Dissertations / Theses on the topic 'Gas chromatography'
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Akbar, Muhammad. "Chip-Scale Gas Chromatography." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/56566.
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Instrument miniaturization is led by the desire to perform rapid diagnosis in remote areas with high throughput and low cost. In addition, miniaturized instruments hold the promise of consuming small sample volumes and are thus less prone to cross-contamination. Gas chromatography (GC) is the leading analytical instrument for the analysis of volatile organic compounds (VOCs). Due to its wide-ranging applications, it has received great attention both from industrial sectors and scientific communities. Recently, numerous research efforts have benefited from the advancements in micro-electromechanical system (MEMS) and nanotechnology based solutions to miniaturize the key components of GC instrument (pre-concentrator/injector, separation column, valves, pumps, and the detector). The purpose of this dissertation is to address the critical need of developing a micro GC system for various field- applications. The uniqueness of this work is to emphasize on the importance of integrating the basic components of μGC (including sampling/injection, separation and detection) on a single platform. This integration leads to overall improved performance as well as reducing the manufacturing cost of this technology. In this regard, the implementation of micro helium discharge photoionization detector (μDPID) in silicon-glass architecture served as a major accomplishment enabling its monolithic integration with the micro separation column (μSC). For the first time, the operation of a monolithic integrated module under temperature and flow programming conditions has been demonstrated to achieve rapid chromatographic analysis of a complex sample. Furthermore, an innovative sample injection mechanism has been incorporated in the integrated module to present the idea of a chip-scale μGC system. The possibility of using μGC technology in practical applications such as breath analysis and water monitoring is also demonstrated. Moreover, a nanotechnology based scheme for enhancing the adsorption capacity of the microfabricated pre-concentrator is also described.Ph. D.
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Al-Othmany, Dheya Shuja'a. "Tritium enrichment by gas chromatography." Thesis, University of Aberdeen, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240675.
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In the studies related to trace analysis in meteorology, hydrology, medical and clinical research, the measurement and monitoring of tritium released from nuclear facilities and its health physics aspects on human and the environment are of growing importance. The techniques employed currently for the enrichment of tritium are carried out using large samples and require long periods of operation (7 days or more) to obtain the enriched tritium sample. In the present investigation, a laboratory scale chromatography based system was designed, constructed and commissioned successfully to collect enriched tritiated water samples which were then counted to determine the levels of activity. The total time taken to conduct the complete enrichment procedure and counting of the collected samples was less than one working day. This system also showed the capability of enriching quantities of water samples as small as 20 ml. This was about ten times less than required in the conventional enrichment techniques. Extensive efforts were made to attain optimum operational, reproducible and efficient measurements of tritium enrichment for quantitative analysis. The developed experimental technique involved injecting a known volume of water into a preheated furnace to react with magnesium turnings, in the presence of a carrier gas, to produce the hydrogen isotopes. These isotopes were separated using the principles of chromatography. Liquid scintillation counting method was employed to determine the activity of the collected samples. Two gases, nitrogen and helium, were utilized as the carrier gases during this investigation. Best values of enrichment were obtained with the use of nitrogen as a carrier gas, but the samples collected were difficult to count due to the formation of ammonia with consequent chemical complications.
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McGill, Robert Andrew. "Physicochemical measurements by gas chromatography." Thesis, University of Surrey, 1988. http://epubs.surrey.ac.uk/847792/.
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First the method of gas-liquid chromatography (GLC) has been used to obtain partition coefficients, K, at infinite dilution on polymeric and non-polymeric phases. About 30-40 solutes were studied per stationary phase. Secondly the method of gas-solid chromatography has been used to obtain adsorption isotherms for a series of adsorbents by the technique of elution by characteristic point (ECP). A single injection of a gas or vapour suffices to obtain the isotherm, and then the limiting Henry's law constant, Kh, for adsorption at low surface coverage. About 20-30 solutes were studied per adsorbent. Experiments were carried out at several levels of relative humidity (RH) 0%, 31% and 53%. The solute compounds used were chosen so as to have a wide range of properties such as polarity (pi*2), hydrogen-bond acidity (alpha[H]2), and hydrogen-bond basicity (beta[H]2). The results as log partition coefficients or -log Henry's constants were analysed by multiple linear regression analysis using equations such as: -LogK[H] or LogK = SPo + s.pi* 2 + a.alpha[H]2 + b.beta[H]2 + 1. LogL[18] where L[18] is the solute Ostwald absorption coefficient on n-hexadecane. In this way, the selectivity of the liquid polymeric phase or solid adsorbent towards classes of compound was investigated and equations for the prediction of further values of LogK or LogK[H] formulated. In parallel with the measurement of partition coefficients on liquid polymeric phases by GLC in this work, partition coefficients for the polymers have been determined using surface acoustic wave (SAW) devices by coworkers at the Naval Research Laboratory, Washington. The results for a series of 8-9 solutes in six polymeric phases show that partition coefficients and patterns of responses predicted through GLC experiments are the same as those found experimentally using coated SAW devices. Hence GLC can be used to evaluate possible coating materials, and by the technique of multiple linear regression analysis, to predict SAW responses for a multitude of vapours.
