(AOM) Spectrophotometry Lesson

Spectrophotometry

Spectrophotometry is the study of the absorption of light by chemical substances. A spectrophotometer is an instrument used to measure and record the absorption spectrum of a chemical substance. Recall from the previous modules what you have learned about Microspectrophotometers. Spectrophotometry works in the same way except that it does not utilize a microscope to magnify the image as in Microspectrophotometry. Spectrophotometry uses the principle of white light being dispersed into a continuum of color known as a spectra. The Spectrophotometer is simply a device to measure the amount of light emitted by a particular wavelength. A beam of light is made up of bundles of light energy, known as photons. When photons strike a surface and are absorbed, the intensity of the beam of light is reduced due to the absorbed photons. This results in a variance of intensity over the wavelength range of light it transmits. The reduced intensity of the light, as well as the quantity of the substance, can then be measured using Spectrophotometry. Essentially, a Spectrophotometer works by shining a source of light through a sample. Some of the light shone through the sample is absorbed while the rest is reflected. The reflected light is captured by a sensor. The sensor directs the light onto the photodetector. The photodetector compares the intensity of the light reflected from the test sample to the light reflected from a reference sample.

Spectrophotometry has many applications in Forensics. Examples of evidence items tested include:

  1. Inks
  2. Explosives
  3. Drugs
  4. Toxins
  5. Chemicals
  6. Minerals
  7. Paint

Because the test sample must be compared to a reference sample, Spectrophotometry is most useful in cases where the tested substance is known.

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