Infrared and Visible Spectroscopy:Fourier Transform Infrared Spectroscopyand Ultraviolet–Visible Spectroscopy

Complex chemical analysis, both of substances that are part of a mixture and their structure, can be performed by spectroscopic absorption methods in an ultraviolet (UV), visible (Vis), or infrared (IR) field. Measurement of the absorbance of light radiation by substances, especially in the Vis and UV ranges, allows qualitative and quantitative determination of substances, while obtaining a characteristic and complex absorption spectrum makes it possible to identify substances, especially in the IR field. The positions of the absorption or emission lines and bands appearing in the spectrum indicate the presence of a particular substance, while the intensity of the emission or absorption lines or bands, both for standards and for unknown substances, allows the concentration of the substances under analysis to be determined. The differentiation between the two types of methods (UV–Vis and IR) is based on the types of transitions that take place at the molecular level. In the UV-Vis spectral region, electronic transitions take place at the level of the interatomic bond, while in the IR region the transitions are of the vibrational type. The IR domain is used to observe the vibrational movements of groups of atoms and molecules. The positions of the absorption bands in the IR field play an equally important role in identifying the functional groups and elucidating the molecular structure as in the case of the UV and Vis domains, but to interpret the total structure of a molecule, the data obtained by UV, Vis, and IR spectrometry must be validated by other methods of analysis.