This method for the determination of trace metals was developed in 1950s by Alan Walsh is now universally popular and widely practiced. Atoms in the ground are excited by absorption light and they return to the ground state with emission of continuous as well as line spectra.
The AAS meth relies on the absorption line spectra of dissociated free metallic atoms. The line spectrum (transition is characteristic for each element present in the sample and the intensity of the transition lines is correlate to the metal atomized by the thermal device (flame or furnace).
Essential components of an AAS set up consist of – (1) a light source for generating characters radiation, (2) an atomizing unit for generation of atomic vapour of the analyte in a hot flame or a furna (3) optical system (monochromator and dispersion unit), detector and recorder system for detection a measurement of absorption signals.
Lines of both emission and absorption spectra for atoms involve transitions to or from ground and occur at identical energies. However, the emission lines are usually more in number than absorption lines. The lines common to both are called on ‘resonance lines.
Atomization by flame method is usually achieved by preparing the sample as a dilute solution an aspirating this with the oxidant or fuel-oxidant mixture before it passes into the combustion area.
The heat of the flame and the action of the reducing gases convert the constituents of the sample to state. AAS measurement is based on the concentration of the ground state atoms in the flame as only measured by the spectrophotometric principle-absorption of light from a beam passing through the flame.
Conversion of sample to its neutral atoms is never complete. The degree of atomization dependent upon various factors like energy levels of electrons in the atom, flame temperature, retention time of the components in the flame, composition of the flame gases (fuel rich or fuel deficient) a various types of matrix effects.