Flame Emission Spectroscopy (FES) is a form of emission spectroscopy in which energy is provided to a sample through use of a flame. This energy is absorbed by the sample by promoting its electrons to a higher energy level. The energy is used in doing work against the electrostatic attraction between the electrons and the nucleus. After a short period of excitation, the electrons drop back to their previous, more stable state, and the absorbed energy is emitted. The wavelength and intensity of this emitted radiation can be measured, resulting in a spectrum.
This technique was pioneered by Robert Bunsen who designed the Bunsen burner and Gustav Kirchoff who designed a suitable prism spectroscope.
Technique
The solution containing the relevant substance to be analysed is drawn into the burner and dispersed into the flame as a fine spray. The solvent evaporates first, leaving finely divided solid particles which move to hottest region of the flame where gaseous atoms and ions are produced. Here electrons are excited as described above. It is common for a monochromator to be used to allow for easy detection.
On a simple level, flame emission spectroscopy can be observed using just a Bunsen burner and samples of metals. For example, sodium metal placed in the flame will glow yellow, whilst calcium metal particles will glow red.
See also