Atomic Emission Spectroscopy

atomizer becomes source of excitation as well as atomization

plasmas are the most widely used sources - usually Ar

inductively coupled plasma source

  • 3 concentric quartz tubes through which Ar gas flows
  • top of the torch is surrounded by water-cooled induction coil powered by RF generator
  • plasma is composed of highly energetic ionized inert gases which is electrically conductive and interacts with the fluctuating magnetic field
  • high temperatures and a longer residence time result in more thorough atomization than AAS and less chemical interferences
  1. argon gas is swirled through torch
  2. RF power is applied to the induction coil inducing an electromagnetic field
  3. ionization of the argon gas is initiated via spark of tesla coil
  4. ions and electrons produced now interact with magnetic field
  5. nebulizer flow carried the sample into the plasma
  • axial viewing - longer path length, higher radiation intensity, higher precision, lower detection limits… requires removal of cool plasma rail to limit chemical interferences, and more susceptable to thermal and contaminant degradation of optical components
  • radial viewing - viewing from the side decreases chemical interferences and matrix effects from the plasma tail… smaller path length, so lower intensity and sensitivity

sample introduction into the plasma: either concentric tube or cross-flow nebulizer

  • liquid or solid samples can also be introduced into plasma via electrothermal vaporization where vapour is formed on an open graphite rod before being pushed to torch by gas - this allows microsampling and low detection limits

sequential instruments: move through emission lines individually, requiring time at each wavelength

  • often use holographic grating with rotation which leads to high sample consumption

simultaneous multichannel instruments: performs multi-wavelength determination via a polychromator or spectrograph

  • 50-60 elements can be analyzed at once, but requires a longer time to get enough intensity so this is a time consuming technique that leads to a lot of sample consumption

advantages of AES

  • lower susceptibility to chemical interferences due to higher operating temperature than AAS
  • easily quantitate refractory elements
  • single excitation conditions can be used for a wide range of elements
  • simultaneous emission spectrum recording
  • determination of nonmetals
  • increased linear range

disadvantages

  • increased spectral interferences due to quantity of emission lines produced by plasma
  • requires higher resolution instrumentation to differentiate atomic lines
  • more expensive then AAS
  • requires higher operator skill

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