analytical chemistry July 1975, Vol. 47, NO. 8 Editor: HERBERT A. LAITINEN EDITORIAL HEADQUARTERS 1155 Sixteenth St N.W. Washington, D.C:’20036 Phone: 202-872-4600 Teletype: 710-8220151 Managing Editor: Josephine M. Petruzzi Associate Editor: Andrew A. Husovsky Editorial Assistants: Barbara Cassatt, Deborah M. Cox GRAPHICS AND PRODUCTION STAFF Manager: Leroy L. Corcoran Associate Manager: Charlotte C. Sarre Art Director: Norman W. Favin Artist: Linda McKnight Assistant Editor: Nancy J. Oddenino EDITORIAL PROCESSING DEPARTMENT, EABTON,P A . Associate Editor: Elizabeth R. Rufe AnvrsoRY BOARD:Allen J. Bard, David F. Roltz. E. G. Ekame. Richard P. Buck. Jr -War;en B; Crurnmett M. A. Evenson A.*’F. Findeis Kenneth W. Gardiner, J a c i M. Gill, RoLert A. Hofatader, Marjorie G. Horning. R. S. Juvet. 31.. Walter C. McCrone, Oacar Menis, Eugene Sawicki INSTRUMENTATION ADVISORY PANEL: Stank R Crouch Robert W Hannah J. J. d r k l a n d Ronhld H. Laesiig, Marvid Margoshes, darold M. McNair, David Seligson, R. K. Skogerboe, Donald E. Smith Contributing Editor: Claude A. Lucchesi Department of Chemistry. Northwestern University, Evanston, 111. 60201 Published by the AMERICAN CHEMICAL SOCIETY 1155 16th Street, N. W. Washington, D.C. 20036
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Analysis of Complex Mixtures An increasing number of analytical problems involve samples containing hundreds of components, even though relatively few of these components may be of concern. Familiar examples include the analysis of biological fluids such as blood plasma or urine and environmental samples such as natural waters or extracts of organic materials from airborne particulate matter or soils. Two contrasting approaches to such a problem may be envisioned. The first approach is to apply a method of great resolution, such as capillary column gas chromatography or high resolution mass spectrometry to isolate and measure the components of interest. The second approach is to apply a sequence of methods of lower resolution, preferably based on different separation principles, such as liquidliquid extraction followed by thin layer chromatography. Of the two, the second approach clearly has the edge for the analysis of practical samples. It permits the analyst to concentrate on the components of interest and to discard others. Yet mixtures of great complexity can be handled with methods of inherent simplicity. For example, a four-stage separation process yielding only four fractions per stage will permit the resolution of 256 components. This conclusion may seem so obvious as to render any argument trivial. Yet within the past few years we have seen several examples of frustrating and inconclusive application of the first approach mentioned above. High resolution mass spectrometry is superbly fitted to the identification of a pure compound as one of hundreds of possibilities, as well as to yielding structural information of enormous value for small samples, but it is being misused when applied to complex mixtures. Similarly, capillary column gas chromatography is an elegant approach to a high resolution separation of volatile components in a complex mixture, but not the most efficient approach to analysis of a sequence of such mixtures for a few components. Another example from a long past and simpler age comes to mind. The goal of classical qualitative analysis, we were told, was to have a specific reagent for each of the (then) 92 elements, in whatever combination. The prospect of testing a sample sequentially with 92 reagents as compared with a small set of group reagents and confirmatory tests gives one pause to wonder about the wisdom of the stated goal. It boils down to the fact that complex mixtures will become increasingly important in the future, but no matter how sophisticated the instrumentation may become, the analytical chemist will continue to be the most important component in the solution of analytical problems.
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