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Wang, Anzi. "Microchip Thermal Gradient Gas Chromatography." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4300.
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Although the airbath oven is a reliable heating method for gas chromatography (GC), resistive heating is needed for higher analytical throughput and on-site chemical analysis because of size, heating rate and power requirements. In the last thirty years, a variety of resistive heating methods were developed and implemented for both benchtop and portable GC systems. Although fast heating rates and low power consumption have been achieved, losses in column efficiency and resolution, complex construction processes and difficulties experienced in recovering damaged columns have also become problematic for routine use of resistively heated columns. To solve these problems, a new resistively heated column technique, which uses metal columns and self-insulated heating wires, was developed for capillary gas chromatography. With this method, the total thermal mass was significantly less than in commercial column assemblies. Temperature-programming using resistive heating was at least 10 times faster than with a conventional oven, while only consuming 1—5% of the power that an oven would use. Cooling a column from 350 °C to 25 °C with an air fan only required 1.5 min. Losses in column efficiency and peak capacity were negligible when compared to oven heating. The major trade-off was slightly worse run-to-run retention time deviations, which were still acceptable for most GC analyses. The resistively heated column bundle is highly suitable for fast GC separations and portable GC instruments. Fabrication technologies for microelectromechanical systems (MEMS) allow miniaturization of conventional benchtop GC to portable, microfabricated GC (µGC) devices, which have great potential for on-site chemical analysis and remote sensing. The separation performance of µGC systems, however, has not been on par with conventional GC. Column efficiency, peak symmetry and resolution are often compromised by column defects and non-ideal injections. The relatively low performance of µGC devices has impeded their further commercialization and broader application. This problem can be resolved by incorporating thermal gradient GC (TGGC) into microcolumns. Negative thermal gradients reduce the on-column peak width when compared to temperature-programmed GC (TPGC) separations. This unique focusing effect can overcome many of the shortcomings inherent in µGC analyses. In this dissertation research, the separation performance of µGC columns was improved by using thermal gradient heating with simple set-ups. The analysis time was ~20% shorter for TGGC separations than for TPGC when wide injections were performed. Up to 50% reduction in peak tailing was observed for polar analytes, which significantly improved their resolution. The signal-to-noise ratios (S/N) of late-eluting peaks were increased by 3 to 4 fold. These results indicate that TGGC is a useful tool for bridging the performance gap between µGC and benchtop GC.
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Prazen, Bryan J. "Development of high speed hyphenated chromatographic analyzers and second order data analysis techniques /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11550.
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Lyne, P. M. "Heater displacement chromatography." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376927.
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Thewalim, Yasar. "Retention time predictions in Gas Chromatography." Doctoral thesis, Stockholm University, Department of Analytical Chemistry, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-55088.
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In gas chromatography, analytes are separated by differences in their partition between a mobile phase and a stationary phase. Temperature-program, column dimensions, stationary and mobile phases, and flow rate are all parameters that can affect the quality of the separation in gas chromatography. To achieve a good separation (in a short amount of time) it is necessary to optimize these parameters. This can often be quite a tedious task. Using computer simulations, it is possible to both gain a better understanding of how the different parameters govern retention and separation of a given set of analytes, and to optimize the parameters within minutes. In the research presented here, this was achieved by taking a thermodynamic approach that used the two parameters ΔH (enthalpy change) and ΔS (entropy change) to predict retention times for gas chromatography. By determining these compound partition parameters, it was possible to predict retention times for analytes in temperature-programmed runs. This was achieved through the measurement of the retention times of n-alkanes, PAHs, alcohols, amines and compounds in the Grob calibration mixture in isothermal runs. The isothermally obtained partition coefficients, together with the column dimensions and specifications, were then used for computer simulation using in-house software. The two-parameter model was found to be both robust and precise and could be a useful tool for the prediction of retention times. It was shown that it is possible to calculate retention times with good precision and accuracy using this model. The relative differences between the predicted and experimental retention times for different compound groups were generally less than 1%. The scientific studies (Papers I-IV) are summarized and discussed in the main text of this thesis.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.
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Hickling, Simon James. "Liquid crystal polymers for gas chromatography." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760726.
