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From Introduction: Buchu leaf is a very widely used household medicine in South Africa, and is usually administered in the form of a brandy tincture or a vinegar, known as "buchu brandy" and "buchu vinegar" respectively. These preparations have a great reputation in curing diseases of the kidney and urinary tract, and in addition are employed as local applications to bruises, and for the relief of rheumatic pains. We owe its introduction into medicine to the Hottentot, who gave the name "buchu" or "bookoo" to any aromatic herb or shrub which they found suitable for use as a dusting powder.

The metabolism of absorbed xenobiotic compounds in humans results in a mixture of target compounds applicable for analysis, trapped in complex biological matrices. Gas chromatography-mass spectrometry (GC-MS) is a powerful analytical technique that has been successfully applied in the analysis of volatile and semi-volatile compounds from complex biological samples. This is due to the ability of GC-MS to separate different sample constituents at trace levels while providing accurate molecular structural information for the resolved compounds. The complexity of biological specimens and their largely aqueous nature, combined with the physicochemical properties of target analytes resulting from metabolism, greatly precludes direct analysis of biosamples by GC-MS. Traditionally, highly laborious and time consuming sample preparation procedures are performed to isolate and chemically alter target analytes to attain suitable amenity for the detection system. Furthermore, routine analytical procedures in clinical toxicology laboratories are signified by short specimen turn-around times. The commonplace use of GC-MS in modern-day laboratories still suffer from prolonged turn-around times that result from both sample preparation steps and lengthy instrumental analysis. Simplified and cost-effective analytical procedures capable of extracting multiple analytes, with divergent functional groups, from biological matrices in a timely manner are therefore required. To address this issue, this work describes the development of validated extractive-derivatization methods combined with fast GC-MS analysis for expedient and accurate quantitation of different analytes in occupational monitoring and workplace drug testing. Extractive alkylation of acidic analytes phenol, o-cresol, mandelic acid, hippuric acid, and (o-, m-, p-) methylhippuric acid for simultaneous urinary bio-monitoring of occupational exposure to benzene, toluene, ethylbenzene, and xylene, respectively, is performed. Extractive acylation for simultaneous urinary confirmation of basic analytes amphetamine, methamphetamine, norephedrine, methcathinone, ephedrine, methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA), methylenedioxyethylamphetamine (MDEA) and N-methyl-1-(3,4 methylenedioxyphenyl)-2-butanamine (MBDB) in workplace drug testing is performed. The successful combination of abovementioned techniques alongside fast GC-MS allows increased sample throughput and decreased turn-around time for routine analysis while maintaining bioanalytical quantitative criteria, as required in a clinical toxicology laboratory setting. / Dissertation (MSc)--University of Pretoria, 2009. / Chemical Pathology / unrestricted

