large molecules. T h e promise of selectivity in MPI techniques, when extended to larger, more complex molecules, is hampered by their lack of volatility, interferences from nonresonant ionization of other species in the mixture, and the fact that molecules with many functional groups will have many broad, overlapping absorption bands. On the other hand, analytical methods that have traditionally relied on thermal ionization reap some immediate benefits from the R I M S techniques. As an analytical technique, laser desorption finds itself in competition with the particle beam techniques, particularly with fast atom bombardment (75), which is compatible with high-resolution, high-mass magnetic scanning instruments. However, it is well-known that desorption methods are also somewhat complementary (76), and the pulsed laserT O F configurations, which collect all of the ions transmitted to the analyzer, may provide better sensitivity (77). Finally, two-laser systems, which combine desorption with multiphoton ionization, may be anticipated. T h e desorption laser will provide species in the gas phase that have not as yet been subjected to resonance techniques, while the multiphoton beam can be used to ionize the large quanti-
ty of desorbed neutrals or to induce fragmentation for structural analysis.
Acknowledgment T h e author acknowledges the helpful discussions on R I M S with Jack Fassett, the continued dialogue on "collective processes" in laser desorption with Franz Hillenkamp, and the contributions in the laboratory by Jean-Claude Tabet. This work was supported by a grant, CHE-80-16440, from the National Science Foundation.
References (1) Berkowitz, J.; Chupka, W. A. J. Chem. Phys. 1964,40,2735. (2) Lincoln, K. A. Anal. Chem. 1965, 37, 541. (3) Knox, B. E.; Vastola, F. J. Laser Focus 1967,3,15. (4) Vastola, F. J.; Pirone, A. J.; Giver, P. H.; Dutcher, R. R. In "Spectrometry of Fuels"; Friedel, R. A., Ed.; Plenum Press: New York, N.Y., 1970; pp. 29-36. (5) Fenner, N. C; Daly, N. R. J. Mater. Sci. 1968, 3, 259. (6) Eloy, J. F. Méthodes Phys. Anal. 1968, 5,161. (7) Wiley, R. H.; Veeravagu, P. J. Phys. Chem. 1968, 72, 2417. (8) Hillenkamp, F.; Unsold, E.; Kaufmann, R.; Nitsche, R. Nature 1975,256,119. (9) Vastola, F. J.; Mumma, R. O.; Pirone, A. J. Org. Mass Spectrom. 1970,3,101. (10) Conzemius, R. J.; Capellen, J. M. Int. J. Mass Spectrom. Ion Phys. 1980,34, 197.
Weve made the transitions easier (and more sensitive). We've always been.proud of the ability of our Ion Chromatography systems to analyze transition metals at a level of sensitivity and convenience comparable to, and in many cases better than, AA and iCR But we still weren't completely satisfied. So we developed the lonPac ''Membrane Reactor for our Series 20001 Ion Chromatographs'that not only makes transition metal analysis many times easier, it also provides a five-foki increase in
Gail or write Dionex for information anc applications; notes or? our now Membrane Reactor. We H show vou how easy and
Dionex Corpoiation - Vi. Sunnyvale, ΠΛ 04006 • (4C
