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prsentation on AAS &FES


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SEMINAR ON: Principle of Atomic Absorption Spectroscopy and Flame photometry . KUVEMPU UNIVERSITY DEPARTMENT OF CHEMISTRY. JNANA SAHYADRI SHANKARAGHATTA . Presented by . NAVEEN M.R 3 rd sem. M.Sc Department of chemistry Kuvempu university

Introduction. :

Introduction. The first observation of atomic absorption spectra was made by ‘ Frounhofer’ while studying dark line in solar spectrum. The use of atomic absorption spectroscopy(AAS) for analysis of metallic elements was first pointed by ‘Alan Walsh’ in 1955. The basic principle of AAS & FES is, FES is based on the measurement of emitted radiation from thermally excited atoms. and AAS is the measurement of absorption of light radiation by ground state atoms in gaseous state .

Principle Of Atomic Absorption Spectroscopy: :

Principle Of Atomic Absorption Spectroscopy: The absorption of energy by ground state atoms in the gaseous state forms the atomic absorption spectroscopy . When a solution containing metallic species is introduced into a flame, the vapours of the metals will be obtained. Some of the metal atoms may be raised to high energy level, but large percentage of metal atoms will remain in the ground state.

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When a light of resonance wavelength is passed through the flame having metal atoms . Part of that light will absorbed. The absorption of light is proportional to the concentration of metallic elements present in the flame. Once the value of absorption is known, the concentration of metallic element can be known. Mathematically the total amount of light absorbed is given by the expression

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At frequency ‘ ν ’ the total amount of light absorbed, Where, e = charge of the electron. m = mass of the electron. c = speed of light. N = number of atoms that can absorb at frequency ’ ν ’ in the light path. f = oscillator strength or ability for each atom to absorb .

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As π , e, m, and c are constant, then the simplified equation, The total amount of light absorbed= constant× N×f There is no term involving the wavelength and temperature in above equation.

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Flame photometry is also named as Flame Emission Spectroscopy (FES), because of the use of a flame to provide the energy of excitation to atoms. When a metallic salts solution introduced into flame, the atom absorbs thermal energy and get excited. Heat of flame can cause excitation of an electron from ground state to higher energy state. But excited atom has a very short life span 10 -9 sec and its returns to ground state is accompanied by the emission of radiation. Principle Of Flame Photometry:

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K + Violet Na + Yellow Li + Brick red FLAME COLOUR

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The following process involved in flame photometry, The solvent is vaporized , leaving particles of the salt. That is converted into the gaseous state. The gaseous molecule is dissociated into gaseous atoms or radicals. These atoms are excited by thermal energy of the flame. The excited atoms are unstable, quickly emits the photon and return to ground state. Measurement of the emitted radiation forms the basis of flame photometry.

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If E 1 and E 2 are represent the energy of lower and higher energy levels. The radiant energy emitted during transition, may be defined as E 2 -E 1 = hν E 2 -E 1 = hc/λ λ = hc/E 2 -E 1 From this equation one can calculate the wavelength of the emitted radiation which is characteristic of the atom of the particular element. The wavelength( λ ) tells about the type of element present in that flame . The intensity of emitted light is enables to know the amount of element present in that flame .

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Conclusion: 1 AAS is rarely used for Qualitative analysis because different hollow cathode lamp is to be used for each element to be detected . 2 Quantitative analysis water analysis ( e.g. Ca, Mg, Fe, Si, Al, Ba content ) Food analysis and analysis of animal feedstuffs ( e.g. Mn , Fe, Cu, Cr, Se, Zn) Clinical analysis (blood samples: whole blood, serum; Ca, Mg, Li, Na, K, Fe) 3. FES is used for both qualitative and quantitative analysis. Detection of alkali and alkaline earth metals. The amount of alkali metals can be determined in water glass cement and metallurgical products etc.. Application of AAS and FES:


references Instrumental method of chemical analysis Gurudeep R.Chatwal Sham K. Anand (Page No: 2.340 – 2.342) Instrumental method of chemical analysis. H.Kaur (Page No:607-619) Instrumental methods of analysis (7 th Edition) Hobart H Willard, Lynne L. Merritt John A.Dean, Frank A.Settle. (Page No:224-243) Principles of instrumental analysis(6 th Edition) F.James Holler Douglas A Skoog. Stanley R. Crouch. (Page No:230-247)

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