Electrostatic probe measurements of electron temperature and number density in helium ICP-MS interface region

Summary form only given. Argon inductively coupled plasma mass spectrometry (Ar ICP-MS) has become the most powerful technique for elemental analysis, and spread quickly all over the world. However, it is considered that the efficient detection capabilities of Ar ICP offered for most metals are not realized for elements such as halogens. If helium ICP is used, it is possible to ionize all the elements except neon because helium has a larger metastable excitation energy (19.81 eV) than argon and the largest ionization energy among all elements. We successfully generated stable helium plasma at the atmospheric pressure using the enhanced vortex flow torch for practical He ICP-MS use. However, the mass analysis device for Ar ICP-MS is not appropriate for He ICP-MS, since the properties (ionization energy, coefficient of kinematic viscosity and etc.) of helium and argon are quite different and a secondary discharge is remarkable in the interface region. A secondary discharge was overcome for Ar ICP by applying several control methods. However, these methods were not effective for He ICP. Therefore, to find other method for controlling the secondary discharge, it is necessary to clarify characteristics of the secondary discharge. We measured the plasma characteristics (electron temperature, electron number density and etc.) with electrostatic probes in He ICP-MS interface region.