DI O N E X
"Π Η Ε: Ι Ο Ν EXPERTES
CIRCLE 46 ON READER SERVICE CARD 502 A · ANALYTICAL CHEMISTRY, VOL. 56, NO. 3, MARCH 1984
(11) Callomon, J. H.; Dunn, T. M. Mills.; I. M. Philos. Trans. R. Soc. London A 1966.259, 499. (12) Johnson, P. M. J. Chem. Phys. 1975, 62,4562. (13) Johnson, P. M. J. Chem. Phys. 1976, 64, 4143. (14) Honig, B.; Jortner, J.; Szoke, A. J. Chem. Phys. 1967,46,2714. (15) Amirov, Α.; Even, U. Jortner, J. J. Chem. Phys. 1979, 71,2319. (16) Blakley, C. R.; Carmody, J. J.; Vestal, M. L. J. Am. Chem. Soc. 1980,102, 3931. (17) Ciupek, J. D.; Zakett, D.; Cooks, R. G.; Wood, K. V. Anal. Chem. 1982,54, 2215. (18) Zandee, L.; Bernstein, R. B. J. Chem. Phys. 1979, 70, 2574. (19) Lichtin, D. Α.; Datta-Ghosh, S.; New ton, K. R.; Bernstein, R. B. Chem. Phys. Lett. 1980, 75, 214. (20) Cooper, C. D.; Williamson, A. O.; Mil ler, J. C ; Compton, R. N. J. Chem. Phys. 1980 73 1527 (21) BOesl', U.; Neusser, H. J.; Schlag, E. W. J. Chem. Phys. 1980, 72, 4327. (22) Reilly, J. P.; Kompa, K. L. J. Chem. Phys. 1980, 73, 5468. (23) Lichtin, D. Α.; Bernstein, R. B.; Vaidu, V. J. Am. Chem. Soc. 1982,104, 1831. (24) Roboz, J. "Mass Spectrometry: In strumentation and Techniques"; WileyInterscience: New York, N.Y., 1968; p. 141. (25) Rockwood, S. D.; Reilly, J.; Hohla, K.; Kompa, K. L. Opt. Commun. 1976,28, 4490. (26) Seaver, M.; Hudgens, J. W.; DeCorpo, J. J. Int. J. Mass Spectrom. Ion Phys. 1980,34,159. (27) Wiley, W. C ; McLaren, I. H. Reu. Sci. Instrum. 1955,26,1150. (28) Boesl, V.; Neusser, H. J.; Weinkauf, R.; Schlag, E. W. J. Phys. Chem. 1982, 86,4857. (29) Irion, M. P.; Bowers, W. D.; Hunter, R. L.; Rowland, F. S.; Mclver, R. T., Jr. Chem. Phys. Lett. 1982,93,375. (30) Carlin, T. J. Freiser, B. S. Anal. Chem. 1983,55,955. (31) Hurst, G. S.; Payne, M. G.; Kramer, S. D.; Young, J. P. Reu. Mod. Phys. 1979, 57,767. (32) Hurst, G. S.; Nayfeh, M. H.; Young, J. P. Phys. Reu. A 1977,15, 2283. (33) Hurst, G. S.; Nayfeh, M. H.; Young, J. P. Appl. Phys. Lett. 1977,30, 229. (34) Hurst, G. S.; Payne, M. G.; Kramer, S. D.; Chen, C. H. Phys. Today, Septem ber 1980, p. 24. (35) Miller, C. M.; Nogar, N. S. Anal. Chem. 1983,55,481. (36) Donohue, D. L.; Young, J. P.; Smith, D. H. Int. J. Mass Spectrom. Ion Phys. 1982 43 293 (37) Young, J. P.; Donohue, D. L. Anal. Chem. 1983,55,88. (38) Fassett, J. D.; Travis, J. C; Moore, L. J.; Lytle, F. E. Anal. Chem. 1983,55, 769. (39) Kramer, S. D.; Bemis, C. E., Jr.; Young, J. P.; Hurst, G. S. Opt. Lett. 1978,3,16. (40) McGilvery, D. C; Morrison, J. O. Int. J. Mass Spectrom. Ion Phys. 1978,28, 81. (41) Mukhtar, E. S.; Griffiths, I. W.; Har ris, F. M.; Beynon, J. H. Int. J. Mass Spectrom. Ion Phys. 1981,37,159. (42) Griffiths, I. W.; Mukhtar, E. S.; Har ris, F. M.; Beynon, J. H. Int. J. Mass Spectrom. Ion Phys. 1981,38,333. (43) Mukhtar, E. S.; Griffiths, I. W.; March, R. E.; Harris, F. M.; Beynon, J. H. Int. J. Mass Spectrom. Ion Phys. 1981,41,61. (44) Mukhtar, E. S.; Griffiths, I. W.; Har ris, F. M.; Beynon, J. H. Int. J. Mass Spectrom. Ion Phys. 1982,42, 77. (continued on p . 504 A)
