A rapid scanning square wave voltammetric detector has been developed for use with high performance liquid chromatography.The electrochemical cell used in the detector was designed so that the HPLC effluent flows through the center of a large diameter platinum disk electrode and is then forced to flow radially across the electrode surface. The arrangement of the electrodes in the cell was intended to result in large analytical currents while minimizing electrical resistance and analyte band spreading in the detection zone. The detector was evaluated in terms of its minimum detectable quantity, linear dynamic range, electrochemical efficiency, and analyte band spreading. The MDQ was found to be in the low parts per billion range for hydroquinone. The detector was shown to provide data that is qualitatively superior to data obtained by amperometric detection and was shown to be compatible with gradient elution HPLC over a broad range of solvent compositions. A sensor based on the quartz crystal microbalance was also developed for use in flowing solvent streams. Quartz crystals were treated with various compounds to produce close - packed monolayer coatings which could interact with solutes entering the flow cell. The solute capacity was determined for one of the monolayer coatings and various factors that influence the magnitude of the OCM signal were investigated. These factors include the solvent flow rate, the solvent strength, solute molecular structure, and bonded phase molecular structure. The QCM sensor was found to be a convenient probe for conducting surface adsorption studies and the molar free energy of adsorption was determined for some chemically related solutes on an amine modified crystal. / Ph. D.

Peanut skins have long been a waste product of the peanut industry. The aim of this project was to find suitable applications for this rich source of natural bioactive compounds. Solvent extracts of peanut skins and a multistep solvent extraction process to yield oligiomeric procyanidin (OPC) extracts were found to be inhibitory towards three types of yeasts (Saccharomyces cerevisiae, Zygosaccharomyces bailli, and Zygosaccharomyces bisporus). All extracts were devoid of solvents that may have interfered with the results. The OPC extract exhibited the highest inhibitory effect, and was chosen for fractionation. Fractionation was conducted by means of a silica or size exclusion high performance liquid chromatography (HPLC) column. Fractions were then subjected to a yeast growth curve assay to determine the active fractions. The fractions were then characterized by liquid chromatography-mass spectrometry (LC-MS). Negative mode electrospray MS determined the fractions to contain mostly procyanidins but also proanthocyanidins. Since it is possible for multiple compounds to display the same molecular ion, multistep MS and retention time differences were utilized to tentatively identify the compounds based upon their fragmentation schemes. However, co-elution was prominent, thus specific compounds responsible for yeast growth inhibition could not be determined. The yeast inhibition assay demonstrated that the procyanidin dimers up to tetramers had the best anti-yeast capabilities. / Ph. D.

A study of six liquid chromatographic column packing materials was conducted. The materials investigated were: SI-60, SI-100, ALOX T, RP-2, RP-8, and RP-18 (E. M. Laboratories, Elmsford, N.Y.). The column packing materials had an average particle diameter of 10 µm and were slurry packed into stainless steel columns that were 3 mm i.d. and 250 mm in length. Two series of probe compounds were utilized to investigate the differences in selectivity exhibited by the column packing materials in the normal phase mode and in the reversed phase mode. A column oven which controlled temperature to within ± 0.2 °C over the range of 0°C to 100°C was utilized throughout the work. Four different mobile phases were used, two for the normal phase work and two for the reversed phase work. The effect of temperature was investigated in both the normal phase mode (20°C - 50°C) and in the reversed phase mode (20°C - 80°C). The results of the selectivity study indicate that the column temperature can have a pronounced effect in normal phase liquid chromatography. As temperature increased, k' values went through a minimum in some cases, indicating a change in retention mechanism. As the temperature is increased, the retention of the compounds may be increased, decreased, or remain constant. RP-2 is a versatile column packing material which is useful in both the normal phase mode and the reversed phase mode. In the normal phase mode it behaves as a low surface area adsorption column and of the three adsorbents, (SI-60, SI-100, and RP-2), it has the widest scope. In the reversed phase mode it also has the widest scope of the three reverse phase columns studied (RP-2, RP-8, and RP-18). In reversed phase liquid chromatography, increases in retention as temperature was increased were not observed and plots of log k' vs. temperature in °C resulted in straight lines with very similar slopes. Column temperature is however an important operating parameter which is useful in optimizing separations. Temperature was found to have little effect on the efficiency of the columns but was found to have a significant effect on the scope of the column packing materials in both the normal phase mode and in the reversed phase mode. When utilizing high surface area column packing materials or column packing materials with a high percentage of hydrocarbon bonded phase, temperature control is essential in order to obtain the best reproducibility. / Doctor of Philosophy

The purpose of this investigation was to test the effect of sample size and carrier gas flowrate on the efficiency (relative to an analytical column) of an annular preparative-scale column. The chromatographic system for this investigation consisted of η-methyl-butyrate injections with nitrogen carrier gas and a liquid phase of Craig polyester succinate on Chromosorb W. The analytical column had an inside diameter of 0.061 inches. The preparative-scale column had an outside diameter of 2.075 inches and an inside diameter of 1.050 inches. The operating temperature for both columns was 215 degrees Fahrenheit. A sample size range of 0.1 to 3.0 milliliters was studied on the preparative-scale unit; this corresponded to a 0.2 to 3.6 microliter range on the analytical unit. Carrier gas flowrates of 4305, 8610 and 17,220 milliliters per minute were studied on the preparative-scale unit. This corresponded to flowrates of 5, 10 and 20 milliliters per minute on the analytical unit. Preparative-scale efficiencies of 20.43, 41.95 and 45.34 per cent were obtained at a sample size of 0.1 milliliter. The above efficiencies correspond to flowwates of 4305, 8610 and 17,220 milliliters per minute. As the sample size was increased to 3.0 milliliters the corresponding efficiencies dropped to 7.20, 17.71 and 27.11 per cent respectively. / Master of Science

