source. A further consequence of the high temperature is the large number of emission lines which are
excited. If the matrix is complex, line overlap may lead to spectral interferences. This situation is to be
contrasted with atomic absorption spectrophotometry where such interferences are very rare. Other
disadvantages are the costly instrumentation and high running costs, especially as large volumes of
argon are required. With some sample types the difficulties of effecting complete dissolution are also
limiting factors.
Applications of Plasma Emission Spectrometry
The potential for the employment of plasma emission spectrometry is enormous and it is finding use in
almost every field where trace element analysis is carried out. Some seventy elements, including most
metals and some non-metals, such as phosphorus and carbon, may be determined individually or in
parallel. As many as thirty or more elements may be determined on the same sample. Table 8.4 is
illustrative of elements which may be analysed and compares detection limits for plasma emission with
those for ICP–MS and atomic absorption. Rocks, soils, waters and biological tissue are typical of
samples to which the method may be applied. In geochemistry, and in quality control of potable waters
and pollution studies in general, the multi-element capability and wide (10^5 ) dynamic range of the
method are of great value. Plasma emission spectrometry is well established as a routine method of
analysis in these areas.
8.4—
Inductively Coupled Plasma-mass Spectrometry (ICP-MS)
Summary
Principles
Qualitative analysis by separation of atomic ions in a mass spectrometer. Quantitative analysis from
magnitude of ion current.
Instrumentation
Ions produced in an ICP torch interfaced to a quadrupole mass spectrometer. Sample introduction by
nebulizer, laser vaporization or electrical heating.
Applications
In principle to all elements at low (ppb) concentrations. Valuable for first look analysis, at solid
samples. Isotopic ratio measurements can distinguish between sources of elements in tracer studies and
environmental samples. Use in geological dating based upon isotopic ratios.
Disadvantages
Complex, expensive instrumentation. Precision sometimes poor. Inter-