Molecular orbitals of the donor, acceptor and the charge transfer complex species

A huge number of chelating agents are used for the spot tests. The intense color of that type metal chelates is frequent because of charge transfer transitions. They simply include the movement of electrons from the metal ion to the ligand, or vice-versa. In the complex among thiocyanate (SCN) and the Fe (III) ions, the absorption of photon transfers an electron from the thiocyanate ion to Fe (III) ion. Besides metal ions, non-metals and their ions also create colored substances that generate features spectra. For instance, the alkaloid brucine reacts along with nitrate ion in concentrated sulphuric acid to form a red compound that quickly turns yellow.

It was mentioned previously that UV-VIS spectrometry could be used for qualitative and quantitative determinations of the analytes. The quantitative determinations are based on the relationship among the absorption of radiation and concentration of the analyte. Let us learn about the principle of spectrometric determinations.