Two on-line multidimensional HPLC systems are described; one coupling two liquid chromatographic columns (LC/LC), and one coupling liquid and gas chromatography (LC/GC). Theoretical equations relating the reproducibility, accuracy and transfer efficiency to system operating variables such as flow rate, retention time, column efficiency and transfer volume have been developed. These effects are explained and verified using experimental systems. Three major applications are shown for each of the systems. For the LC/LC systems, these include; the analysis of caffeine and theophylline in biological fluids; the analysis of hydrocarbon group types in fuels and oils and the analysis of catecholamines in urine with electrochemical detection. For the LC/GC system, the applications include; the analysis of pesticides in butter, the analysis of hydrocarbon group types in fuels and the analysis of polycyclic aromatic hydrocarbons in petroleum related samples. / Ph. D.

This dissertation presents an analysis of two aspects of the chromatographic separation process known as Simulated Moving Bed (SMB) chromatography. The first aspect is system design, and the second is improving computer simulations to generate heuristics for choosing operational modes. For the past 15-20 years, there has been a surge of interest in the use of Simulated Moving Bed systems for the chromatographic separation of chemicals¹. A wide variety of methods, nomenclatures, and conventions have been adopted over the years²⁻⁴, as teams from different backgrounds adopt and improve on the SMB technology. This work presents a unifying discussion of the two major design methods, Triangle Theory and Standing Wave Design, used in the SMB field. We provide the complete computer code required to execute both design methods. A sample problem is worked, which demonstrates the novelty and ease of use that such tools provide. Mathematica was chosen for the implementation of these design methods, because of its strong symbolic analysis capabilities, and simplicity of creating interfaces for new users. We present derivations of the classic Langmuir results in Mathematica, and proceed to extend those implementations. When analytic solutions are impossible, we use Mathematica's numerical methods. This work also develops a distributed computing tool known as ChromRunner which allows large numbers of detailed numerical simulations to be run simultaneously. The motivations and benefits of this approach are discussed alongside implementation details. We apply the distributed computing system to two separate SMB separations in order to optimize them, as well as determine heuristics governing their operational modes. We wrote ChromRunner in C#, and took advantage of Visual Studio's Entity Framework to create the database backend. The user interface for this software was created using Microsoft's "Windows Presentation Foundation" (WPF) technologies. / Ph. D.

The chromatographic properties of various silicone stationary phases for capillary gas chromatography have been extensively studied, yet the properties of nonsilicone phases have not been so well investigated. The most popular nonsilicone phases are the high molecular weight polyethylene glycols (HMW PEG) which are commercially available in a wide range of molecular weights, cross-linkable and uncross-linkable (Carbowax 2OM and 4OM, the Superox series, etc.). Their most outstanding features are their unique polarity and selectivity; for this reason these phases are widely used in the analysis of aqueous solutions, essential oils, and perfumes. Unfortunately HMW-PEG's are very sensitive to slight differences in preparation and handling procedures which can cause analyses to differ with each laboratory, each column, and even each use. HMWâ PEG's also suffer from low temperature stability, a high minimum allowable operating temperature, and have lower diffusion coefficients than silicone phases. This study examines the efficiency differences of eight columns differing only in immobilization procedure and added functional groups. Comparison is made using HETP versus u and separation number (TZ) versus u curves. These curves offer important information, in particular, the effect of carrier gas, u, column operating temperature, degree of cross-linking, and cross-linking temperature on chromatographic efficiency and separation number. In addition, the contributions of the CL (resistance to mass transfer in the liquid phase) and DL (diffusion coefficient in the liquid phase) terms in the Golay equation are calculated [1]. Solids at room temperature, PEG stationary phases undergo a solid-liquid phase transition within their useful temperature range. The effect of this transition on the chromatographic properties is investigated using efficiency, separation number, capacity ratio, and retention index versus temperature curves. Four more columns, in addition to the eight mentioned above, demonstrate the influence of end-groups and the molecular weight of the stationary phase on the phase transition temperature range. / Master of Science

