The effects of a torch shield on performance of the vacuum interface of an inductively coupled plasma mass spectrometer

Abstract

The effects of a torch shield on the performance of a vacuum interface for an inductively coupled plasma mass spectrometer (ICP-MS) have been studied by laser excited atomic and ionic fluorescence. A metallic shield was inserted between the torch and load coil of the ICP, which was alternately grounded and floated. Relative ion and atom densities upstream from the sampling cone and downstream from the tip of the skimmer cone of the interface were determined by laser excited fluorescence. Doppler shifts in the excitation spectra were used to determine ion and atom velocities inside the skimmer cone. Pb atoms, Ba and Sc ions, and Ar metastable atoms were used as the probe species. The shield had no measurable effect on the densities of the probe species upstream from the sampling cone. Inside the skimmer cone, the densities of all probe species dropped significantly when the shield was floated. No changes were observed in the velocities of the probe species as the shield was floated and grounded.