Plasma Emission Spectroscopy :
Principle : Mostly referred as Inductively Coupled Plasma (ICP) Emission Spectroscopy, is
also an atomic emission technique, most closely related to the preceded flame photometry
except that the atoms and ions present in the sample are excited in high temperature gas
plasma. Since the plasma provides very high temperature and hence the energy, almost all
the atoms present in the sample can be excited with this technique ending up with high
efficiency (a hotter source increases both atomization efficiency and excitation efficiency).
Thus, the emissions from the atoms would be more intense and even very small
concentrations of metals/metal ions can be detected and accurately measured.
Instrumentation: This is basically an emission spectrometer comprising nebulizer, RF coil,
ICP Source (Argon plasma), monochromator, detector and recorder.
A plasma source or jet is a flame-like system of ionized, very hot flowing argon gas. At high
temperatures (≈ 6000 K) a gas such as argon will contain a high proportion of ions and free
electrons constituting plasma (This ionisation is initiated by “Tesla” coil). Additional energy
may be supplied to the electrons in the plasma by the application of an external
electromagnetic field through RF coil. By collisions between the electrons and other species
in the plasma this additional energy is uniformly distributed. As the collisions increase, the
energy transfer becomes more efficient, which leads to a substantial temperature
enhancement to a range of 8000 - 10000 K. It is the temperature at which the samples are
introduced and analysed.
Applications : Similar to atomic emission spectroscopy but it covers very widespread for both
qualitative and quantitative analysis of metals and some non-metals too, at trace levels.
Because of the high temperature and homogeneity of the source, it offers better signal
stability and hence the analytical precision. The technique when utilising an optical emission
detector is termed as Inductively Coupled Plasma – Optical Emission Spectrometer (ICP-
OES) and if it utilises a mass spectrometer (refer section 9.6) as detector then it is termed as
Inductively Coupled Plasma – Mass Spectrometer (ICP-MS).
Disadvantages: Samples require dissolution before analysis. Instrumentation is complex and
requires high operator’s skill and is very expensive.
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