Flame photometry involves measurement of intensity of radiations emitted when a salt or its pollution is introduced into a flame. Heat converts the salt into gaseous state a part of which dissociates into free atoms or radicals. These are excited by the thermal energy of the flame, emit radiant energy and return back to unexcited state.
The wave length of the radiations emitted which is characteristic for the element concerned provides a means for its identification while the measurement of intensity of the radiations enables us to determine the concentration of the element in the sample. Flame photometry is usually used to detect and measure Group I and Group II elements of the periodic table.
The instrument used in Flame photometry is called Flame photometer which has the usual component of a spectrophotometer, i.e., there is a flame, the energy-source to bring about vaporization and dissociation of constituent atoms in the sample as well as excite them to produce radiations, a prism or grating type monochromator to isolate the desired wave length band and a sensitive detector with photoemissive or photomultiplier cell to measure intensity of the desired wave length band. In some photometers filters are used to isolate the desired wave length band.
When the sample is introduced in the flame it is vapourized and dissociated into constituent atoms which also get excited by heat of the flame to produce radiations. These radiations are collected by a collimating mirror and are passed on to the monochromator which isolates the desired wave length band to be read out by the detector. With the help of monochromator it is possible to set the detector to read any wave length band.
ADVERTISEMENTS:
For example, wave length bands of 3962 and 4840 A if present show the presence of Aluminium in the sample. If the photometer detects presence of 4555 and 5536 A bands, Barium is present in the sample. The concentration of different elements in sample is usually measured by comparing the intensities of different wave length bands produced with intensities produced by a series of solution of the same element of known strength or concentration.