Fundamental description of spectrochemical inductively coupled plasmas

For the determination of the optimum conditions for spectrochemical analysis with plasmas a simple and yet accurate description of the plasma state is essential. In this paper, which should be regarded as a review of earlier and more recent work, non-equilibrium modelling of slowly flowing atmospheric ICPs and experimental results are described. The results of modelling are in fair agreement with experimental values from the literature, in particular for lower excitation frequencies. However, for high frequencies the model plasmas tend to remain too close to the wall. It is concluded that even in argon plasmas, dissociative recombination of molecular ions gives an additional recombination route close to the wall, where the neutral ground state density is high and the temperature low. Results of experimental analysis by active and passive spectrometry are given. In addition, the possibilities inherent in time-dependent studies, such as in power interruption experiments, are indicated. The processes of droplet evaporation and analyte excitation and ionization are also summarized. The virtues of the ICP for spectrochemical analysis are briefly discussed.