Basic Instrumentation

• Photometry


  Measure either absorption or emission
• Properties of lightProvide a sufficient light which is suitable for making a measurement
• Transmittance

  Ratio of the total radiant/luminous flux transmitted by a transparent object
• Beer's Law

  Absorbance of a solution is directly proportional to the concentration of the solution
• Increase in absorbance

  Increase in concentration
• Lambert's Law

  Absorbance of a solution is directly proportional to the thickness of the optical path
• Types of lamps

  • Tungsten
  • Hydrogen
  • Mercury
• Increase in thickness of optical path

  Increase in absorbance
• Increase in thickness of optical path

  Decrease in transmittance
• Dispersion devices

  • Cause different wavelengths of light to be dispersed at different angles
  • Prism to isolate different wavelengths
  • Filters to separate different parts of the electromagnetic spectrum by absorbing/reflecting
• Diffraction grating

  • Provide a narrower spectrum
  • Test results more accurate
• Cuvettes


  Hold solution whose absorbance is to be measured
• Dust will scratch cuvettes
• Colorimeter


  Uses prism like a spectrophotometer
• Turbidometry

  An absorption photometry
• Nephelometry


  Measure the intensity of radiation scattered by a suspension
• Reflectance photometry

  Measure light intensity of a specific wavelength that is reflected by a coloured product
• Photodetector/Galvanometer


  Measure the transmitted light which is reciprocally related to the absorbance
• Properties of light

  • Provide a sufficient light which are suitable for marking a measurement