Atomic Absorption
and Emission
Flame Tests
Picture from:
http://aarcaro.wordpress.com/1
0th/mathenvirochem/flametest-lab/
What causes the colour of the
metal ions in the flame test?
Photon of
light released
when electron
returns to
lower energy
level
Photon of
light released
when electron
returns to
lower energy
level
Electron is
excited to
higher
energy level
Limitations of Flame Test





Not sensitive
Qualitative only
Can only be used for a small number of
metal ions
Contamination of salts will result in
inaccurate analysis as the flame colour
will alter
There can be difficulty distinguishing
the flame colour.
Emission Spectrum of Hydrogen
Animation of
spectral
lines for H
Picture from: http://www.800mainstreet.com/spect/emission-flame-exp.html
Balmer Series for Hydrogen
Adapted from: http://www.avogadro.co.uk/light/bohr/spectra.htm
Ground state
Excite
Balmer Series
Atomic Absorption Spectroscopy
(AAS)


http://www.youtube.com/watch?v=HBegTB_WDxQ
http://www.youtube.com/watch?v=WkcioQGfAgU&feature=player_embedded
*
* Photons of specific
wavelenghts
Sample compound
chopped into pulses
atomises
Hollow Cathode Lamp
Hg *
Hg *
Specific wavelengths
are not absorbed if
atom is not Hg – move
to monochromator and
detector
Hg*
Excited Hg atoms release photons
(*) of specific wavelengths when
electrons return to ground state
Hg atoms absorb
specific wavelengths
of light – causes
electrons to excite –
light not transmitted
to monochromator or
detector
Y
Hg
X
Z
Hg
Sample injected
More detailed animations
http://www.umd.umich.edu/casl/natsci/slc/slconline/ADVAA/AdvAA.swf
http://www.shsu.edu/~chm_tgc/sounds/sound.html - flash video with sound