The current process of selecting a column to perform a chiral separation can be characterized as more of an art than a science. This dissertation describes CHIRULE, a "chromatographic assistant" to aid in developing chiral separations. CHIRULE constructs an n-dimensional information space from a large number of known chiral separations by fragmenting the molecules at their chiral center, producing four molecular fragments. Molecular properties are calculated for each of these fragments. The properties are the axes used to place known separations into the information space. To suggest a column, the target molecule is added to the information space. Similarity property searching is used to select all known separations similar to the target molecule. The chemistry-based expert system shell CHESS used to develop CHIRULE also includes features such as functional group recognition and automated knowledge extraction techniques based on Personal Construct Theory. The results suggest that fragment property values are a route to enhanced understanding and improved selection of chiral separation methods. / Ph. D.

Size Exclusion Chromatography (SEC) is a liquid chromarographic technique used for the characterization of polymers and polymer related materials and also for the separation of small molecules. The major drawback of SEC is the lack of availability of a universal and true mass detector for providing a homogeneous response for all samples. Indirect detection methods have demonstrated to supply an alternative way to obtain a universal, sensitive and mass response in liquid chromatography. This research evaluated the indirect conductivity detection method for the size exclusion chromatographic separation of small molecules. Several studies were developed in order to understand the performance of this novel indirect detection mode. The evaluation of the initial experimental conditions snowed a dependence on the response, efficiency and elution time with the concentration of the conductivity probe added to the mobile phase. The SEC calibration curves developed for a series of standards indicated that selected conditions do not affect the separation by size. Response factors revealed a slight increase with molecular weight when they are expressed in volume or mass. Limits of detection were in the order of 20 nanoliters for small molecules. The effect of different conductivity probes on the separation and response was also studied. A modification of the original detector cell design resulted in improvement in the signal to noise ratio. / Master of Science

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

In recent years supercritical fluid chromatography has gained attention as an alternative technique to high performance liquid chromatography for the analyses of nonvolatile or thermally labile compounds, whose analysis with gas chromatography is impossible. The work presented here demonstrates a system that allows supercritical fluid extraction of the sample with subsequent direct introduction of a fraction of. this extract onto the column for analysis with supercritical fluid chromatography. Such a procedure has several inherent advantages to traditional sampling, where extraction or dissolution of the sample is done in a liquid. A valving scheme is described to accomplish this task and is evaluated for use with several different samples, including fuels and food products, with direct comparisons made between traditional sampling and direct on-line extraction. In most cases, the chromatograms were very similar, however later eluting components were sometimes lower in concentration with this method when compared to traditional sampling techniques. The apparatus was demonstrated in the analysis of high boiling coal derived material. Analysis of this material is accomplished by preliminary class separation with subsequent supercritical fluid extraction and analysis by packed column supercritical fluid chromatography. Detection included variable wavelength UV and FTIR spectrometry. The coal derived products studied were taken from a bench scale coal liquefaction reactor, in which the same catalyst was used for twenty-five consecutive days. The changes that occur as the catalyst decays were determined chromatographically for a portion of the high boiling products. The changes were noted best in the aromatic fraction analysis, where a trend towards molecules with higher numbers of condensed rings was observed as the catalyst decayed. / 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

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.

The separation of basic nitrogen-containing compounds has been investigated via supercritical CO₂ and 1% methanol modified CO₂. Packed columns with the following stationary phases were employed: silica, octadecyl (C₁₈), propylamino (NH₂), and polystyrene-divinyl benzene (PRP). Without modifier the range of basicities which could be eluted increased in the order of silica < PRP < C₁₈ = NH₂. Chromatographic peak shapes and selectivity were much better with propylamino column. Different aromatic amines and azaarenes were successfully separated on both analytical scale and microbore propylamino bonded phase packed columns with 100% supercritical CO₂. Separation is compared with both reversed phase and normal phase high performance liquid chromatography (HPLC). The retention mechanism study for these aromatic amines and azaarenes shows that the elution order not only depends on basicity and steric hindrance, but also on the solubility of the solute in CO₂. New cross-linked cyanopropyl and phenyl bonded phases are studied as stationary phases for packed column SFC, as well as for separation of nitrogen-containing compounds. The cross-linked bonded phase impedes access to uncapped silanol sites, thereby giving rise to better peak shapes, and more rapid elution without the necessity of a polar modifier in the mobile phase. Experiments both at elevated temperature and in the presence of methanol modifier revealed that there is no short or long term deleterious effect on the column. The separation of model mixtures of nitrated diphenylamine and nitrated anilines via SFC employing cyanopropyl packed and capillary columns is described. Peak identification and peak purity were performed by on-line Fourier transform infrared spectrometric detection. Supercritical CO₂ is employed with cyanopropyl packed columns for separation of non-polymeric components in double-base rocket propellants. Both supercritical CO₂ and CH₂Cl₂ were compared as a solvent for extraction of nonpolymeric components in "good" and "bad" double-base propellant. Finally, twenty-four phenylthiohydantion amino acids (PTH-AA) have been rapidly and efficiently separated on a cyanopropyl packed column by gradient elution of supercritical CO₂ and tetramethyl ammonium hydroxide-modified methanol. Complete or partial resolution of 22 derivatives is observed with only valine co-eluting with norleucine and lysine co-eluting with asparagine. No modifier was required for elution of neutral PTH-AA's from the cross·linked stationary phase. The addition of base plays a major role in elution of acidic and basic PTH-AA's. / Ph. D. / incomplete_metadata

The Variable Temperature Size Exclusion Chromatography (VTSEC) was used to study the dilute solution properties of various homo- and block copolymers as well as polymer blends, focus being primarily on the configuration-dependent properties such as average chain dimensions and hydrodynamic behavior of polymers. The study constituted of three parts. In the first part, the dilute solution properties of a series of poly(alkyl methacrylates) with varying side alkyl(ester) group were investigated as to the effect of the size of the side group on the average chain dimensions at various temperatures. The VTSEC results were found to reveal that the effect of the side group depends on the extent of chain flexibility imparted by the side group. In the second part, VTSEC was employed to investigate the applicability and validity of the various models for block copolymers in solution. For this purpose, several series of samples (all anionically synthesized) with various composition and molecular weight were used: i) poly(alkyl methacrylates), their diblock copolymers and blends and ii) diblock and triblock copolymers of poly(styrene/substituted styrene) and poly(butadiene/isoprene). VTSEC results showed that the applicability of each model to a block copolymer in solution depends on the compatibility among the components, the composition of the samples, the solvating power of the solvent used and the operating temperature. Micellization in the hydrocarbon diblock copolymer solutions was found to occur in selective solvent, its extent depending on the solubility parameter difference between the components, molecular weight, composition and solvent power. In the third part, poly(methyl methacrylate) samples with varying tacticities were studied as to the effect of stereochemical configuration on their dilute solution behavior and found to indicate that both syndiotactic and isotactic stereosequences are required for stereoassociation. Two new VTSEC data reduction procedures were devised in order to correct for the temperature drifts due to instrumentation in the first and to neutralize the effect of molecular weight in the second. In the second, termed as the Molecular Weight-Elution Volume Superposition Procedure, the effect of molecular weight alone was enutralized leaving only the effect of the intrinsic character (such as the size of the side group) of the sample in the elution behavior. Numerical computations, using the Matxrix Generation method based on the Rotational Isomeric State approximation, were carried out for stereoregular chains in order to evaluate their chain dimensions at various temperatures. / Ph. D.

