Page 75 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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The atomization temperature is usually chosen so as to give a rapid peak. It should not be so hot as to
damage the tube unnecessarily or distil off involatile contaminants, or so cool as to lose sensitivity or
create memory effects (although a tube clean, i.e. a high-temperature cycle, can be included in the
programme).

A spectrometer with rapid response electronics should be used for electrothermal atomization, as it
must follow the transient absorption event in the tube. Automatic simultaneous background
correction (see Section 2.2.5.2) is virtually essential, as non-specific absorption problems are very
severe. It is important that the continuum light follows exactly the same path through the furnace as the
radiation from the line source (assuming a deuterium lamp is being used rather than Smith-Hieftje or
Zeeman effect). The time interval between the two source pulses should be as short as possible (a
chopping frequency of at least 50 Hz) because of the transient nature of the signal.

Usually peak area of the transient absorption signal is measured as it provides greater precision. Peak
height measurements may also be used, but may yield erroneous results if the analyte is in a different
chemical form in the standards compared with the samples.

Q. What are the advantages of pyrolytic graphite coatings for furnaces?

Q. Why is argon preferred to nitrogen as the purge gas?

Q. Why are fast response electronics and background correction essential when using furnace
atomization?

3.3 Other Atomizers.

Several other types of atomizer have been developed. Some of these are based on the design of the West
rod, but others have made tubular atomizers from extremely refractory metals such as tungsten,
tantalum and molybdenum. This latter class of atomizers tend to be made in-house by some laboratories
and, at present, do not have any commercial suppliers. They have the advantage of being inert and non-
porous so there is little interaction with the analyte, so that they can be used for the determination of
elements which form refractory carbides. However, after extended use and in the presence of some
acids, many of these atomizers become brittle and distorted.

Commercially available tantalum filaments used to be produced, but these too suffered similar
disadvantages and have since ceased to be marketed.