In Search of an Ideal Modulator for Comprehensive Two-Dimensional Gas Chromatography
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Date
2019-10-24
Authors
Boswell, Haleigh
Journal Title
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Publisher
University of Waterloo
Abstract
Gas chromatography has been a prevailing technique to separate different mixtures of volatile and semi-volatile compounds in order to qualitatively and quantitatively identify each individual component. With more complex mixtures, co-elutions can occur, leading to misidentification or an inadequate separation. This led to the need of a more complex instrumentation that could confront the challenges of one-dimensional gas chromatography. In 1991, Phillips successfully completed the first comprehensive two-dimensional gas chromatographic analysis. By implementing two columns of differing stationary phases, more complex samples can be separated without co-elutions occurring. In order to connect the two columns, an interface or modulator must preserve the primary column separation and refocus the analytes before re-injecting them into the secondary column. To make this technique available to a wide range of scientists, it must be cost-effective, user-friendly, and applicable to a wide range of applications and samples. Due to the many available commercial and experimental modulators, deciding which one is the ideal platform can be daunting. Understanding the operational capabilities, as well as the advantages and disadvantages of each platform is crucial for the desired application. In this thesis, various modulator platforms were optimized, evaluated and improved upon in search of the ideal modulator for GC×GC. The UW consumable-free, thermal modulator is a heater-based platform that performs modulation by trapping and focusing analytes through the cooling of a sorbent material within a metal capillary, which is subsequently released through an electrical discharge event. Various treatments were applied to determine the parameters to achieve an optimized coating within the trapping capillary. An optimized phase was obtained that allowed proper trapping of analytes, without breakthrough, and complete desorption. Two sections within the trapping capillary of different adsorptivity were beneficial in obtaining adequate separation with active and passive cooling at lower modulation voltages. Base oils, an extremely complex matrix, were chosen to challenge the UW thermal modulator and a commercial flow modulator. Neither model was found superior to the other and both platforms achieved comprehensive separation of the specific classes of compounds and allowed differentiation of the oils. A commercial flow modulator was further improved upon by adding a cryogen-free focusing mechanism to test a proof of concept hybrid interface. Thinner film traps of 0.5 and 3.0 µm provided significant focusing while operating under 2D flow rates compatible with mass spectrometric detection. Finally, a commercial thermal modulator was evaluated by determining the operational capabilities and its ability to analyze bitumen. The platform successfully achieved adequate separations of two standard mixtures of different volatilities and polarities, providing an affordable option to achieve GC×GC separation without the need for consumables. Total group and biomarker classification were also successfully performed to differentiate homologous compounds within a bitumen sample. The work presented in this thesis provides a better understanding of the benefits and limitations of various modulator designs, which is vital in the search of an ideal modulator for GC×GC.