Multiplex methods using multiple detectors

These are also known as multi-channel spectroscopic methods and are based on a peculiar multiplexing mode denominated optical multiplexing or wave-length-division multiplexing . The detection system commonly used involves several Independent detectors strategically located so that the dispersed radiation strikes each of them discriminately. The optical dispersion can be accomplished with the aid of a diffraction grating or prism, or both (6chelle dispersion ). 

The simplest application of these multiplexing methods involves the so-called direct-reading spectrometer , which was used with some success for a short period in atomic spectroscopy [42]. This instrument consists of a dispersion system with an array of exit silts arranged at appropriate locations. Behind each silt Is a photodetector —usually a photomultiplier. These multiplexing methods have also been used In UV-vIsIble spectroscopy, although to a lesser extent they have been Implemented on automatic discrete analysers featuring an optical system of this type with 5-10 channels or wavelengths 

These systems have two major limitations on the one hand, the number of channels must be small as each sensing element, however miniaturized, occupies considerable space with Its independent associated electronics on the other hand, and as a result of the first limitation, the spectral Information obtained is necessarily partial, although in some cases (e.g. in atomic spectroscopy and routine UV-vIsible determinations) It Is more than sufficient. Nevertheless, the development and consolidation of electronic image sensors have displaced them to a less prominent place in the context of simultaneous multi-detection. 

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