A direct-current arc plasma generator is described which uses a concentric electrode configuration and a magnetic field parallel to the electrode axis to obtain rotation of the arc current channel at a frequency in the 1–3 kHz range. The anode is a hollow graphite cylinder, and the cathode is a thoriated tungsten wire. A magnetic field of several hundred gauss is obtained from one or more ring-shaped permanent ceramic magnets. For a 5-mm anode diameter, the plasma is diffuse, and the current channel has the form of a thin radial sheet which undergoes relatively small periodic perturbations at the rotational frequency. Design features, performance data, and plasma structure are considered.

A direct-current arc device using coaxial electrodes and an external magnetic field is combined with a glass-frit nebulizer for the analysis of metallic elements in aqueous samples. The magnetic field is applied parallel to the electrode axis to produce a magnetron-type rotation of the arc current channel. The resulting plasma is diffuse and is more easily penetrated by the aerosol particles. The plasma is viewed normal to its axis at one end of the cylindrical electrode assembly. The intense continuum background from the current channel is masked by withdrawing the center electrode into the outer cylindrical electrode. The effects of electrode configuration and plasma current on analysis line-to-background ratios are described. Preliminary analytical data are presented for Cu, Mn, Mg, and Ca.

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The magnetic field produced by a pair of electromagnets is used to alter the shape and location of the current channel in a two-electrode direct-current plasma (DCP) designed for solution aerosol analysis. 'Ihe magnetic field B is oriented normal to the electric field E in the plasma. This results in an E-cross-B (E x B) drift motion of plasma electrons. Experiments are described using both cw and oscillating magnetic fields. With continuous wave (cw) fields of 10-20 G, the current channel can be shaped to improve sample aerosol penetration. Oscillating fields in the frequency range 25-500 Hz cause the current channel to oscillate. At the higher frequencies, the current channel loses its discrete character and the plasma becomes more diffuse.

The effects of the concomitant species Li, K, and Zn on analyte emission line intensities from a magnetron rotating direct-current arc plasma are described. The arc plasma has the form of a radial current sheet which completely covers the end of the graphite anode. The sample vapor from a graphite furnace is forced to pass through the current sheet. The presence of an easily ionized element (EIE) does not significantly alter the sample/plasma interaction. Large increases in emission intensities from both neutral-atom and ion lines of the analyte are observed in the presence of K or Li. This is probably the result of increased electron density in the plasma tail flame. Concomitant species which are not easily ionized have a smaller effect on analyte emission intensities, and either intensity enhancement or suppression effects are observed. Significantly lower detection limits are obtained in the presence of an EIE.