Wide-bore, fused-silica capillary columns can be an excellent replacement for packed columns in many cases. They can provide higher surface inertness and thermal stability, as well as higher efficiency or speed of analysis. Wide-bore, open-tubular (WBOT) columns with thick films have higher sample capacities than conventional narrow-bore capillary columns and can be used in unmodified packed-column gas chromatographs. The majority of gas chromatographic analyses are still performed using packed columns. Many chromatographers associate open-tubular columns exclusively with split injection, often perceived as less repeatable or quantitative. Also, many packed-column methods use application-specific stationary phases which are not readily available on capillary columns. WBOT columns with standard phases can often be substituted due to higher available efficiencies. While several studies have been published on qualitative differences, there is little comparative quantitative data available on O.53â mm I.D. and packed columns. / Master of Science

A ready-to-deploy implementation of microfabricated gas chromatography (microGC) system characterized for detecting hazardous air pollutants (HAPs) at parts-per-billion (ppb) concentrations in complex mixtures has been described. A microfabricated preconcentrator (microPC), a MEMS separation column with on-chip thermal conductivity detector (microSC-TCD), the flow controller unit, and all the necessary flow and thermal management as well as user interface circuitry are integrated to realize the fully functional microGC system. The work reports extensive characterization of microPC, microSC and micro]TCD for target analytes: benzene, toluene, tetrachloroethylene, chlorobenzene, ethylbenzene, and p-xylene. Limit of Detection (LOD) of ~1 ng was achieved, which corresponds to 10 min sampling time at a flow rate of 1 mL/min for analyte present at ~25 ppbv concentration. An innovative method for generating very sharp injection plugs from the microPC even in the presence of flow sensitive detectors like micro]TCD is described. A one-to-one comparison between microGC system and conventional Automated Thermal Desorption-Gas Chromatograph-Flame Ionization Detector (ATD GC-FID) system for real gasoline samples in simulated car refueling scenario is reported. / Master of Science

The experimental parameters controlling the rate and mechanism of the decomposition of compounds and the products formed, in a moving carrier gas stream were investigated. The parameters studied included the effects of pyrolysis temperature, sample size, sample weight, flow rate of the carrier gas, the method of introducing the sample into the pyrolysis unit. An apparatus for pyrolysis-gas chromatography, using tho commonly used boat and furnace technique, was developed. Commercial grade sodium dodecylbenzene sulfonate was chosen for a model compound. The optimum conditions for the pyrolysis-gas chromatographic analysis of this material were established by the careful study of the experimental parameters. The most serious limitations to this method of pyrolysis-gas chromatography appeared to be the strong dependence on the sample size and tho dependence on pyrolysis temperature, i.e., on the rate at which the sample was brought to the pyrolysis temperature. As the size of the sample was increased the amount of residue in the boat also increased. Also, although the majority of the sample was pyrolyzed at 580°C the amount of residue would decrease as the temperature was raised to a maximum of 710°C. A certain amount of residue always remained in the boat. The residue can be explained as the product of secondary reactions occurring between the initial pyrolysis intermediates (free radicals) and the unpyrolyzed portion of the sample. In an attempt to eliminate these effects of secondary reactions a new technique of pyrolysis-gas chromatography by direct injection of solutions was developed. By handling the samples in dilute solution it was shown that a much smaller sample could be pyrolyzed such that the probability or secondary reactions was greatly reduced. Also the very small samples allow an apparent instantaneous heating of the samples to a given pyrolysis temperature. This approach offers a means of obtaining the simplest possible products from the pyrolysis of a compound, therefore offering a more accurate insight into the mechanism of the pyrolysis. These products then offer a means of establishing the structure of the original compound. Using this technique a method was developed for analyzing aqueous solutions containing the alkylbenzene sulfonates. This method provides not only a measure of the total detergent present but also differentiates between the various alkyl groups found in the commercial products. The alkyl groups form the 1-alkenes which can be easily identified chromatographically. The conditions for this analysis along with curves showing the products obtained from the pyrolysis of samples with both straight and branched alkyl groups are given. While the majority of the work done here was with aqueous solutions an attempt was made to determine the stability or some of the common organic solvents under such pyrolysis conditions. Those solvents studied were methylene chloride, chloroform, carbon tetrachloride, methanol, ethanol, and acetone. All of these solvents were round to be stable up to 500°C; however, at temperatures greater than this the decomposition of the solvents limits their use. The technique of pyrolysis-gas chromatography by direct injection or solutions was also applied to certain amino acids in ethanol-water solutions. The results were again much more accurate than those found with the boat technique. This technique was also shown to be useful in determining the structure of organic chelates bound to metal atoms. Solutions of copper II and chromium III acetyl-acetonates in chloroform were pyrolyzed and the product identified as acetylacetone. This offers a means of determining both the number and type of chelates bound to a given metal atom. / Ph. D.

