Forensic Applications of UV-Vis Spec

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bkkrafft
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38364
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Forensic Applications of UV-Vis Spec
Updated:
2010-10-23 15:36:32
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BU Forensic Chem
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Forensic Chem Lecture 3.1
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  1. What uses do most labs employ UV-Vis for?
    • 1) A screening technique for purity determinations
    • 2)Detector systems in other instruments
  2. What are the primary uses of UV-Vis in forensic labs?
    Screening methods in drug analysis and some applications in trace analysis
  3. What are the two steps involved in the absorption of UV or Vis light?
    • 1) Electronic Excitation
    • 2)Electronic Relaxation
  4. What eefects the production of UV-Vis spectra to create broaader peaks?
    molecular interactions
  5. What are the components required to measure UV-Vis absorption?
    • -source
    • -wavelength selector
    • -sample container
    • -radiation transducer
    • -signal processor/ readout device
  6. What would be the ideal source for UV or Vis light?
    One that provides UV or Vis light that will maintain similar intensity over the range of wavelengths that are of interest.
  7. What range of wavelengths is the Deuterium and Hydrogen lamp useful for?
    160-375 nm with emission lines produced at wavelengths over 400nm
  8. Tungsten filament lamps are useful for the rance of ____nm to _____nm.
    350 to 2500
  9. For what range of wavelengths can the xenon arc lamps emit a continuous spectrum?
    200-1000nm
  10. For what range of wavelengths can the xenon arc lamps emit a continuous spectrum?
    200-1000nm
  11. What are the two types of filters for wavelength selectors?
    interference and absorption
  12. What are the basic components of a monochromator?
    entrance slit, dispersion device, exit slit
  13. What are the three types of UV-Vis instruments?
    • single-beam
    • double-beam and double beam in time
    • multichannel
  14. T/F: Electromagnetic Radiation can only be considered as a particle.
    False! Electromagnetic radiation can be considered as a particle (photon) or as a wave.
  15. T/F: As wavelength increases, frequency also increases.
    False! As wavelength increases, frequency decreases.
  16. Lower frequencies approach which region of the electromagnetic spectrum?
    the infrared region
  17. Higher frequencies approach which region of the electromagnetic spectrum?
    ultraviolet region
  18. What is UV-Vis spectroscopy?
    the measurement of the wavelength and intensity of absorption of near- ultraviolet and visible light by a sample
  19. Matter can capture electromagnetic radiation and convert the energy of a photon into internal energy. What is this process called.
    absorption
  20. What are the three types of electrons responsible for electronic transitions?
  21. 1. π,σ, and n electrons
    • 2. d and f electrons
    • 3. charge transfer elcetrons
  22. What type of electron produces broad bands of absorption and is highly influenced by solvent and bonding environment?
    d electrons
  23. What types of metrals are included in the d electron transition?
    transition metals
  24. f electron transitions produce what result?
    narrow peaks or bands of absorption and are uneffected by solvent and bonding species
  25. What is the theory of charge transfer electrons?
    It is electron transfer between an electron donor and an elctron acceptor within a molecule.
  26. The product of charge transfer elcetrons is similar to what other common reaction?
    oxidation-reduction
  27. UV-Vis spectroscopy spans what wavelength region?
    ~175-800nm
  28. UV-Vis spectroscopy is very useful for __________ measurements.
    quantitative
  29. What is the Beer-Lambert law?
    The amount of light absorbed by a chemical is directly related to the concentration of the chemical in a solution
  30. Beer-Lambert Law:

    A=-log10(I/I0)=εсb

    What do the variables stand for?
  31. A= measured absorbance =-logT (T= transmittance)
    • I0= intensity of the incident light at a given wavelength
    • I= transmitted intensity
    • b = path length through the sample
    • c = concentration of the absorbing species
    • ε= *molar absorptivity constant aka. Extinction coefficient
  32. What is the purpose of the radiation transducer in the UV-Vis instrument?
    to convert radiant energy into an electrical signal

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