Ultraviolet and Visible Absorption Spectroscopy (uv-vis)
UV-vis spectroscopy is the measurement of the wavelength and intensity of absorption of near-ultraviolet and visible light by a sample. Ultraviolet and visible light are energetic enough to promote outer electrons to higher energy levels. UV-vis spectroscopy is usually applied to molecules and inorganic ions or complexes in solution. The uv-vis spectra have broad features that are of limited use for sample identification but are very useful for quantitative measurements. The concentration of an analyte in solution can be determined by measuring the absorbance at some wavelength and applying the Beer-Lambert Law.
The light source is usually a hydrogen or deuterium lamp for uv measurements and a tungsten lamp for visible measurements. The wavelengths of these continuous light sources are selected with a wavelength separator such as a prism or grating monochromator. Spectra are obtained by scanning the wavelength separator and quantitative measurements can be made from a spectrum or at a single wavelength.
Schematic of a single beam uv-vis spectrophotometer
Pictures of single beam uv-vis spectrophotometers (Spectronic 20 and 20D)
Larger picture of the Spectronic 20D with labels.
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