Page 69 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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3
Electrothermal Atomization

3.1 Historical Development

In 1905 and 1908, King, generally regarded as the first worker in this field, reported on fundamental
spectral studies using an electrically heated tubular furnace. The classical work in analytical chemistry
is that of L'Vov, who began to publish his results in 1959. Here the sample was applied to the tip of a
carbon electrode which was introduced into a cylindrical heated furnace through a transverse aperture
at the centre of the tube. At first, the sample was preheated using a powerful DC arc (arced to the
electrode with the sample in position). Later this arrangement was replaced by simpler resistive heating
of the electrode (Fig. 3.1). The graphite tube was 30-50 mm in length, with an internal diameter of 2.5-
5.0 mm and an external diameter of 6.0 mm. At first, the cylinders were lined with tungsten or tantalum
foil to retard vapour diffusion, but later this was changed to a coating of pyrolytic graphite. The tube
did not act as an atomizing furnace, merely as an atom cell hindering the loss of atoms. The sample
electrode was responsible for atomization. Both the tube and the electrode were heated via step-down
transformers of 4 kW (at 10 V) and 1 kW (at 15 V), respectively. The atomizer was placed within a
chamber filled with argon or nitrogen and light passed down the tube for AAS measurements. L'Vov's
apparatus offers some of the best absolute sensitivities for AAS yet obtained, but has been criticized for
being too cumbersome. Current commercial atomizers are based on a simpler design.

In 1967, Massmann described a heated graphite furnace in which no auxiliary electrode was used, i.e.
the graphite tube was both the resistance element and the furnace. The sample was micro-pipetted
directly into a 55 mm long, 6.5 mm internal diameter, 1.5 mm wall thickness tube via a small 2 mm
diameter orifice. The absorption tube device and a graphite