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What is a Fluorescence Spectrophotometer?

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  • Written By: Kari Wolfe
  • Edited By: Angela B.
  • Images By: Wisky, Stanod, Matt Janicki
  • Last Modified Date: 04 December 2016
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A fluorescence spectrophotometer, also known as a fluorimeter, is a scientific instrument used in fluorescence spectroscopy to determine the fluorescence spectrum of a sample. This spectrum is then analyzed to provide or confirm identification of the sample’s composition. A fluorescence spectrophotometer often can found in chemical, biochemical, and medical labs to assist in the analysis of organic compounds.

Fluorescence spectroscopy is the study of the fluorescence of a sample. When certain compounds are passed through light, ultraviolet (UV) light in this case, they emit a low-level radiation, often revealed as visible light. The resulting fluorescence contains varying wavelengths and, thus, looking at its emission and excitation spectra can be used to help identify the elements within the compound.

A fluorescence spectrophotometer traditionally contains a monochromator with a diffraction grating or a filter that acts as a diffraction grating. Monochromators are scientific instruments that allow the user to select a particular wavelength of light using a diffraction grating. Once the excitation wavelength is selected, it is focused onto the sample, exciting the molecules inside it to fluoresce. A detector is placed at a 90° angle from the excitation light so as not to contaminate the result with the excitation light. The result is an emission spectrum.

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Many types of fluorescence spectrophotometer can record both a fluorescence spectrum and an excitation spectrum. Excitation spectrums are the result of holding the emission wavelength at a particular value, instead of a constant excitation wavelength. This spectrum is then passed through many different wavelengths and the results are recorded for later analysis. The intensity of the fluorescence is proportional to the absorption of the light into the sample, which makes the two types of spectrums identical.

One example of the use of a fluorescence spectrophotometer is to study the composition of scorpion fluorescence when under UV light. It is not known why scorpions fluoresce under ultraviolet radiation, and this is one area of biological study that remains without an answer. Scientists in California have shown this fluorescence may assist the scorpion in recognizing and detecting UV light.

Don’t confuse fluorescence with phosphorescence. Fluorescent material gives off radiation when under UV light as a result of the absorption of a photon exciting the electrons in the material. When the light is taken away, the material no longer glows. Phosphorescent materials store the light and then release it gradually. This is why glow-in-the-dark objects continue to glow, even when the lights are turned off.

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