs. Incoherent Light • Incoherent light: collection of waves possessing different frequencies and wavelengths. • Coherent light: light that is pulsating in unison.

  7. Light as a continuous wave f = c λ f is frequency (# of crests or troughs), measured as cycles per second. c is speed of light in a vacuum (3 x 108 m/s). λ is wavelength, measured as nanometers.

  8. Light as a stream of particles called photons E = hf E is energy of the photon. f is frequency of radiation h is Planck’s constant (6.626 x 10-34 J-sec)

  9. UV, IR and Visible Spectrophotometry

  10. Spectrophotometry • Measures the amount (or quantity) of radiation a particular material absorbs as a function of wavelength / frequency. • Absorption of electromagnetic radiation by chemical substances is selective.

  11. Beers’ Law A= kc A is absorption of light at a single frequency. k is the proportionality constant. c is the concentration of absorbing material. Use Beer’s law for all spectrophotometric applications.

  12. The Spectrophotometer • Radiation source (visible, UV or IR) • Monochromator (frequency/wavelength selector) • Sample holder • Detector (convert radiation to electrical signal) • Recorder (graph the signal)

  13. Components of a Spectrophotometer.

  14. Which radiation source?Visible, Ultraviolet or Infrared. • Visible radiation sources are used for many applications but produce very similar spectra. • UV spectra can be similar for many substances. • IR spectra are different for each substance. • IR spectrophotometry is one of the few tests available for specific identification.

  15. IR absorption spectra of dichloromethane

  16. MassSpectrometry Aim a beam of high energy electrons at the sample. • electrons are lost and they acquire a positive charge (“ions”) • decompose into small fragments • magnetic field will separate them according to their mass Results are graphed as afragmentation pattern.

  17. Forensic applications of mass spectrometry • No two substances have the same fragmentation pattern. • Only need 0.000001 grams • Widest application is in identification of drug mixtures.

  18. Gas Chromatography-Mass Spectrometry (GC-MS) • Gas chromatograph can be linked directly to the mass spectrometer for definitive identification.

  19. Inside the GC-MS

  20. How a GC/MS works Gas chromatography-mass spectrometry

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