Qualitative and Quantitative Analysis
Only arc/spark, plasma emission, plasma mass spectrometry and X-ray emission spectrometry are
suitable techniques for qualitative analysis as in each case the relevant spectral ranges can be scanned
and studied simply and quickly. Quantitative methods based on the emission of electromagnetic
radiation rely on the direct proportionality between emitted intensity and the concentration of the
analyte. The exact nature of the relation is complex and varies with the technique; it will be discussed
more fully in the appropriate sections. Quantitative measurements by atomic absorption spectrometry
depend upon a relation which closely resembles the Beer–Lambert law relating to molecular absorption
in solution (p. 357 et al.).
8.1—
Arc/Spark Atomic (Optical) Emission Spectrometry
Summary
Principles
Emission of electromagnetic radiation in the visible and ultraviolet regions of the spectrum by atoms
and ions after electronic excitation in electrical discharges.
Instrumentation
Emission spectrometer incorporating sample and counter electrodes, means of excitation, prism or
grating monochromator, photomultiplier detection system, microprocessors or computers for data
processing, interference correction and data display.
Applications
Used for qualitative detection of metals and some non-metals particularly at trace levels. Quantitative
determination of metals mainly in solid samples such as minerals, ores and alloys. Relative precision 3–
10%.
Disadvantages
Instability of electrical discharges and matrix effects lead to only moderate precision.
An electric arc or spark will cause volatilization and dissociation of a solid or liquid sample and
electronic excitation of atomic species present. At the high temperatures (4000–10 000 K) attained
within such discharges, collisions between atoms and electrons of the discharge result in a high degree
of excitation and the spectra produced are thus comparatively rich in lines. Elements with low
ionization potentials may become completely ionized whilst others may undergo thermal excitation
largely as unionized atoms. Emission lines originating from the high temperature 'core' of an arc tend to
be characteristic of ionic species whereas those coming from the cooler