Inductively Coupled Argon Plasma as an Ion Source for Mass Spectrometric Determination of Trace Elements

Solution aerosols are injected into an inductlvety coupled argon plasma (ICP) to generate a relatively high number density of positive ions derived from elemental constituents. A small fraction of these ions is extracted through a sampling orifice into a differentially pumped vacuum system housing an ion lens and quadrupole mass spectrometer. The positive ion mass spectrum obtained during nebullration of a typical solvent (1 % HNO, in H20) consists mainly of ArH', Ar', H30+, H20+, NO', 02', HO+, Ar2', Ar2H+, and Ar2+. The mass spectra of the trace elements studied consist principally of singly charged monatomic (M') or oxide (MO') ions in the correct relatlve isotopic abundances. Analytical calibration curves obtained in an integration mode show a working range covering nearly 4 orders of magnitude with detection limits of 0.002-0.06 pg/mL for those elements studied. This approach offers a direct means of performing trace elemental and isotopic determinations on solutions by mass spectrometry.