A Dissertation submitted in fulfillment of the requirements for the degree Master of Science In the Faculty of Sciences at the University of the Witwatersrand, Johannesburg Johannesburg, January 2015 / Three methods, for the analyses of low levels of moisture in gas samples, were developed and optimized. The analytical techniques included Fourier Transform Infrared Spectroscopy (FTIR) and Pulsed Discharge Helium Ionization/Gas Chromatography (PDHID/GC). The methods included the direct analyses of moisture in gas samples using FTIR as well as the analysis of acetylene (C2H2) by FTIR and GC/PDHID. For the latter methods, the purpose was to convert the moisture in a gas sample to C2H2 by hydrolization of the calcium carbide (CaC2) with moisture to C2H2 and then analyze the resulting C2H2 content by FTIR or GC/PDHID. The C2H2 result was then converted back to moisture to obtain the moisture content of the sample. The FTIR moisture method developed provided eleven different wavenumbers for quantitation providing a wide analytical scope, specifically in complex gas matrices, where there is often peak overlap between matrix and moisture. A heated eight meter glass long path gas cell and a mercury cadmium telluride (MCT) detector were utilized. The FTIR method required much greater volumes of sample than the GC method but allowed for direct analysis of moisture without prior conversion to acetylene. Moisture permeation standards were used for calibration and the LOD’s ranged from 0.5 to 1 ppm with quantification possible from 0.5 to 10ppm. For the FTIR C2H2 method various concentration ranges were established from 50 up to 2000 ppm. Three wavenumbers were evaluated for C2H2 and methane was introduced as an internal standard. The use of methane as an internal standard provided better r2 values on the calibration data than for the tests run without internal standard. A gas chromatographic (GC), pulsed discharge helium ionization detector (PDHID) method for the determination of moisture content in small quantities of gases, based on the conversion of the moisture to acetylene (C2H2) prior to analysis, was developed. The method developed on the GC/PDHID for C2H2, provided a quantitation range from 0.6 to 7.7 ppm. Conversion of the moisture to acetylene was achieved by hydrolysing an excess of calcium carbide (CaC2) in a closed reaction vessel with a measured volume of a sample containing a known quantity of moisture. The gaseous reaction mixture was transferred, using helium (He) carrier gas, to a GC/PDHID, set up with “sample injection and heart cut to detector” to prevent matrix disturbances on the PDHID, for analysis. The acetylene concentration values thus obtained were converted back to moisture values and percentage recoveries calculated. A similar conversion process was applied on FTIR. The conversion of moisture to C2H2 using CaC2 was tested and proven to be viable. Quantification was not possible as the available sample holder could not be adequately sealed to prevent air ingress. This led to higher C2H2 values than expected. This process can be optimized by the design and production of a sealed sample holder.

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Gas Chromatography (GC) is one of the most important and widely used tools in analytical chemistry. However, they are bulky, have a longer measurement cycle, and consume a high amount of power. Micro-Gas Chromatography (µGC) is portable and energy-efficient, which allows onsite, real-time biological, forensic, and environmental analyses. This thesis presents a ready-to-deploy implementation of microfabricated gas chromatography (µGC) system capable of separating complex samples. We describe robust, modular, and scalable hardware and software architecture based on Real-Time Operating System (RTOS) and Python Graphical User Interface (GUI) integrated with various microfabricated devices to realize a fully functional µGC system. A sample heater for headspace injection, microfabricated separation column (µSC), a Photoionization Detector (PI-D), and a flow controller unit are integrated with the modular hardware and software to realize a fully functional Vacuum Outlet µGC system. We have designed a novel auto-calibration method for temperature calibration of the microfabricated devices which does not require changing the electronic circuitry or reprogramming the device. The vacuum outlet µGC setup is tested with various mixture of analytes. For these experiments, an average relative standard deviation (RSD) for retention time repeatability of 2.5% is achieved. Data processing techniques for raw chromatograms, including baseline correction and peak detection, are implemented on a microcontroller board and tested extensively as a part of this work. A novel algorithm for multidimensional analysis for the identification of co-eluting compounds in complex samples is implemented with a prediction accuracy of 94%. / Master of Science / Toxic volatile organic compounds (VOCs) such as benzene and toluene found in gasoline and xylene used in ink, rubber, and leather industries are of concern as they are present at elevated concentrations due to their higher vapor pressure. Sufficient exposure to these toxicants, even at lower concentrations like 100 parts-per-billion-volume (ppbv), may cause adverse health effects. Gas Chromatography (GC) has been the established method for assessing the presence and concentration of VOCs in the environment. Traditional GC systems are bulky, power-hungry, expensive, and require expert supervision for analysis. Recent research in microelectromechanical systems (MEMS) has reduced the size of the GC components, also called micro-GC (µGC), while improving the performance. The majority of the research and development of µGC is aimed at advancing microfabricated components such as preconcentrators, separation columns, and gas detectors. However, the integration of these different components is an important topic that requires more investigation. In this thesis, we present a robust and scalable software and hardware architecture that can be used to develop a portable and modular µGC system. The thesis discusses different experiments to calibrate various microfabricated devices, which are then used to build a fully modular µGC system. We show the separation capacity of the modular µGC system by passing complex compounds like kerosene and diesel. As the chromatogram from the µGC system has noise, the second part of the thesis explores data analysis techniques such as baseline correction, peak detection. These data analysis tools are used to filter the noise, detect relevant peaks in the chromatograms, and identify the compounds in a complex sample.

