Characteristics of secondary discharge at the interface region in helium ICP-MS

Summary form only given. Argon inductively coupled plasma has been successfully used as an ion source for mass spectrometry (Ar ICP-MS). 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 cannot generate substantial quantities of elements possessing high ionization energies, for example halogens. Major argon-related plasma species preclude the detection of /sup 40/Ca/sup +/, /sup 56/Fe/sup +/, /sup 80/Se/sup +/, which are the most abundant ions of Ca, Fe and Se. 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 nonmetals. Furthermore, helium is low mass (4 amu) and nearly mono isotopic abundance. To generate stable helium plasma in the atmospheric pressure, we designed and manufactured the enhanced vortex flow torch. A stable doughnut-type helium plasma can be produced when using 27 to 40 MHz RF input power that is larger than 500 W. The helium excitation temperature, 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.