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