INSTRUMENTAT/ON produce only pseudo-molecular ion species. This readily provides molecu lar weight information, but it also re quires CID or other techniques to pro duce structurally useful information. No reports of EI mass spectra via APIMS have appeared to date. Like any analytical technique, APIMS has both strengths and limita tions. We have focused on the many strengths of APIMS and the limited structural information that is available unless CID is used. There are various ways of gaining CID information from single analyzer mass spectrometers, in cluding accelerating voltages in the free-jet expansion region similar to the repeller effect in some thermospray systems. There is also the possibility for multiple mass spectrometric analy sis (MSn) with tandem MS, FT-MS, and ion trap MS systems. For example, it has been reported that electrospray ionization was implemented on an ion trap mass spectrometer (4) and on an FT-MS system (3). One problem with APIMS is the propensity to form low molecular weight cluster ion adducts that produce high chemical noise, which can interfere with the trace de tection of low molecular mass com
pounds (below 300 Da). Further devel opments will surely resolve this prob lem. We are optimistic about the future of APIMS. It has taken a long time for us to rediscover the analytical potential of this technique following the pioneering reports of Carroll, Dzidic, Horning, and Stillwell (34). The future is indeed bright as manufacturers scramble to produce their versions of APIMS and researchers explore exciting new ana lytical and bioanalytical applications for this technology. A quantum jump has occurred in the field of MS—one that should allow major analytical ad vances in areas most of us would have never imagined. T. E. Covey, A. P. Bruins, E. D. Lee, L. Weidolf, P. O. Edlund, and W. Muck contributed directly to instrumentation development and applications. We also thank the other members of the Equine Drug Testing and Toxicology Program for the unique environment and opportunities for carry ing out and applying our instrumentation develop ments. We acknowledge the following organiza tions that have made significant financial contri butions to this work: the U.S. Environmental Protection Agency, the U.S. Pood and Drug Ad ministration, the U.S. Department of Agriculture, Food Safety and Inspection Service, the Eastman Kodak Company, Sciex, Inc., and Immunobiology Research Institute.
References (1) Knewstubb, P. F.; Sugden, T. M. Na ture 1958,181, 474. (2) Sakairi, M.; Kambara, H. Anal. Chem. 1988,60, 774. (3) Wang, B. H.; Williams, E. R.; Henry, K.D.; McLafferty, F. W.; Shabanowitz, J.; Hunt, D. F. Proc. of the 37th ASMS Conference on MS and Allied Topics; Mi ami Beach, FL, May 21-26,1989. (4) Van Berkel, G. J.; Glish, G. L.; McLuckey, S. A. Anal. Chem. 1990, 62, 1284. (5) Proctor, C. J.; Todd, J. F. J. Org. Mass Spectrom. 1983,18, 509. (6) Carroll, D. I.; Stillwell, R. N.; Haegele7 K. D.; Horning, E. C. Anal. Chem. 1975, 47, 2369. (7) Mitchum, R. K.; Korfmacher, W. A. Anal. Chem. 1983,55,1485 A. (8) Wentworth, W. E.; Batten, C. F.; Desai, D. E. J. Chromatogr. 1987,390,249. (9) Siegel, M. W.; Fite, W. L. J. Phys. Chem. 1976,80,2871. (10) Kambara, H.; Kanomata, I. Mass Spectrosc. 1976,24, 229. (11) Kambara, H.; Kanomata, I. Mass Spectrosc. 1976,24, 271. (12) French, J. B.; Reid, Ν. Μ.; Buckley, J. A. U.S. Patent 4,121,099, Oct. 17,1978. (13) Thomson, Β. Α.; Iribarne, J. V. J. Chem. Phys. 1979, 71,4451. (14) Blakely, C. R.; Carmody, J. J.; Vestal, M. L. J. Am. Chem. Soc. 1980,102, 5931. (15) Yamashita, M.; Fenn, J. B. J. Phys. Chem. 1984,88,4451. (16) Fenn, J. B.; Mann, M.; Meng, C. K.;
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