A mass spectrometer in which atoms from a 0.1-mm2 surface of a target are sputtered and ionized under bombardment by a beam of inert-gas ions has been perfected. To exploit the capabilities of this analytical tool for the detection of trace elements in solids, a drastic reduction of the instrumental background had to be achieved. This was accomplished by using spectroscopically pure structural material in the ion source and by eliminating all sources of hydrocarbons. In particular, since the presence of pump-oil contamination on the surface under analysis was readily detectable, the resulting cracking pattern obscured a large portion of the atomic-mass scale. A combination of liquid-nitrogen-trapped mercury diffusion pumps, zeolite sorption pumps, and sputter-ion pumps has reduced the instrumental background sufficiently to facilitate the routine parts-per-billion trace analysis of the surface and of the bulk of conducting and nonconducting solids.