Supercritical fluid chromatography (SFC) has been gaining much exposure over recent years. The characteristics inherent to SFC give it capabilities in separating nonvolatile, thermally labile compounds inseparable by GC, and with greater efficiency per unit time than HPLC. As in the past with the more conventional chromatographic methods, the need for higher information detectors, such as IR, exists for SFC. The interface of a Fourier Transform Infrared (FTIR) spectrometer to a packed column (analytical scale) SFC is demonstrated. Characterization of mobile phases for SFC-FTIR is presented. Also, parameters for the optimization of spectral sensitivity, such as mobile phase transparency and flow cell design, are discussed. Demonstrations are made via model mixture separations. Finally, the application of this technique to the analysis of free fatty acids is presented. Identification of carboxylic acids of carbon number 6-18 is made on several standard mixtures and on free fatty acids extracted from various complex samples. The spectral identification of the compounds as free fatty acids is presented, and spectral evidence for dimerization of the acids in CO 2 and the coelution of saturated and unsaturated carboxylic acids is shown. / Master of Science

The performance of a Hewlett Packard Particle Beam LC/MS interface is evaluated using EPA appendix VIII and IX compounds. The behavior of these priority pollutants in the interface could determine its feasibility as a future EPA certified technique. The evaluation process consists of studies to determine minimum detectable quantities (MDQ), linear response, and band broadening contributions. The MDQ's of the analytes in electron impact and chemical ionization modes are extrapolated from experimental signal to noise data. The linearity study involves ten compounds analyzed at five different concentrations. The response factors (RF) are calculated and discussed. The study concerning the band broadening contributions of the interface involves four independent variables (helium flow, desolvation chamber temperature, source temperature, and 96 methanol) and their effects on peak width. A Box–Behnken experimental design is used and described. Response surfaces are generated from the best fit equation describing the data. / Master of Science

The scope of supercritical fluid chromatography continues to enlarge. The use of open tublar and packed columns, nearly universal detectors and the introduction of new mobile phases make it more important. In this work sulfur hexafluoride is evaluated as a mobile phase for supercritical fluid chromatography. The separation of a model aromatic hydrocarbon mixture using different packed columns and operational parameters with UV as a detector is presented. The chromatographic properties of supercritical sulfur hexafluoride and supercritical carbon dioxide are compared under corresponding chromatographic parameters. / Master of Science

An LSI-11 micro-processor and a Spectra-Physics model 3500B gradient elution liquid chromatography were interfaced for the purpose of automating the chromatograph, incorporating it into the laboratory data network system and collecting data for Michael Starlings' project. The automation involved the construction of hardware for the control of the chromatograph and for data acquisition and display and the writing of software to operate the interface. The LSI-11 collects data by clock interrupts while displaying the current data buffer on the oscilloscope. It stores all data files on a floppy disk storage device, accessed through the main host computer. An analysis of the data is performed by a peak processing routine, calculating peak area and retention time. The network is the DEC Rr-11/REMOTE system. It operates on a PDP-11-03 with a floppy disk system for mass storage. The laboratory system has three satellites operating under it. They can utilize all of the facilities of the main computer while maintaining a minimal operational configuration. The project also had the purpose of being assimilated into Michael Starlings' data correlation system. The LSI-11 will collect data and send it to the NOVA computer system where it will be stored. The system was tested with several mixtures and the results were found to be accurate and easily obtainable, / Master of Science

Carbon tetrachloride (CCl₄ ) was closely evaluated as a carrier solvent in high-performance liquid chromatography (HPLC). The separation and retention trends of ninety-two selected compounds from eleven chemical classes (furans, thiophenes, aromatic hydrocarbons, ethers, esters, ketones, aldehydes, aromatic amines, azaarenes, alcohols and phenols) on three analytical silica-bonded phase (amino (NH₂), cyano (CN) and polar amino-cyano (PAC)) columns were investigated with CCl₄ and refractive index (RI) detection. The sample capacity and column efficiency of each of the NH₂ and PAC columns were measured and compared. Besides, a method of determining unmeasurable capacity factors (k' values) was found and illustrated. / M.S.

Microbore columns were investigated for their application to High Performance Liquid Chromatography. Microbore columns consist of stainless steel tubing, 1/16¹¹ OD x 1mm ID, packed with silica gel or other suitable material. These columns were evaluated in terms of extra-column variance effects, mass sensitivity, and solvent consumption. Three methods of extracting the extra-column variance effects were evaluated. When used with an instrument whose contribution to total peak variance is small compared to the column, microbore columns provide the best performance for analyses where sample is limited or where reduction of solvent usage is desirable. A method from the literature for extracting extra column variance effects was found to be easy and reliable. It is proposed as a useful way of allowing column performance to be compared from instrument to instrument and for determining whether a particular instrument is suitable for use with microbore columns. / M.S.