Atomic Absorption and Atomic Fluorescence Spectrometry Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Atomic Absorption and Atomic Fluorescence Spectrometry Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9 Chapter 9

Atomization Processes Solution of analyte Atomization Processes Spray Nebulization Desolvation Solid/gas aerosol Gaseous molecules Volatilization Excited molecules hn molecular Dissociation (reversible) Atoms Excited atoms hn atomic Atomic ions Ionization (reversible) Excited ions hn ionic

Regions in a Flame Stable molecular oxides Secondary combustion zone Interzonal region Primary combustion zone Rich in free atoms C2, CH and other radicals

Temperature Profile in oC for a Natural Gas /Air Flame 5 1863 1858 1830 1800 4 1750 1700 1600 3 1400 Distance above orifice cm 2 1 1.5 1.0 0.5 0 0.5 .0 1.5 Burner tip

Stable products Atoms

Flame Absorbance profile for Some Elements Absorption Cr Ag Mg 0 1.0 2.0 Height cm

The Premixed Burner Fuel Oxidant

Laminar-flow burner

Graphite Furnace 3000 Atomize 600 Ash 150 Dry oC

Graphite Furnace Cooled electrical connections External gas inlet Graphite tube Entrance window Exit window L’vov platform Internal gas inlet

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Output Signal 0.8 Ash 0.7 0.6 0.5 0.4 0.2 0.3 2 mL of canned juice 0.1 Dry Atomize 0.05 0.1 0.0 Standards mg/L Sample

Electrothermal atomizer

Graphite Furnace

Atomic Absorption Instrumentation Radiation Sources Hollow cathode lamps Electrodless discharge lamps Source modulation Spectrophotometers Single beam Double beam

Radiation Sources Atomic lines are narrow (0.002-0.005nm). In chapter 13: Beer’s law is obeyed when line width of the source is narrower than absorption line width. When ordinary spectrophotometers with continium source is used nonlinear calibration curves are obtained. Line sources are used

Hollow Cathode Lamp Hollow cathode Anode Quartz or pyrex Ne or Ar at 1-5 torr Quartz or pyrex window Glass shield

Sputtering

Typical Single Beam Flame Atomic Absorption Spectrophotometer Detector Lamp supply Ebert monochromator Burner

Interferences in Atomic Absorption Spectroscopy Spectral Interferences Chemical Interferences

Spectral Interferences Line Broadband Scattering nm

Scattering Absorption

Background Correction Signal = ( Background + Signal ) – ( Backgound )

Continuum Source Method Monochromator at analytical wavelength: signal + background are measured Slit is opened, source is replaced by deuterium lamp (continuum source): tiny amount of light is absorbed by sample and the rest is scattered by backgound. Signal = the difference Monochromator bandwidth

Schematic of a continuum source background Deuterium lamp Analyte Hollow cathode lamp To monochromator Electrothermal atomizer Chopper Schematic of a continuum source background correction system

Chemical Interferences Formation of Compounds of Low Volatility Anion Cation To eliminate the effect: Higher temperature Releasing agents Protective agents

Chemical Interferences Dissociation Equilibria MO M + O M(OH)2 M + 2 OH Ionization Equilibria M M+ + e-