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regulated by controlling the ratio of the inert gas to oxygen, as the amount of the inert gas

increases or the amount of oxygen decreases, the temperature of the flam e decreases. It is

possible to control the temperature up to a maximum of that of the acetylene-oxygen flame
(3100°C) while using a single burner and without changing the flame gases.

Electro Thermal atomizer

Electro Thermal atomizers are of three types

1. Tubular graphite furnace
2. Platform tubular graphite furnace

3. Carbon rod atomizer

There are many differences in the atomization process in a flame and in a graphite
furnace. One very important difference to keep in mind is that in FAAS, the sample solution is

aspirated into the flame continuously for as long as it takes to make the absorbance

measurement. This is usually not long about 30 s once the flame has stabilized after introducing
the sample solution, but it is a continuous process. GFAAS is not a continuous process, as will be

seen; the atomization step produces a transient signal that must be measured in less than 1 s. We
will again consider an aqueous acidic solution of our sample. A small volume of solution,

between 5 and 50 mL, is injected into the graphite tube via a micropipette or an auto sampler.

The analyte is once again in the form of dissolved ions in solution, and the same process outlined
in Fig. must occur for atomic absorption to take place.

The graphite furnace tube is subjected to a multistep temperature program. The program
controls the temperature ramp rate, the final temperature at each step, the length of time the final

temperature is held at each step and the nature and flow rate of the purge gas through the furnace

at each step. A typical graphite furnace program consists of six steps: (1) dry, (2) pyrolyze (ash,
char), (3) cool, (4) atomize, (5) clean out, and (6) cool down.

Tubular graphite furnaces

Tubular graphite furnaces and carbon rod atomizers are commercially available. The
tubular furnace consists of a hollow tube of graphite into which the sample is placed. Electrical

connection is made at opposite ends of the tube. Radiation from the source passes along the

length and through the center of the tube. A sketch of a tubular furnace and a picture of a
commercial furnace module are shown in Fig. Often tubular graphite furnaces are coated with

pyrolytic graphite in order to prevent diffusion of atomic species of the sample through the walls
of the furnace. Pyrolytic graphite is prepared by heating graphite in an inert atmosphere. Upon

cooling, the pyrolytic graphite is not as porous as graphite.

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