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ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Sp PowerPoint Presentation
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ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Sp

ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Sp

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ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Sp

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  1. ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Spectral Chemical Atomic Fluorescence Spectroscopy

  2. AA Source Modulation • Need to eliminate emission from analyte atoms • Source beam is chopped Chopper placed here

  3. Beam chopper for subtracting flame background emission • Lamp and flame • emission reach detector • Only flame • emission reaches • detector (c) Resulting signal

  4. ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Spectral Chemical Atomic Fluorescence Spectroscopy

  5. Spectral Interferences • 1) Undesired signals overlapping analyte signal • e.g., V at 308.11 nm near Al at 308.215 nm • ∴ use Al at 309.27 nm • 2) combustion products  broadband absorption • subtract signal from a blank • 3) matrix interferences (most serious) • use higher T • use radiation buffer • add excess of known interferent

  6. Other methods of correcting for matrix effects • Continuum Source (D2) Correction Method • D2 lamp provides continuum • UV abs. is subtracted from analyte signal • Fig. 9-14

  7. Fig 9-14Continuum-source background correction

  8. Other methods of correcting for matrix effects • Continuum Source (D2) Correction Method • D2 lamp provides continuum • UV abs. is subtracted from analyte signal • Fig. 9-14 • Zeeman Background Correction • based on splitting of absorption lines • by a magnetic field • lines absorb different polarizations

  9. Fig 9-14 Background correction by Zeeman effect • B field splits atomic absorption lines (Zeeman effect) • Line absorption differs with polarization of source

  10. Chemical interferences (very common) • 1) Certain components of the sample decrease • the extent of atomization • e.g., SO42- and PO43- hinder atomization of Ca2+ • Add releasing agent: Sr+, La3+, etc. • Add protecting agent: EDTA, hydroxyquinoline • Ionization interference • Occurs when O2 or N2O is oxidant • Analyte ionizes and releases electrons at high T • M ⇌ M+ + e-

  11. Table 9-2 Degree of Ionization with temperature • Add ionization supressor: K, Rb, Cs salts • Provides high concentration of electrons to flame • M ⇌ M+ + e- shifted to the left

  12. Fig 9-17 Effect of K as ionization suppressor for Ca

  13. Table 9-3 Detection limits (ppb) for selected elements

  14. ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Source Modulation Interferences in Atomic Absorption Spectral Chemical Atomic Fluorescence Spectroscopy

  15. Absorption and fluorescence by atoms in a flame

  16. Set-up for a Luminescence Experiment Fig. 7-1 (b) 90° • If source is at fixed λ and monochromator is scanned an emission spectrum results. • If source is scanned, and monochromator is at a fixed λ, an excitation spectrum results.