Ventilation in underground mines is vital to creating a safe working environment. Though there have been numerous improvements in mine ventilation, it is still difficult to ascertain data on the state of the ventilation system following a disaster in which ventilation controls have been potentially damaged. This information is important when making the decision to send rescue personnel into the mine. By utilizing tracer gas techniques, which are powerful techniques for monitoring ventilation systems, especially in remote or inaccessible areas, analysis of the ventilation system immediately following a mine emergency can be more rapidly ascertained. However, the success of this technique is largely dependent on the accuracy of release and sampling methods. Therefore, an analysis of sampling methods is crucial for rapid response and dependable results during emergencies. This research project involves evaluating and comparing four well-accepted sampling techniques currently utilized in the mining industry using sulfur hexafluoride, an industry standard, as the tracer gas. Additionally, Solid Phase Microextraction (SPME) fibers are introduced and evaluated as an alternative sampling means. Current sampling methods include plastic syringes, glass syringes, Tedlar bags, and vacutainers. SPME fibers have been successfully used in a variety of industries from forensics to environmental sampling and are a solvent-less method of sampling analytes. To analyze these sampling methods, samples were taken from a 0.01% standard mixture of SF6 in nitrogen and analyzed using electron capture gas chromatography (GC). The technical and practical issues surrounding each sampling method were also observed and discussed. Furthermore, the use of multiple tracer gases could allow for rapid assessment of the functionality of ventilation controls. This paper describes experimentation related to the determination of a novel mine tracer gas. Multiple tracer gases greatly increase the level of flexibility when conducting ventilation surveys to establish and monitor controls. A second tracer would substantially reduce the time it takes to administer multiple surveys since it is not necessary to wait for the first tracer to flush out of the mine which can take up to a few days. Additionally, it is possible to release different tracers at different points and follow their respective airflow paths, analyzing multiple or complex circuits. This would be impossible to do simultaneously with only one tracer. Three different tracer gases, carbon tetrafluoride, octofluoropropane, and perfluoromethlycyclohexane, were selected and evaluated on various GC columns through utilizing different gas chromatographic protocols. Perfluoromethylcyclohexane was selected as the novel tracer, and a final protocol was established that ensured adequate separation of a mixture of SF6 and perfluoromethylcyclohexane. Since there is limited literature comparing sampling techniques in the mining industry, the findings and conclusions gained from the sampling comparison study provide a benchmark for establishing optimal sampling practices for tracer gas techniques. Additionally, the determination of a novel tracer gas that can be used with and separated from SF6 using the same analytical method increases the practicality and robustness of multiple mine tracer gas techniques. This initial work will contribute to the larger project scope of determining a methodology for the remote characterization of mine ventilation systems through utilizing multiple mine tracer gases and computational fluid dynamics (CFD). This will be completed through several phases including initial laboratory testing of novel tracer gases in a model mine apparatus to develop a methodology for releasing, sampling, and modeling a mine ventilation plan and tracer gas dispersion in CFD and eventually completing field trials to validate and enhance the multiple tracer gas methodology. / Master of Science

