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 nm near Al at nm
∴ use Al at 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 9-14 Continuum-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.