This paper describes a new approach for the quantitative resolution of mixtures of structural isomers. The method is based on the observation that rate constants for the cyclodextrin-catalyzed hydrolysis of selected structural isomers are significantly different. By using cure-fitting methods, it is possible to use these differences in rate constants to resolve kinetic responses for mixtures into the responses for the individual components. The new approach is evaluated for the ortho-, meta-, and para-isomers of nitrophenyl acetate. At pH 10, with beta-cyclodextrin as catalyst, ratios of rate constants for the three isomers differ by ratios of 1:6.7:1.6 in the order mentioned above. Results are reported for both two- and three-component mixtures. For two-component mixtures of the ortho- and para-isomers which have rate constants differing by only 1.6-fold, linear least-squares slope and intercept of determined vs prepared concentrations for the ortho-isomer were 1.00 +/- 0.02 and 2 +/- 2.2 mumol/L for three runs on each of five samples in the concentration range from 22 to 176 mumol/L. The pooled standard deviation for these 15 runs was 3.7 mumol/L, corresponding to a relative standard deviation of 3.7% for the average concentration. Similar results were obtained for other two- and three-component mixtures.
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