Lecture 2
M.Sc.
AA Spectrometer Components
Lamp and Flame
Detector
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Fuel Oxidant
Nebulizer
Nebulizer Components
Nebulizer Operation
• Vacuum within chamber due to combustion process in the
flame of the slot burner.
• Vacuum results in aspiration (suction) of the analyte solution
through the sampling tube.
• Sample solution enters nebulizer at speed and strikes bead
which breaks sample stream into tiny droplets.
• Resulting mist/vapour is moved under low pressure through
the nebulizer to pass a series of baffles.
• Larger droplets strike the baffles and precipitate to the waste
outlet.
• Vapour consisting of the smallest droplets proceeds unimpeded
to the flame.
Interferences
• 1. Chemical Interference: Formation of stable analyte
compounds.
• Usually due to the presence of phosphate, silicate or aluminate
• These cause the suppression of alkaline earth metal absorption
signal in the flame, e.g., effect of PO43- on Ca.
• To overcome this interference:
- use hotter flame
- add a releasing agent such as Sr, or La which preferentially
react with phosphate.
- add protective chelating agent such as EDTA, which will
preferentially complex with the analyte.
Interferences
• 2. Ionisation Interference: Most common for alkali and
alkaline earth metals with low ionisation potentials
• Reduces atom concentration
• To reduce add ionisation suppressor or buffer.
• Typically Caesium is used.
• 3. Physical Interference: Due to differences between solvent
and standards and sample. E.g.
• Viscosity: viscous solvent aspirated with slower uptake rate,
delivers less analyte per unit time to the flame.
• Therefore, absorbance is lower than for an equivalent
concentration in a less viscous solvent.
Interferences
• 3. Physical Interference continued:
• Surface Tension: Solvent with lower surface tension provides
smaller average droplet size.
• Less sample lost to drain and larger analyte concentrations
reach flame per unit time, i.e., absorbance higher than for an
equivalent concentration in a solvent with higher surface
tension.
• Overcome by trying to match physical characteristics of
standard and sample.
Interferences
• 4. Spectral Interference: Due to overlapping spectral lines.
• Rare due to the narrow line emission of Hollow Cathode
Lamp.
• However, can occur if separation between two lines is around
0.01nm e.g.
ANALYTE
INTERFERENT
Mg 285.02
Na 285.03 nm
Al 308.215
V 308.211
Cu 324.753
Eu 324.754
• Main spectral interference due to molecular absorbance and
scatter of source radiation.
Interferences
• Molecular absorbance: commonly due to molecules such as
NaCl and Ca(OH)2
• Spectral interferences are overcome by various background
correction methods.
Interferences
• 4. Spectral Interference continued:
• Both reduce transmitted intensity and lead to positive
analytical errors.
• Scattering can be caused by Carbon particles in the flame or by
unvapourised solid particles.
• Usually caused by elements such as Ti, Zr and W, which form
stable metal oxide particles.
• 5. Occlusion: e.g., effect of Fe on Cr in steel analysis.
• High concentration of Fe causes formation of particles where
Cr is trapped and cannot evaporate or be reduced to atoms
efficiently.
• To overcome add EDTA or NH4Cl to standard and samples.
Interferences
• 5. Occlusion continued:
• EDTA complexes Fe and Cr and helps prevent formation of
occlusion sites.
• NH4Cl is highly volatile salt that explosively evaporates in the
flame, resulting in a smaller, more easily evaporated particles.