ICP/OES is one of the most powerful and popular
analytical tools for the determination of trace elements
in a myriad of sample types (Table 1). The technique is
based upon the spontaneous emission of photons from
atoms and ions that have been excited in a RF discharge.
Liquid and gas samples may be injected directly into
the instrument, while solid samples require extraction or
acid digestion so that the analytes will be present in a
solution. The sample solution is converted to an aerosol
and directed into the central channel of the plasma. At
its core the inductively coupled plasma (ICP) sustains a
temperature of approximately 10 000 K, so the aerosol
is quickly vaporized. Analyte elements are liberated
as free atoms in the gaseous state. Further collisional
excitation within the plasma imparts additional energy to
the atoms, promoting them to excited states. Sufficient
energy is often available to convert the atoms to ions and
subsequently promote the ions to excited states. Both
the atomic and ionic excited state species may then relax
to the ground state via the emission of a photon. These
photons have characteristic energies that are determined
by the quantized energy level structure for the atoms or
ions. Thus the wavelength of the photons can be used
to identify the elements from which they originated. The
total number of photons is directly proportional to the
concentration of the originating element in the sample