Focus
The Affordable Alternative
freely, thus ensuring continuous expo sure of a fresh supply of sample mole cules to the primary beam for an ex tended period of time. FAB has proved especially valuable for the de tection of large involatile organic mol ecules. A third SIMS category, according to Honig, involves the use of primary ions with MeV-level energies that are generated from the spontaneous fis sion of Cf-252 nuclei or that are pro duced in tandem accelerators (Table I). Like FAB, Cf-252 plasma desorption MS (PDMS) and heavy-ion-in duced desorption MS have found con siderable application in the identifica tion of large involatile molecules. Photon beams, the fourth type of SIMS primary beam in Honig's classi fication scheme (Table I), are used in laser desorption MS, the latest com mercial versions of which are the Leybold-Heraeus laser microprobe mass analysis (LAMMA) instrument and the Cambridge laser-induced ioniza tion mass analyzer (LIMA). Laser de sorption has proved valuable for the analysis of microparticulates, among other applications.
Planetary research One of the most fascinating applica tions of MS to date has been in space exploration. Dozens of specially de signed mass spectrometers have al ready flown on U.S. and U.S.S.R. space probes, for atmospheric studies on Earth, Mars, and Venus, and to test for the possible presence of organ ic molecules in Mars surface soil. "Later in this decade," said Alfred 0 . Nier of the University of Minnesota, "a mass spectrometer will be included in the complement of instruments on the Galileo spacecraft to be launched on a mission designed to investigate the atmosphere of the planet Jupiter." Nier also recommended that MS be considered for use on comet probes: "While a fly-by mission to a comet could produce some useful scientific results," Nier said, "the time available would be limited. Accordingly, there is general agreement that a rendezvous mission would be highly desirable, since it would give time to make com prehensive measurements, including studies of the nucleus. Such a mission would certainly be a challenge for mass spectrometry." Stuart A. Borman
LSI
laser science, inc.
' 80 Prospect Street Cambridge, Massachusetts 0P139 (617) 868-4350ITT-TLX 443-0136
CIRCLE 127 ON READER SERVICE CARD
1276 A · ANALYTICAL CHEMISTRY, VOL. 56, NO. 12, OCTOBER 1984
References (1) Hurst, G. S. et al. Rev. Mod. Phys. 1979,57,767-77. (2) Kimock, F. M.; Baxter, J. P.; Winograd, N. Nucl. Instr. Meth. 1983, 218, 287-92 (3) Becker, C. H.; Gillen, Κ. Τ. Anal. Chem. 1984,56,1671-74.
