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.

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

Gaseous phase is a critical state of matter around us. It mediates between the solid crust on earth and inter-stellar vacuum. Apart from the atmosphere surrounding us where compounds are present, natively, in a gaseous phase, they are also trapped within soil and dissolved in oceanic water. Further, those that are less volatile do enter the gaseous phase at high temperatures. It is this gaseous phase that we inhale every second. It is thus critical that we possess the tools to analyze a mixture of gaseous compounds. One such method is to separate the components in time and then identify, primarily based on the retention times, also known as gas chromatography. This research focuses on the development of gas detectors and their integration, in different styles, primarily for gas chromatography. Utilizing fabrication techniques used in semiconductor industry and exploiting scaling laws we investigate the ability to improve on conventional gas separation and identification techniques. Specifically, we have provided a new spin to the age-old thermal conductivity detector enabling its monolithic integration with a separation column. A reference-less, two-port integration architecture and a one-of-its-kind released resistor on glass are some of its salient features. The operation of this integrated device with a preconcentrator and in a matrix array was investigated. The more unique contribution of this research lies in the innovative discharge ionization detector. An ultra-low power, sensitive, easy to fabricate detector, it requires more investigation for a thorough understanding and will likely mature to replace the thermal conductivity detector, as the detector of choice for universal detection, in time to come. / Ph. D.

Advances in micro-electro-mechanical-systems (MEMS) along with nanotechnology based methods have enabled the miniaturization of analytical chemistry instrumentation. The broader aim is to provide a portable, low-cost, and low-power platform for the real-time detection and identification of organic compounds in a wide variety of applications. A benchtop gas chromatography (GC) system is considered a gold standard for chemical analysis by analytical chemists. Similarly, miniaturization of key GC components (preconcentrator, separation column, detector, and pumps) using micro- and nanotechnology based techniques is an on-going research field. This dissertation specifically deals with the design, fabrication, coating, and chromatographic testing of microfabricated separation columns for GC. This work can be broadly categorized into three research areas: design and development of new column designs, introduction of new stationary phases and the development of novel fabrication methodologies for integrating functionalized thin-film into microchannels for chromatographic separations. As a part of this research, two high performance new micro column designs namely width-modulated and high-density semi-packed columns are introduced for the first time. Similarly, two new types of functionalized stationary phases are also demonstrated i.e. a highly stable and homogenous silica nanoparticles coating deposited using a layer-by-layer self-assembly scheme and a highly conformal functionalized thin aluminum oxide film deposited using atomic layer deposition. Moreover, novel thin-film patterning methods using different microfabrication technologies are also demonstrated for high-aspect ratio multicapillary and semi-packed columns. / Ph. D.

Gas Chromatography (GC) is an analytical technique in the chemistry field widely used to separate compounds present in a sample mixture. Conventional GC systems are an extremely versatile and powerful tool to perform complex separations. However, these systems come with the cost of being bulky and requiring a high amount of power for operation. With considerable research for over 40 years, the advent of Micro-Gas Chromatography (µGC) made it possible for miniaturized, compact, low-power, and field portable GC systems. This thesis presents a portable µGC system that enables real-time analysis of complex compound separations, made possible with the use of multiple separation columns and a novel multidimensional compound identification algorithm. The system architecture and the software design with multiple features enabling portability of the µGC system are discussed. A set of microfabricated separation columns (µSCs) and photoionization detectors (PIDs) are integrated to realize a fully functional µGC system that is tested with different types of complex compound mixtures. An in-depth analysis of processing the output chromatograms obtained from the setup for signal filtering and peak detection is described in this thesis. A multidimensional analysis for compound identification in complex mixtures is presented. / Master of Science / Volatile organic compounds (VOCs) are generally chemicals that have high vapor pressure and low boiling points used and produced in the processing of petroleum products, paint, refrigerants, pharmaceuticals, and adhesives. VOCs are emitted as gases from certain solids or liquids, some of which may have short- and long-term adverse health effects even with minute exposure. Gas Chromatography (GC) is a common analytical technique used to detect, identify, and quantify VOCs in the environment, and conventional GC Systems have been utilized for this purpose. The separation of compounds occurs inside an analytical column that has selective interaction between the column and the analytes passing through. However, these systems are expensive, bulky, consume high power, and require expertise to operate. Recently, advancements in the Microelectromechanical systems (MEMS) field has paved the way to create Micro-Gas Chromatography (µGC) systems with improved performance when compared to traditional systems. Active research is ongoing to improve the portability of µGC systems for reliable and quick on-field analysis. In this thesis, we present a µGC system that has a robust and scalable design that allows the development of a portable µGC system. The compound separation of complex mixtures is showcased using the portable µGC system setup. The output chromatograms obtained from the µGC system are pre-processed, which involves noise filtering and peak detection, followed by an analysis using a multidimensional compound identification algorithm.

