CC LEC PRELIMS 3

• Spectrophotometry


  It measures the array of lights or radiant energy absorbed or transmitted
• photometry

  • Measurement of light’s luminous intensity
  • Conventionally did not consider wavelength
• Conventional

  • No isolation of a wavelength of light
• Modern

  • Uses filters for isolation of a narrow wavelength of light
• spectrophotometry

  • Measurement of light intensity at selected wavelengths
• spectrophotometers

  • Uses prisms or gratings for isolation of a narrow wavelength range
• Tungsten

  • Most common light source for visible region & near-infrared
  • Visible region: Only 15% of light emitted
• Tungsten

  • Heat-absorbing filter - Inserted between lamp & sample Absorption of infrared radiation
• Tungsten

  • presence of iodine/bromine vapor
• Deuterium-discharge lamp

  • measurement in the UV region
  • continuous spectra down to 165 nm
• hydrogen lamp

  • Measurement in the UV region
  • Less stable & shorter life than deuterium-discharge
• Mercury-arc lamp

  • Measurement in the UV region
• Low-pressure mercury lamp

  • Emit a sharp-line for UV & visible regions
  • Calibration purposes
  • Not practical for absorbance measurements
• Medium & high-pressure mercury lamp

  • Continuum from UV to mid-visible region
• xenon lamp

  • also for the Measurement in the UV region
• Laser

  • Light Amplification by Stimulated Emission of Radiation
  • Extremely intense, focused, & non-divergent light
• 193 nm/ 248 nm


  Argon fluoride
• 325 nm/ 442 nm

  Helium- Cadmium
• 337


  Nitrogen
• 488


  Argon (blue)
• 514 nm


  Argon (green)
• 543 nm


  Helium-neon (green)
• 633


  Helium-neon (red)
• Entrance slit

  • Minimizes & prevents entry of stray light into monochromator
• monochromator

  • Isolates a specific wavelength of light 
  • Characterized with a specific bandpass
• bandpass

  • Range of wavelengths permitted to impinge on the sample
• bandpass

  • Width at more than half the maximum transmittance
• Filters

  Prisms

  Gratings


  monochromator
• Colored-glass filters

  Sharp cut-off filter

  Narrow-bandpass filters

  interference filters


  filters
• 
  

  colored-glass filters

  • Aka wide-bandpass filters
  • Bandwidth of about 50 nm
  • Low transmittance of selected wavelength
  • Not precise
• Sharp cut-off filters

  • Sharp rise in transmittance over a narrow portion of spectrum
  • Eliminates light below a given
• Narrow-bandpass filters

  • 2 or more sharp cut-off filters and regular filters
• interference filters

  • Utilizes constructive interference
  • Cancelling out of undesired wavelengths
  • Destructive interference
• interference filters

  • Transmit harmonics
  • Multiples of the desired wavelength
  • Requires utilization of accessory cut- off filters
• prisms

  • Separates white light into continuous spectrum by refraction
  • Shorter wavelength is refracted
  • Longer wavelength passes through
• Diffraction gratings

  • Most commonly utilized
  • Parallel grooves etched onto a polished surface
• exit slit

  • Allows passage of the isolated wavelength to the sample
• Sample cell

  • Aka absorptive cells/ cuvets
• 1 cm


  Light path made constant
• Glass cuvets

  • cuvets that are Applied in visible range only