Atomic-Absorption (AA) SpectroscopyOverviewExcitation and Decay: Interplay of electron state and photonsInstrument SchematicLight Source: Hollow Cathode LampAtomizationDetectorFlameCalibrationGetting a ConcentrationMonroe L. Weber-Shirk School of Civil and Environmental EngineeringAtomic-Absorption (AA) SpectroscopyAtomic-Absorption (AA) SpectroscopyOverviewOverviewExcitation and Decay: Interplay of electron state and photonsEmissionAbsorptionInstrument ComponentsDouble beam configurationLight sourceProduction of free atomsGraphite furnaceFlameDetectorExcitation and Decay: Interplay of electron state and photonsEmissionAbsorptionInstrument ComponentsDouble beam configurationLight sourceProduction of free atomsGraphite furnaceFlameDetectorExcitation and Decay: Interplay of electron state and photonsExcitation and Decay: Interplay of electron state and photonsEmission – decay from high energy stateAbsorption – excitation to high energy stateTwo fundamentally different ways of quantifying the concentration of an element!Emission – flame provides energy to excite atomsAbsorption – Gas phase atoms absorb photons from light sourceNarrow band! (unlike molecular absorption)Emission – decay from high energy stateAbsorption – excitation to high energy stateTwo fundamentally different ways of quantifying the concentration of an element!Emission – flame provides energy to excite atomsAbsorption – Gas phase atoms absorb photons from light sourceNarrow band! (unlike molecular absorption)Instrument SchematicInstrument SchematicFlameLampChopperReference BeamMonochromatorDetectorElectronicsBeam RecombinertVV refV sampleLight Source: Hollow Cathode LampLight Source: Hollow Cathode LampThe electric potential ionizes rare gas atoms and accelerates them into the cathode where they sputter metal atoms into the gas phaseCollisions with gas atoms or electrons excite the metal atomsOn decay the metal atoms emit lightThe electric potential ionizes rare gas atoms and accelerates them into the cathode where they sputter metal atoms into the gas phaseCollisions with gas atoms or electrons excite the metal atomsOn decay the metal atoms emit lightanodecathode+-windowlightCup made of metal of interestPower SupplyAtomizationAtomizationAtomic absorption and emission requires gas-phase atomsLiquid and solid samples must be vaporized FlameGraphite furnaceThe gas-phase atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels.What about the inevitable subsequent emission of photons on decay?Atomic absorption and emission requires gas-phase atomsLiquid and solid samples must be vaporized FlameGraphite furnaceThe gas-phase atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels.What about the inevitable subsequent emission of photons on decay?DetectorDetectorPhoto multiplier tubeExtremely sensitiveCan detect single photonsProduce a small current that is proportional to the number of photonsOp-amps produce a voltage that is then digitized for analysis.Photo multiplier tubeExtremely sensitiveCan detect single photonsProduce a small current that is proportional to the number of photonsOp-amps produce a voltage that is then digitized for analysis.FlameFlameDifferent temperatures required for different elementsAir-Acetylene flamePreferred flame for 35 elementsTemperature of 2300 CNitrous Oxide-Acetylene flameTemperature of 2900 COptimal temperature produces free gas phase atoms but doesn’t ________ themDifferent temperatures required for different elementsAir-Acetylene flamePreferred flame for 35 elementsTemperature of 2300 CNitrous Oxide-Acetylene flameTemperature of 2900 COptimal temperature produces free gas phase atoms but doesn’t ________ themionizeCalibrationCalibration________ LawNon linearity (according to Perkin Elmer)Stray lightNon homogeneities of temperature and space in the absorbing cellLine broadeningAbsorption at nearby linesWhat else could be causing non linearity?________ LawNon linearity (according to Perkin Elmer)Stray lightNon homogeneities of temperature and space in the absorbing cellLine broadeningAbsorption at nearby linesWhat else could be causing non linearity?Beer’sCorrect for this by subtracting VdarkWhat is the physics?emissionGetting a ConcentrationGetting a ConcentrationFlameMeasures absorbance proportional to the ______________ of the sampleAnalysis in the mg/L range (ppm)Graphite FurnaceMeasures an absorbance peak with an area proportional to _______ of the sampleAnalysis in the g/L range (ppb)FlameMeasures absorbance proportional to the ______________ of the sampleAnalysis in the mg/L range (ppm)Graphite FurnaceMeasures an absorbance peak with an area proportional to _______ of the sampleAnalysis in the g/L range