Micro gas chromatography (μGC) system is a miniaturized and portable version of the conventional GC system, suitable for various applications such as healthcare and environmental analysis. The process of gas chromatography requires precise temperature control for the micro-fabricated preconcentrators and separation columns used since temperature changes directly affect retention time. Proportional Integral and Derivative (PID) controllers provide reliable temperature control and can be tuned to obtain the desired response. The conventional method of tuning the PID control parameters by trial and error is a tedious process and time-consuming process. This thesis aims to develop a PID auto-tuning and control system for auto-tuning microfabricated heaters in modular μGC systems. The developed system is based on the Ziegler Nichols rule-based PID tuning method for closed-loop systems, which uses the relay response of the micro-heater to calculate the PID tuning parameters. The system also includes an analysis system to verify the performance of the PID-tuned values and a tuning system where the PID values can be further tuned to obtain more precise control for the heaters. The aim of developing this system is to reduce the effective tuning time for heaters while satisfying the control requirements. In this thesis, we discuss the tuning methodology and the implementation of the PID tuning and control system, followed by a performance evaluation of the heaters tuned using the proposed system is discussed. / Master of Science / Gas chromatography (GC) is an established technique used for the qualitative and quantitative analysis of compounds present in a mixture. Micro-gas chromatography (μGC) systems are miniaturized versions of conventional GC systems. They are portable, energy-efficient, and facilitate on-site analysis in real-time, which is suitable for applications such as health care, forensics, and environmental analysis, requiring in-field analysis. GC is based on the principle that components of a gaseous mixture, when passed through a heated column coated with a stationary phase, separate out based on their extent of interaction with the stationary phase. The temperature control needs to be precise since it directly affects the process. PID control is the most common and reliable method for temperature control. It can be tuned to obtain the desired response, which can, however, be a tedious process. This thesis aims to develop a PID auto-tuning and control system for μ-fabricated heaters in μGC systems. As a part of this thesis, a system facilitating faster tuning of PID parameters for a given heater using the Ziegler Nichols closed-loop tuning method is developed. It uses the relay response of the micro-heater to determine the tuning value. The obtained PID values can be evaluated using the analysis system developed as a part of the system and can be further fine-tuned using the provided system to obtain the desired response. As a part of this thesis, we first discuss the development of the PID tuning and control system, after which the performance of the tuned values is evaluated for two micro-heaters.

This thesis describes the implementation of zero-cost auto-tuning techniques for embedded Proportional Integral and Derivative (PID) controllers, specifically focusing on their application in the control of proportional valves within Micro Gas Chromatography (uGC) systems. uGC systems are miniaturized versions of conventional GC systems, and require precise temperature, flow and pressure control for the micro-fabricated preconcentrators and micro columns. PID controllers are widely used in process control applications due to their simplicity and effectiveness. The Commercial Off The Shelf (COTS) available controllers are expensive, bulky, need system compatibility and have high lead times. The proposed auto-tuner features simple Python-implemented empirical calculations based on Ziegler Nichols relay-based PID tuning method to determine the optimal PID gains. Leveraging Wi-Fi the system enables tuning for any embedded platform while visualizing transient response through the Graphical User Interface (GUI). The embedded-GUI interface provides a customizable auto-tuning experience extending usage across diverse temperature, pressure and flow regulation applications in environmental analysis. Specifically for uGC systems, the GUI integrates with existing hardware stack using minor software enhancements to enable rapid, automated PID tuning for thermal and flow control applications. The performance is analyzed by evaluating response metrics including overshoot, rise time, and steady-state error. / Master of Science / Commercially available flow and thermal regulators are expensive and bulky. In applications like micro gas chromatography (uGC) systems, these commercial tools to regulate actuator control reduce portability and may require different regulators for different control ranges. To overcome these challenges, we developed an open-source, transparent Proportional-Integral-Derivative (PID) auto-tuner for micro-electromechanical systems (MEMS) actuators in uGC systems. The proposed Python-based Graphical User Interface (GUI) approach leverages simple empirically-driven calculations to determine optimal gains. By interfacing with any embedded system through standard connection like Wi-Fi, the auto-tuner enables interactive, vendor-agnostic tuning while visualizing full transient response. This provides accessible, customizable auto-tuning capabilities to enhance closed-loop PID control across instrumentation and device applications at no or minimal additional hardware cost. In uGC systems, we utilize the same setup for thermal, flow, and pressure control, with additional sensor costs offset by the implementation of multiple closed loops on the same system.Precise temperature and flow control is critical in many applications, such as minimizing fluctuations in analyte retention times in uGC systems. PID control offers reliable closed-loop control for such applications, but tedious manual tuning is required for each system. The proposed auto-tuner presented in this work will greatly simplify PID tuning to improve temperature and flow rate precision in these systems. The performance is analyzed by evaluating response metrics including overshoot, rise time, and steady-state error. This thesis discusses the auto-tuning technique, PID implementation, and experimental performance analysis. Overall, this work presents a novel embedded PID automated methodology for rapid and precise thermal and flow control in uGC and other precision regulation applications. The proposed auto-tuning method provides effective tuning across a wide variety of applications such as motors, temperature and pressure control, and flow regulation systems.

