Download Powerpoint

What is Atomic Spectroscopy? – Sec 20-1
Atomic Absorption Spectroscopy (AAS)
versus Atomic Emission Spectroscopy (AES)
Flame Atomization – Sec 20-2
Atomization process =
Complete atomization results in ____________________
Fuels and Flame Temperatures – Table 20-1
Fuel
Oxidant
Temperature
(K)
acetylene
air
2400 - 2700
acetylene
Nitrous oxide
(N2O)
2900 - 3100
acetylene
oxygen
3300 - 3400
hydrogen
air
2300 - 2400
hydrogen
oxygen
2800 - 3000
Cyanogen
oxygen
4800
Instrumentation – Sec 20-4
The Linewidth Problem – absorbance is proportional to
concentration (i.e. Beer’s Law holds) when the linewidth of
the probing light is narrower than the absorption band
Line Broadening Mechanisms
Both mechanisms result in more line broadening
as the temperature increases.
1. Doppler Effect – atom moving towards the
lamp samples EM wave more often = higher
frequency (shorter wavelength) absorbed
2. Pressure Broadening – colliding atoms (and
molecules) absorb a broader range of frequencies
(wavelengths)
Hollow Cathode Lamps
Cathode composed of the same element as the analyte.
As long as line broadening within the cathode is less
than within the flame, the linewidth of the lamp is always
less than the linewidth of the absorbing atoms and Beer’s
Law is followed.
Detection Limits
Interferences – Sec 20-5
1. Spectral Interference -
2. Chemical Interference -
3. Ionization Interference -