Page 82 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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Figure 3.6
Temperature distribution in (a) longitudinally and (b) transversely heated graphite furnace.
of atomization is increased, there is less tailing of the absorption signal, there is a substantial decrease in
the carry-over (or memory) effect and refractory analytes may be determined more readily. The effects
of the different modes of heating are shown diagrammatically in Fig. 3.6.

3.6.3 Isothermal Operation

The early L'Vov design had the advantage that the sample was atomised into a hot environment (so-
called isothermal operation). In the Massmann-style furnace, the atoms form as soon as the temperature
of the tube wall reaches atomization temperature. The gas within the tube will be somewhat cooler so
when the atoms leave the tube wall, they immediately cool and may then condense or recombine with
other matrix components and will then be lost analytically. This leads to a variety of possible
interferences which for many years caused serious problems. L'Vov then suggested a simple device that
gives many of the advantages of isothermal atomization while essentially retaining the simplicity of the
Massmann design. The sample is pipetted on to a small graphite platform only loosely connected to the
tube walls (Fig. 3.7). This platform is then heated, partly by radiative and convective means, and
atomization occurs only when the surrounding gas is relatively hot. This device is sometimes referred
to as the L'Vov platform and miniature graphite plates can be purchased for this purpose.
Alternatively, an old tube may be broken to provide fractions of the tube about one quarter of the
circumference wide and 5 mm long. Some more