Dc Plasma Arcs for Elemental Analysis

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Abstract
The development of plasma arc devices as replacements for chemical combustion flames in trace element analyses by emission spectrometry is traced with particular emphasis on those devices in which the spectrometric observation is made in the non-current-carrying portion of the discharge or “plume.” The question of local thermal equilibrium in both the arc column and plasma plume is discussed and the dependence of temperature on experimental variables is considered in terms of a model. In addition to the temperature attained, the performance of various gas stabilized arcs and plasma jets is discussed with reference to interferences, background emission, limits of detection, and precision. Particular attention is paid to the problem of sample aerosol introduction into the high temperature plasma. The dc plasma arc at its present level of development is compared with the inductively coupled plasma for use as a source in emission spectroscopy.