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Ali, Syed Aftab. "Semi-Packed Micro Gas Chromatography Columns." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/35201.
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Separation of complex gaseous mixtures using gas chromatography (GC) is an important step in analytical systems for environmental monitoring, medical diagnosis, and forensic science. Due to its high resolving power, analysis speed, and small sample size, GC, has become the premier technique for separation and analysis of volatile and semi-volatile organic compounds. Miniaturization of analytical systems has become a major trend which is mainly driven by advancements in microfabrication techniques and a need for portable lab-on-a-chip systems for onsite monitoring. Microfabricated columns have been explored for applications in analytical processes like GC in several research studies. These microGC columns typically have open rectangular or open circular cross sections which is a result of the etching process utilized in the fabrication. This work reports the fabrication and performance of a new generation of silicon-on-glass micro-electro-mechanical systems (MEMS) based GC columns with microposts namely â semi-packed.â These columns can be fabricated on a 2 cm2-die for a 1 m-long channel or a 1 cm2-die for a 25 cm-long channel. The semi-packed columns have a higher sample capacity as the overall surface area is larger than that of open rectangular columns of the same dimensions. The separation efficiency of these columns is also superior to that of open columns due to the presence of the microposts. As compared to conventional packed columns, the semi-packed columns show lower pressure drops and a more uniform flow profile, both of which contribute to, performance in terms of separation efficiency.Master of Science
10
Contreras, Jesse Alberto. "Axial Temperature Gradients in Gas Chromatography." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2645.
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The easiest and most effective way to influence the separation process in gas chromatography (GC) is achieved by controlling the temperature of the chromatographic column. In conventional GC, the temperature along the length of the column is constant at any given time, T(t). In my research, I investigated the effects of temperature gradients on GC separations as a function of time and position, T(t,x), along the column. This separation mode is called thermal gradient GC (TGGC). The research reported in this dissertation highlights the fundamental principles of axial temperature gradients and the separation potential of the TGGC technique. These goals were achieved through the development of mathematical models and instrumentation that allowed study of the effects of axial temperature gradients. The use of mathematical models and computer simulation facilitated evaluation of different gradient profiles and separation strategies prior to development of the instrumentation, providing theoretical proof of concept. Three instruments capable of generating axial temperature gradients, based on convective cooling and resistive heating, were developed and evaluated. Unique axial temperature gradients, such as nonlinear and moving sawtooth temperature gradients with custom profiles were generated and evaluated. The results showed that moving sawtooth temperature gradients allowed continuous analysis and were well-suited for comprehensive GCxGC separations. The use of custom temperature profiles allowed unique control over the separation power of the system, improving separations, as well as selectively increasing the peak capacity and signal-to-noise. A direct comparison of TGGC with conventional GC methods showed that TGGC produces equivalent separations to temperature programmed GC. This technology holds great promise for performing smart separations in which the column volume is most efficiently utilized and optimum separations can be quickly achieved. Moreover, precise control of the elution of compounds can be used to greatly reduce method development time in GC. This feature can be automated using feedback to develop efficient separations with minimum user intervention. This technology is of special interest in micro-GC systems, which allows relatively easy incorporation of resistive heating elements in the micro-column design.
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Reiner, George Allen. "An explosive vapor generator based on capillary gas chromatography." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39761.
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Foster, Austin Richard. "Thermal Gradient Characterization and Control in Micro-Fabricated Gas Chromatography Systems." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7481.
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In order to make gas chromatography (GC) more widely accessible, considerable effort has been made in developing miniaturized GC systems. Thermal gradient gas chromatograpy (TGGC), one of the heating methods used in GC, has recieved attention over the years due to it's ability to enhance analyte focusing. The present work seeks to develop high performance miniaturized GC systems by combining miniaturized GC technology with thermal gradient control methods, creating miniaturized thermal gradient gas chromatography (µTGGC) systems. To aid in this development a thermal control system was developed and shown to successfully control various µTGGC systems. DAQ functionality was also included which allowed for the recording of temperature and power data for use in modeling applications. Thermal models of the various µTGGC systems were developed and validated against the recorded experiemental data. Thermal models were also used to aid in decisions required for the development of new µTGGC system designs. The results from the thermal models were then used to calibrate and validate a stochastic GC transport model. This transport model was then used to evaluate the effect of thermal gradient shape on GC separation performance.
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Vilorio, Carlos R. "Gas Chromatography Micro-Chip with High Temperature Interface and Silk Screen Heaters." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8690.
