ATOMIC SPECTROSCOPY Presentation Transcript:
2.ATOMIC ABSORPTION SPECTROSCOPY (AAS) concerns the absorption of radiation by the atomised analyte element in the ground state.
Only applicable for the detection of trace metals.
3. In atomic emission spectrometry, atoms are thermally excited so that they emit light and the radiation emitted is measured.
Only applicable to determination of alkali and alkaline earth metals.
In an atom, electrons have specific and discrete energies in which electron are arranged in definite energy levels. When an electronic transitions (‘jumps’) from one energy level to another (by an electric arc ,temperature or flame), it emits or absorbs light – a photon – with a discrete, specific wavelength, the collection of all these specific wavelengths ( spectral lines) form the spectrum of the atom and it will be the characteristic of particular atom…so atomic spectra are the spectra of atoms.
6. ATOMIC LINE SPECTRA ARE CHARACTERISTIC FOR EVERY ELEMENT
7.Atomic absorption spectra
Atomic emission spectra
8.ATOMIC ABSORPTION SPECTRA
When an electron is excited to a higher energy level it must absorbed energy.
The energy absorbed as an electron jump from an orbit of low energy to one of the higher energy is characteristic of that transition.
This mean that the excitation of electron in a particular element result in energy absorption at specific wavelength it will be the characteristic of particular atom thus in addition to emission spectrum every atom possess a characteristic absorption spectrum.
9.When a sodium salt is heated in a flame the outer electron in the volatilized atoms are excited and returned to ground state with emission of energy, which appears as a yellow light (wavelength 589.5)
The major line in the sodium emission spectrum is due to an electron falling from 3p excited state to 3s ground state.
Common atom which give their bands in the emission spectrum are Ca, Ba , Na, Li, k.
10.COMPARISON OF THE ABSORPTION(a) AND EMISSION LINES (b)OF SODIUM
11.PRINCIPLE OF ATOMIC SPECTROSCOPY
12.PRINCIPLE OF ATOMIC ABSORPTION SPECTROSCOPY
The absorption of energy by ground state atoms in the gaseous state forms the basis of atomic absorption spectroscopy.
By the help of atomic absorption spectroscopy, one can determine the amount of light absorbed
13.Atoms of a metal are volatilized in a flame
and their absorbance of a narrow band of
radiation produced by a hollow cathode
lamp, coated with the particular metal
being determined is measured.
Absorption will be proportional to the density of atoms in flame.
14. Once absorption is known the concentration of the metallic element can also be known because absorption is proportional to concentration of atoms in the flame. Mathematically, the total amount of light absorbed is given by:
15. Once absorption is known the concentration of the metallic element can also be known because absorption is proportional to concentration of atoms in the flame. Mathematically, the total amount of light absorbed is given by: