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Spectroscopic detection and hyphenated techniques in microfluidic enabled gas chromatography
thesisposted on 2023-05-28, 09:26 authored by Gras, RL
This thesis introduces newly innovated techniques and associated novel method developments in gas chromatography. There are two major emphases presented in this work: The first emphasis is in improving selectivity, sensitivity, and portability of analytical instrumentation with the use of molecular spectroscopy technique as a gas phase detector. Performance, benefit, and impact of using spectroscopic techniques with focus on ultraviolet (UV) detection were investigated first with a gas phase photometer and subsequently with a diode array detector. As a selectable multiwavelength UV based detector, the diode array detector was originally designed for liquid chromatography but successfully repurposed for gas chromatography. Contemporary diode array detector brings ultraviolet ‚Äöv†v¿ visible spectroscopy onto the capillary gas chromatography timescale. The range of analytes compatible with this detector was substantially expanded to include active compounds enabled by effective passivation techniques and to semi-volatile compounds with boiling point equivalent to hexadecene (285 ¬¨‚àûC) with the augmentation of a purposely designed heated optical cell. The optical cell was powered by a highly compact isothermal semiconductor positive temperature coefficient heater offering substantial benefits for miniaturized and portable analytical devices in key aspects such as safety in overheating, energy efficiency, size, scalability, and in discovering new thermal management strategies. The userselectable multi-wavelength, over a range of 190‚Äö-640 nm affords efficient and effective analysis of many volatile and semi-volatile organic compounds. The second emphasis focuses on benefits of combining selective detection with contemporary planar microfluidic devices. Hyphenation, multi-hyphenation, and multidimensional approaches enhance analytical capabilities without compromising performance nor incurring additional analytical time. These approaches have resulted in the development and implementation of innovative analytical methods to address challenging problems encountered in the community of practice. When correctly applied, selective detection can substantially ease the burden of separation traditionally imposed on the analytical column, especially in complex sample matrices. Selective and sensitive detection are enablers to high-speed gas chromatography which are also critical components in the development of portable and hand-held analytical devices. Therefore, research conducted in this field is essential to the capability of sustainable development for gas chromatographic techniques. The synergy in combining a selectable multi-wavelength UV based detector with other contemporary selective detectors and hyphenated techniques like atomic emission detector (AED), micromachined differential mobility spectrometer (˜í¬¿DMS), and the mass spectrometer (MS) operating in selected ion monitoring mode was illustrated in challenging industrial applications. In this work, critical development, use, and implementation of planar microfluidics in capillary gas chromatography were realized with multiple chromatographic system configurations. The successful use of these devices for mid-point and post column backflush, for hyphenated techniques, and multi-dimensional gas chromatography are highlighted.
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