Spectrophotometry is used in forensics to identify drugs or other toxins. When identifying an unknown drug or chemical, forensic scientists will use spectrophotometry to analyze how the unknown substance reacts to ultraviolet and infrared light to identify its composition.
After the rays have been transmitted, the resulting light is measured and recorded on a graph by the spectrophotometer. Depending on the chemical structure of the substance, a varying amount of wavelengths can be absorbed. While ultraviolet spectrophotometry is not extremely accurate, it allows for the possibilities to be narrowed down considerably. Infrared spectrophotometry is much more accurate, as the resulting wavelength patterns are all unique. The traditional spectrophotometry process is to identify unknown substances first using ultraviolet rays to narrow down the list of possibilities. This is followed up with infrared rays to positively identify the chemical.
A spectrophotometer typically contains a light source with a known wavelength, a place to hold the chemical sample and a system of lenses and photocells that measure the light shining on the sample against the light passing through. Generally, a decrease in the amount of light passing through the substance suggests the existence of materials that take in light at the known wavelength.