Measurement of light in Laboratory

Solutions are often analyzed in the biotechnology lab by measuring how the solutes interact with light.

  1. A spectrophotometer measures the amount of light that is absorbed by a solution at a specific wavelength or over a range of wavelengths. If you know a wavelength at which a specific substance absorbs light, you can calculate the amount of that substance in a solution from the measured absorbance of that solution at that wavelength.
  1. A visible (VIS) spectrophotometer measures absorbance of light in the visible region of the spectrum (wavelength of about 400-700 nm). A small vessel called a cuvette, which is generally plastic or glass and which usually has an internal diameter of 1.0 cm, is filled with the solution and placed in the spectrophotometer for measurements.
  1. An ultraviolet/visible (UV/VIS) spectrophotometer can also measure absorbance of light in the ultraviolet region of the spectrum (about 100-400nm). These spectrophotemeters require a halogen light bulb that emits ultraviolet light and require special cuvettes that don’t absorb UV light.
  1. A scanning spectrophotometer can measure the absorbance of a solution over a range of wavelengths, creating an absorbance spectrum that can be used to identify substances in a solution.
  1. A polarimeter measures the angle by which plane-polarized light is rotated as it passes through a solution with an optically active compound such as a sugar. The solution is placed in a polarimeter tube that is at least 10 cm long.

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