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Call number: LD2668 .T4 1964 M26 / Master of Science

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During the course of study of reversed phase ion partition chromatography, it was observed that non-ionic substances such as alcohols, ester, and ketones undergo chromatographic separation in some as yet undefined association with cationic dyes (methylene blue chloride or brilliant green). Detection of non-chromophore trace level compounds has been a major problem in liquid chromatography due to the lack of a universal detector. Refractive index detector, although a universal detector lacks sensitivity. The U.V. absorbance detector is the work horse of liquid chromatography. Its major drawback is its lack of universality. It is often desirable to extend the utility of this detector to compounds toward which they are normally insensitive. This research was directed to developing the U.V.-Visible absorbance detector into a 'universal detector'. Using a mixture of methanol/water or dioxane/water solvent containing 1 x 10⁻⁴ M cationic dye such as the mobile phase it was shown to separate on Partisil ODS or on Zorbax ODS a series of C₂-C₅ alcohols and other neutrals at submicrogram levels with good base line separation. The alcohols carry with them some dye which must come from the presaturated dye ODS column. The dye peaks are detected spectrophotometrically at λ maximum of dye and becomes a measure of the eluting alcohol concentration. Normally, these aliphatic alcohols have a poor sensitivity either with refractive index or U.V. absorbance detector. This novel mode of detection and separation of trace quantities of alcohols and other neutral species represents a significant increase in sensitivity and should be widely applicable. The experimental data on which these separations are based, poses very interesting questions. For example, is there a specific kind of interaction between the alcohol and the dye or do the alcohols distribute between the Partisil ODS and mobile phase in their customary fashion and dissolve some of the immobilized dye because of their local excess concentration? Furthermore why do the slopes of the linear calibration curves obtained for each of the alcohols vary with the particular alcohol? Retention model based on dye alcohol complex formation and equilibrium partitioning of these species is advanced.

Significant advances in the understanding of chemical interactions at the solid-liquid interface have been made in this research through the use of diagnostic separations as a surface analysis technique. Diagnostic liquid chromatography has been employed in a detailed investigation of the thermodynamic and kinetic quantities which describe the interactions associated with a temperature induced conformational change in the octadecyldimethylsilane moieties of two different bonded silica materials. As a result of this study the nature of the structure and interactions of the ∼20Å thick interfacial region which acts as the stationary phase in reversed-phase liquid chromatography (RPLC) has been elucidated. The location and orientation of the average intermolecular interactions in the solvated layer stationary phase for solutes of differing hydrogen bonding ability and geometry has been determined as affected by bonded surface coverage, solvent hydrogen bonding competition and the structure of the solvated layer. These refinements in the model of the stationary phase solvated layer provide a much more detailed and accurate description of the intermolecular interactions responsible for retention and selectivity in RPLC than was previously available. A new modification of the method of measuring column mobile phase volume in RPLC employing retention linearization of an homologous series of compounds has been described from fundamental themodynamic principles and a statistically valid data reduction approach. The added advantage of providing thermodynamic information about the chromatographic system under study is inherent in this new technique. The experimental and theoretical bases for the new separation technique of magnetic field-flow fractionation (magnetic FFF) have been demonstrated. It has been shown that FFF techniques can be used in a diagnostic mode to study the dynamic stability of particle suspensions. The application of an external magnetic field to non-aqueous suspensions of sub-micron sized γFe₂O₃ particles, whose surface character has been modified by the adsorption of water, has been shown to enhance the suspension stability with respect to sedimentation. With the choice of proper operational conditions, magnetic FFF has also been demonstrated to be useful in monitoring particle flocculation as a result of its ability to separate particle flocculates on the basis of size.

No description available.

No description available.

No description available.

No description available.