Ultraviolet And Visible Absorption Spectroscopy

Ultraviolet and Visible Absorption Spectroscopy (uv-vis) Introduction 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 BeerLambert Law.

Instrumentation 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)

Dual-Beam uv-vis Spectrophotometer Introduction uv-vis spectroscopy

Instrumentation Schematic of a dual-beam uv-vis spectrophotometer

Pictures of Lambda 3A and 4B dual-beam uv-vis spectrophotometers

Larger picture of the Lambda 3a spectrophotometer Close-up of the control panel / Close-up of the sample compartment

Pictures of a Hitachi dual-beam uv-vis spectrophotometer