AXIAL VIEWING AND MODIFIED CUP DESIGN FOR DIRECT SAMPLE INSERTION INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

Axial viewing generally provides an advantage over lateral viewing of the plasma for direct sample insertion. The signal change is element-s pecific and has produced detection limit improvements as high as a fac tor of 10 in the set studied. In the axial viewing mode the incandesce nt cup does not contribute to an increased background; however, the ba ckground and subsequent background noise levels are increased for most elements. Carrier gases were introduced into the cup via a hollow ste m resulting in a reduction in the background signal, notably in the lo nger wavelength region. When 1000 ppm Freon-12 in argon is used as a c arrier through the center of the cup, the normally problematic refract ory elements are vaporized easily. Modifications and improvements to t he design of the direct sample insertion device are also discussed.