Instrumentation
The outline of the construction of a typical plasma emission spectrometer is to be seen in Figure 8.10.
The example shown has an inductively coupled plasma, excitation source, but the outline would be
similar were a dc source to be fitted. Different combinations of prisms and diffraction gratings may be
used in the dispersion of the emitted radiation, and in the presentation of the analytical signal.
Instruments are computerized in operation and make use of automatic sample handling. Sophisticated
data handling packages are employed routinely to deal with interferences, and to provide for clarity in
data output.
Figure 8.10
Schematic layout of an ICP-AES spectrometer.
(Source: Perkin-Elmer Instruments)In the analysis of clinical, biological and environmental samples it is often important to have
information on the speciation of the analyte, e.g. metal atoms. Thus an initial sample solution may be
subjected to a separation stage using chromatography or electrophoresis. Measurements may, of course,
be made on fractions from a fraction collector, but with plasma sources, interfacing in order to provide a
continuous monitoring of the column effluent can be possible. This relies upon the ability of the high-
temperature plasma to break down the matrix and produce free ions.
The Direct-Current Plasma Source
In a direct-current plasma source (DCP) initial heating of an inert gas, usually argon, is produced by a
dc-arc. Experimentally it is arranged for the plasma to be established in a high-velocity gas stream.
When the edges of the plasma are cooled with an inert gas vortex, the cooler outer parts have