L21 - Metal Analysis Part I CHM410/ENV1410 December 1 2011...

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M e t a l A n a l y s i s Part I CHM410/ENV1410 December 1, 2011 Holly Lee [email protected]
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Applications of Metal Analysis Risk Assessment e.g. lead paint Food Analysis Environmental Analysis Forensic Analysis
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Sample Preparation: Microwave acid digestion wet chemical digestion with mineral acids (HCl, HNO 3 , HF, H 2 SO 4 , etc.), H 2 O 2 , other liquid reagents in open system or closed vessels under heating usually for solid samples (<1 g) or samples that are insoluble in solvent, making it difficult for aerosolization during sample introduction in AAS and AES
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Sample Preparation: Microwave acid digestion HNO 3 as strong acid to dissolve inorg. oxides CaO + 2H 3 O + Ca 2+ + 3H 2 O HNO 3 as acid/oxidizing agent to dissolve zero-valence inorg. metals & nonmetals Fe 0 + 3H 3 O + + 3HNO 3 (conc.) Fe 3+ + 3NO 2 ↑ (brown) + 6H 2 O 3Cu 0 + 6H 3 O + + 2HNO 3 (dil.) 3Cu 2+ + 2NO↑ (clear) + 10H 2 O HNO 3 forms mostly soluble compounds with all elements except with Au, Pt, Al, B, Cr, Ti, Zr [ ] > 2M maintain oxidizing ability
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Methods of Metal Analysis Graphite furnace- atomic absorption spectroscopy (GF- AAS ) Inductively coupled plasma- atomic emission spectroscopy (ICP- AES ) Inductively coupled plasma- mass spectrometry (ICP- MS )
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Atomic Spectroscopy Atomic absorption of EMR Atomic emission of EMR Absorption, emission, or fluorescence by gaseous atomic particles (atoms or ions) Electronic transitions between the ground state to higher energy levels within an atom depend on absorption/emission of energy equal to the difference between the levels Electron excitation or Electron relaxation
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Atomic Spectroscopy Sodium Magnesium λ ~ 285 nm ( green ) λ ~ 589 nm ( yellow )
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Wavelength, λ (nm) Molecular absorption band Half-width, Δλ ½ (ca. 500 Å) Atomic absorption/emission lines (ca. 0.05 Å) VS. Radiative Intensity Molecular vs. Atomic Broadening effects: 1.Natural 2.Doppler 3.Collisions with atoms or electrons
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Atomic Absortion Spectroscopy (AAS) P O P Beer-Lambert Law A = log(P o /P) = ε bc
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Atomic Absortion Spectroscopy (AAS) Ni Hollow cathode lamp emits radiation with λ of Ni resonance line Absorption by Ni atoms in the flame λ (nm) P P A Slit Slit Selective λ passing through monochromator Absorbance readout of radiation that is not absorbed by Ni atoms
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AAS Light Source: Hollow Cathode Lamp Coated with element of interest; cylindrical (+) (-) Ar or Ne at 1-5 torr Gaseous atoms
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