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-specific and has produced detection limit improvements as high as a factor of 10 in the set studied. In the axial viewing mode the incandescent cup does not contribute to an increased background; however, the background and subsequent background noise levels are increased for most elements. Carrier gases were introduced into the cup via a hollow stem resulting in a reduction in the background signal, notably in the longer wavelength region. When 1000 ppm Freon-12 in argon is used as a carrier through the center of the cup, the normally problematic refractory elements are vaporized easily. Modifications and improvements to the design of the direct sample insertion device are also discussed.