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There has been substantial market demand for a portable Gas Chromatography (GC) system. Throughout the years, much progress has been made on fabricating a micro system that works as well as a benchtop system. Unfortunately, even though many substrates, channel types, channel widths, temperature control systems, and interface solutions have been attempted, existing versions of the micro-GC still fall short of the ideal. This thesis presents the design, fabrication, and testing of a silicon based micro-GC column that presents a solution for interfacing and heating of the chip. A polyimide resin is used to create a durable high temperature low thermal mass interface with the chip, while a silk screen method is demonstrated for easy printing of heaters. Chromatogram results are shown in both Temperature Program and Thermal Gradient runs.
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McBrady, Adam Dewey. "Microfabricated chromatographic instrumentation for micro total analysis systems /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/8570.
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Michelsen, Peter J. "Relationship between chromatographic retention and donor and acceptor numbers /." Online version of thesis, 1990. http://hdl.handle.net/1850/10688.
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Doolan, K. P. "Pyrolysis gas chromatography mass spectrometry of paints." Thesis, Queen's University Belfast, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269081.
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Bagheri, Habib. "Vapour-phase fluorescence detection in gas chromatography." Thesis, University of East Anglia, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280036.
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Chow, W. M. L. "Capilliary column gas chromatography in forensic science." Thesis, University of Strathclyde, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371945.
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McLaughlin, Paul John. "Temperature programmed, multiple probe, inverse gas chromatography." Thesis, Manchester Metropolitan University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393284.
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Perera, Ibon. "Characterisation of heterogeneous surfaces by gas chromatography." Thesis, Manchester Metropolitan University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431240.
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Bao, Jianxiong. "Negative Temperature Programming using Microwave Gas Chromatography." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33828.
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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
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Urias, Kari R. "Experimental Studies in Temperature Programmed Gas Chromatography." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/36026.
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Temperature programmed gas chromatography (TPGC) is commonly used for the analysis of complex samples with a wide range of boiling points. It is estimated that 80% of GC users implement TPGC on a regular basis. In 1962, John Calvin Giddings was the first to publish a simple model for TPGC. His theories concerning TPGC are still accepted as the benchmark for explaining the underlying theory.
The purpose of this research was to investigate, as speculated by Giddings, if temperature programming rate (b) is the dominant contribution in determining fundamental chromatographic values, such as retention time, retention temperature and resolution. Comparison of these effects was made by studying column length and linear velocity in conjunction with temperature programming rates. Experimental determinations using a combination of three different column lengths, five linear velocities and three ramping rates on a three-component sample were investigated. A late eluting peak, C14, was evaluated by statistical analysis to determine the dominant contribution on retention time, retention temperature and resolution.
Results from statistically analysis show that temperature programming rate (b), column length and linear velocity all have contributions on retention time, retention temperature and resolution, however b dominates at high programming rates.Master of Science
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Hirtenstein, Daniel andre. "Surface Modifications for Gas Chromatography Micro Columns." W&M ScholarWorks, 2013. https://scholarworks.wm.edu/etd/1539626945.
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Al-Sayegh, A. J. "Determination of mixtures of sulfonamides by pyrolysis-gas chromatography following thin-layer chromatographic separation." Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379714.
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Lu, Yao. "Forensic Applications of Gas Chromatography-Differential Mobility Spectrometry, Gas Chromatography/Mass Spectrometry, and Ion Mobility Spectrometry with Chemometric Analysis." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1267816777.
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Noh, Hongseok "Moses." "Parylene Microcolumn for Miniature Gas Chromatograph." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4983.
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This research contributes to worldwide efforts to miniaturize one of the most powerful and versatile analytical tools, gas chromatography (GC). If a rapid, sensitive and selective hand-held GC system is realized, it would have a wide range of applications in many industries and research areas. As a part of developing a hand-held GC system, this research focuses on the separation column, which is the most important component of a GC system. This thesis describes the development of a miniature separation column that has low thermal mass and an embedded heating element for rapid thermal cycling. The worlds first thin polymer film (parylene) GC column has been successfully developed. This thesis includes: first, a study of theoretical column performance of rectangular GC column; second, the design optimization of parylene column and embedded heating element; third, the development of new processes such as parylene micromolding and stationary phase coating technique for parylene column; fourth, the fabrication of parylene GC column with an embedded heating element; and lastly, the testing and evaluation of parylene GC column through GC analysis.
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Silwal, Indira K. C. "Characterization of Unknown Chemicals Using Gas Chromatography/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and AB-Initio Calculations." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/SilwalIKC2008.pdf.
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Heslop, Mark J. "Binary gas adsorption in molecular sieves." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/6861.
