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electrophoresis or ion chromatography. A significant step toward this goal was the recent development of a coronaspray ionization source for IMS (13). By introducing the effluent from a liq uid stream into the spectrometer via an electrically charged capillary, ion mo bility spectra from nonvolatile neutral and ionic compounds dissolved in liq uids have been obtained (29, 30). Al though simple liquid chromatographic separations have been reported (29), some difficult operational problems re main. Reactant ions and analyte re sponse factors vary considerably with small changes in geometry of the coronaspray source. Also, the high tempera tures and high drift gas flow rates need ed to break up solvent clusters have led to problems with sample decomposi tion, corona instability, and detector noise. The considerable practical potential of IMS for monitoring applications re mains largely untapped, in spite of its high sensitivity, low cost, small size, and versatility. This lack of develop ment is largely a result of initial dis couragement caused by overload and matrix problems. It must be recognized that IMS functions best with trace lev els of analytes that make only minor perturbations of drift tube conditions. Each application presents challenges such as analyte sensitivity and volatili ty as well as matrix interferences, and must be considered individually. The powerful techniques of preseparation by membranes, selective adsorption, and chromatographic inlets coupled with reactant ion modifications are helpful in many cases. Some fundamental problems remain in developing IMS. The resolving pow er of existing instruments seems to be less than expected on the basis of diffu sion and initial pulse width (55), and the reason for this is not understood. The extra broadening may be attribut able to ion-molecule reactions in the drift space, inhomogeneity of the elec tric field, or even coulombic repulsion. The FT mode should be able to probe reactions in the drift space, but it has not yet been used for this purpose. Oth er detection modes, such as an organophosphorus selective configuration that would simulate the nitrogen/phos phorus detector (56), have been pro posed but not yet implemented. Final ly, recent articles on peak shape analy sis (55) and a second-derivative algo rithm for separation of overlapping peaks (57) are reminders that several powerful signal-processing techniques are not fully used in IMS. Although IMS is considered an old technology, in many ways it is new technology waiting to be discovered. Its
1208 A · ANALYTICAL CHEMISTRY, VOL. 62, NO. 23, DECEMBER 1, 1990
low detection limits and simplicity of design assure IMS a strategic position in analytical chemistry between uni versal nonspecific detectors, such as flame ionization and electron capture, and the more powerful qualitative techniques, such as MS. IMS research in the authors' laboratory has been sponsored in part by a grant from the Public Health Service (GM29523). The authors are most grateful to Glenn E. Spangler for his careful critical reading of this manuscript and many helpful suggestions.
References (1) Karasek, F. W. Anal. Chem. 1974, 46, 710 A-717 A. (2) Carroll, D. I.; Dzidic, I.; Stillwell, R. N.; Horning, E. C. Anal. Chem. 1975, 47, 1956-59. (3) Shumate, C; St. Louis, R. H.; Hill, H. H., Jr. J. Chromatogr. 1986, 373, 14173. (4) Karasek, F. W.; Kane, D. M. J. Chroma togr. Sci. 1972,10, 673-77. (5) Griffin, G. W.; Dzidic, I.; Carroll, D. I.; Stillwell, R. N.; Horning, E. C. Anal. Chem. 1973,45,1204-09. (6) Karasek, F. W.; Hill, Η. Η., Jr.; Kim, S. H.; Rokushika, S. J. Chromatogr. 1977, 135 329-39. (7) Karasek, F. W.; Spangler, G. E. In Elec tron Capture: Theory and Practice in Chromatography; Zlatis, Α.; Poole, C. F., Eds.; Elsevier: Amsterdam, 1981; Chapter 15, pp. 377-406. (8) Bairn, Μ. Α.; Hill, Η. Η., Jr. Anal. Chem. 1982,54, 38-43. (9) Bairn, Μ. Α.; Eatherton, R. L.; Hill, Η. Η., Jr. Anal. Chem. 1983, 55, 1761-66. (10) Lubman, D. M; Kronick, M. N. Anal. Chem. 1982,54,1546-51. (11) Kolaitis, L.; Lubman, D. M. Anal. Chem. 1986, 58, 1993-2001. (12) Spangler, G. E.; Kim, S. H.; Epstein, J.; Campbell, D. N.; Carrico, J. P., Jr. Pro ceedings of the 1988 CRDEC Scientific Conference on Chemical Defense Re search; CRDEC: Aberdeen Proving Ground, MD, 1988; U.S. Patent 4 839 143, June 13,1989; U.S. Patent 4 928 033, May 22 1990. (13) 'Shumate, C. B.; Hill, Η. Η., Jr. Anal. Chem. 1989,61, 601-06. (14) Carr, T. W. Anal. Chem. 1979,51, 70511. (15) Proctor, C. J.; Todd, J. F. Anal. Chem. 1984,56,1794-97. (16) Lawrence, A. H.; Neudorfl, P. Anal. Chem. 1988,60,104-09. (17) Spangler, G. E.; Carrico, J. P.; Camp bell, D. N. J. Test. Eval. 1985,13(3), 23440. (18) Kim, S. H.; Karasek, F. W. Anal. Chem. 1977,50,152-55. (19) Spangler, G. E.; Campbell, D. N.; Car rico, J. P. Presented at the 1983 Pitts burgh Conference and Exposition on An alytical Chemistry, Atlantic City, NJ, March 1983; U.S. Patent 4 551 624, No vember 5,1985. (20) Revercomb, H. E.; Mason, E. A. Anal. Chem. 1975,47, 970-83. (21) Lubman, D. M. Anal. Chem. 1984, 56, 1298-1302. (22) Preston, J. M.; Rajadhyax, L. Anal. Chem. 1988,60, 31-34. (23) Spangler, G. E.; Cohen, M. J. In Plas ma Chromatography; Carr, T. W., Ed.; Plenum Press: New York, 1984; p. 6. (24) Carrico, T. F.; Sickenberger, D. W.; Spangler, G. E.; Vora, K. N. J. Phys. E.
