The absorption spectra of matter are essentially the light energy of some specific wavelengths in the incident light absorbed by the molecules and atoms in the matter, and the results of the transition of the molecular vibrational energy level and the transition of the electron energy level have occurred correspondingly. The absorption of light energy will not be the same because various materials have different molecular, atomic and molecular space structures. Therefore, each substance has its own unique, fixed absorption spectrum curve, can be based on the absorption spectrum of some characteristic wavelength at the height of the absorbance to determine or determine the content of the substance, which is the basis of qualitative and quantitative analysis of spectrophotometric. Spectrophotometric analysis is an effective means to study the composition, structure and interaction between substances according to the absorption spectra of substances.
Because many substances have characteristic absorption peaks in the ultraviolet-visible area, they can be determined by ultraviolet spectrophotometry (quantitative analysis and qualitative analysis). Ultraviolet spectrophotometry is used based on Lambert-ear law.