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.

Une nouvelle technique de dépôt de phases stationnaires solides pour la fabrication de micro colonnes de chromatographie en phase gazeuse a été proposée : pour dépasser les limites des phases stationnaires liquides conventionnelles (ou occasionnellement solides) en termes de rétention des composés très volatiles et/ou de fabrication par lots en salle blanche, une approche consistant en le dépôt direct de l'adsorbant sur le substrat par pulvérisation cathodique a été mise en œuvre. La méthode est par nature compatible avec le procédé de fabrication en salle blanche et industrialisable, et a montré de bons résultats en termes de précision. La séparation d'hydrocarbures volatiles a été rendue possible sur silice, alumine, graphite et magnésie. Différents types de colonnes (structure, phase stationnaire) ont été fabriquées sous la forme de puces en silicium de 2x2 cm², et leurs caractérisations thermodynamique et cinétique ont été réalisées. Des efficacités très satisfaisantes ont été obtenues (plus de 5700 plateaux, des hauteurs de plateau de 250 µm). La possibilité d'utiliser des colonnes à phase stationnaire déposée par pulvérisation cathodique pour l'analyse automatisée en temps réel d'hydrocarbures légers sur site pétrolier a été démontrée par l'implémentation d'un système de programmation en température de la puce et divers tests d'adaptabilité (haute température, gaz vecteur, humidité) : une séparation complète des alcanes linéaires C1-C9 en moins de 15 secondes a été obtenue, ainsi que des séparations de mélanges plus complexes (isomères, insaturés). Une application industrielle confidentielle a été brevetée et développée. / 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.

This thesis in microscale gas chromatography (μGC) creates a paradigm shift in rapidly analyzing chemicals in the environment or analytes. We are looking for unexpected chemical changes that have been added purposefully or unintentionally. The work examines various aspects of μGC technology, including the optimization of ionic liquid stationary phase coatings for microfabricated columns, achieving up to 8300 theoretical plates per meter for naphthalene using 1-butylpyridinum bis(trifluoromethylsulfonyl)imide [BPY][NTf2] at 240°C. The development of portable systems for fuel adulteration detection is demonstrated, capable of discriminating 5% kerosene adulterated diesel fuel with four seconds of chromatogram analysis. The research also presents a novel parallel column configuration using three ionic liquid-coated semi-packed columns, each 1 m long and 240 μm deep, for complex gas analysis of up to 46 compounds. Key innovations discussed include optimized coating procedure of GC separation columns and implementation of GC based miniaturized electronic nose with the integration of machine learning algorithms. An evaluation of a prototype modular electric and fluidic μGC was evaluated and validated for benzene toluene, ethylbenzene, and xylene (BTEX). This research highlights the versatility of μGCs in applications ranging from environmental monitoring to quality control in the fuel industry, showcasing their potential as powerful tools for on-site chemical analysis with improved selectivity, resolution, and portability. / Doctor of Philosophy / This thesis advances the development of miniature chemical analytical systems, specifically gas chromatography, which is the gold standard for detecting volatile organic compounds in the environment. The work encompasses comprehensive improvements to these systems, from optimizing fabrication and coating of separation columns for better chemical separation to developing rapid prototyping methods for both hardware and software components. Through the integration of machine learning and innovative system designs, the thesis demonstrates significant improvements in detection capabilities, including identifying fuel tampering within seconds and monitoring harmful air pollutants at parts-per-billion levels over extended periods. These advances pave the way for making sophisticated chemical analysis accessible outside of traditional laboratories, enabling direct testing at locations where immediate results are crucial for safety and quality control.