Monochromator:

You have learnt about monochromators on UV-VIS spectrophotometry. Commonly a grating or a prism monochromator is employed. The role of a monochromator is to disperse a radiation coming from the flame and falling on it. The dispersed radiation from the outlet slit of the monochromator goes to the detector. In that case a low temperatures flame is used, the spectral lines from just a few components are emitted. In that such a case, for many routine analyses, a filter could be used as a monochromator to isolate a particular spectral line. Filters are commonly made from materials that are transparent within a small selective wavelength region. The filter selected is one that has a wavelength range in that it is transparent to emission from the element of interest. Within such a case, a condenser lens system is employed to collect the emitted light and send the rays by the filter as an approximately collimated (parallel) beam to reach the detector. Filters have been designed for use within the determination of lithium, potassium, sodium, calcium and other components.