This study concerns the effect of column temperature on selectivity in gas chromatography (GC). Reversal of peak elution order at different temperatures is observed when selectivity is sufficiently changed by changing the temperature. A study of homologous functional groups and the elution order of a test mixture was made at several temperatures, by keeping constant operating chromatographic parameters such as column head pressure, split ratio, sample concentration, injector and detector temperature. The homologous series studied were esters, carboxylic acids, ketones and alkanes. The stationary phases used were Carbowax (Supelcowax 10), and 5% diphenyl and 95% dimethyl silicone ( HP Ultra 2). The identification of each compound was confirmed by two methods : comparing retention times, and spiking the sample. The results of an investigation for accurately determining the dead time is also presented. The experimental results of using 10% methane in helium and the results of a theoretical model based on Poiseuille's equation were studied and compared. It is concluded that dead time calculations are a major source of error for the calculations in this work. In addition, a derived thermodynamic equation based on the Van't Hoff equation was obtained and used to calculate the molar enthalpy and entropy of compounds over a range of temperatures. The experimental thermodynamic values were compared with the theoretical values obtained from the Clausius- Clapeyron equation. From the data obtained, a graph of In k' (retention factor) versus 1/ temperature for a homologous series, known as a Van't Hoff plot, predicts a reversal of elution order where an intersection of two lines occur. Selectivity of the stationary phase has changed solely due to temperature effects. This can only occur when different solute/solvent interactions are present. This work is an attempt to predict when peak inversion should occur based on the Van Hoff's plot. Experimental result are presented that confirm the prediction. / Master of Science

The microwave region of the electromagnetic spectrum lies between the infrared radiation and radio frequency region and corresponds to wavelengths of 1 cm to 1 m (frequencies of 30 GHz to 300 MHz respectively). Gaisford and Walters developed the microwave GC oven in 2000, which operated at 919 MHz. The microwave GC oven has been engineered to generate a uniform microwave field around an open tubular capillary column with elimination of cold spots which are common in a domestic microwave oven. Only the column is heated in a microwave GC oven. In microwave GC, ramp rates in excess of 6 degree/sec, isotherms as high as 450 degree, and 1 min cool-down times from 300 to 50 degree can be achieved. In conventional GC, only positive temperature programming is used because the oven cools down slowly due to the great thermal mass of the oven. Short cool-down time in microwave-heating GC makes it possible to employ negative temperature programming for the separation of compounds during the process. The theory and feasibility of negative temperature programming in microwave GC were investigated in this research. Negative temperature programming was employed to analyze and quantitate four different critical pairs of non-volatile and volatile compounds. The influence of cooling rate, holding time, and reheating rate in negative temperature programs for enhanced resolution were investigated. The results obtained from negative temperature programming were compared to those from positive temperature programming. Negative temperature programming afforded greater resolution of critical pairs of analytes. / Master of Science

The analysis of polar compounds has been studied by SFC using 100% CO₂ or methanol modified CO₂ as the mobile phase. Both microbore packed and capillary columns are employed to separate the mixtures of steroids and agricultural compounds of various chemical classes such as amides, sulfonamides and ureas. The highly deactivated and crosslinked stationary phases used for both packed and capillary columns afford the elution of polar analytes with 100% CO₂ which in turn makes the on-line FT-IR detection of these analytes feasible. The flow cell interface is employed which provides very low detection limits. Spectra with high signal to noise ratio are obtained for the analytes with real time data acquisition. Some polar and structurally similar triazine herbicides are separated using a gradient mobile phase and a rapid separation of all the components with complete resolution is achieved. The effect of flow rate, column outlet pressure and the temperature on resolution is also studied for these analytes. The performance of microbore packed and capillary columns is compared using polar and nonvolatile solutes and the retention and resolution offered by both the columns are also compared. Several van Deemter plots are generated at various constant operating densities and temperatures. Also, the effect of density and temperature on efficiency and resolution is studied for capillary column with split and splitless injection techniques. Several conclusions regarding the favorable operating conditions in each case can be drawn based on the results obtained here. / Ph. D.