Liquid Chromatography Detectors - The UV Detectors > The Diode Array Detector > Page 50

A diagram of a diode array detector is shown in figure 30. Light from the broad emission source is collimated by an achromatic lens system so that the total light passes through the detector cell onto a holographic grating. In this way the sample is subjected to light of all wavelengths generated by the lamp. The dispersed light from the grating is allowed to fall onto a diode array. The array may contain many hundreds of diodes and the output from each diode is regularly sampled by a computer and stored on a hard disc. At the end of the run, the output from any diode can be selected and a chromatogram produced using the UV wavelength that was falling on that particular diode.

Figure 30. The Diode Array Detector


During chromatographic development, the output of one diode is recorded in real time producing a real time chromatogram. It is seen that by noting the time of a particular peak, a spectrum can be obtained by recalling from memory the output of all the diodes at that particular time.