1004
Anal. Chem. ISSO,62, 1804-1808
been directed toward the development of the quantitative methodology.
(9) Sturaro, A.; Doretti, L.; Parvoll, G.; Cecchinato, F.; Frlson, G.; Trakli, P. Biomed. Environ. Mass Spectrom. 1889, 78, 707. (IO) Langvardt, P. W.; Brzak, K. A.; Kastl, P. E. Proceedings of the 34th
CONCLUSIONS The results here clearly illustrate the ability of flow injection sampling with membrane introduction mass spectrometry to be used to monitor and quantify the major products and the metabolites of Bacillus polymyxa and Klebsiella oxytoca fermentations. It has been shown that membrane introduction mass spectrometry can provide continual on-line quantification of the liquid-phase products of comparable quality to off-line gas chromatography. Furthermore, it has been demonstrated that mass spectrometry is an excellent method for monitoring the dissolved gases and off-gases in these fermentations. The results also show that membrane introduction tandem mass spectrometry can enable one to detect the presence of trace metabolites.
Annual ASMS Conference on Mass Spectrometry and Allied Topics, Cincinnati, OH, June 1986. (11) Reuss, M.; Plehl, H.; Wagner, F. Eur. J . Appl. Microbiol. 1975, 7 .
ACKNOWLEDGMENT The help of J. Williams, K. Cox, and R. Jullian in preparing this document is acknowledged. Registry NO. 02,7782-44-7;COP,124-38-9;acetic acid, 64-19-7; acetoin, 513-86-0; 2,3-butanediol, 513-85-9;ethanol, 64-17-5. LITERATURE CITED (1) Riebe, M. T.; Eustace, E. H. Anal. Chem. 1990, 62, 65A. (2) Ruzicka, J.; Hansen, E. H. Anal. Chlm. Acta 1988, 779, 1. (3) Cooks, R. G.; Bier, M. E.; Brodbelt. J. S.; Tou, J. C.; Westover, L. B. U S . Patent 4,791,292,1989. (4) Hoch, G.; Kok, B. Arch. Blochem. Biophys. 1983, 707, 160. (5) Llewellyn, P. M.; Lmlejohn, D. P. U S . Patent 3,429,105,1969. (6) Westover, L. 6.; Tou, J. C.; Mark, J. H. Anal. Chem. 1974, 46, 568. (7) Weaver, J. C.; Abrams, J. H. Rev. Sci. Inshum. 1979, 50, 478. (8) Dheandhanoo, S.;Dulak, J. Rapid Common. Mass Spectrom. 1989,
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RECEIVED for review February 20, 1990. Accepted May 14, 1990. Support from the National Science Foundation (EE 7-87 12867) is acknowledged. Support from the Emil Aaltonen Foundation and Suomen Kulttuurirahasto is acknowledged
(T. K.).
Variations in Detection Efficiency of Halobenzenes Studied by Using Gas ChromatographylLaser Ionization Mass Spectrometry: Correlation with Excited-State Lifetimes Charles W. Wilkerson, Jr.,l and James P. Reilly*
Department of Chemistry, Indiana University, Bloomington, Indiana 47405
Fluoro-, chloro-, bromo-, and lodobenzene are studied wRh gas chromatographyAaser Ionization mass spectrometry. Picosecond llght pulses are found to be much more effective at lonirlng the heavier halogenated species (Cl, Br, and I ) than are nanosecond pulses. I n a separate experiment, the S, exclted-state IHetlmes of these species are measured by uslng pkosecond pump-probe laser Ionization mass spectrometry. The variation of the observed ilfetlmes expialns the GC/MS results.
INTRODUCTION The laser multiphoton ionization efficiency of a molecule is a function of a number of parameters, and it is necessary Current address: Los Alamos National Laboratory,Los Alamos, NM 87545.
to understam. them if laser ionization techniques are to become viable tools for quantitative analysis. Arguably, the two molecular characteristics that most influence laser-induced ion yield are the ground-state absorption cross section and the lifetime of the intermediate electronic state that is initially excited. Laser ionization is significantly more efficient if it proceeds through a resonant state, and currently available lasers can be tuned to absorption features of many molecules. Nevertheless, different types of transitions are characterized by different line strengths, and each exhibits an absorption contour over which the cross section can vary significantly. If a species has a radiative lifetime that is very short compared to the laser pulse duration, it may relax after excitation and not be ionized. Pulsed lasers used in most laser ionization experiments have multinanosecond durations. Therefore, molecules with subnanosecond lifetimes can be difficult, if not impossible, to detect (1-6). This problem can be solved by employing laser pulses that are at least as short as the excited-state lifetime. We have recently reported an improve-
0003-2700/90/0362-1804$02.50/00 1990 American Chemical Society
p
ANALYTICAL CHEMISTRY, VOL. 62, NO. 17, SEPTEMBER 1, 1990
molecule benzene fluorobenzene chlorobenzene bromobenzene iodobenzene
MW, amu
IP," eb (266 eV nm)
78 9.25 96 9.20 112.5 9.06 157 8.98 204 8.69
GC/MS concn, pg/mL
10
5.1
250 150 200 500
6.2 7.3 10.1 13.3
i n
nl
Table I. Selected Properties of Halobenzenes lifetime: ps 5500 600 30