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This thesis is concerned with the development of sorption-effect chromatography as a rapid method for the determination of binary gas-mixture adsorption isotherms.There are many alternative non-chromatographic methods but these have inherent disadvantages the direct experimental methods require excessive equilibration times and the predictive methods require the respective pure-component isotherms and an ideal adsorbed phase. A computer simulation has shown that for an alternative chromatographic method, good results will only be obtained if both binary isotherms are close to linear. Sorption-effect chromatography is characterised by the flowrate retention time (TN) which measures the change in column inventory when a perturbation is made to the system. Along with the standard composition retention time (Tx), this extra measurement allows the gradient of each binary isotherm to be evaluated. Subsequent integration will give the respective mixture isotherm. Three gas systems (nitrogen-argon, nitrogen-helium and argon-helium) have been investigated over zeolite 5A at different temperatures. The results confirm that the adsorbed phase amounts decrease, with increasing temperature and that there are degrees of component interaction. Experimentally, thermal fluctuations in the oven will cause noise on the flowrate record making TN determination difficult. Isolation of the column from direct air flow was seen to reduce the noise level. Also, using a computer simulation model, the heat of adsorption for the above zeolite 5A systems will be easily dissipated preventing any unwanted gas temperature rises; the comparatively small column diameter was found to be a significant factor. The employment of delay lines (empty tubes) in various locations has been investigated. To directly determine TN it is necessary to used delay lines downstream of the column. Also, the chromatographic method has been extended to determine mixture isotherms by considering the change in average column pressure rather than the motion of a composition front through the column. Delay lines situated upstream of the column are able to separate these two effects, and preliminary results are satisfactory. However, the use of delay lines anywhere in the system changes the measured retention times and the theory has to be adjusted to account for this.
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Venter, Andre. "Comprehensive two-dimensional supercritical fluid and gas chromatography (SFCxGC)." Thesis, Pretoria : [s.n.], 2003. http://upetd.up.ac.za/thesis/available/etd-03132003-161136.
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Perera, S. P. "Gas chromatography and surface chemistry of porous polymers." Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376652.
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Hunter, Maxwell Charles. "Analysis of atmospheric oxygenated hydrocarbons by gas chromatography." Thesis, University of Leeds, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399908.
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Dias, H. "Gas and liquid chromatography on porous graphitic carbon." Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/13643.
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A new hydrophobic support material, Porous Graphitic (or Graphitised) Carbon (PGC) has been studied using both Liquid (LC) and Gas Chromatography (GC). The heat of adsorbtion (AH) of typical LC solvents determined on PGC, using GC, showed that AH increased with the molecular area (Ax) of solvents for well graphitised carbons, but that AH/Ax values were similar for all solvents studied. By definition, AH/Ax is a measure of eluotropic strength. The results reveal that a strong eluotropic series does not exist on carbon. A strong eluotropic series does exist on silica. In this case, AH/Ax values of solvents were dependent upon their eluotropic strengths (Eo), determined by LC. GC work was carried out using alcohols, ketones and aliphatic hydrocarbons on PGC, modified with different amounts of Carbowax 1500. Symmetrical peaks were obtained with coated materials. The column efficiency (N), first increased and then dropped with increasing Carbowax content on the PGC surface. The retention of ketones and hydrocarbons decreased with increasing amount of Carbowax on PGC. In the case of alcohols, the retention decreased with the initial introduction of Carbowax on to PGC. Some alcohols displayed enhanced retention at 0.10% of Carbowax. All alcohols showed increased retention at the monolayer coverage of Carbowax. In the quest for a perfect material for adsorption GC, PGC samples were hydrogen treated at elevated temperatures (230-1030°C). All hydrogen treated samples failed to display signficantly improved chromatographic properties. PGC was then treated with toluene in a stream of either hydrogen (at 630°C) or nitrogen (at 630°C or 300°C) to eliminate any active sites present on the surface. Hexane was used us an alternative to toluene at 630°C in a stream of hydrogen. Such surface treatments yielded improved materials for adsorption GC. On heating the columns (beyond 230"C), containing these materials, with carrier gas running through the columns, the Chromatography deteriorated in the cases of toluene-treated PGC whilst the Chromatography of the hexane-treatcd PGC remained unaffected. LC work on some aromatic compounds using PGC, coated with surfactants such as Tween 80 or Span 80 showed that, analyte retention decreased with increasing surfactant concentration (up to 0.03% of Tween and 0.02% of Span) in the eluent. N dropped with the introduction of Tween to the PGC. Increasing the ratio of water to mcthanol in the eluent, at a constant eluent concentration of surfactant, resulted in diminishing N, increasing eluent polarity and analyte retention values. Ion pairing was carried out on PGC using cetyltrimethylammonium-bromide (CTAB) as the ion pairing agent, at an eluent pH of 12.5. The retention of solutes, that ionise under these conditions, increased whereas the retention of analytes, that do not ionise, decreased with increasing eluent concentration of CTAB. The coated or chemically modified PGC surfaces are useful in GC whilst the dynamically coated PGC surfaces are important in LC. Such surface treatments can alter the following properties of PGC; (a) Retention characteristics, (b) the selectivity and (c) chromatographic efficiency.
