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CHEM7113 - Atomic Spectroscopy !
!!

Analytical Techniques
"!

Absorption (AAS)
"! Flame AAS "! Vapour

generation AAS furnace (electrothermal) AAS

"! Graphite

"!

Emission (AES)
"! ICP-AES "! AFS

(atomic fluorescence)

Some diagrams and Tables are reproduced from Skoog ‘Principles of Instrumental Analysis’, 5th/6th ed.
1 !

Atomic Spectroscopy !
!!

Electronic transitions : UV - visible radiation excitation of outer-shell electrons of atoms in the gas phase

energy levels of atomic Na

Line thicknesses represent probability of transition!
2 !

Energy Levels of Na vs Mg+ ! energy levels of free Na and Mg+

Na!

Mg+!

Units here are angstroms (0.1 nm)!

3 !

Ca

Ar

Na

Hg

http://astro.u-strasbg.fr/~koppen/discharge/

4 !

Atomic Spectroscopy Options !
Atomic spectra can be measured in 3 ways
"! "! "!

Emission - from thermally excited atoms (and ions) (AES) Absorption - from ground-state atoms (AAS) Fluorescence - photo-excitation of ground-state atoms, followed by emission (AFS)

Fundamentals of AAS, Analytik Jena
5 !

Atomic Spectroscopy !

Atomic transitions suitable for analytical measurements have energies corresponding to UV or visible radiation (vacuum UV can also be used)

!E = h! = hc/" !
Lines used in AAS are usually given in wavelength units "/nm!

6 !

Line Spectra of Atoms !
!!

Atomic linewidths are very narrow ( < 0.01 nm )
Spectrum of a steel hollow cathode lamp

7 !

Band and Continuum Spectra !
Molecular species give band spectra; in the gas phase these can show vibrational structure Continuum emission is observed from hot materials (blackbody radiation); spectral profile depends on the temperature Both must be considered in the context of AAS (and later in ICP-AES), since they can affect the observed signal
8 !

Emission spectrum of brine!

Atomisation methods – overview "
!! !!

Flame:

2000 - 3400 K

Vapour generation: Hydride and cold

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