AN IMPROVED MICROWAVE PLASMA TORCH FOR ATOMIC SPECTROMETRY

The analytical performance of a microwave plasma torch was improved th rough mechanical alterations. Several problems reported in earlier des igns were addressed: the ignition and stabilization of a helium plasma in the MPT was difficult; high powers were required to both ignite an d operate the plasma; otherwise, the plasma would erratically change f rom an annular to a filament type discharge. In the new torch, the hel ium discharge was stabilized by replacing the copper central tube with one made of quartz. In addition, air entrainment was alleviated throu gh use of a sheathing gas. This modification simplified the background mass spectrum and raised the effective ionization temperature of the discharge. A detailed schematic diagram of the new microwave plasma to rch is presented. (C) 1997 Elsevier Science B.V.