High-resolution gas chromatography for analysis of plant extracts

This thesis focuses on new high-resolution gas chromatography (GC) techniques to separate complex mixtures, especially plant extracts. First, serially-coupled high-resolution capillary columns are investigated for single-dimensional GC separation of plant extracts. The first research chapter highlights the potential and indicates the limitations of high-resolution one-dimensional analysis of complex plant extracts. Comprehensive two-dimensional GC (GC ‚àöv= GC) is an extended version of single-dimensional GC that offers exceptionally high peak capacity. This thesis employs a commercially available dual stage GC ‚àöv= GC modulator as a platform for exploring new high-resolution GC techniques. To this end, a multiplexed dual-secondary column comprehensive two-dimensional gas chromatography approach (GC ‚àöv= 2GC) designed for analysis of complex mixtures is introduced. GC ‚àöv= 2GC with a single detector and two second-dimension columns is made possible by the development of contra-directional modulation. Contra-directional modulation leads to two single two-dimensional chromatograms in a single window for each injection. A selection of different classes of compounds is analysed to demonstrate the approach. The chromatogram from this single detector system provides complementary information due to the unique selectivity of the three separation columns and the result is similar to GC ‚àöv= 2GC with multiple detectors previously described in the literature. Next, a new multiplexed dual first-dimension comprehensive two-dimensional gas chromatography approach (2GC ‚àöv= GC) is introduced. 2GC ‚àöv= GC is achieved by installing the two first-dimension columns contra-directionally through a dual-stage modulator. This study is divided into two parts: the first part discusses the benefits of 2GC ‚àöv= GC analysis compared to normal GC ‚àöv= GC and GC ‚àöv= 2GC analysis with a similar column configuration. In the second part, 2GC ‚àöv= GC is coupled to mass spectrometry for the characterisation of Australian tea tree (M. alternifolia) essential oil. The concept of dual channel GC is also explored. A multiplexed dual channel GC using a single detector system (2GC- MS) is introduced. This study utilises polar and non-polar columns for the analysis of parsley essential oil. A comprehensive analysis strategy using mass spectrometry and multiple linear retention indices using 2GC-MS is discussed. Finally, an ultra-dimensional separation technique called multiplexed dual first and second-dimensions column comprehensive GC ‚àöv= GC (2GC ‚àöv= 2GC) or 2(GC ‚àöv= GC)‚ÄövÑvp with a single detector system is introduced. A combination of non-polar ‚àöv= polar and polar ‚àöv= non-polar separation columns is utilised for separation of parsley and hop essential oils to demonstrate the approach. The dual two-dimensional chromatograms from this single detector system provide complementary information due to the selectivity differences of the four separation columns.