A study of the retention mechanism and selectivity of cyano and amino normal bonded-phase high-performance liquid chromatography.
Item
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Title
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A study of the retention mechanism and selectivity of cyano and amino normal bonded-phase high-performance liquid chromatography.
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Identifier
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AAI9000735
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identifier
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9000735
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Creator
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Tang, Yonghua.
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Contributor
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Adviser: David C. Locke
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Date
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1989
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Analytical
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Abstract
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Normal bonded-phase chromatography has been studied less extensively than reversed bonded-phase liquid chromatography, which accounts in part for its being less used analytically than reversed bonded-phase chromatography. To improve the fundamental understanding of normal bonded-phase chromatography, we studied the retention of a wide variety of solutes in diverse mobile phases on cyano and amino stationary phases. The data allow development of a new model of retention in normal bonded-phase chromatography.;Initially, the effect of strong adsorption sites, i.e. residual silanols, on retention using the cyano phase was isolated. Columns containing these silanol groups were compared with end-capped columns. An on-column silanization end-capping procedure was developed. Approximately 53% of the residual silanol groups were converted to non-adsorptive trimethylsilyl derivatives. Chromatographic behavior of phenols, anilines and other hydrogen-bonding solutes were completely changed. The retention interaction on the end-capped column involves only the bonded cyano groups.;The retention behavior of various solutes on cyanopropyl and aminopropyl columns with binary solvent mobile phases shows significant changes in the retention of solutes as the % polar solvent modifier is varied. For high % polar solvents, retention is changed from one involving specific adsorptive molecular interactions with the functional group of the stationary phase to a liquid-liquid partitioning of solutes between a surface-adsorbed liquid layer and a bulk-liquid mobile phase.;To account for this behavior, a new retention model for normal bonded-phase liquid chromatography was proposed. Equations are derived that expand upon the Snyder displacement model, which is useful at low concentration of polar modifier, and describe retention data over the entire range of mobile phase compositions. The new model is based on the balancing of two comparable processes, the Snyder displacement adsorption interaction and the partitioning effect. The dominant process is determined by the mobile phase polarity and solute structure. The new model is consistent with our experimental data for all solutes and mobile phases studied.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