If the gas chromatographic retention behavior of a compound is known under isothermal conditions at several temperatures, then it is possible to predict accurately the retention time under temperature programmed conditions. This work details the calculations required to perform such predictions. A discussion of isothermal and temperature programmed retention is presented, along with a discussion of carrier gas flow relationships. These theories are then applied to the problem of predicting temperature programmed retention times from isothermal data. It is shown that accurate and precise predictions are possible for many situations. These predicted retention times are then applied to qualitative analysis by the use of retention indices. An architecture for a retention time or index database is proposed. Finally, the use of gas chromatography for the determination of thermodynamic quantities and gas viscosities is demonstrated. / 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

A digital computer was used to measure accurate gas chromatographic peak symmetry, position and dispersion by central statistical moments. Benzene samples were chromatographed on squalane for columns of 3, 6 and 12 foot lengths and 1/8", 1/ 4" and 1/2" diameters as a function of sample size. Peak symmetry was monitored by measuring skew, γ₁ , and "excess," γ₂ two quantities derived from the higher central moments. Skew was found to increase in a positive manner for tailing peaks, pass through a maximum and approach a limiting step form for extremely overloaded columns. Skew could be used to indicate saturation of the liquid phase when it passes through a maximum. Negative skew for fronting peaks also approached a zero limiting form. Excess, γ₂ was found to decrease rapidly for all columns. A few microliters of sample were sufficient to cause significant negative values of excess. Excess provides a semi-quantitative measure of column capacity. Three general types of peak shapes were observed with increasing sample sizes: 1) gaussian behavior at very low sample sizes; 2) distorted peaks suitable characterized by central moments at normal analytical size samples; and 3) highly distorted peaks at larger sample sizes where central moments no longer reflect the step shapes observed. Moments can be used to set limits on sample sizes which will produce these highly distorted peaks. Two moment related measures of skewness were also calculated. Pearson’s skew, (Mean - Mode)/(variance)^½, along with Pearson’s β, γ measure of skewness, were found to qualitatively reflect peak shape behavior only in the region of analytical sample sizes. Pearson's skew is subject to difficult interpretation due to equivalent modal values for large samples and the β, γ measure was insensitive to fronting peaks. Third and fourth central moments were observed to have regular behavior as a function of sample size. A moment definition of resolution was derived R = 0.5 (M(1)₂ - M(1)₁) /( √M(2)₁ + √M(2)₂ ) where M(1) = mean and M(2) = variance. This definition was used to compare solvent efficiency for the separation of benzene and cyclohexane on three liquid phases, squalane, dinonalphalate and TRIS. In terms of equivalent throughput, defined as moment resolution per unit time per gram of sample, TRIS was found to be 175 times more selective than squalane. A preparative chromatograph was built with four thermal conductivity detectors at 50' intervals in a 200' x 3/8" column. Column efficiency was measured by comparison of moment parameters at the end of each 50' section. The column was operated both at normal, high pressure drop (ambient outlet pressure) and low differential pressure (constricted outlet). The condition of high pressure drop caused acceleration of samples through the last two column sections and resulted in much poorer column efficiency. The low differential pressure column, inlet 350 psi, outlet approximately 150 psi produced a more linear velocity and greater column efficiency. In fact 100 feet of the low differential pressure column generated the same resolution as 200 feet of the high pressure column. For most chromatographic peaks manual methods of peak evaluation are subject to significant operator errors due to the subjective nature of assigning base width and peak retention time. The use of moments greatly increases the accuracy of two important measurements; (1) retention time as measure from the first moment and (2) resolution for preparative scale samples as measured from the first and second moments. The method of moments provides an accurate means of measuring retention time, dispersion, resolution and preparative scale equivalent throughput. / Ph. D.