A status report on helium inductively coupled plasma mass spectrometry

The current status of helium inductively coupled plasma - mass spectrometry (He ICPMS) is examined, its potentials and limitations are reviewed, and a summary of fundamental properties of atmospheric pressure He ICP discharges is presented. Also included are results of He ICPMS studies with a new helium plasma torch (18 mm i.d.) operated at four sets of operating conditions. Under the "cold plasma" condition (600 W forward power), no secondary discharge is observed and ion kinetic energies ranging from 2.0 eV to 9.5 eV for 6 elements (mass range: 39-208) are measured. At higher power levels, the secondary discharge still is strong. In general, detection limits for certain elements are improved by 1-3 orders of magnitude compared to previous data acquired in 1993 with a 13-mm He ICP torch. Elements such as K, Fe, Cr, Mn, Ni, and Co that suffer from spectral interferences in Ar ICPMS can be detected at pg/mL-levels with an analogue detector and a prototype ICPMS instrument having no photon stops or obstacles present in the ion trajectory path.