Chemistry

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Browsing Chemistry by Author "Gorecki, Tadeusz"

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    Development and Application of a Consumable-Free Modulator for Comprehensive Two-Dimensional Gas Chromatography
    (University of Waterloo, 2024-02-16) Edwards, Matthew; Gorecki, Tadeusz
    Comprehensive two-dimensional gas chromatography (GC×GC), is a separation method recognized as offering far greater peak capacity than conventional one-dimensional separations. Today, the most frequently used GC×GC systems require consumables such as liquid N2 for the trapping function of the modulator. Although these systems are recognized as being very effective, their initial and running costs are a hindrance to more widespread use. A consumable-free, single-stage thermal modulator for GC×GC has been developed to overcome these problems. The device traps analytes through the use of a specially prepared coated stainless steel capillary compressed between two ceramic cooling pads. Analytes are thermally released from the trap into the secondary column via resistive heating. Thermal treatment of the trapping capillary plays an important role in the function of the device and advanced imaging and material characterization techniques were used to reveal changes in the stationary phase coating of the trap. These experiments revealed the polydimethylsiloxane stationary phase coating was being converted to carbon doped, oxygen rich silica nanoparticles. These spherical particles coated the internal surface of the capillary evenly and provided an effective and highly sorptive phase for use in GC×GC modulation. This modulator’s performance was evaluated by applying it to real world analytical challenges. Samples such as honeybush tea volatiles, polychlorinated biphenyls, perfumes and petroleum products were successfully analyzed with performance comparable to commercially available instruments. This work demonstrates the single-stage, consumable-free GC×GC modulation system described herein is an excellent instrumental option for analysts across a wide breadth of application areas in the world of complex volatile and semi-volatile analysis.
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    In Search of an Ideal Modulator for Comprehensive Two-Dimensional Gas Chromatography
    (University of Waterloo, 2019-10-24) Boswell, Haleigh; Gorecki, Tadeusz
    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.