Part~I. Evaluation of thermodynamic and kinetic parameters for electron transfer and following chemical reaction from a global analysis of current-potential-time data. Part~II. Electro-catalytic detection in high-performance liquid chromatography of vitamin B(12) and other molecules of biological and environmental interest.
Item
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Title
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Part~I. Evaluation of thermodynamic and kinetic parameters for electron transfer and following chemical reaction from a global analysis of current-potential-time data. Part~II. Electro-catalytic detection in high-performance liquid chromatography of vitamin B(12) and other molecules of biological and environmental interest.
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Identifier
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AAI9304688
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identifier
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9304688
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Creator
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Kumar, Vimal T.
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Contributor
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Adviser: Ronald L. Birke
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Date
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1992
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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 | Chemistry, Pharmaceutical | Chemistry, Physical
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Abstract
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Part I. Simultaneous evaluation of electron transfer rate constant, k{dollar}\sp{lcub}\rm o{rcub}{dollar}, following chemical reaction rate constant, k{dollar}\sb{lcub}\rm f{rcub}{dollar}, electron transfer coefficient, {dollar}\alpha{dollar} and standard potential, E{dollar}\sp{lcub}\rm o\prime{rcub}{dollar} for an electrochemical reaction following the EC mechanism is described. A mathematical model for the current response to a potential step is developed, starting with the Butler-Volmer equation for electrode kinetics and concentration expressions for the redox couple. The resulting integral equations are solved numerically via the Step Function method. Current-potential and current-time curves are simulated and tested under limiting conditions. The four parameters of the system are then evaluated by fitting simulated current-voltage-time (i-E-t) surface to the theoretical equation, thus demonstrating the validity of the method. The method is then applied to study an important biological molecule, viz., methyl cobalamin, in DMSO. The parameters determined for this system are: {dollar}\alpha{dollar} = 0.552 {dollar}\pm{dollar} 0.004; k{dollar}\sp{lcub}\rm o{rcub}{dollar} = 0.0052 {dollar}\pm{dollar} 0.0005 cm s{dollar}\sp{lcub}-1{rcub}{dollar}; kf = 1500 {dollar}\pm{dollar} 140 s{dollar}\sp{lcub}-1{rcub}{dollar}; E{dollar}\sp{lcub}\rm {lcub}o\sp\prime{rcub}{rcub}{dollar} = {dollar}-1.54{dollar} {dollar}\pm{dollar} 0.01 V. Included in the discussion part, is the use of kinetic zone diagrams, to depict chronoamperometric current response as a function of dimensionless rate constants, for the EC reaction scheme. This compact display of the influence of the two rate constants on current in all time windows can be used to select the best data for analysis. Theoretical limits of measurable rate constants can also be estimated from the zone diagram.;Part II. The development of a dropping mercury electrode detector for High Performance Liquid Chromatography (HPLC) and its application to analysis of B{dollar}\sb{12}{dollar} and other vitamins is described. This EC detector is able to achieve high levels of sensitivity by exploiting the catalytic hydrogen evolution undergone by many nitrogenous organic molecules. The detector could be used in conjunction with a simple pulse polarograph of a more sophisticated computer system offering a wide choice of waveforms and other data handling options. Vitamin B{dollar}\sb{12}{dollar}, thiamine, riboflavin and niacinamide were analyzed individually and in mixtures on reverse phase C18 column. The detection limit and linear dynamic range compared very favorably with UV-Vis detection using a modern commercial instrument (Waters 600E). Preliminary results from the analysis of commercial multivitamin preparations are also discussed.
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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.
