DC arc excitation — is it obsolete?

Abstract

The significance of direct current arc plasmas as radiation sources for optical emission spectroscopy is discussed. Their development is discussed in view of the other radiation sources such as flames, discharges under reduced pressure and high-frequency plasmas. It is shown, that the wall-stabilized arc as one of the current-carrying DC-plasma arcs is also today still of use, for instance, for the analysis of powder samples. Transferred arc plasmas also include a series of plasmajets of which the three-electrode DC arc plasma (DCP) is commercially available. The significance and use of these arc discharges are compared with those of other radiation sources such as the inductively coupled plasma (ICP) and the glow discharge lamp, by means of the number of publications made in the course of time. For the analysis of solid samples, DC arcs can be universally used; they have high power of detection and are simple and therefore cannot, up to now, be replaced. Because of the low investment and operation costs, the DCP is a viable alternative to the ICP for the analysis of solutions. Furthermore, the power of detection of the DCP is comparably high and is in some cases, because of the high tolerable salt concentrations, even higher than in the case of the ICP. Matrix effects, however, are high in the case of DCP, due to varying concentrations of easily ionized elements. The capabilities of high power arcs with respect to lower matrix effects and a possible increase of the dynamic range by use of different lines of the elements to be determined are discussed. It is also claimed that the availability of different commercial DC arc systems is prerogative for their further development.