CC Lab Spectrophotometry

• Analytic techniques and instrumentation provide the foundation for all measurements
• The majority of techniques in analytic chemistry fall into four basic disciplines:

  • Spectrometry
  • Luminescence
  • Electroanalytic
  • Chromatography
• Spectrophotometry measures the array of light or radiant energy absorbed or transmitted
• Principles of Spectrophotometry:

  • Chemical reaction produces a substance that absorbs light
  • Measures light in specific wavelengths
  • Based on Beer-Lambert's Law
• Light energy is a form of electromagnetic radiation that includes electrical energy, magnetic energy, and frequency
• Wavelength is the distance between two peaks of a wave, while frequency refers to the number of waves that pass a fixed point in a given time
• Energy is the capacity to do work, and the electromagnetic spectrum includes all forms of electromagnetic radiation
• In spectrophotometry, the selected wavelength is crucial as it will be absorbed by the colored product produced from the reaction
• Components of a spectrophotometer include:

  • Light source
  • Monochromator
  • Photodetector
  • Entrance slit
  • Exit slit
  • Cuvette well
• Light sources used in spectrophotometry include:

  • Incandescent lamps (e.g., Tungsten, Deuterium, Hydrogen, Mercury-arc, Xenon)
• Monochromators in spectrophotometry utilize interference filters or prisms to isolate specific wavelengths for analysis
• Sample cells in spectrophotometry are used to hold the solution being analyzed and ensure a constant light path
• Photodetectors in spectrophotometry convert transmitted radiant energy into electrical energy for analysis
• Electricity is the flow of electrons through a conductor, and in spectrophotometry, photodetectors convert radiant energy to electrical energy
• Types of photodetectors include:

  • Photocell
  • Phototube
  • Photomultiplier tube
  • Photodiode
• Sample operation of a single-beam spectrophotometry involves calculations based on Beer's Law for colorimetric analysis