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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 Spectral Chemical Atomic Fluorescence Spectroscopy. AA Source Modulation. Need to eliminate emission from analyte atoms Source beam is chopped. Chopper placed here.

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slide1

ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY

Chap 9

Source Modulation

Interferences in Atomic Absorption

Spectral

Chemical

Atomic Fluorescence Spectroscopy

slide2

AA Source Modulation

  • Need to eliminate emission from analyte atoms
  • Source beam is chopped

Chopper

placed

here

slide3

Beam chopper for

subtracting flame

background emission

  • Lamp and flame
  • emission reach detector
  • Only flame
  • emission reaches
  • detector

(c) Resulting signal

slide4

ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY

Chap 9

Source Modulation

Interferences in Atomic Absorption

Spectral

Chemical

Atomic Fluorescence Spectroscopy

slide5

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
slide6

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
slide8

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
slide9

Fig 9-14 Background correction by Zeeman effect

  • B field splits atomic absorption lines (Zeeman effect)
  • Line absorption differs with polarization of source
slide10

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-
slide11

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
slide14

ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY

Chap 9

Source Modulation

Interferences in Atomic Absorption

Spectral

Chemical

Atomic Fluorescence Spectroscopy

slide16

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.