Atomic Absorption Spectroscopy COPY Flashcards
What are low temperature flames more subject to?
Low temp. flame subject to more interferences from incomplete atomization
Acetylene/air flame (common), 2400-2700 K
Acetylene/NO2, 2900-3100 K
Acetylene/O2, 3300-3400 K
Hydrogen/Air, 2300-4200 K
Excess fuel (rich) vs excess oxidant (lean) flame
Excess fuel = reduced flame = hotter
Excess oxidant = oxidizing flame = cooler
Types of interferences (AAS)
Spectral interferences
(atomic spectral interferences from other elements)
(spectral/chemical interferences from oxides)
(background absorption)
Chemical Interferences
Matrix Interferences
Atomic spectral interferences (from other elements) (AAS)
How to reduce it?
Mainly a problem when trying to measure absorption of one element in presence of high concentration of another element with similar absorption line
Overlap occurs when lines separated by <0.01 nm
Reduce by selecting wavelength with no overlap (maybe second or third most intense instead of first)
Extract interference (but ensure no loss of analyte)
Spectral/chemical interferences (from oxides) (AAS)
How to reduce it?
Molecular band from metal oxide/hydroxide
(eg CaOH interferes with Na and Ba lines)
Reduce by using hotter flame (or increase fuel in fuel/oxidant ratio)
Background absorption (AAS)
How to reduce it?
Absorption of radiation from hollow cathode lamp by molecules or polyatomic species in atomizer
More common problem for low wavelengths
(eg incomplete combustion of organic solvent in flame, more common in GFAAS)
Reduce by continuum-source correction method or Zeeman background correction method (generally better)
Chemical interferences (AAS)
How to reduce it?
Most commonly observed in presence of anions that are found in sample matrix (PO4 3-, SO4 2-)
Anions affect stability of metal
More thermally stable complexes Ca3(PO4)2 decrease atomization (not enough energy in flame to break these bonds)
If known matrix, add ions to standards - add another metal ion that forms a more stable complex with anions (La 3+)
Add another complexing agent that does not interfere with atomization (EDTA)
Use hotter flame
Matrix interferences (AAS)
How to reduce it?
Important to GFAAS
Organic solvents enhance nebulization
High acid % in aqueous solutions can increase viscosity and decrease nebulization
Reduce by matching solutions to sample matrix or adding releasing agents
Use standard addition approach
Matrix modification
Types of interferences (OES)
Chemical interferences
Excitation interferences
Ionization interferences
Spectral interferences
(background radiation)
(overlapping emission lines different elements)
Chemical interference (OES)
How to reduce it?
(same as AAS)
Reduce by adding supressing agent such as EDTA to form a complex with Ca2+, sample preparation, add a releasing agent (La3+)
Excitation interferences (OES)
How to reduce it?
Presence of other element in solution increases the normal population of excited state of analyte of interest
(eg Na and K can go to excited state, can excite eachother)
Reduce by matrix matching, use standard addition approach
Ionization interferences (OES)
How to reduce it?
Excited atoms ionized, they cannot emit light of desired wavelength, observed for easily ionized alkali metals and alkali earth metals)
Reduce by adding large amount of ionization suppressant (like Cs which is easily ionized)
Background radiation (OES)
How to reduce it?
Excited molecules and radicals from combustion products in the flame can emit light over broad region
Reduce by correcting absorbances against a blank
(external standard calibration, standard addition calibration)
Overlapping emission lines of different elements (OES)
How to reduce it?
(self explanatory)
High-res OES see less
Reduce by selecting different wavelength with no overlap, or extracting interference prior to analysis
