FIU CHM 4130 - CHAPTER 9_Xiao_AAS_and_AFS_2018 (70 pages)

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CHAPTER 9_Xiao_AAS_and_AFS_2018



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From molecular to elemental analysis there are three major techniques used for elemental analysis Optical spectrometry Mass spectrometry X ray spectrometry Chapter 9 Atomic Absorption and fluorescence Spectroscopy Both AA and AF require a light source Like Molecular Absorption Fluorescence in AA high intensity is not required in AF high intensity results in greater sensitivity Sample Atomization Atomic Absorption AA Atomization Fluorescence AF Absorption E1 E0 Molecular Absorption Emol Eelectronic Evibration Erotation Ej Ei Atomic Absorption Emol Eelectronic www docstoc com Docs Document Detail Google aspx doc id 42331615 What happens inside the flame Sample processes occurring during atomization 1 Atomiza on in Flame MgCl2 solution MgCl2 S MgO S MgCl2 S or MgO S MgCl2 g or MgO g MgCl2 g or MgO g Mg0 Cl0 O0 toc com Docs Document Detail Google aspx doc id 42331615 Evaporation Volatilization Atomization FLAMES Regions in a flame Rich in free atoms Temperature profile oxidation Variation due to the degree of oxidation for a given element A different portion of the flame should be used for the determination of each element Atomiza on cell Transport sample aerosol to flame Desolvation Atomization 1 Flame Atomizers Cheap Simple Flame stability Low temperature Flame Atomizers Disadvantages Low sampling efficiency n Only about 5 reach the flame and large portion of the sample flows down the drain n The residence time of individual atoms in the optical path in the flame is brief 10 4 s Used for atomic absorption fluorescence and emission spectroscopy Why are electroThermal atomizers Short atomization period Long average residence time of the atoms s 2 ElectroThermal Atomizers The sample is contained in a heated graphite furnace The furnace is heated by passing an electrical current through it thus it is electro thermal To prevent oxidation of the furnace it is sheathed in gas Ar usually There is no nebulziation etc The sample is introduced as a drop usually 5 20 uL slurry or



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