Solution aerosols are injected into an inductively 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 nebulization of a typical solvent (1 percent HNO3 in H2O) consists mainly of ArH(+), Ar(+), H3O(+), H2O(+), NO(+), O2(+), HO(+), Ar2(+), Ar2H(+), and Ar(+2). The mass spectra of the trace elements studied consist principally of singly charged monatomic (M+) or oxide (MO+) ions in the correct relative 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 microgram per milliliter for those elements studied. This approach offers a direct means of performing trace elemental and isotopic determinations on solutions by mass spectrometry.