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Webster, Caroline S. "Applications of coupled gas chromatography-atomic emission detection." Thesis, Sheffield Hallam University, 1995. http://shura.shu.ac.uk/20507/.
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This thesis describes the evaluation and application of the atomic emission detector as a detector for capillary gas chromatography. Chapter 1 is a general introduction to the technique, describing the development of the atomic emission detector, the theory of its operation, and some of its applications. This chapter also includes a detailed description of chromatography theory. Chapter 2 describes the experimental conditions used throughout the course of this work. Chapter 3 concentrates on compound independent calibration, beginning with a general introduction to the area and a discussion of studies already made. Four groups of compounds were used to determine the ability of the atomic emission detector to perform compound independent calibration. Initial studies with a group of similar hydrocarbons showed little or no compound/structure dependence. However, results from the same study with a group of phenols did indicate some structure dependence for carbon and oxygen, but when chloroanisoles were tested, this compound dependence was not apparent. A group of different nitrogen-containing compounds was then studied. Here structure dependence was observed on all channels, ie carbon, oxygen and nitrogen. It was also noted that the responses became non-linear at higher concentrations. This would normally indicate detector overload, but not in this case as non-linearity occurred to different extents for the same element in different compounds. A study was also made on the effect of discharge tube ageing on response. Clean and dirty discharge tubes were used for the phenols and the nitrogen-containing compounds. The phenol, carbon and chlorine results showed a decreased sensitivity with the old tube, but the oxygen responses were not affected. The same drop in sensitivity was seen with the nitrogen-containing compounds, but here oxygen was also affected. Chapter 4 describes the use of the atomic emission detector and mass spectrometry as complementary techniques. Perfume samples were analysed using both instruments. A comparison of 'real' and 'fake' perfumes was also made. Results indicated that the atomic emission data was useful in deciding whether to accept or reject mass spectral library guesses. Chapter 5 describes the application of the atomic emission detector for the analysis of refinery streams. The use of the 'backamount' correction facility was also effectively demonstrated. Chapter 6 is a general discussion of the instrument including operational problems encountered and possible modifications to overcome these problems. The overall objective of the thesis is to place the GC-AED combination in the context of the commonly used chromatographic techniques.
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Chan, Ryan. "Density Modulated Semi-Packed Micro Gas Chromatography Columns." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/83448.
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With the continued evolution of MEMS-based gas chromatography, the drive to develop new standalone systems with lower power consumptions and higher portability has increased. However, with improvements come tradeoffs, and trying to reduce the pressure drop requirements of previously reported semi-packed columns causes a significant sacrifice in separation efficiency. This thesis covers the techniques for evaluating the separation column in a gas chromatography system as well as the important parameters that have the most effect on a column’s efficiency. Ionic liquids are introduced as a stable and versatile stationary phase for micro separation columns. It then describes a MEMS-based separation column design utilizing density modulation of embedded micro-pillars which attempts to optimize the balance between separation efficiency and pressure drop.Master of Science
Gas chromatography is a technique used by scientists to separate and identify chemical compounds present in a given test mixture. It is a versatile technique that can be used for qualitative and quantitative analysis of complex mixtures in a variety of applications. However, typical gas chromatography systems are confined to a lab because they are large and consume a lot of power. In order to overcome these problems, different research groups have focused their attention towards the development of portable MEMS-based gas chromatography systems. By miniaturizing the various components of a gas chromatography system, these two main issues can be alleviated. This thesis covers the strategies used to develop and evaluate the separation column of a gas chromatography system and introduce a new MEMS-based column design that will further reduce the power consumption.
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Turner, Kelly A. "Polyethylene glycol stationary phases for capillary gas chromatography." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/44090.
Full textAbstract:
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, crossâ 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 crossâ 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
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Williamson, Yuping. "Studies on concentration overload in micellar electrokinetic chromatography and peak overlap in gas chromatography /." Available to subscribers only, 2006. http://proquest.umi.com/pqdweb?did=1240704131&sid=7&Fmt=2&clientId=1509&RQT=309&VName=PQD.
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Johnson, Kevin J. "Strategies for chemometric analysis of gas chromatographic data /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/8513.
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Heng, Kien Chhiev. "Effect of column temperature on elution order in gas chromatography." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-01312009-063555/.
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Snow, Nicholas Harrer. "Numerical extrapolations for retention time prediction in capillary gas chromatography." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-170350/.
