Chapter 10. Spectrometry: Ultraviolet and Visible Spectra

C.B. COLLOCA AND VIRGINIA E. SOSA

Book Series: Research Methods in Plant Science: Allelopathy. Volume Chemistry: Isolation, Identification and Characterization of allelochemicals/Natural Products.

Science Publishers, USA

Lugar: Plymouth; Año: 2009; p. 220 - 253

The principle of the ultraviolet-visible (UV) spectroscopy involves the absorption of ultraviolet-visible radiation by a molecule, causing the promotion of an electron from a basal to an excited state. The absortion spectra of plant constituents can be measured in very dilute solution against a solvent blank using an automatic recording spectrophometer. Absorbance is measured at wavelengths comprised between 190 and 800 nm. The ultraviolet-visible spectroscopy is a tool that provides limited information about a compound, however, it probes the electron distribution in a molecule and is particularly useful when conjugated p electron systems are present. The transitions involved in uv-visible spectroscopy are those between electron energy levels. However, methods of ultraviolet-visible molecular absorption are often used, among all the techniques of quantitative analysis, in the chemical and clinical laboratories along the world (i.e. a fast analysis of the contains of tannis in wine, flavonoids quantification in extract of plants). This spectroscopic method is mainly applied to the analysis of aromatic and unsaturated compounds. As mentioned above, UV-visible spectroscopy may be used in both qualitative and quantitative analysis. In the following sections, both analytical methods will be described as they are applied to the analysis of natural products.