Local thermodynamic equilibrium modeling of ionization of impurities in argon inductively coupled plasma

Essentially higher ionization degree of small concentrations of elements in inductively coupled plasma in comparison to the ionization of pure elements is emphasized. This conclusion is used to determine the relative dependence of the sensitivity of the inductively coupled plasma mass spectrometer on the atomic mass. The possibility of evaluation of the ionization temperature and electron density from mass spectrometric signals is proposed. Temperatures about 7000 K and 8000 K were obtained from the ionization ratio dependences on ionization potentials. Electron densities of the order of magnitude 1015 cm− 3, in excess to the local thermodynamic equilibrium values, follow from the application of the Saha equation to the measurement results and indicate the recombining character of the plasma in the mass spectrometer measurement region. Effects due to additional ionization from matrix were discussed. The effect is largest on minor abundant ionization state components. Matrix effect is restricted to some temperature interval, which depends on the whole matrix composition and the plasma state. The results show that the local thermodynamic equilibrium modeling, if adequately matching the sample composition, can be useful as a quantitative basis for both description of the plasma state and indication of the character of the nonequilibrium effects.