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OPTICAL ATOMIC SPECTROMETRYOPTICAL ATOMIC SPECTROMETRY
Chap 8Chap 8
Three major typesThree major types
Optical spectrometryOptical spectrometry
Mass spectrometryMass spectrometry
(X-ray spectrometry)(X-ray spectrometry)
In all three, atoms or ions are In all three, atoms or ions are atomizedatomized
ENERGY LEVEL DIAGRAMS
Sodium “D-lines” at Sodium “D-lines” at 589.6 and 590.0 nm589.6 and 590.0 nm
SHC, 6e, Fig. 8-1 (a)SHC, 6e, Fig. 8-1 (a)
Profile of an Atomic LinewidthSHC, 6e, Fig. 8-6
Signal Δλ1/2 = FWHM
λ0
FWHM FWHM ≡ ≡ Full Width at Half MaximumFull Width at Half Maximum
SOURCES OF LINE BROADENINGSOURCES OF LINE BROADENING(in order of increasing effect)(in order of increasing effect)
(1)(1) Uncertainty Effect (Natural Linewidths)Uncertainty Effect (Natural Linewidths)
ΔΔνν · · ΔΔt > 1t > 1
Because excited state lifetimes (t) are Because excited state lifetimes (t) are brief (brief (∼ns – ∼ns – μμs), the uncertainty (s), the uncertainty (ΔΔt) is t) is
small and small and ∴ ∴ ΔΔνν is relatively large is relatively large
(2)(2) Doppler BroadeningDoppler Broadening
Wavelength shift caused by motion of Wavelength shift caused by motion of atoms relative to detectoratoms relative to detector
(3)(3) Pressure Broadening (Collisional Broadening)Pressure Broadening (Collisional Broadening)
Collisions cause small changes in ground Collisions cause small changes in ground state energy levels (i.e., smearing)state energy levels (i.e., smearing)
ΔλΔλ1/21/2 >> >> ΔλΔλ1/21/2 of isolated atom of isolated atom
At high pressures At high pressures continuum radiation continuum radiation
e.g., high-pressure Hg and Xe lampse.g., high-pressure Hg and Xe lamps
TEMPERATURE EFFECT ON ATOMIC SPECTRATEMPERATURE EFFECT ON ATOMIC SPECTRA
Effect described by Boltzmann distributionEffect described by Boltzmann distribution
kT
E
P
P
N
N jjj exp00
j
0 ooooooooooooooooooo
oooo o o
P ≡ degeneracy of level
TEMPERATURE EFFECT ON ATOMIC SPECTRATEMPERATURE EFFECT ON ATOMIC SPECTRA
At low TAt low Tj
0 ooooooooooooooooooo
ooo
At high TAt high T
0
j
ooooooooooooo
ooooooooo
SAMPLE INTRODUCTION METHODSSAMPLE INTRODUCTION METHODS
Common Types of AtomizersCommon Types of Atomizers (from SHC, 6e, Table 8-1) (from SHC, 6e, Table 8-1)
FlameFlame 1700 – 3100 °C1700 – 3100 °C
Electrothermal (“furnace”)Electrothermal (“furnace”) 1200 – 3000 1200 – 3000 °C°C
Inductively coupled plasma (ICP)Inductively coupled plasma (ICP) 4000 – 6000 4000 – 6000 °C°C
Electric arc Electric arc 4000 – 5000 °C4000 – 5000 °C
(e.g., Vreeland spectroscope)(e.g., Vreeland spectroscope)
SHC, 6e, Fig. 8-6SHC, 6e, Fig. 8-6
Processes leading to sample atomizationProcesses leading to sample atomization
INTRODUCTION OF SOLUTION SAMPLESINTRODUCTION OF SOLUTION SAMPLES
Nebulization: sample is aspirated (“sucked in”) and Nebulization: sample is aspirated (“sucked in”) and converted to fine mist or aerosolconverted to fine mist or aerosol
PneumaticPneumatic
Ultrasonic Ultrasonic
Hydride generation (for species of low volatility, e.g., Hydride generation (for species of low volatility, e.g., Hg, Pb, Se, Sb, etc.)Hg, Pb, Se, Sb, etc.)
INTRODUCTION OF SOLID SAMPLESINTRODUCTION OF SOLID SAMPLES
Electrothermal (introduces Electrothermal (introduces andand vaporizes sample) vaporizes sample)
Arc AblationArc Ablation
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