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Armstrong, Stephanye Dawn. "The effects of carrier gas viscosity on column efficiency in capillary gas chromatography." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06162009-063602/.
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FRAZER, SCOTT RAYMOND. "INFORMATION EXTRACTION IN CHROMATOGRAPHY USING CORRELATION TECHNIQUES." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187978.
Full textAbstract:
While research into improving data quality from analytical instrumentation has gone on for decades, only recently has research been done to improve information extraction methods. One of these methods, correlation analysis, is based upon the shifting of one function relative to another and determining a correlation value for each displacement. The cross correlation algorithm allows one to compare two files and find the similarities that exist, the convolution operation combines two functions two dimensionally (e.g. any input into an analytical instrument convolves with that instrument response to give the output) and deconvolution separates functions that have convolved together. In correlation chromatography, multiple injections are made into a chromatograph at a rate which overlaps the instrument response to each injection. Injection intervals must be set to be as random as possible within limits set by peak widths and number. When the input pattern representation is deconvolved from the resulting output, the effect of that input is removed to give the instrument response to one injection. Since the operation averages all the information in the output, random noise is diminished and signal-to-noise ratios are enhanced. The most obvious application of correlation chromatography is in trace analysis. Signal-to-noise enhancements may be maximized by treating the output data (for example, with a baseline subtraction) before the deconvolution operation. System nonstationarities such as injector nonreproducibility and detector drift cause baseline or "correlation" noise, which limit attainable signal-to-noise enhancements to about half of what is theoretically possible. Correlation noise has been used to provide information about changes in system conditions. For example, a given concentration change that occurs over the course of a multiple injection sequence causes a reproducible correlation noise pattern; doubling the concentration change will double the amplitude of each point in the noise pattern. This correlation noise is much more amenable to computer analysis and, since it is still the result of signal averaging, the effect of random fluctuations and noise is reduced. A method for simulating conventional coupled column separations by means of time domain convolution of chromatograms from single column separations is presented.
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Haudebourg, Raphael. "Application of sputtering to micro gas chromatography : a novel collective stationary phase disposition technique for micro gas chromatography columns fabrication : feasibility, evaluations and oilfield applications." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2014. http://tel.archives-ouvertes.fr/tel-00987621.
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A totally new solid stationary phase deposition technique for micro machined gas chromatography (GC) columns fabrication was proposed: to overcome the limitations of conventional liquid (or occasionally solid) stationary phases in terms of very volatile compounds retention and/or clean room batch production, an approach consisting of the collective direct deposition of the adsorbent in micro columns channels by sputtering was performed. The process was fully compatible with clean room fabrication flow and industry-ready, with very good precision results. Silica, alumina, graphite and magnesia were proven able to separate volatile hydrocarbons. Various types of columns (structure, stationary phase) were fabricated in the form of 2x2 cm² silicon-Pyrex chips, and their thermodynamic and kinetic evaluations were reported. Retentions were observed to increase from magnesia to graphite through alumina and silica and with phase ratio decrease, as expected; very satisfying efficiencies were obtained: more than 5700 plates, and 250 µm-high plates. The possibility to use such columns for fast in-situ and autonomous monitoring of light hydrocarbons in oilfield environments was demonstrated by the implementation of a chip temperature-programming system and various versatility tests (high temperatures, carrier gas, humidity): a complete C1-C9 linear alkanes separation was performed in less than 15 seconds, as well as complex mixtures fast separations (isomers, unsaturated), and an industrial confidential application was developed and patented. Therefore, sputter-deposited stationary phase micro columns opened numerous perspectives for the developments of miniaturized GC apparatuses.
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Alcala, Saavedra Monica. "Design of solid state composites for enantiomeric separations /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Kehoe, Jonathan Joseph. "Total marine lipid profiling by short column gas chromatography /." Internet access available to MUN users only, 2003. http://collections.mun.ca/u?/theses,157942.
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Song, Shin Miin, and shinmiin@singnet com sg. "Comprehensive two-dimensional gas chromatography (GCxGC ) for drug analysis." RMIT University. Applied Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080627.114511.
