Question

Why alkali metals are analysed by flame emission spectroscopy?

Answer 1

Flame Emission Spectroscopy (FES)

In flame emission spectrometry, the sample solution is nebulized (converted into a fine aerosol) and

introduced into the flame where it is desolvated, vaporized, and atomized, all in rapid succession.

Subsequently, atoms and molecules are raised to excited states via thermal collisions with the

constituents of the partially burned flame gases. Upon their return to a lower or ground electronic state,

the excited atoms and molecules emit radiation characteristic of the sample components. The emitted

radiation passes through a monochromator that isolates the specific wavelength for the desired

analysis. A photodetector measures the radiant power of the selected radiation, which is then amplified

and sent to a readout device, meter, recorder, or microcomputer system.

Combustion .flames provide a means of converting analytes in solution to atoms in the vapor phase

freed of their chemical surroundings. These free atoms are then transformed into excited electronic

states by one of two methods: absorption of additional thermal energy from the flame or absorption of

radiant energy from an external source of radiation.

In the first method, known as flame emission spectroscopy {FES), the energy from the flame also

supplies the energy necessary to move the electrons of the free atoms from the ground state to excited

states. The intensity of radiation emitted by these excited atoms returning to the ground state provides

the basis for analytical determinations in FES.

INSTRUMENTATION FOR FLAME SPECTROMETRIC METHODS The basic components of

flame spectrometric instruments are discussed in this section. These components provide the following

functions required in each method: (1) deliver the analyte to the flame, (2) induce the spectral

transitions (absorption or emission) necessary for the determination of the analyte, (3) isolate the

spectral lines required for the analysis, (4) detect the increase or decrease in intensity of radiation at the

isolated lines(s), and (5) record these intensity data.