Production of helium ICP-MS system for detection of higher ionization energy elements

Summary form only given. Argon inductively coupled plasma mass spectrometry (Ar ICP-MS) is a multielement technique with excellent detection limits and the added ability to provide isotopic information. However, the use of argon as a plasma gas has some limitations. The argon plasma does not generate substantial quantities of elements possessing high ionization energies. To overcome these problems of Ar ICP-MS, He ICP-MS device was developed. Because the ionization energy of He (24.6 eV) is higher than that of Ar (15.8 eV), the use of He ICP as an ion source for MS has potential of enhancing the degree of ionization for every element, in particular for non-metals. By utilizing flow visualization along with a spark-tracing method, it was found that with a conventional torch for Ar ICP an adequate helium gas vortex flow to sustain a stable plasma could not be formed. To generate stable helium plasma, we designed and manufactured the enhanced vortex flow torch. A stable doughnut-type helium plasma can be produced when using 21/spl sim/40 MHz RF input power that is larger than 500 W. The helium excitation temperature, OH rotational temperature and electron number density are 4100 K, 2200 K and 0.75/spl times/10/sup 14/ cm/sup -3/ respectively at 900 W of RF input power. Significant increase in electron number densities but decreases in rotational temperatures were observed, upon increased introduction of carrier gas. The experimental results suggest that the local thermodynamic equilibrium (LTE) is not consistent.