Full textAbstract:
Separation technologies have occupied a central role in the current practices of analytical methods used for drug analysis today. As the emphasis in contemporary drug analysis shifts towards ultra-trace concentrations, the contribution from unwanted matrix interferences takes on greater significance. In order to single out a trace substance with confidence from a rapidly expanding list of drug compounds (and their metabolites) in real complex specimens, analytical technologies must evolve to keep up with such trends. Today, the task of unambiguous identification in forensic toxicology still relies heavily upon chromatographic methods based on mass spectrometric detection, in particular GC-MS in electron ionisation (EI) mode. Although the combined informing power of (EI) GC-MS has served faithfully in a myriad of drug application studies to date, we may ask if (EI) GC-MS will remain competitive in meeting the impending needs of ultra-trace drug analysis in the fut ure? To what extent of reliability can sample clean-up strategies be used in ultra-trace analysis without risking the loss of important analytes of interest? The increasing use of tandem mass spectrometry with one-dimensional (1D) chromatographic techniques (e.g. GC-MS/MS) at its simplest, considers that single-column chromatographic analysis with mass spectrometry alone is not sufficient in providing unambiguous confirmation of the identity of any given peak, particularly when there are peak-overlap. Where the mass spectra of the individual overlapping peaks are highly similar, confounding interpretation of their identities may arise. By introducing an additional resolution element in the chromatographic domain of a 1D chromatographic system, the informing power of the analytical system can also be effectively raised by the boost in resolving power from two chromatographic elements. Thus this thesis sets out to address the analytical challenges of modern drug analysis through the application of high resolut ion comprehensive two-dimensional gas chromatography (GCeGC) to a series of representative drug studies of relevance to forensic sciences.
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Samiveloo, Silverraji Chemistry Faculty of Science UNSW. "High speed comprehensive two-dimenstional gas chromatography/mass spectrometry." Awarded by:University of New South Wales, 2005. http://handle.unsw.edu.au/1959.4/39732.
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The use of short columns, higher carrier gas velocity and fast temperature programs in Comprehensive Two-Dimensional Gas Chromatography coupled to Time-of- Flight Mass Spectrometry (GC x GC/TOFMS) technique is expected to increase the speed of analysis up to several orders of magnitude when compared to conventional gas chromatography (GC) or gas chromatography/mass spectrometry (GC/MS). A systematic evaluation of the GC x GC/TOFMS configuration for high-speed applications has received little attention in the literature. The feasibility of High Speed Comprehensive Two-Dimensional Gas Chromatography coupled to Mass Spectrometry (High speed GC x GC/MS) for complex mixtures has been investigated in this thesis. A particular focus was placed on comparing conventional scanning quadrupole mass spectrometry (qMS) with a newly available non-scanning time-of-flight instruments (TOFMS). Experiments were carried out using GC/qMS, GC x GC/qMS, GC/TOFMS and GC x GC/TOFMS both in normal (slow) and fast temperature rates coupled with high frequency modulation in GC x GC. Initially a complex mixture consists of 24 semivolatile compounds was used as the analyte for the above purpose. In the initial experiments parameters like acquisition rate and duty cycle for qMS were determined to evaluate the effectiveness of the instrument for fast analysis. The practical duty cycle value obtained for the qMS was only about 18 % for single ion and one compound at a dwell time of 10 ms in SIM mode. In both high-speed GC/qMS and high-speed GC x GC/qMS techniques only about 40 % of the components in the complex mixture were found to be well separated. The acquisition rate of scanning instruments like qMS is incompatible for fast eluting peaks in high speed GC. TOFMS that has an acquisition rate of several hundred spectra per second offer the potential to define the fast GC peaks accurately. The high quality spectra from TOFMS also enable deconvolution of coeluting peaks in the complex mixtures. The advantage of the automated spectral deconvolution is demonstrated for the identification of the coeluting peaks in the complex mixtures. Coelution of peaks is also observed with highspeed GC/TOFMS technique. The high-speed GC x GC/TOFMS was also tested with two different analyte system ??? A pesticide mixture and platformate (an aromatic mixture) to evaluate the suitability for high-speed analysis of complex mixtures. A poor resolution was observed for the pesticide mixture in the two-dimensional plane and it appeared, as there was nearly no orthogonal separation in the second dimension. The platformate mixture displayed a better two-dimensional separation. Chromatographic peak resolution is not really a primary requirement for locating and identifying the coeluting compounds in high-speed GC x GC/TOFMS technique. However, it was observed that the high-speed GC x GC/TOFMS too faced problem to unscramble the mass spectra of those compounds with similar structure and sharing the same unique masses.
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Dremetsika, Assimina V., Panayotis A. Siskos, and Nicholas A. Katsanos. "Coefficients in solid-state diffusion by inverse gas chromatography." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196477.
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Manurkar, Shaunak Sudhir. "Modular GC: A Fully Integrated Micro Gas Chromatography System." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/105044.
Full textAbstract:
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.
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Drake, Samantha Jane. "Chiral profiling of methylamphetamine using gas chromatography/mass spectrometry." Thesis, University of the West of Scotland, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.734170.
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Dremetsika, Assimina V., Panayotis A. Siskos, and Nicholas A. Katsanos. "Coefficients in solid-state diffusion by inverse gas chromatography." Diffusion fundamentals 2 (2005) 89, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14424.
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