Liquid Chromatography - The Multi-Wavelength Dispersive Detector 2
Figure 19. The Multiwave Length Dispersive Detector
Due to the limited information provided by UV spectra and the similarity between many spectra of widely different types of compound, UV spectra are not very reliable for solute identification. The technique is useful, however, for determining the homogeneity of a peak by obtaining spectra from a sample on both sides of the peak. The technique is to normalize both spectra, then either subtract one, from the other, and show that the difference is close to zero or take the ratio and show it is constant throughout the peak.
A more common use of the multi-wavelength detector is to select a wavelength that is characteristically absorbed by a particular component or components of a mixture. This can be done to either enhance the sensitivity of the detector to those particular solutes, or render the detector more specific and consequently, not give a significant response to other substances in the mixture. The multi-wavelength dispersive detector is probably the most useful type of UV detector providing adequate sensitivity, versatility and a linear response. It is however somewhat bulky, due to the need for an relatively large internal 'optical bench', has mechanically operated wavelength selection and requires a stop/flow procedure to obtain spectra "on-the-fly". The Diode Array Detector has the same advantages but none of the disadvantages, though, as one might expect, is somewhat more expensive.