Question

Briefly describe why an ICP-ES is able to observe elemental information in the visible light range, which is normally associated with electronic transitions of bonding orbitals.

Answer 1

A convenient means of obtaining high temperatures required for ICP ES is to generate an inert-gas plasma. Plasma is a gaseous state of matter containing major concentrations of essential free electrons and highly charged ions. It is a very effective medium for volatilization and atomization (and ionization) of liquid droplets. When the aerosol droplets enter the hot area of the plasma they are converted into salt particles by desolvation. These salt particles are split into individual molecules that will subsequently fall apart to atoms and ions. Most elements get ionized very efficiently (> 90%). Almost no molecules and ground state atoms are present in plasma. In the plasma, even more energy is transferred to the atoms and ions, promoting the excitation of their electrons to higher energy levels. When these excited atoms and ions return to their ground state or to lower excitation states they will emit electromagnetic radiation in the ultra-violet/visible range of the spectrum. Each excited element emits specific wavelengths (λ), i.e. has a typical emission spectrum.