Atomic Spectros PDF
Atomic Spectros PDF
Atomic Spectros PDF
Atomic Spectroscopy
• Atomic Energy Diagrams Revisited
• Information Provided:
– Energies of atomic orbitals,
degeneracy
– “allowed” transitions
– Resonance vs. nonresonance
lines
• Atomic Processes:
– Emission
– Absorption
– Fluorescence
1. Uncertainty Broadening
– Because excited state lifetimes are finite (and small), the
uncertainty principle leads to an uncertainty in the measured
energy of the transition
– Remember ∆t ∆E > h ?
– Relatively small contribution
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N
∝ e −E / kT
N0
• So, small change in T results in large change in population
• Most important in?
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Form Gas
Sample Excitation/ Detect
Phase Readout
Intro. Emission Photons
Atoms
• Solution Methods:
– Nebulization:
– Electrothermal Vaporization:
– Hydride Generation:
– May also induce excitation: ETV, Arc and Spark, Glow Discharge
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– Secondary combustion zone: outermost region, also fairly cool, oxide formation
– Interzonal region: Where the action is. Hottest part of the flame → lots of atoms
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• Continuum background is
produced in the core
– also contains argon spectrum
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• DC Power supply
– (high voltage)
• Plasma becomes self-
sustaining
• ~5000K in Excitation Region
• Similar sensitivity as ICP,
higher maintenance
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– High voltage ionizes gas, charged ions are accelerated toward electrodes
• Produces sputtering of atoms (ground and excited)
• Excited atoms emit light at atomic lines
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– Chemical Interferences
Spectral Interference:
• Several sources
– Overlapping lines due to contaminants
• Correct by:
– Matrix effects
• Correct by:
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• Two-Line Method
– compare response of a line that is absorbed by the analyte to a line that isn’t
absorbed
• Zeeman Effect
– Introduction of a magnetic field causes splitting of absorption lines
– Result is polarization-dependent absorption
• analyte absorption only occurs in one polarization
• Source Reversal
– at high source current, self absorption takes place
• decreases intensity of source at the peak
– Alternating current results in background correction (like continuum source
method)
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• Volatility:
– some salts have inherently low volatility
• Slow atomization rate = fewer atoms in the GP
– Correct by:
• Increasing temperature
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• Ionization Interference:
M = M+ + e-
– Correct by:
• Adding an ionization suppressor:
• Advantages of Plasmas:
– High Temperature leads to:
• more efficient volatilization
• fewer chemical interferences
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• Echelle optics
– Two dispersing elements
• Coarsely ruled grating
• Prism
– Forms two-dimensional array of lines
• Echelle Polychromator
– fix exit “slits” in strategic places
on focal plane
– Scan single PMT across slits
– Fix several PMTs, one per slit
– Use multichannel detector
(CCD, CID)
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• Depends on:
– required sensitivity
– optical characteristics
– sample composition (matrix effects)
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