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ATOMIC ABSORPTION AND ATOMIC ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRYFLUORESCENCE SPECTROMETRY
Chap 9Chap 9
Source Modulation
Interferences in Atomic AbsorptionInterferences in Atomic Absorption
SpectralSpectral
ChemicalChemical
Atomic Fluorescence SpectroscopyAtomic Fluorescence Spectroscopy
AA Source ModulationAA Source Modulation
• Need to eliminate emission from analyte atomsNeed to eliminate emission from analyte atoms• Source beam is choppedSource beam is chopped
Chopperplacedhere
Beam chopper forBeam chopper for subtracting flame subtracting flame background emissionbackground emission
(a)(a) Lamp and flameLamp and flame
emission reach detectoremission reach detector
(b)(b) Only flameOnly flame
emission reachesemission reaches
detectordetector
(c) Resulting signal(c) Resulting signal
ATOMIC ABSORPTION AND ATOMIC ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRYFLUORESCENCE SPECTROMETRY
Chap 9Chap 9
Source Modulation Source Modulation
Interferences in Atomic Absorption
Spectral
Chemical
Atomic Fluorescence SpectroscopyAtomic Fluorescence Spectroscopy
Spectral InterferencesSpectral Interferences
1) Undesired signals overlapping analyte signal1) Undesired signals overlapping analyte signal
e.g., V at 308.11 nm near Al at 308.215 nme.g., V at 308.11 nm near Al at 308.215 nm
∴∴ use Al at 309.27 nmuse Al at 309.27 nm
2) combustion products 2) combustion products broadband absorption broadband absorption
• subtract signal from a blanksubtract signal from a blank
3) matrix interferences (3) matrix interferences (most seriousmost serious))
• use higher Tuse higher T
• use radiation buffer use radiation buffer
• add excess of known interferentadd excess of known interferent
Other methods of correcting for matrix effectsOther methods of correcting for matrix effects
• Continuum Source (DContinuum Source (D22) Correction Method) Correction Method
• DD22 lamp provides continuum lamp provides continuum
• UV abs. is subtracted from analyte signalUV abs. is subtracted from analyte signal
• Fig. 9-14Fig. 9-14
Fig 9-14Fig 9-14 Continuum-sourceContinuum-source background correction
Other methods of correcting for matrix effectsOther methods of correcting for matrix effects
• Continuum Source (DContinuum Source (D22) Correction Method) Correction Method
• DD22 lamp provides continuum lamp provides continuum
• UV abs. is subtracted from analyte signalUV abs. is subtracted from analyte signal
• Fig. 9-14Fig. 9-14
• Zeeman Background CorrectionZeeman Background Correction
• based on splitting of absorption lines based on splitting of absorption lines by a magnetic fieldby a magnetic field
• lines absorb different polarizationslines absorb different polarizations
Fig 9-14 Background correction by Zeeman effectFig 9-14 Background correction by Zeeman effect
• B field splits atomic absorption lines (Zeeman effect)
• Line absorption differs with polarization of source
Chemical interferencesChemical interferences (very common) (very common)
1) Certain components of the sample decrease 1) Certain components of the sample decrease the extent of atomizationthe extent of atomization
e.g., SOe.g., SO442-2- and PO and PO44
3-3- hinder atomization of Ca hinder atomization of Ca2+2+
• Add Add releasing agentreleasing agent: Sr: Sr++, La, La3+,3+, etc. etc.
• Add Add protecting agentprotecting agent: EDTA, hydroxyquinoline: EDTA, hydroxyquinoline
2)2) Ionization interferenceIonization interference
•Occurs when OOccurs when O22 or N or N22O is oxidantO is oxidant
•Analyte ionizes and releases electrons at high TAnalyte ionizes and releases electrons at high T
M M ⇌⇌ M M++ + e + e--
Table 9-2 Degree of Ionization with temperatureTable 9-2 Degree of Ionization with temperature
•Add Add ionization supressorionization supressor: K, Rb, Cs salts: K, Rb, Cs salts
•Provides high concentration of electrons to flameProvides high concentration of electrons to flame
•M M ⇌⇌ M M++ + e + e- - shifted to the leftshifted to the left
Fig 9-17 Effect of K as ionization suppressor for CaFig 9-17 Effect of K as ionization suppressor for Ca
Table 9-3 Detection limits (ppb)Table 9-3 Detection limits (ppb)
for selected elementsfor selected elements
ATOMIC ABSORPTION AND ATOMIC ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRYFLUORESCENCE SPECTROMETRY
Chap 9Chap 9
Source ModulationSource Modulation
Interferences in Atomic AbsorptionInterferences in Atomic Absorption
SpectralSpectral
ChemicalChemical
Atomic Fluorescence Spectroscopy
Absorption and fluorescence by atoms in a flameAbsorption and fluorescence by atoms in a flame
Set-up for a Luminescence ExperimentSet-up for a Luminescence Experiment
• 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.
Fig. 7-1 (b)
90°