difficult to determine with classical liquid extraction. In SFE as well as other sample preparation method development schemes, a variety of chemical and physi cal interactions must be considered. I thank David M. Johnson of DuPont Agricul tural Products for his careful review of this manuscript and his helpful suggestions.
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Mary Ellen P. McNally, a memberofAna lytical Chemistry's A-page Advisory Panel, ÎS a research associate at DuPont, where her primary research interests include SFE, LC, SFC, and CZE. Address correspondence about this article to her at E. I. du Pont de Nemours and Co., Agricultural Products Department, Experimental Station, E402/3328B, Wilmington, DE 19880Ό402.
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