Importance of isosbestic point in spectroscopy: a review

General trends in the development of investigations of isosbestic point, involving the chemical reaction in aqueous solutions are considered. The electronic absorption spectra, fluoresce spectral, equilibrium, and terminological aspects, as well as the possible schemes of formation of two compounds at the same wavelength, are discussed. The contributions of different methods to estimate the concentration of a substance by isosbestic point are analyzed. The interrelationship between the characteristics isosbestic point and phase rule is discussed.