ABSTRACT
Visible and ultraviolet emission and absorption characteristics of compounds have long aided chemists to establish structural characteristics. The determination of ammonia, as possible detection of sewage contamination in water by colorimetric methods developed by Nessler, serves as an early example of the application of light absorption in food analysis. Spectrophotometric techniques were greatly enhanced with the development of instruments capable of measuring ultraviolet absorption at wavelengths as short as 200 nm. Spectrophotometers were developed largely after 1940, and are the basic tool in analytical work. The processes of absorption, fluorescence, and emission all involve transfer of energy within chemical species of a sample. Scattering of electromagnetic radiation does not involve transfer of energy, but rather the randomization in direction of a beam of electromagnetic radiation. The absorption of electromagnetic radiation by organic compounds in the visible and ultraviolet regions involves the transition of electrons from the ground state to an excited energy state.
