Liquid Chromatography Detectors - The UV Detectors > The UV Absorption Detectors > Page 37

The UV Detectors

Although over the years a large number of LC detectors have been developed  and described, the vast majority of all contemporary LC analyses are carried out using one of four detectors, the UV detector in one of its forms, the electrical conductivity detector, the fluorescence detector and the refractive index detector. In addition, some form of the UV detector probably accounts for 80% of those analyses.

The UV Absorption Detectors

UV absorption detectors respond to those substances that absorb light in the range 180 to 350 nm. Many (but not all) substances absorb light in this wavelength range, including those substances having one or more double bonds (p electrons) and substances having unshared (unbonded) electrons, e.g. all olefins, all aromatics and compounds, for example, containing >C=O, >C=S, –N=N– groups. The sensor of a UV detector consists of a short cylindrical cell having a capacity between 1 ml and 10 ml through which passes the column eluent. UV light is arranged to pass through the cell and fall on a photo–electric cell (or array). The output from the photocell passes to a modifying amplifier and then to a recorder or data acquisition system.

The relationship between the intensity of UV light transmitted through a cell (IT) and the concentration of solute contained by it (c) is given by Beer's Law.