Atomizers in AAS

Electeothermal atomizer ( graphite furnance ) and flame atomizer, are the instruments which help us to convert the analyte into the gas state and they both achieve that. My question is, what's the difference in their way of workig ? I know the flame has its nebulisator which converts the liquid analyte into mist aerosols and then the gas helps the analyte to arrive to the flame. How does the electrothermal atomizer work ? Whats the nebulisator substitution in the graphite furnance ? 
Why do we have to turn the analytie in mist aerosol in flame AAS ? 




AAS, atom absorption spectroscopy, is a step-wise process to remove a surrounding matrix, and subsequent analysis.


In both variants, the sample is diluted by applying a solvent. But the solution obtained is destroyed by evaporation, and the mist is desolvatized leading to an aerosol. The aerosol is then vaporized, yielding individual gaseous molecules (that may be analyzed spectroscopically). The gaseous molecules may dissociate reversibly into individual atoms (that may be analyzed spectroscopically). The atoms may ionize (reversibly) into atomic ions (that may be analyzed spectroscopically).


The nebulizer is a typical device for a continuous supply of analyte into the optical path of your instrument, for example between the hollow-cathode lamp and your detector. You may prepare easily 50 mL of a dilute solution of your sample that is sprayed at constant flow over minutes into the flame observed.


In the instance of the graphite furnace, the supply is discrete, batch-wise. There is a fixed volume of soluted analyte that is evaporated in a small vessel, and incinerated. Than -- for a short moment --, the heating is increased at high rate affording the generation of the individual atoms spectroscopically analyzed. One trick for this is to use a L'vov plate, a little boat of graphite accommodating the analyte solution, that is hold by a surrounding (equally horizontally aligned) tube of graphite. Because the L'vov plate is heated by the surrounding hotter graphite tube, deposition of analyte on the graphite tube is less likely. Similar to the graphite furnace, spectrometers based on the electric spark as method of atomization are working discontinuously.




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Beside the atom absorption spectroscopy (AAS) are, for example, atom emission spectroscopy (AES), atom fluorescence spectroscopy (AFS), and inductively coupled plasma spectroscopy (ICP) as related means of investigation.


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