Very early in the history of atomic emission spectroscopy (AES) it was understood to be a powerful analytical tool. Until the 1930's the usefulness of atomic spectroscopy was not utilized very extensively even though its fundamental power was understood. The breakthrough that placed it in the standard chemistry laboratory was the discovery and implementation of the photoelectric effect. Since this discovery there has been a revolution in atomic spectroscopy which has brought it from the role of a humble servant used for primary elemental screening to an outstanding leader in applications of elemental analysis. Atomic emission spectroscopy of complex samples has long suffered from matrix effects which result in overlapping of spectral lines, fluctuating backgrounds and changing conditions in the source. Investigations employing an echelle polychromator with a two dimensional solid state array detector show great promise in minimizing the effects of these interferences on multielement analyses of complex samples. The Charge Injection Device (CID) detector used exhibits many characteristics which make it uniquely qualified for simultaneous, multielement detection in AES. With only slight modifications to the optics of a commercial spectrometer and the employment of a CID detector, detection limits for a number of elements are quite favorable. Dynamic ranges of over seven orders of magnitude are obtainable with this experimental system. The reduction of matrix effects by utilizing the huge wealth of information available from over 60,000 individual detector elements are demonstrated through results from several complex matrix standards. This CID-polychromator system was also employed for the element selective detection of gas chromatographic (GC) effluents. A microwave-induced plasma (MIP) based on the Surfatron design was built. A helium plasma from this device has shown to have resilience to organic samples and give good emission response to non-metallic atoms. A number of studies with this GC-AES-polychromator system are presented. This system is capable of monitoring atomic emissions from C, H, F, Cl, Br, I, O, N and S all simultaneously, and the selectivity of this system is unsurpassed. Elemental ratios for separated compounds are also presented as a precursor to empirical formula prediction.

Thesis (MSc)-- Stellenbosch University, 2012. / ENGLISH ABSTRACT: Over the past two decades, field flow fractionation (FFF), as a polymer characterization technique, has become cutting edge technology. The demand for molar mass and size characterisation of complex polymer systems has increased, especially in cases where classical calibration techniques such as size exclusion chromatography (SEC) has shown several shortcomings. FFF is a technique resembling chromatography. It has several significant advantages over SEC, especially for the characterisation of ultrahigh molar mass (UHMM), branched and gel-containing polymers. In this study, polybutadienes, which often contain the abovementioned species, were analysed by SEC and asymmetric flow field flow fractionation (AF4). Both separation techniques were coupled to refractive index and multi-angle laser light scattering detection. Similarly, polyrotaxanes, which are polymers with complex and unique molecular architectures, were also investigated. Results showed that AF4 can explicitly be used as a superior tool over SEC. In the case of UHMM polybutadienes, much higher molar masses could be detected by AF4, due to the absence of shear degradation which is often encountered in SEC. Gel-containing species could be detected by AF4 as no filtering is required prior to injection. Abnormal retention behaviour, a phenomenon often encountered in UHMM branched polymers, was observed in SEC analysis of the polyrotaxanes materials. AF4 provided sufficient separation from low to high molar masses, without out any irregularities. / AFRIKAANSE OPSOMMING: Gedurende die afgelope twee dekades het veldvloeifraksionering (FFF) as ‘n polimeerkarakteriseringstegniek groot veld gewen. Die aanvraag na molekulêre massa en groottekarakterisering van komplekse polimeersisteme het toegeneem, veral in die gevalle waar klassieke kalibrasietegnieke soos grootte-uitsluitingschromatografie (SEC) etlike tekortkominge getoon het. FFF is ‘n tegniek soortgelyk aan chromatografie, en het voorheen bewys dat dit oor ‘n redelike aantal voordele bo SEC beskik, veral in die geval van ultrahoë molekulêre massa- (UHMM-), vertakte- en jelbevattende spesies. In die huidige studie is polibutadieenpolimere, wat dikwels bogenoemde spesies bevat, geanaliseer met behulp van SEC en onsimmetriese vloei-veldvloeifraksionering (AF4). Beide skeidingstegnieke is gekoppel aan ‘n brekingsindeks en multihoek-laserligverstrooiingsdetektors. Op dieselfde wyse is polirotaksane (polyrotaxanes) met komplekse molekulêre argitektuur bestudeer. Daar is bewys dat AF4 uitsluitlik gebruik kan word as ‘n meer geskikte tegniek bo SEC. Baie hoër molekulêre massas kon deur middel van AF4 vir UHMM polibutadieenpolimere raakgesien word as gevolg van die verminderde afbrekende degradasie wat dikwels voorkom met SEC. Jel-bevattende spesies is suksesvol geïdentifiseer met behulp van AF4 waartydens geen filtrering vir analise nodig was nie. Abnormale retensie was sigbaar tydens SEC analise van monsters van polirotaksane, wat dikwels voorkom in vertakte polimere. In teenstelling het AF4 bewys dat ‘n bevredigende skeiding van klein na groot molekulêre massas, sonder enige tekortkominge, moontlik is.