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File: Spectrophotometry Slideshare 66795 | Ppt Chapter5
spectrophotometry and photometry spectrophotometry and photometry photometric instruments measure light intensity without consideration of wavelength most instruments use filters photometers prisms or gratings spectrometers to select isolate a narrow range ...

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   Spectrophotometry and Photometry
   Spectrophotometry and Photometry
    • Photometric instruments measure light intensity without 
      consideration of wavelength.
       – Most instruments use filters (photometers), prisms, or 
          gratings (spectrometers) to select (isolate) a narrow 
          range of incident wavelength.
    • Beer Law: Concentration of a substance is directly 
      proportional to right amount of light absorbed or inversely 
      proportional to logarithm of transmitted light.
    • Spectrophotometric Instruments: measure light 
      transmitted by a solution to determine concentration of 
      light-absorbing substance in solution.
                        Copyright © 2018 Wolters Kluwer • All Rights Reserved
   Spectrophotometry and Photometry 
   Spectrophotometry and Photometry 
   (cont.)
   (cont.)
     • Components of a Spectrophotometer
        – Light source
        – Monochromators
        – Sample cell
        – Photodetectors
     • Spectrophotometer Quality Assurance
        – Wavelength accuracy
        – Stray light
        – Linearity 
                        Copyright © 2018 Wolters Kluwer • All Rights Reserved
  Spectrophotometry and Photometry 
  Spectrophotometry and Photometry 
  (cont.)
  (cont.)
    • Single-beam spectrophotometer—see Figure 5.5
                        Copyright © 2018 Wolters Kluwer • All Rights Reserved
   Spectrophotometry and Photometry 
   Spectrophotometry and Photometry 
   (cont.)
   (cont.)
     • Atomic Absorption Spectrophotometer
         –  Measures concentration by detecting absorption of 
            electromagnetic radiation by atoms rather than by molecules
         –  Sensitive, precise
         –  Routinely used to measure concentration of trace metals that 
            are not easily excited
         –  See Figure 5.11
     • Flame Photometry
         –  Measures light emitted by excited atoms
         –  Was used to determine concentration of Na, K, or Li
         –  No longer routinely used; replaced by ion-selective electrodes
                            Copyright © 2018 Wolters Kluwer • All Rights Reserved
   Spectrophotometry and Photometry 
   Spectrophotometry and Photometry 
   (cont.)
   (cont.)
    • Fluorometry
        – Basic instrumentation
            • Measure concentrations of solutions that contain 
              fluorescing molecules.
            • Emits short-wavelength high-energy excitation light.
            • Mechanical attenuator controls light intensity.
        – Advantages and disadvantage of fluorometry
            • Advantages: greater specificity and sensitivity
            • Disadvantage: very sensitive to environmental 
              changes
                         Copyright © 2018 Wolters Kluwer • All Rights Reserved
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...Spectrophotometry and photometry photometric instruments measure light intensity without consideration of wavelength most use filters photometers prisms or gratings spectrometers to select isolate a narrow range incident beer law concentration substance is directly proportional right amount absorbed inversely logarithm transmitted spectrophotometric by solution determine absorbing in copyright wolters kluwer all rights reserved cont components spectrophotometer source monochromators sample cell photodetectors quality assurance accuracy stray linearity single beam see figure atomic absorption measures detecting electromagnetic radiation atoms rather than molecules sensitive precise routinely used trace metals that are not easily excited flame emitted was na k li no longer replaced ion selective electrodes fluorometry basic instrumentation concentrations solutions contain fluorescing emits short high energy excitation mechanical attenuator controls advantages disadvantage greater specifi...

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