Ultraviolet–visible (UV–visible or UV–Vis) spectroscopy is an analytical technique that investigates the interaction between matter and UV–Vis light within the electromagnetic spectrum. This method is widely used for its versatility, simplicity, and relatively quick data acquisition, making it valuable for both qualitative and quantitative analysis. When UV–Vis radiation passes through a material, molecules absorb light depending on the energy required for electronic transitions. As a result of energy absorption, atoms or molecules pass from the ground state to an excited state or higher energy state. If a molecule absorbs UV light, a UV spectrum is generated; if it absorbs visible light, a visible spectrum is produced.
When continuous radiation is transmitted through a material, some wavelengths are absorbed by the molecules, resulting in a decrease in the intensity of transmitted light. This selective absorption leads to the formation of an absorption spectrum that displays peaks corresponding to specific wavelengths absorbed by a molecule. The UV wavelength range of light is from 180 to 400 nanometers, as visible light has a wavelength ranging from 400 to 780 nanometers. This spectrum, which displays gaps corresponding to absorbed wavelengths, reveals information about the molecule's chemical structure.
In qualitative analysis, UV–Vis can be used to identify functional groups or confirm the identity of a compound by matching its absorbance to the absorbance of a known compound. Compared to other spectroscopy techniques, such as fluorescence, which has a higher sensitivity, UV–Vis is moderately sensitive but widely accessible due to its straightforward instrumentation and ease of use. UV–Vis instruments typically consist of components such as a light source, sample holder, monochromator or filter for wavelength selection, and detector. The path length, or the distance light travels through the sample, is an important factor in absorbance measurements, as it affects the amount of light absorbed. However, UV–Vis does have a similar sensitivity to other absorbance measurements, such as infrared spectroscopy.
Ultraviolet and visible spectroscopy is mainly used to identify compounds with conjugated double bonds.
When light passes through a particle, it will absorb either ultraviolet or visible light based on the energy required for transitioning electrons from the initial or ground state to a higher energy excited state.
The ultraviolet or UV spectrum is obtained if the molecule absorbs light between the wavelengths of 180 to 400 nanometers, whereas a visible spectrum is obtained if the absorption occurs between 400 to 780 nanometers.
Since the energy of the radiation is inversely proportional to wavelength, ultraviolet radiation with shorter wavelengths have greater energy than visible light.
UV and visible spectroscopy are used to identify compounds in quantitative analysis by comparing their absorbance values with those of known compounds.
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