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
Beam chopper for
subtracting flame
background emission
(a) Lamp and flame
emission reach detector
(b) Only flame
emission reaches
detector
(c) Resulting signal
ATOMIC ABSORPTION AND ATOMIC
FLUORESCENCE SPECTROMETRY
Chap 9

Source Modulation

Interferences in Atomic Absorption


Spectral

Chemical
Atomic Fluorescence Spectroscopy
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
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
Fig 9-14 Continuum-source background correction
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
Fig 9-14 Background correction by Zeeman effect
• B field splits atomic absorption lines (Zeeman effect)
• Line absorption differs with polarization of source
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
2) Ionization interference
•Occurs when O2 or N2O is oxidant
•Analyte ionizes and releases electrons at high T
M
⇌
M+ + e -
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
Fig 9-17 Effect of K as ionization suppressor for Ca
Table 9-3 Detection limits (ppb)
for selected elements
ATOMIC ABSORPTION AND ATOMIC
FLUORESCENCE SPECTROMETRY
Chap 9

Source Modulation

Interferences in Atomic Absorption


Spectral

Chemical
Atomic Fluorescence Spectroscopy
Absorption and fluorescence by atoms in a flame
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.